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path: root/src/backenddb/plugin_merchantdb_postgres.c
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/*
  This file is part of TALER
  (C) 2014--2019 Taler Systems SA

  TALER is free software; you can redistribute it and/or modify it under the
  terms of the GNU Lesser General Public License as published by the Free Software
  Foundation; either version 3, or (at your option) any later version.

  TALER is distributed in the hope that it will be useful, but WITHOUT ANY
  WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
  A PARTICULAR PURPOSE.  See the GNU General Public License for more details.

  You should have received a copy of the GNU General Public License along with
  TALER; see the file COPYING.  If not, see <http://www.gnu.org/licenses/>
*/
/**
 * @file merchant/plugin_merchantdb_postgres.c
 * @brief database helper functions for postgres used by the merchant
 * @author Sree Harsha Totakura <sreeharsha@totakura.in>
 * @author Christian Grothoff
 * @author Marcello Stanisci
 */
#include "platform.h"
#include <gnunet/gnunet_util_lib.h>
#include <gnunet/gnunet_pq_lib.h>
#include <taler/taler_util.h>
#include <taler/taler_pq_lib.h>
#include <taler/taler_json_lib.h>
#include "taler_merchantdb_plugin.h"

/**
 * How often do we re-try if we run into a DB serialization error?
 */
#define MAX_RETRIES 3


/**
 * Wrapper macro to add the currency from the plugin's state
 * when fetching amounts from the database.
 *
 * @param field name of the database field to fetch amount from
 * @param amountp[out] pointer to amount to set
 */
#define TALER_PQ_RESULT_SPEC_AMOUNT(field,amountp) TALER_PQ_result_spec_amount ( \
    field,pg->currency,amountp)

/**
 * Wrapper macro to add the currency from the plugin's state
 * when fetching amounts from the database.  NBO variant.
 *
 * @param field name of the database field to fetch amount from
 * @param amountp[out] pointer to amount to set
 */
#define TALER_PQ_RESULT_SPEC_AMOUNT_NBO(field, \
                                        amountp) TALER_PQ_result_spec_amount_nbo ( \
    field,pg->currency,amountp)


/**
 * Wrapper macro to add the currency from the plugin's state
 * when fetching amounts from the database.
 *
 * @param field name of the database field to fetch amount from
 * @param amountp[out] pointer to amount to set
 */
#define TALER_PQ_RESULT_SPEC_AMOUNT(field,amountp) TALER_PQ_result_spec_amount ( \
    field,pg->currency,amountp)


/**
 * Type of the "cls" argument given to each of the functions in
 * our API.
 */
struct PostgresClosure
{

  /**
   * Postgres connection handle.
   */
  struct GNUNET_PQ_Context *conn;

  /**
   * Which currency do we deal in?
   */
  char *currency;

  /**
   * Underlying configuration.
   */
  const struct GNUNET_CONFIGURATION_Handle *cfg;

  /**
   * Name of the currently active transaction, NULL if none is active.
   */
  const char *transaction_name;

};


/**
 * Drop merchant tables
 *
 * @param cls closure our `struct Plugin`
 * @return #GNUNET_OK upon success; #GNUNET_SYSERR upon failure
 */
static int
postgres_drop_tables (void *cls)
{
  struct PostgresClosure *pg = cls;
  struct GNUNET_PQ_ExecuteStatement es[] = {
    GNUNET_PQ_make_try_execute (
      "DROP TABLE IF EXISTS merchant_transfers CASCADE;"),
    GNUNET_PQ_make_try_execute (
      "DROP TABLE IF EXISTS merchant_deposits CASCADE;"),
    GNUNET_PQ_make_try_execute (
      "DROP TABLE IF EXISTS merchant_transactions CASCADE;"),
    GNUNET_PQ_make_try_execute (
      "DROP TABLE IF EXISTS merchant_proofs CASCADE;"),
    GNUNET_PQ_make_try_execute (
      "DROP TABLE IF EXISTS merchant_contract_terms CASCADE;"),
    GNUNET_PQ_make_try_execute (
      "DROP TABLE IF EXISTS merchant_refunds CASCADE;"),
    GNUNET_PQ_make_try_execute (
      "DROP TABLE IF EXISTS exchange_wire_fees CASCADE;"),
    GNUNET_PQ_make_try_execute ("DROP TABLE IF EXISTS merchant_tips CASCADE;"),
    GNUNET_PQ_make_try_execute (
      "DROP TABLE IF EXISTS merchant_tip_pickups CASCADE;"),
    GNUNET_PQ_make_try_execute (
      "DROP TABLE IF EXISTS merchant_tip_reserve_credits CASCADE;"),
    GNUNET_PQ_make_try_execute (
      "DROP TABLE IF EXISTS merchant_tip_reserves CASCADE;"),
    GNUNET_PQ_make_try_execute (
      "DROP TABLE IF EXISTS merchant_orders CASCADE;"),
    GNUNET_PQ_make_try_execute (
      "DROP TABLE IF EXISTS merchant_session_info CASCADE;"),
    GNUNET_PQ_EXECUTE_STATEMENT_END
  };

  return GNUNET_PQ_exec_statements (pg->conn,
                                    es);
}


/**
 * Check that the database connection is still up.
 *
 * @param pg connection to check
 */
static void
check_connection (struct PostgresClosure *pg)
{
  GNUNET_PQ_reconnect_if_down (pg->conn);
}


/**
 * Do a pre-flight check that we are not in an uncommitted transaction.
 * If we are, try to commit the previous transaction and output a warning.
 * Does not return anything, as we will continue regardless of the outcome.
 *
 * @param cls the `struct PostgresClosure` with the plugin-specific state
 */
static void
postgres_preflight (void *cls)
{
  struct PostgresClosure *pg = cls;
  struct GNUNET_PQ_ExecuteStatement es[] = {
    GNUNET_PQ_make_execute ("COMMIT"),
    GNUNET_PQ_EXECUTE_STATEMENT_END
  };

  if (NULL == pg->transaction_name)
    return; /* all good */
  if (GNUNET_OK ==
      GNUNET_PQ_exec_statements (pg->conn,
                                 es))
  {
    GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
                "BUG: Preflight check committed transaction `%s'!\n",
                pg->transaction_name);
  }
  else
  {
    GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
                "BUG: Preflight check failed to commit transaction `%s'!\n",
                pg->transaction_name);
  }
  pg->transaction_name = NULL;
}


/**
 * Start a transaction.
 *
 * @param cls the `struct PostgresClosure` with the plugin-specific state
 * @param name unique name identifying the transaction (for debugging),
 *             must point to a constant
 * @return #GNUNET_OK on success
 */
static int
postgres_start (void *cls,
                const char *name)
{
  struct PostgresClosure *pg = cls;
  struct GNUNET_PQ_ExecuteStatement es[] = {
    GNUNET_PQ_make_execute ("START TRANSACTION ISOLATION LEVEL SERIALIZABLE"),
    GNUNET_PQ_EXECUTE_STATEMENT_END
  };

  check_connection (pg);
  postgres_preflight (pg);
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Starting merchant DB transaction\n");
  if (GNUNET_OK !=
      GNUNET_PQ_exec_statements (pg->conn,
                                 es))
  {
    TALER_LOG_ERROR ("Failed to start transaction\n");
    GNUNET_break (0);
    return GNUNET_SYSERR;
  }
  pg->transaction_name = name;
  return GNUNET_OK;
}


/**
 * Roll back the current transaction of a database connection.
 *
 * @param cls the `struct PostgresClosure` with the plugin-specific state
 * @return #GNUNET_OK on success
 */
static void
postgres_rollback (void *cls)
{
  struct PostgresClosure *pg = cls;
  struct GNUNET_PQ_ExecuteStatement es[] = {
    GNUNET_PQ_make_execute ("ROLLBACK"),
    GNUNET_PQ_EXECUTE_STATEMENT_END
  };

  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Rolling back merchant DB transaction\n");
  GNUNET_break (GNUNET_OK ==
                GNUNET_PQ_exec_statements (pg->conn,
                                           es));
  pg->transaction_name = NULL;
}


/**
 * Commit the current transaction of a database connection.
 *
 * @param cls the `struct PostgresClosure` with the plugin-specific state
 * @return transaction status code
 */
static enum GNUNET_DB_QueryStatus
postgres_commit (void *cls)
{
  struct PostgresClosure *pg = cls;
  struct GNUNET_PQ_QueryParam params[] = {
    GNUNET_PQ_query_param_end
  };

  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Committing merchant DB transaction\n");
  pg->transaction_name = NULL;
  return GNUNET_PQ_eval_prepared_non_select (pg->conn,
                                             "end_transaction",
                                             params);
}


/**
 * Retrieve proposal data given its proposal data's hashcode
 *
 * @param cls closure
 * @param contract_terms where to store the retrieved proposal data
 * @param h_contract_terms proposal data's hashcode that will be used to
 * perform the lookup
 * @return transaction status
 */
static enum GNUNET_DB_QueryStatus
postgres_find_contract_terms_from_hash (void *cls,
                                        json_t **contract_terms,
                                        const struct
                                        GNUNET_HashCode *h_contract_terms,
                                        const struct
                                        TALER_MerchantPublicKeyP *merchant_pub)
{
  struct PostgresClosure *pg = cls;
  struct GNUNET_PQ_QueryParam params[] = {
    GNUNET_PQ_query_param_auto_from_type (h_contract_terms),
    GNUNET_PQ_query_param_auto_from_type (merchant_pub),
    GNUNET_PQ_query_param_end
  };
  struct GNUNET_PQ_ResultSpec rs[] = {
    TALER_PQ_result_spec_json ("contract_terms",
                               contract_terms),
    GNUNET_PQ_result_spec_end
  };

  check_connection (pg);
  return GNUNET_PQ_eval_prepared_singleton_select (pg->conn,
                                                   "find_contract_terms_from_hash",
                                                   params,
                                                   rs);
}


/**
 * Retrieve proposal data given its proposal data's hashcode
 *
 * @param cls closure
 * @param contract_terms where to store the retrieved proposal data
 * @param h_contract_terms proposal data's hashcode that will be used to
 * perform the lookup
 * @return transaction status
 */
static enum GNUNET_DB_QueryStatus
postgres_find_paid_contract_terms_from_hash (void *cls,
                                             json_t **contract_terms,
                                             const struct
                                             GNUNET_HashCode *h_contract_terms,
                                             const struct
                                             TALER_MerchantPublicKeyP *
                                             merchant_pub)
{
  struct PostgresClosure *pg = cls;
  struct GNUNET_PQ_QueryParam params[] = {
    GNUNET_PQ_query_param_auto_from_type (h_contract_terms),
    GNUNET_PQ_query_param_auto_from_type (merchant_pub),
    GNUNET_PQ_query_param_end
  };
  struct GNUNET_PQ_ResultSpec rs[] = {
    TALER_PQ_result_spec_json ("contract_terms",
                               contract_terms),
    GNUNET_PQ_result_spec_end
  };

  /* no preflight check here, runs in its own transaction from
     caller (in /pay case) */
  check_connection (pg);
  return GNUNET_PQ_eval_prepared_singleton_select (pg->conn,
                                                   "find_paid_contract_terms_from_hash",
                                                   params,
                                                   rs);
}


/**
 * Retrieve proposal data given its order id.  Ignores if the
 * proposal has been paid or not.
 *
 * @param cls closure
 * @param[out] contract_terms where to store the retrieved contract terms
 * @param order id order id used to perform the lookup
 * @return transaction status
 */
static enum GNUNET_DB_QueryStatus
postgres_find_contract_terms (void *cls,
                              json_t **contract_terms,
                              const char *order_id,
                              const struct
                              TALER_MerchantPublicKeyP *merchant_pub)
{
  struct PostgresClosure *pg = cls;
  struct GNUNET_PQ_QueryParam params[] = {
    GNUNET_PQ_query_param_string (order_id),
    GNUNET_PQ_query_param_auto_from_type (merchant_pub),
    GNUNET_PQ_query_param_end
  };
  struct GNUNET_PQ_ResultSpec rs[] = {
    TALER_PQ_result_spec_json ("contract_terms",
                               contract_terms),
    GNUNET_PQ_result_spec_end
  };

  *contract_terms = NULL;
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Finding contract term, order_id: '%s', merchant_pub: '%s'.\n",
              order_id,
              TALER_B2S (merchant_pub));
  check_connection (pg);
  return GNUNET_PQ_eval_prepared_singleton_select (pg->conn,
                                                   "find_contract_terms",
                                                   params,
                                                   rs);
}


/**
 * Retrieve order given its order id and the instance's merchant public key.
 *
 * @param cls closure
 * @param[out] contract_terms where to store the retrieved contract terms
 * @param order id order id used to perform the lookup
 * @param merchant_pub merchant public key that identifies the instance
 * @return transaction status
 */
static enum GNUNET_DB_QueryStatus
postgres_find_order (void *cls,
                     json_t **contract_terms,
                     const char *order_id,
                     const struct TALER_MerchantPublicKeyP *merchant_pub)
{
  struct PostgresClosure *pg = cls;
  struct GNUNET_PQ_QueryParam params[] = {
    GNUNET_PQ_query_param_string (order_id),
    GNUNET_PQ_query_param_auto_from_type (merchant_pub),
    GNUNET_PQ_query_param_end
  };
  struct GNUNET_PQ_ResultSpec rs[] = {
    TALER_PQ_result_spec_json ("contract_terms",
                               contract_terms),
    GNUNET_PQ_result_spec_end
  };

  *contract_terms = NULL;
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Finding contract term, order_id: '%s', merchant_pub: '%s'.\n",
              order_id,
              TALER_B2S (merchant_pub));
  check_connection (pg);
  return GNUNET_PQ_eval_prepared_singleton_select (pg->conn,
                                                   "find_order",
                                                   params,
                                                   rs);
}


/**
 * Insert proposal data and its hashcode into db
 *
 * @param cls closure
 * @param order_id identificator of the proposal being stored
 * @param merchant_pub merchant's public key
 * @param timestamp timestamp of this proposal data
 * @param contract_terms proposal data to store
 * @return transaction status
 */
static enum GNUNET_DB_QueryStatus
postgres_insert_contract_terms (void *cls,
                                const char *order_id,
                                const struct
                                TALER_MerchantPublicKeyP *merchant_pub,
                                struct GNUNET_TIME_Absolute timestamp,
                                const json_t *contract_terms)
{
  struct PostgresClosure *pg = cls;
  struct GNUNET_HashCode h_contract_terms;
  struct GNUNET_PQ_QueryParam params[] = {
    GNUNET_PQ_query_param_string (order_id),
    GNUNET_PQ_query_param_auto_from_type (merchant_pub),
    GNUNET_PQ_query_param_absolute_time (&timestamp),
    TALER_PQ_query_param_json (contract_terms),
    GNUNET_PQ_query_param_auto_from_type (&h_contract_terms),
    GNUNET_PQ_query_param_end
  };

  if (GNUNET_OK !=
      TALER_JSON_hash (contract_terms,
                       &h_contract_terms))
  {
    GNUNET_break (0);
    return GNUNET_SYSERR;
  }
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "inserting contract terms: order_id: %s, merchant_pub: %s, h_contract_terms: %s.\n",
              order_id,
              TALER_B2S (merchant_pub),
              GNUNET_h2s (&h_contract_terms));
  check_connection (pg);
  return GNUNET_PQ_eval_prepared_non_select (pg->conn,
                                             "insert_contract_terms",
                                             params);
}


/**
 * Insert order into the DB.
 *
 * @param cls closure
 * @param order_id identificator of the proposal being stored
 * @param merchant_pub merchant's public key
 * @param timestamp timestamp of this proposal data
 * @param contract_terms proposal data to store
 * @return transaction status
 */
static enum GNUNET_DB_QueryStatus
postgres_insert_order (void *cls,
                       const char *order_id,
                       const struct TALER_MerchantPublicKeyP *merchant_pub,
                       struct GNUNET_TIME_Absolute timestamp,
                       const json_t *contract_terms)
{
  struct PostgresClosure *pg = cls;
  struct GNUNET_PQ_QueryParam params[] = {
    GNUNET_PQ_query_param_string (order_id),
    GNUNET_PQ_query_param_auto_from_type (merchant_pub),
    GNUNET_PQ_query_param_absolute_time (&timestamp),
    TALER_PQ_query_param_json (contract_terms),
    GNUNET_PQ_query_param_end
  };

  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "inserting order: order_id: %s, merchant_pub: %s.\n",
              order_id,
              TALER_B2S (merchant_pub));
  check_connection (pg);
  return GNUNET_PQ_eval_prepared_non_select (pg->conn,
                                             "insert_order",
                                             params);
}


/**
 * Mark contract terms as payed.  Needed by /history as only payed
 * contracts must be shown.
 *
 * NOTE: we can't get the list of (payed) contracts from the
 * transactions table because it lacks contract_terms plain JSON.  In
 * facts, the protocol doesn't allow to store contract_terms in
 * transactions table, as /pay handler doesn't receive this data (only
 * /proposal does).
 *
 * @param cls closure
 * @param h_contract_terms hash of the contract that is now paid
 * @param merchant_pub merchant's public key
 * @return transaction status
 */
static enum GNUNET_DB_QueryStatus
postgres_mark_proposal_paid (void *cls,
                             const struct GNUNET_HashCode *h_contract_terms,
                             const struct
                             TALER_MerchantPublicKeyP *merchant_pub)
{
  struct PostgresClosure *pg = cls;
  struct GNUNET_PQ_QueryParam params[] = {
    GNUNET_PQ_query_param_auto_from_type (h_contract_terms),
    GNUNET_PQ_query_param_auto_from_type (merchant_pub),
    GNUNET_PQ_query_param_end
  };

  TALER_LOG_DEBUG ("Marking proposal paid, h_contract_terms: '%s',"
                   " merchant_pub: '%s'\n",
                   GNUNET_h2s (h_contract_terms),
                   TALER_B2S (merchant_pub));
  return GNUNET_PQ_eval_prepared_non_select (pg->conn,
                                             "mark_proposal_paid",
                                             params);
}


/**
 * Store the order ID that was used to pay for a resource within a session.
 *
 * @param cls closure
 * @param session_id session id
 * @param fulfillment_url URL that canonically identifies the resource
 *        being paid for
 * @param order_id the order ID that was used when paying for the resource URL
 * @param merchant_pub public key of the merchant, identifying the instance
 * @return transaction status
 */
enum GNUNET_DB_QueryStatus
postgres_insert_session_info (void *cls,
                              const char *session_id,
                              const char *fulfillment_url,
                              const char *order_id,
                              const struct
                              TALER_MerchantPublicKeyP *merchant_pub)
{
  struct PostgresClosure *pg = cls;

  struct GNUNET_TIME_Absolute now = GNUNET_TIME_absolute_get ();
  struct GNUNET_PQ_QueryParam params[] = {
    GNUNET_PQ_query_param_string (session_id),
    GNUNET_PQ_query_param_string (fulfillment_url),
    GNUNET_PQ_query_param_string (order_id),
    GNUNET_PQ_query_param_auto_from_type (merchant_pub),
    GNUNET_PQ_query_param_absolute_time (&now),
    GNUNET_PQ_query_param_end
  };

  return GNUNET_PQ_eval_prepared_non_select (pg->conn,
                                             "insert_session_info",
                                             params);
}

/**
 * Retrieve the order ID that was used to pay for a resource within a session.
 *
 * @param cls closure
 * @param[out] order_id location to store the order ID that was used when
 *             paying for the resource URL
 * @param session_id session id
 * @param fulfillment_url URL that canonically identifies the resource
 *        being paid for
 * @param merchant_pub public key of the merchant, identifying the instance
 * @return transaction status
 */
enum GNUNET_DB_QueryStatus
postgres_find_session_info (void *cls,
                            char **order_id,
                            const char *session_id,
                            const char *fulfillment_url,
                            const struct TALER_MerchantPublicKeyP *merchant_pub)
{
  struct PostgresClosure *pg = cls;

  struct GNUNET_PQ_QueryParam params[] = {
    GNUNET_PQ_query_param_string (fulfillment_url),
    GNUNET_PQ_query_param_string (session_id),
    GNUNET_PQ_query_param_auto_from_type (merchant_pub),
    GNUNET_PQ_query_param_end
  };
  struct GNUNET_PQ_ResultSpec rs[] = {
    GNUNET_PQ_result_spec_string ("order_id",
                                  order_id),
    GNUNET_PQ_result_spec_end
  };
  // We don't clean up the result spec since we want
  // to keep around the memory for order_id.
  return GNUNET_PQ_eval_prepared_singleton_select (pg->conn,
                                                   "find_session_info",
                                                   params,
                                                   rs);
}


/**
 * Insert payment confirmation from the exchange into the database.
 *
 * @param cls closure
 * @param order_id identificator of the proposal associated with this revenue
 * @param merchant_pub merchant's public key
 * @param coin_pub public key of the coin
 * @param amount_with_fee amount the exchange will deposit for this coin
 * @param deposit_fee fee the exchange will charge for this coin
 * @param refund_fee fee the exchange will charge for refunding this coin
 * @param wire_fee wire fee changed by the exchange
 * @param signkey_pub public key used by the exchange for @a exchange_proof
 * @param exchange_proof proof from exchange that coin was accepted
 * @return transaction status
 */
static enum GNUNET_DB_QueryStatus
postgres_store_deposit (void *cls,
                        const struct GNUNET_HashCode *h_contract_terms,
                        const struct TALER_MerchantPublicKeyP *merchant_pub,
                        const struct TALER_CoinSpendPublicKeyP *coin_pub,
                        const char *exchange_url,
                        const struct TALER_Amount *amount_with_fee,
                        const struct TALER_Amount *deposit_fee,
                        const struct TALER_Amount *refund_fee,
                        const struct TALER_Amount *wire_fee,
                        const struct TALER_ExchangePublicKeyP *signkey_pub,
                        const json_t *exchange_proof)
{
  struct PostgresClosure *pg = cls;
  struct GNUNET_PQ_QueryParam params[] = {
    GNUNET_PQ_query_param_auto_from_type (h_contract_terms),
    GNUNET_PQ_query_param_auto_from_type (merchant_pub),
    GNUNET_PQ_query_param_auto_from_type (coin_pub),
    GNUNET_PQ_query_param_string (exchange_url),
    TALER_PQ_query_param_amount (amount_with_fee),
    TALER_PQ_query_param_amount (deposit_fee),
    TALER_PQ_query_param_amount (refund_fee),
    TALER_PQ_query_param_amount (wire_fee),
    GNUNET_PQ_query_param_auto_from_type (signkey_pub),
    TALER_PQ_query_param_json (exchange_proof),
    GNUNET_PQ_query_param_end
  };

  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Storing payment for h_contract_terms `%s', coin_pub: `%s', amount_with_fee: %s\n",
              GNUNET_h2s (h_contract_terms),
              TALER_B2S (coin_pub),
              TALER_amount2s (amount_with_fee));
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Merchant pub is `%s'\n",
              TALER_B2S (merchant_pub));
  check_connection (pg);
  return GNUNET_PQ_eval_prepared_non_select (pg->conn,
                                             "insert_deposit",
                                             params);
}


/**
 * Insert mapping of @a coin_pub and @a h_contract_terms to
 * corresponding @a wtid.
 *
 * @param cls closure
 * @param h_contract_terms hashcode of the proposal data paid by @a coin_pub
 * @param coin_pub public key of the coin
 * @param wtid identifier of the wire transfer in which the exchange
 *             send us the money for the coin deposit
 * @return transaction status
 */
static enum GNUNET_DB_QueryStatus
postgres_store_coin_to_transfer (void *cls,
                                 const struct GNUNET_HashCode *h_contract_terms,
                                 const struct
                                 TALER_CoinSpendPublicKeyP *coin_pub,
                                 const struct
                                 TALER_WireTransferIdentifierRawP *wtid)
{
  struct PostgresClosure *pg = cls;
  struct GNUNET_PQ_QueryParam params[] = {
    GNUNET_PQ_query_param_auto_from_type (h_contract_terms),
    GNUNET_PQ_query_param_auto_from_type (coin_pub),
    GNUNET_PQ_query_param_auto_from_type (wtid),
    GNUNET_PQ_query_param_end
  };

  check_connection (pg);
  return GNUNET_PQ_eval_prepared_non_select (pg->conn,
                                             "insert_transfer",
                                             params);
}


/**
 * Insert wire transfer confirmation from the exchange into the database.
 *
 * @param cls closure
 * @param exchange_url URL of the exchange
 * @param wtid identifier of the wire transfer
 * @param execution_time when was @a wtid executed
 * @param signkey_pub public key used by the exchange for @a exchange_proof
 * @param exchange_proof proof from exchange about what the deposit was for
 * @return transaction status
 */
static enum GNUNET_DB_QueryStatus
postgres_store_transfer_to_proof (void *cls,
                                  const char *exchange_url,
                                  const struct
                                  TALER_WireTransferIdentifierRawP *wtid,
                                  struct GNUNET_TIME_Absolute execution_time,
                                  const struct
                                  TALER_ExchangePublicKeyP *signkey_pub,
                                  const json_t *exchange_proof)
{
  struct PostgresClosure *pg = cls;
  struct GNUNET_PQ_QueryParam params[] = {
    GNUNET_PQ_query_param_string (exchange_url),
    GNUNET_PQ_query_param_auto_from_type (wtid),
    GNUNET_PQ_query_param_absolute_time (&execution_time),
    GNUNET_PQ_query_param_auto_from_type (signkey_pub),
    TALER_PQ_query_param_json (exchange_proof),
    GNUNET_PQ_query_param_end
  };

  check_connection (pg);
  return GNUNET_PQ_eval_prepared_non_select (pg->conn,
                                             "insert_proof",
                                             params);
}


/**
 * Lookup for a proposal, respecting the signature used by the
 * /history's db methods.
 *
 * @param cls db plugin handle
 * @param order_id order id used to search for the proposal data
 * @param merchant_pub public key of the merchant using this method
 * @param cb the callback
 * @param cb_cls closure to pass to the callback
 * @return transaction status
 */
static enum GNUNET_DB_QueryStatus
postgres_find_contract_terms_history (void *cls,
                                      const char *order_id,
                                      const struct
                                      TALER_MerchantPublicKeyP *merchant_pub,
                                      TALER_MERCHANTDB_ProposalDataCallback cb,
                                      void *cb_cls)
{
  struct PostgresClosure *pg = cls;
  json_t *contract_terms;
  enum GNUNET_DB_QueryStatus qs;
  struct GNUNET_PQ_QueryParam params[] = {
    GNUNET_PQ_query_param_string (order_id),
    GNUNET_PQ_query_param_auto_from_type (merchant_pub),
    GNUNET_PQ_query_param_end
  };
  struct GNUNET_PQ_ResultSpec rs[] = {
    TALER_PQ_result_spec_json ("contract_terms",
                               &contract_terms),
    GNUNET_PQ_result_spec_end
  };

  qs = GNUNET_PQ_eval_prepared_singleton_select (pg->conn,
                                                 "find_contract_terms_history",
                                                 params,
                                                 rs);
  if (qs <= 0)
    return qs;
  if (NULL != cb)
    cb (cb_cls,
        order_id,
        0,
        contract_terms);
  GNUNET_PQ_cleanup_result (rs);
  return qs;
}


/**
 * Closure for #find_contracts_cb().
 */
struct FindContractsContext
{
  /**
   * Function to call on each result.
   */
  TALER_MERCHANTDB_ProposalDataCallback cb;

  /**
   * Closure for @e cb.
   */
  void *cb_cls;

  /**
   * Transaction status code to set.
   */
  enum GNUNET_DB_QueryStatus qs;
};


/**
 * Function to be called with the results of a SELECT statement
 * that has returned @a num_results results.
 *
 * @param cls of type `struct FindContractsContext *`
 * @param result the postgres result
 * @param num_result the number of results in @a result
 */
static void
find_contracts_cb (void *cls,
                   PGresult *result,
                   unsigned int num_results)
{
  struct FindContractsContext *fcctx = cls;

  for (unsigned int i = 0; i < num_results; i++)
  {
    char *order_id;
    json_t *contract_terms;
    uint64_t row_id;
    struct GNUNET_PQ_ResultSpec rs[] = {
      GNUNET_PQ_result_spec_string ("order_id",
                                    &order_id),
      TALER_PQ_result_spec_json ("contract_terms",
                                 &contract_terms),
      GNUNET_PQ_result_spec_uint64 ("row_id",
                                    &row_id),
      GNUNET_PQ_result_spec_end
    };

    if (GNUNET_OK !=
        GNUNET_PQ_extract_result (result,
                                  rs,
                                  i))
    {
      GNUNET_break (0);
      fcctx->qs = GNUNET_DB_STATUS_HARD_ERROR;
      return;
    }
    fcctx->qs = i + 1;
    fcctx->cb (fcctx->cb_cls,
               order_id,
               row_id,
               contract_terms);
    GNUNET_PQ_cleanup_result (rs);
  }
}


/**
 * Return proposals whose timestamp are older than `date`.
 * Among those proposals, only those ones being between the
 * start-th and (start-nrows)-th record are returned.  The rows
 * are sorted having the youngest first.
 *
 * @param cls our plugin handle.
 * @param date only results older than this date are returned.
 * @param merchant_pub instance's public key; only rows related to this
 * instance are returned.
 * @param start only rows with serial id less than start are returned.
 * In other words, you lower `start` to get older records. The tipical
 * usage is to firstly call `find_contract_terms_by_date`, so that you get
 * the `nrows` youngest records. The oldest of those records will tell you
 * from which timestamp and `start` you can query the DB in order to get
 * furtherly older records, and so on. Alternatively, you can use always
 * the same timestamp and just go behind in history by tuning `start`.
 * @param nrows only nrows rows are returned.
 * @param past if set to #GNUNET_YES, retrieves rows older than `date`.
 * @param ascending if GNUNET_YES, results will be sorted in chronological order.
 * This is tipically used to show live updates on the merchant's backoffice
 * Web interface.
 * @param cb function to call with transaction data, can be NULL.
 * @param cb_cls closure for @a cb
 * @return transaction status
 */
static enum GNUNET_DB_QueryStatus
postgres_find_contract_terms_by_date_and_range (void *cls,
                                                struct GNUNET_TIME_Absolute
                                                date,
                                                const struct
                                                TALER_MerchantPublicKeyP *
                                                merchant_pub,
                                                uint64_t start,
                                                uint64_t nrows,
                                                int past,
                                                unsigned int ascending,
                                                TALER_MERCHANTDB_ProposalDataCallback
                                                cb,
                                                void *cb_cls)
{
  struct PostgresClosure *pg = cls;
  struct GNUNET_PQ_QueryParam params[] = {
    GNUNET_PQ_query_param_absolute_time (&date),
    GNUNET_PQ_query_param_auto_from_type (merchant_pub),
    GNUNET_PQ_query_param_uint64 (&start),
    GNUNET_PQ_query_param_uint64 (&nrows),
    GNUNET_PQ_query_param_end
  };
  const char *stmt;
  enum GNUNET_DB_QueryStatus qs;
  struct FindContractsContext fcctx = {
    .cb = cb,
    .cb_cls = cb_cls
  };

  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "DB serving /history with date %s\n",
              GNUNET_STRINGS_absolute_time_to_string (date));
  stmt =
    (GNUNET_YES == past)
    ? ( (GNUNET_YES == ascending)
        ? "find_contract_terms_by_date_and_range_past_asc"
        : "find_contract_terms_by_date_and_range_past")
    : ( (GNUNET_YES == ascending)
        ? "find_contract_terms_by_date_and_range_asc"
        : "find_contract_terms_by_date_and_range");
  check_connection (pg);
  qs = GNUNET_PQ_eval_prepared_multi_select (pg->conn,
                                             stmt,
                                             params,
                                             &find_contracts_cb,
                                             &fcctx);
  if (0 >= qs)
    return qs;
  return fcctx.qs;
}


/**
 * Closure for #find_tip_authorizations_cb().
 */
struct GetAuthorizedTipAmountContext
{
  /**
   * Total authorized amount.
   */
  struct TALER_Amount authorized_amount;

  /**
   * Transaction status code to set.
   */
  enum GNUNET_DB_QueryStatus qs;

  /**
   * Plugin context.
   */
  struct PostgresClosure *pg;

};


/**
 * Function to be called with the results of a SELECT statement
 * that has returned @a num_results results.
 *
 * @param cls of type `struct GetAuthorizedTipAmountContext *`
 * @param result the postgres result
 * @param num_result the number of results in @a result
 */
static void
find_tip_authorizations_cb (void *cls,
                            PGresult *result,
                            unsigned int num_results)
{
  struct GetAuthorizedTipAmountContext *ctx = cls;
  struct PostgresClosure *pg = ctx->pg;
  unsigned int i;

  for (i = 0; i < num_results; i++)
  {
    struct TALER_Amount amount;
    char *just;
    json_t *extra;
    struct GNUNET_HashCode h;
    struct GNUNET_PQ_ResultSpec rs[] = {
      GNUNET_PQ_result_spec_string ("justification",
                                    &just),
      GNUNET_PQ_result_spec_auto_from_type ("tip_id",
                                            &h),
      TALER_PQ_RESULT_SPEC_AMOUNT ("amount",
                                   &amount),
      TALER_PQ_result_spec_json ("extra",
                                 &extra),
      GNUNET_PQ_result_spec_end
    };

    if (GNUNET_OK !=
        GNUNET_PQ_extract_result (result,
                                  rs,
                                  i))
    {
      GNUNET_break (0);
      ctx->qs = GNUNET_DB_STATUS_HARD_ERROR;
      return;
    }

    if (0 == i)
    {
      ctx->authorized_amount = amount;
    }
    else
    {
      if (GNUNET_OK !=
          TALER_amount_add (&ctx->authorized_amount,
                            &ctx->authorized_amount,
                            &amount))
      {
        GNUNET_break (0);
        GNUNET_PQ_cleanup_result (rs);
        ctx->qs = GNUNET_DB_STATUS_HARD_ERROR;
        return;
      }
    }
    GNUNET_PQ_cleanup_result (rs);
  }

  if (0 == i)
  {
    ctx->qs = GNUNET_DB_STATUS_SUCCESS_NO_RESULTS;
  }
  else
  {
    /* one aggregated result */
    ctx->qs = GNUNET_DB_STATUS_SUCCESS_ONE_RESULT;
  }
}


/**
 * Get the total amount of authorized tips for a tipping reserve.
 *
 * @param cls closure, typically a connection to the db
 * @param reserve_priv which reserve to check
 * @param[out] authorzed_amount amount we've authorized so far for tips
 * @return transaction status, usually
 *      #GNUNET_DB_STATUS_SUCCESS_ONE_RESULT for success
 *      #GNUNET_DB_STATUS_SUCCESS_NO_RESULTS if the reserve_priv
 *      does not identify a known tipping reserve
 */
static enum GNUNET_DB_QueryStatus
postgres_get_authorized_tip_amount (void *cls,
                                    const struct
                                    TALER_ReservePrivateKeyP *reserve_priv,
                                    struct TALER_Amount *authorized_amount)
{
  struct PostgresClosure *pg = cls;
  struct GNUNET_PQ_QueryParam params[] = {
    GNUNET_PQ_query_param_auto_from_type (reserve_priv),
    GNUNET_PQ_query_param_end
  };
  enum GNUNET_DB_QueryStatus qs;
  struct GetAuthorizedTipAmountContext ctx = {
    .pg = pg
  };

  check_connection (pg);
  qs = GNUNET_PQ_eval_prepared_multi_select (pg->conn,
                                             "find_tip_authorizations",
                                             params,
                                             &find_tip_authorizations_cb,
                                             &ctx);
  if (0 >= qs)
    return qs;
  *authorized_amount = ctx.authorized_amount;
  return ctx.qs;
}


/**
 * Return proposals whose timestamp are older than `date`.
 * The rows are sorted having the youngest first.
 *
 * @param cls our plugin handle.
 * @param date only results older than this date are returned.
 * @param merchant_pub instance's public key; only rows related to this
 * instance are returned.
 * @param nrows at most nrows rows are returned.
 * @param cb function to call with transaction data, can be NULL.
 * @param cb_cls closure for @a cb
 * @return transaction status
 */
static enum GNUNET_DB_QueryStatus
postgres_find_contract_terms_by_date (void *cls,
                                      struct GNUNET_TIME_Absolute date,
                                      const struct
                                      TALER_MerchantPublicKeyP *merchant_pub,
                                      uint64_t nrows,
                                      TALER_MERCHANTDB_ProposalDataCallback cb,
                                      void *cb_cls)
{
  struct PostgresClosure *pg = cls;
  struct GNUNET_PQ_QueryParam params[] = {
    GNUNET_PQ_query_param_absolute_time (&date),
    GNUNET_PQ_query_param_auto_from_type (merchant_pub),
    GNUNET_PQ_query_param_uint64 (&nrows),
    GNUNET_PQ_query_param_end
  };
  enum GNUNET_DB_QueryStatus qs;
  struct FindContractsContext fcctx = {
    .cb = cb,
    .cb_cls = cb_cls
  };

  check_connection (pg);
  qs = GNUNET_PQ_eval_prepared_multi_select (pg->conn,
                                             "find_contract_terms_by_date",
                                             params,
                                             &find_contracts_cb,
                                             &fcctx);
  if (0 >= qs)
    return qs;
  return fcctx.qs;
}


/**
 * Closure for #find_payments_cb().
 */
struct FindPaymentsContext
{
  /**
   * Function to call with results.
   */
  TALER_MERCHANTDB_CoinDepositCallback cb;

  /**
   * Closure for @e cls.
   */
  void *cb_cls;

  /**
   * Plugin context.
   */
  struct PostgresClosure *pg;

  /**
   * Contract term hash used for the search.
   */
  const struct GNUNET_HashCode *h_contract_terms;

  /**
   * Transaction status (set).
   */
  enum GNUNET_DB_QueryStatus qs;
};


/**
 * Function to be called with the results of a SELECT statement
 * that has returned @a num_results results.
 *
 * @param cls of type `struct FindPaymentsContext *`
 * @param result the postgres result
 * @param num_result the number of results in @a result
 */
static void
find_payments_cb (void *cls,
                  PGresult *result,
                  unsigned int num_results)
{
  struct FindPaymentsContext *fpc = cls;
  struct PostgresClosure *pg = fpc->pg;

  for (unsigned int i = 0; i<num_results; i++)
  {
    struct TALER_CoinSpendPublicKeyP coin_pub;
    struct TALER_Amount amount_with_fee;
    struct TALER_Amount deposit_fee;
    struct TALER_Amount refund_fee;
    struct TALER_Amount wire_fee;
    json_t *exchange_proof;
    char *exchange_url;
    struct GNUNET_PQ_ResultSpec rs[] = {
      GNUNET_PQ_result_spec_auto_from_type ("coin_pub",
                                            &coin_pub),
      GNUNET_PQ_result_spec_string ("exchange_url",
                                    &exchange_url),
      TALER_PQ_RESULT_SPEC_AMOUNT ("amount_with_fee",
                                   &amount_with_fee),
      TALER_PQ_RESULT_SPEC_AMOUNT ("deposit_fee",
                                   &deposit_fee),
      TALER_PQ_RESULT_SPEC_AMOUNT ("refund_fee",
                                   &refund_fee),
      TALER_PQ_RESULT_SPEC_AMOUNT ("wire_fee",
                                   &wire_fee),
      TALER_PQ_result_spec_json ("exchange_proof",
                                 &exchange_proof),
      GNUNET_PQ_result_spec_end
    };

    if (GNUNET_OK !=
        GNUNET_PQ_extract_result (result,
                                  rs,
                                  i))
    {
      GNUNET_break (0);
      fpc->qs = GNUNET_DB_STATUS_HARD_ERROR;
      return;
    }
    fpc->qs = i + 1;
    fpc->cb (fpc->cb_cls,
             fpc->h_contract_terms,
             &coin_pub,
             exchange_url,
             &amount_with_fee,
             &deposit_fee,
             &refund_fee,
             &wire_fee,
             exchange_proof);
    GNUNET_PQ_cleanup_result (rs);
  }
}


/**
 * Lookup information about coin payments by proposal data hash
 * (and @a merchant_pub)
 *
 * @param cls closure
 * @param h_contract_terms key for the search
 * @param merchant_pub merchant's public key
 * @param cb function to call with payment data
 * @param cb_cls closure for @a cb
 * @return transaction status
 */
static enum GNUNET_DB_QueryStatus
postgres_find_payments (void *cls,
                        const struct GNUNET_HashCode *h_contract_terms,
                        const struct TALER_MerchantPublicKeyP *merchant_pub,
                        TALER_MERCHANTDB_CoinDepositCallback cb,
                        void *cb_cls)
{
  struct PostgresClosure *pg = cls;
  struct GNUNET_PQ_QueryParam params[] = {
    GNUNET_PQ_query_param_auto_from_type (h_contract_terms),
    GNUNET_PQ_query_param_auto_from_type (merchant_pub),
    GNUNET_PQ_query_param_end
  };
  struct FindPaymentsContext fpc = {
    .h_contract_terms = h_contract_terms,
    .cb = cb,
    .cb_cls = cb_cls,
    .pg = pg
  };
  enum GNUNET_DB_QueryStatus qs;

  /* no preflight check here, run in its own transaction by the
     caller! */
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Finding payment for h_contract_terms '%s'\n",
              GNUNET_h2s (h_contract_terms));
  check_connection (pg);
  qs = GNUNET_PQ_eval_prepared_multi_select (pg->conn,
                                             "find_deposits",
                                             params,
                                             &find_payments_cb,
                                             &fpc);
  if (qs <= 0)
    return qs;
  return fpc.qs;
}


/**
 * Closure for #find_payments_by_coin_cb().
 */
struct FindPaymentsByCoinContext
{
  /**
   * Function to call with results.
   */
  TALER_MERCHANTDB_CoinDepositCallback cb;

  /**
   * Closure for @e cls.
   */
  void *cb_cls;

  /**
   * Plugin context.
   */
  struct PostgresClosure *pg;

  /**
   * Coin we are looking for.
   */
  const struct TALER_CoinSpendPublicKeyP *coin_pub;

  /**
   * Hash of the contract we are looking for.
   */
  const struct GNUNET_HashCode *h_contract_terms;

  /**
   * Transaction status (set).
   */
  enum GNUNET_DB_QueryStatus qs;
};


/**
 * Function to be called with the results of a SELECT statement
 * that has returned @a num_results results.
 *
 * @param cls of type `struct FindPaymentsByCoinContext *`
 * @param result the postgres result
 * @param num_result the number of results in @a result
 */
static void
find_payments_by_coin_cb (void *cls,
                          PGresult *result,
                          unsigned int num_results)
{
  struct FindPaymentsByCoinContext *fpc = cls;
  struct PostgresClosure *pg = fpc->pg;

  for (unsigned int i = 0; i<num_results; i++)
  {
    struct TALER_Amount amount_with_fee;
    struct TALER_Amount deposit_fee;
    struct TALER_Amount refund_fee;
    struct TALER_Amount wire_fee;
    char *exchange_url;
    json_t *exchange_proof;
    struct GNUNET_PQ_ResultSpec rs[] = {
      TALER_PQ_RESULT_SPEC_AMOUNT ("amount_with_fee",
                                   &amount_with_fee),
      TALER_PQ_RESULT_SPEC_AMOUNT ("deposit_fee",
                                   &deposit_fee),
      TALER_PQ_RESULT_SPEC_AMOUNT ("refund_fee",
                                   &refund_fee),
      TALER_PQ_RESULT_SPEC_AMOUNT ("wire_fee",
                                   &wire_fee),
      GNUNET_PQ_result_spec_string ("exchange_url",
                                    &exchange_url),
      TALER_PQ_result_spec_json ("exchange_proof",
                                 &exchange_proof),
      GNUNET_PQ_result_spec_end
    };

    if (GNUNET_OK !=
        GNUNET_PQ_extract_result (result,
                                  rs,
                                  i))
    {
      GNUNET_break (0);
      fpc->qs = GNUNET_DB_STATUS_HARD_ERROR;
      return;
    }
    fpc->qs = i + 1;
    fpc->cb (fpc->cb_cls,
             fpc->h_contract_terms,
             fpc->coin_pub,
             exchange_url,
             &amount_with_fee,
             &deposit_fee,
             &refund_fee,
             &wire_fee,
             exchange_proof);
    GNUNET_PQ_cleanup_result (rs);
  }
}


/**
 * Retrieve information about a deposited coin.
 *
 * @param cls closure
 * @param h_contract_terms hashcode of the proposal data paid by @a coin_pub
 * @param merchant_pub merchant's public key.
 * @param coin_pub coin's public key used for the search
 * @param cb function to call with payment data
 * @param cb_cls closure for @a cb
 * @return transaction status
 */
static enum GNUNET_DB_QueryStatus
postgres_find_payments_by_hash_and_coin (void *cls,
                                         const struct
                                         GNUNET_HashCode *h_contract_terms,
                                         const struct
                                         TALER_MerchantPublicKeyP *merchant_pub,
                                         const struct
                                         TALER_CoinSpendPublicKeyP *coin_pub,
                                         TALER_MERCHANTDB_CoinDepositCallback cb,
                                         void *cb_cls)
{
  struct PostgresClosure *pg = cls;
  struct GNUNET_PQ_QueryParam params[] = {
    GNUNET_PQ_query_param_auto_from_type (h_contract_terms),
    GNUNET_PQ_query_param_auto_from_type (merchant_pub),
    GNUNET_PQ_query_param_auto_from_type (coin_pub),
    GNUNET_PQ_query_param_end
  };
  struct FindPaymentsByCoinContext fpc = {
    .cb = cb,
    .cb_cls = cb_cls,
    .pg = pg,
    .h_contract_terms = h_contract_terms,
    .coin_pub = coin_pub
  };
  enum GNUNET_DB_QueryStatus qs;

  check_connection (pg);
  qs = GNUNET_PQ_eval_prepared_multi_select (pg->conn,
                                             "find_deposits_by_hash_and_coin",
                                             params,
                                             &find_payments_by_coin_cb,
                                             &fpc);
  if (0 >= qs)
    return qs;
  return fpc.qs;
}


/**
 * Closure for #find_transfers_cb().
 */
struct FindTransfersContext
{
  /**
   * Function to call on results.
   */
  TALER_MERCHANTDB_TransferCallback cb;

  /**
   * Closure for @e cb.
   */
  void *cb_cls;

  /**
   * Hash of the contract we are looking under.
   */
  const struct GNUNET_HashCode *h_contract_terms;

  /**
   * Transaction status (set).
   */
  enum GNUNET_DB_QueryStatus qs;
};


/**
 * Function to be called with the results of a SELECT statement
 * that has returned @a num_results results.
 *
 * @param cls of type `struct FindTransfersContext *`
 * @param result the postgres result
 * @param num_result the number of results in @a result
 */
static void
find_transfers_cb (void *cls,
                   PGresult *result,
                   unsigned int num_results)
{
  struct FindTransfersContext *ftc = cls;

  for (unsigned int i = 0; i<PQntuples (result); i++)
  {
    struct TALER_CoinSpendPublicKeyP coin_pub;
    struct TALER_WireTransferIdentifierRawP wtid;
    struct GNUNET_TIME_Absolute execution_time;
    json_t *proof;

    struct GNUNET_PQ_ResultSpec rs[] = {
      GNUNET_PQ_result_spec_auto_from_type ("coin_pub",
                                            &coin_pub),
      GNUNET_PQ_result_spec_auto_from_type ("wtid",
                                            &wtid),
      GNUNET_PQ_result_spec_absolute_time ("execution_time",
                                           &execution_time),
      TALER_PQ_result_spec_json ("proof",
                                 &proof),
      GNUNET_PQ_result_spec_end
    };

    if (GNUNET_OK !=
        GNUNET_PQ_extract_result (result,
                                  rs,
                                  i))
    {
      GNUNET_break (0);
      ftc->qs = GNUNET_DB_STATUS_HARD_ERROR;
      return;
    }
    ftc->qs = i + 1;
    ftc->cb (ftc->cb_cls,
             ftc->h_contract_terms,
             &coin_pub,
             &wtid,
             execution_time,
             proof);
    GNUNET_PQ_cleanup_result (rs);
  }
}


/**
 * Lookup information about a transfer by @a h_contract_terms.  Note
 * that in theory there could be multiple wire transfers for a
 * single @a h_contract_terms, as the transaction may have involved
 * multiple coins and the coins may be spread over different wire
 * transfers.
 *
 * @param cls closure
 * @param h_contract_terms key for the search
 * @param cb function to call with transfer data
 * @param cb_cls closure for @a cb
 * @return transaction status
 */
static enum GNUNET_DB_QueryStatus
postgres_find_transfers_by_hash (void *cls,
                                 const struct GNUNET_HashCode *h_contract_terms,
                                 TALER_MERCHANTDB_TransferCallback cb,
                                 void *cb_cls)
{
  struct PostgresClosure *pg = cls;
  struct GNUNET_PQ_QueryParam params[] = {
    GNUNET_PQ_query_param_auto_from_type (h_contract_terms),
    GNUNET_PQ_query_param_end
  };
  struct FindTransfersContext ftc = {
    .h_contract_terms = h_contract_terms,
    .cb = cb,
    .cb_cls = cb_cls
  };
  enum GNUNET_DB_QueryStatus qs;

  check_connection (pg);
  qs = GNUNET_PQ_eval_prepared_multi_select (pg->conn,
                                             "find_transfers_by_hash",
                                             params,
                                             &find_transfers_cb,
                                             &ftc);
  if (0 >= qs)
    return qs;
  return ftc.qs;
}


/**
 * Closure for #find_deposits_cb().
 */
struct FindDepositsContext
{

  /**
   * Function to call for each result.
   */
  TALER_MERCHANTDB_CoinDepositCallback cb;

  /**
   * Closure for @e cb.
   */
  void *cb_cls;

  /**
   * Plugin context.
   */
  struct PostgresClosure *pg;

  /**
   * Transaction status (set).
   */
  enum GNUNET_DB_QueryStatus qs;
};


/**
 * Function to be called with the results of a SELECT statement
 * that has returned @a num_results results.
 *
 * @param cls of type `struct FindDepositsContext *`
 * @param result the postgres result
 * @param num_result the number of results in @a result
 */
static void
find_deposits_cb (void *cls,
                  PGresult *result,
                  unsigned int num_results)
{
  struct FindDepositsContext *fdc = cls;
  struct PostgresClosure *pg = fdc->pg;

  for (unsigned int i = 0; i<PQntuples (result); i++)
  {
    struct GNUNET_HashCode h_contract_terms;
    struct TALER_CoinSpendPublicKeyP coin_pub;
    struct TALER_Amount amount_with_fee;
    struct TALER_Amount deposit_fee;
    struct TALER_Amount refund_fee;
    struct TALER_Amount wire_fee;
    char *exchange_url;
    json_t *exchange_proof;
    struct GNUNET_PQ_ResultSpec rs[] = {
      GNUNET_PQ_result_spec_auto_from_type ("h_contract_terms",
                                            &h_contract_terms),
      GNUNET_PQ_result_spec_auto_from_type ("coin_pub",
                                            &coin_pub),
      TALER_PQ_RESULT_SPEC_AMOUNT ("amount_with_fee",
                                   &amount_with_fee),
      TALER_PQ_RESULT_SPEC_AMOUNT ("deposit_fee",
                                   &deposit_fee),
      TALER_PQ_RESULT_SPEC_AMOUNT ("refund_fee",
                                   &refund_fee),
      TALER_PQ_RESULT_SPEC_AMOUNT ("wire_fee",
                                   &wire_fee),
      GNUNET_PQ_result_spec_string ("exchange_url",
                                    &exchange_url),
      TALER_PQ_result_spec_json ("exchange_proof",
                                 &exchange_proof),
      GNUNET_PQ_result_spec_end
    };

    if (GNUNET_OK !=
        GNUNET_PQ_extract_result (result,
                                  rs,
                                  i))
    {
      GNUNET_break (0);
      fdc->qs = GNUNET_DB_STATUS_HARD_ERROR;
      return;
    }
    fdc->qs = i + 1;
    fdc->cb (fdc->cb_cls,
             &h_contract_terms,
             &coin_pub,
             exchange_url,
             &amount_with_fee,
             &deposit_fee,
             &refund_fee,
             &wire_fee,
             exchange_proof);
    GNUNET_PQ_cleanup_result (rs);
  }
}


/**
 * Lookup information about a coin deposits by @a wtid.
 *
 * @param cls closure
 * @param wtid wire transfer identifier to find matching transactions for
 * @param cb function to call with payment data
 * @param cb_cls closure for @a cb
 * @return transaction status
 */
static enum GNUNET_DB_QueryStatus
postgres_find_deposits_by_wtid (void *cls,
                                const struct
                                TALER_WireTransferIdentifierRawP *wtid,
                                TALER_MERCHANTDB_CoinDepositCallback cb,
                                void *cb_cls)
{
  struct PostgresClosure *pg = cls;
  struct GNUNET_PQ_QueryParam params[] = {
    GNUNET_PQ_query_param_auto_from_type (wtid),
    GNUNET_PQ_query_param_end
  };
  struct FindDepositsContext fdc = {
    .cb = cb,
    .cb_cls = cb_cls,
    .pg = pg
  };
  enum GNUNET_DB_QueryStatus qs;

  check_connection (pg);
  qs = GNUNET_PQ_eval_prepared_multi_select (pg->conn,
                                             "find_deposits_by_wtid",
                                             params,
                                             &find_deposits_cb,
                                             &fdc);
  if (0 >= qs)
    return qs;
  return fdc.qs;
}


/**
 * Closure for #get_refunds_cb().
 */
struct GetRefundsContext
{
  /**
   * Function to call for each refund.
   */
  TALER_MERCHANTDB_RefundCallback rc;

  /**
   * Closure for @e rc.
   */
  void *rc_cls;

  /**
   * Plugin context.
   */
  struct PostgresClosure *pg;

  /**
   * Transaction result.
   */
  enum GNUNET_DB_QueryStatus qs;
};


/**
 * Function to be called with the results of a SELECT statement
 * that has returned @a num_results results.
 *
 * @param cls of type `struct GetRefundsContext *`
 * @param result the postgres result
 * @param num_result the number of results in @a result
 */
static void
get_refunds_cb (void *cls,
                PGresult *result,
                unsigned int num_results)
{
  struct GetRefundsContext *grc = cls;
  struct PostgresClosure *pg = grc->pg;

  for (unsigned int i = 0; i<num_results; i++)
  {
    struct TALER_CoinSpendPublicKeyP coin_pub;
    uint64_t rtransaction_id;
    struct TALER_Amount refund_amount;
    struct TALER_Amount refund_fee;
    char *reason;
    struct GNUNET_PQ_ResultSpec rs[] = {
      GNUNET_PQ_result_spec_auto_from_type ("coin_pub",
                                            &coin_pub),
      GNUNET_PQ_result_spec_uint64 ("rtransaction_id",
                                    &rtransaction_id),
      TALER_PQ_RESULT_SPEC_AMOUNT ("refund_amount",
                                   &refund_amount),
      TALER_PQ_RESULT_SPEC_AMOUNT ("refund_fee",
                                   &refund_fee),
      GNUNET_PQ_result_spec_string ("reason",
                                    &reason),
      GNUNET_PQ_result_spec_end
    };

    if (GNUNET_OK !=
        GNUNET_PQ_extract_result (result,
                                  rs,
                                  i))
    {
      GNUNET_break (0);
      grc->qs = GNUNET_DB_STATUS_HARD_ERROR;
      return;
    }
    grc->qs = i + 1;
    grc->rc (grc->rc_cls,
             &coin_pub,
             rtransaction_id,
             reason,
             &refund_amount,
             &refund_fee);
    GNUNET_PQ_cleanup_result (rs);
  }
}


/**
 * Obtain refunds associated with a contract.
 *
 * @param cls closure, typically a connection to the db
 * @param merchant_pub public key of the merchant instance
 * @param h_contract_terms hash code of the contract
 * @param rc function to call for each coin on which there is a refund
 * @param rc_cls closure for @a rc
 * @return transaction status
 */
static enum GNUNET_DB_QueryStatus
postgres_get_refunds_from_contract_terms_hash (void *cls,
                                               const struct
                                               TALER_MerchantPublicKeyP *
                                               merchant_pub,
                                               const struct
                                               GNUNET_HashCode *h_contract_terms,
                                               TALER_MERCHANTDB_RefundCallback
                                               rc,
                                               void *rc_cls)
{
  struct PostgresClosure *pg = cls;
  struct GNUNET_PQ_QueryParam params[] = {
    GNUNET_PQ_query_param_auto_from_type (merchant_pub),
    GNUNET_PQ_query_param_auto_from_type (h_contract_terms),
    GNUNET_PQ_query_param_end
  };
  struct GetRefundsContext grc = {
    .rc = rc,
    .rc_cls = rc_cls,
    .pg = pg
  };
  enum GNUNET_DB_QueryStatus qs;

  /* no preflight check here, run in transaction by caller! */
  TALER_LOG_DEBUG ("Looking for refund %s + %s\n",
                   GNUNET_h2s (h_contract_terms),
                   TALER_B2S (merchant_pub));
  check_connection (pg);
  qs = GNUNET_PQ_eval_prepared_multi_select (pg->conn,
                                             "find_refunds_from_contract_terms_hash",
                                             params,
                                             &get_refunds_cb,
                                             &grc);
  if (0 >= qs)
    return qs;
  return grc.qs;
}


/**
 * Insert a refund row into merchant_refunds.  Not meant to be exported
 * in the db API.
 *
 * @param cls closure, tipically a connection to the db
 * @param merchant_pub merchant instance public key
 * @param h_contract_terms hashcode of the contract related to this refund
 * @param coin_pub public key of the coin giving the (part of) refund
 * @param reason human readable explaination behind the refund
 * @param refund how much this coin is refunding
 * @param refund_fee refund fee for this coin
 */
static enum GNUNET_DB_QueryStatus
insert_refund (void *cls,
               const struct TALER_MerchantPublicKeyP *merchant_pub,
               const struct GNUNET_HashCode *h_contract_terms,
               const struct TALER_CoinSpendPublicKeyP *coin_pub,
               const char *reason,
               const struct TALER_Amount *refund,
               const struct TALER_Amount *refund_fee)
{
  struct PostgresClosure *pg = cls;
  struct GNUNET_PQ_QueryParam params[] = {
    GNUNET_PQ_query_param_auto_from_type (merchant_pub),
    GNUNET_PQ_query_param_auto_from_type (h_contract_terms),
    GNUNET_PQ_query_param_auto_from_type (coin_pub),
    GNUNET_PQ_query_param_string (reason),
    TALER_PQ_query_param_amount (refund),
    TALER_PQ_query_param_amount (refund_fee),
    GNUNET_PQ_query_param_end
  };

  TALER_LOG_DEBUG ("Inserting refund %s + %s\n",
                   GNUNET_h2s (h_contract_terms),
                   TALER_B2S (merchant_pub));

  check_connection (pg);
  return GNUNET_PQ_eval_prepared_non_select (pg->conn,
                                             "insert_refund",
                                             params);
}


/**
 * Store information about wire fees charged by an exchange,
 * including signature (so we have proof).
 *
 * @param cls closure
 * @paramm exchange_pub public key of the exchange
 * @param h_wire_method hash of wire method
 * @param wire_fee wire fee charged
 * @param closing_fee closing fee charged (irrelevant for us,
 *              but needed to check signature)
 * @param start_date start of fee being used
 * @param end_date end of fee being used
 * @param exchange_sig signature of exchange over fee structure
 * @return transaction status code
 */
static enum GNUNET_DB_QueryStatus
postgres_store_wire_fee_by_exchange (void *cls,
                                     const struct
                                     TALER_MasterPublicKeyP *exchange_pub,
                                     const struct
                                     GNUNET_HashCode *h_wire_method,
                                     const struct TALER_Amount *wire_fee,
                                     const struct TALER_Amount *closing_fee,
                                     struct GNUNET_TIME_Absolute start_date,
                                     struct GNUNET_TIME_Absolute end_date,
                                     const struct
                                     TALER_MasterSignatureP *exchange_sig)
{
  struct PostgresClosure *pg = cls;
  struct GNUNET_PQ_QueryParam params[] = {
    GNUNET_PQ_query_param_auto_from_type (exchange_pub),
    GNUNET_PQ_query_param_auto_from_type (h_wire_method),
    TALER_PQ_query_param_amount (wire_fee),
    TALER_PQ_query_param_amount (closing_fee),
    GNUNET_PQ_query_param_absolute_time (&start_date),
    GNUNET_PQ_query_param_absolute_time (&end_date),
    GNUNET_PQ_query_param_auto_from_type (exchange_sig),
    GNUNET_PQ_query_param_end
  };

  /* no preflight check here, run in its own transaction by the caller */
  check_connection (pg);
  GNUNET_log (GNUNET_ERROR_TYPE_INFO,
              "Storing wire fee for %s starting at %s of %s\n",
              TALER_B2S (exchange_pub),
              GNUNET_STRINGS_absolute_time_to_string (start_date),
              TALER_amount2s (wire_fee));
  return GNUNET_PQ_eval_prepared_non_select (pg->conn,
                                             "insert_wire_fee",
                                             params);
}


/**
 * Obtain information about wire fees charged by an exchange,
 * including signature (so we have proof).
 *
 * @param cls closure
 * @param exchange_pub public key of the exchange
 * @param h_wire_method hash of wire method
 * @param contract_date date of the contract to use for the lookup
 * @param[out] wire_fee wire fee charged
 * @param[out] closing_fee closing fee charged (irrelevant for us,
 *              but needed to check signature)
 * @param[out] start_date start of fee being used
 * @param[out] end_date end of fee being used
 * @param[out] exchange_sig signature of exchange over fee structure
 * @return transaction status code
 */
static enum GNUNET_DB_QueryStatus
postgres_lookup_wire_fee (void *cls,
                          const struct TALER_MasterPublicKeyP *exchange_pub,
                          const struct GNUNET_HashCode *h_wire_method,
                          struct GNUNET_TIME_Absolute contract_date,
                          struct TALER_Amount *wire_fee,
                          struct TALER_Amount *closing_fee,
                          struct GNUNET_TIME_Absolute *start_date,
                          struct GNUNET_TIME_Absolute *end_date,
                          struct TALER_MasterSignatureP *exchange_sig)
{
  struct PostgresClosure *pg = cls;
  struct GNUNET_PQ_QueryParam params[] = {
    GNUNET_PQ_query_param_auto_from_type (exchange_pub),
    GNUNET_PQ_query_param_auto_from_type (h_wire_method),
    GNUNET_PQ_query_param_absolute_time (&contract_date),
    GNUNET_PQ_query_param_end
  };
  struct GNUNET_PQ_ResultSpec rs[] = {
    TALER_PQ_RESULT_SPEC_AMOUNT ("wire_fee",
                                 wire_fee),
    TALER_PQ_RESULT_SPEC_AMOUNT ("closing_fee",
                                 closing_fee),
    GNUNET_PQ_result_spec_absolute_time ("start_date",
                                         start_date),
    GNUNET_PQ_result_spec_absolute_time ("end_date",
                                         end_date),
    GNUNET_PQ_result_spec_auto_from_type ("exchange_sig",
                                          exchange_sig),
    GNUNET_PQ_result_spec_end
  };

  check_connection (pg);
  return GNUNET_PQ_eval_prepared_singleton_select (pg->conn,
                                                   "lookup_wire_fee",
                                                   params,
                                                   rs);
}


/**
 * Closure for #process_refund_cb.
 */
struct FindRefundContext
{

  /**
   * Plugin context.
   */
  struct PostgresClosure *pg;

  /**
   * Updated to reflect total amount refunded so far.
   */
  struct TALER_Amount refunded_amount;

  /**
   * Set to #GNUNET_SYSERR on hard errors.
   */
  int err;
};


/**
 * Function to be called with the results of a SELECT statement
 * that has returned @a num_results results.
 *
 * @param cls closure, our `struct FindRefundContext`
 * @param result the postgres result
 * @param num_result the number of results in @a result
 */
static void
process_refund_cb (void *cls,
                   PGresult *result,
                   unsigned int num_results)
{
  struct FindRefundContext *ictx = cls;
  struct PostgresClosure *pg = ictx->pg;

  for (unsigned int i = 0; i<num_results; i++)
  {
    /* Sum up existing refunds */
    struct TALER_Amount acc;
    struct GNUNET_PQ_ResultSpec rs[] = {
      TALER_PQ_RESULT_SPEC_AMOUNT ("refund_amount",
                                   &acc),
      GNUNET_PQ_result_spec_end
    };

    if (GNUNET_OK !=
        GNUNET_PQ_extract_result (result,
                                  rs,
                                  i))
    {
      GNUNET_break (0);
      ictx->err = GNUNET_SYSERR;
      return;
    }
    if (GNUNET_SYSERR ==
        TALER_amount_add (&ictx->refunded_amount,
                          &ictx->refunded_amount,
                          &acc))
    {
      GNUNET_break (0);
      ictx->err = GNUNET_SYSERR;
      return;
    }
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "Found refund of %s\n",
                TALER_amount2s (&acc));
  }
}


/**
 * Closure for #process_deposits_cb.
 */
struct InsertRefundContext
{
  /**
   * Used to provide a connection to the db
   */
  struct PostgresClosure *pg;

  /**
   * Amount to which increase the refund for this contract
   */
  const struct TALER_Amount *refund;

  /**
   * Merchant instance public key
   */
  const struct TALER_MerchantPublicKeyP *merchant_pub;

  /**
   * Hash code representing the contract
   */
  const struct GNUNET_HashCode *h_contract_terms;

  /**
   * Human-readable reason behind this refund
   */
  const char *reason;

  /**
   * Transaction status code.
   */
  enum GNUNET_DB_QueryStatus qs;
};


/**
 * Function to be called with the results of a SELECT statement
 * that has returned @a num_results results.
 *
 * @param cls closure, our `struct InsertRefundContext`
 * @param result the postgres result
 * @param num_result the number of results in @a result
 */
static void
process_deposits_for_refund_cb (void *cls,
                                PGresult *result,
                                unsigned int num_results)
{
  struct InsertRefundContext *ctx = cls;
  struct PostgresClosure *pg = ctx->pg;
  struct TALER_Amount current_refund;
  struct TALER_Amount deposit_refund[GNUNET_NZL (num_results)];
  struct TALER_CoinSpendPublicKeyP deposit_coin_pubs[GNUNET_NZL (num_results)];
  struct TALER_Amount deposit_amount_with_fee[GNUNET_NZL (num_results)];
  struct TALER_Amount deposit_refund_fee[GNUNET_NZL (num_results)];

  GNUNET_assert (GNUNET_OK ==
                 TALER_amount_get_zero (ctx->refund->currency,
                                        &current_refund));

  /* Pass 1:  Collect amount of existing refunds into current_refund.
   * Also store existing refunded amount for each deposit in deposit_refund. */
  for (unsigned int i = 0; i<num_results; i++)
  {
    struct TALER_CoinSpendPublicKeyP coin_pub;
    struct TALER_Amount amount_with_fee;
    struct TALER_Amount refund_fee;
    struct GNUNET_PQ_ResultSpec rs[] = {
      GNUNET_PQ_result_spec_auto_from_type ("coin_pub",
                                            &coin_pub),
      TALER_PQ_RESULT_SPEC_AMOUNT ("amount_with_fee",
                                   &amount_with_fee),
      TALER_PQ_RESULT_SPEC_AMOUNT ("refund_fee",
                                   &refund_fee),
      GNUNET_PQ_result_spec_end
    };
    struct FindRefundContext ictx = {
      .err = GNUNET_OK,
      .pg = pg
    };
    enum GNUNET_DB_QueryStatus ires;
    struct GNUNET_PQ_QueryParam params[] = {
      GNUNET_PQ_query_param_auto_from_type (&coin_pub),
      GNUNET_PQ_query_param_end
    };

    if (GNUNET_OK !=
        GNUNET_PQ_extract_result (result,
                                  rs,
                                  i))
    {
      GNUNET_break (0);
      ctx->qs = GNUNET_DB_STATUS_HARD_ERROR;
      return;
    }
    GNUNET_assert (GNUNET_OK ==
                   TALER_amount_get_zero (ctx->refund->currency,
                                          &ictx.refunded_amount));
    ires = GNUNET_PQ_eval_prepared_multi_select (ctx->pg->conn,
                                                 "find_refunds",
                                                 params,
                                                 &process_refund_cb,
                                                 &ictx);
    if ( (GNUNET_OK != ictx.err) ||
         (GNUNET_DB_STATUS_HARD_ERROR == ires) )
    {
      GNUNET_break (0);
      ctx->qs = GNUNET_DB_STATUS_HARD_ERROR;
      return;
    }
    if (GNUNET_DB_STATUS_SOFT_ERROR == ires)
    {
      ctx->qs = GNUNET_DB_STATUS_SOFT_ERROR;
      return;
    }
    deposit_refund[i] = ictx.refunded_amount;
    deposit_amount_with_fee[i] = amount_with_fee;
    deposit_coin_pubs[i] = coin_pub;
    deposit_refund_fee[i] = refund_fee;
    if (GNUNET_SYSERR ==
        TALER_amount_add (&current_refund,
                          &current_refund,
                          &ictx.refunded_amount))
    {
      GNUNET_break (0);
      ctx->qs = GNUNET_DB_STATUS_HARD_ERROR;
      return;
    }
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "Existing refund for coin %s is %s\n",
                TALER_B2S (&coin_pub),
                TALER_amount2s (&ictx.refunded_amount));
  }

  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Total existing refund is %s\n",
              TALER_amount2s (&current_refund));

  /* stop immediately if we are 'done' === amount already
   * refunded.  */
  if (0 >= TALER_amount_cmp (ctx->refund,
                             &current_refund))
  {
    ctx->qs = GNUNET_DB_STATUS_SUCCESS_NO_RESULTS;
    return;
  }

  /* Phase 2:  Try to increase current refund until it matches desired refund */
  for (unsigned int i = 0; i<num_results; i++)
  {
    const struct TALER_Amount *increment;
    struct TALER_Amount left;
    struct TALER_Amount remaining_refund;

    /* How much of the coin is left after the existing refunds? */
    if (GNUNET_SYSERR ==
        TALER_amount_subtract (&left,
                               &deposit_amount_with_fee[i],
                               &deposit_refund[i]))
    {
      GNUNET_break (0);
      ctx->qs = GNUNET_DB_STATUS_HARD_ERROR;
      return;
    }

    if ( (0 == left.value) &&
         (0 == left.fraction) )
    {
      /* coin was fully refunded, move to next coin */
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                  "Coin %s fully refunded, moving to next coin\n",
                  TALER_B2S (&deposit_coin_pubs[i]));
      continue;
    }

    /* How much of the refund is still to be paid back? */
    if (GNUNET_SYSERR ==
        TALER_amount_subtract (&remaining_refund,
                               ctx->refund,
                               &current_refund))
    {
      GNUNET_break (0);
      ctx->qs = GNUNET_DB_STATUS_HARD_ERROR;
      return;
    }

    /* By how much will we increase the refund for this coin? */
    if (0 >= TALER_amount_cmp (&remaining_refund,
                               &left))
    {
      /* remaining_refund <= left */
      increment = &remaining_refund;
    }
    else
    {
      increment = &left;
    }

    if (GNUNET_SYSERR ==
        TALER_amount_add (&current_refund,
                          &current_refund,
                          increment))
    {
      GNUNET_break (0);
      ctx->qs = GNUNET_DB_STATUS_HARD_ERROR;
      return;
    }

    /* actually run the refund */
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "Coin %s deposit amount is %s\n",
                TALER_B2S (&deposit_coin_pubs[i]),
                TALER_amount2s (&deposit_amount_with_fee[i]));
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "Coin %s refund will be incremented by %s\n",
                TALER_B2S (&deposit_coin_pubs[i]),
                TALER_amount2s (increment));
    {
      enum GNUNET_DB_QueryStatus qs;

      if (GNUNET_DB_STATUS_SUCCESS_ONE_RESULT !=
          (qs = insert_refund (ctx->pg,
                               ctx->merchant_pub,
                               ctx->h_contract_terms,
                               &deposit_coin_pubs[i],
                               ctx->reason,
                               increment,
                               &deposit_refund_fee[i])))
      {
        GNUNET_break (GNUNET_DB_STATUS_SOFT_ERROR == qs);
        ctx->qs = qs;
        return;
      }
    }

    /* stop immediately if we are done */
    if (0 == TALER_amount_cmp (ctx->refund,
                               &current_refund))
      return;
  }

  /**
   * We end up here if not all of the refund has been covered.
   * Although this should be checked as the business should never
   * issue a refund bigger than the contract's actual price, we cannot
   * rely upon the frontend being correct.
   */
  GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
              "The refund of %s is bigger than the order's value\n",
              TALER_amount2s (ctx->refund));

  ctx->qs = GNUNET_DB_STATUS_HARD_ERROR;
}


/**
 * Function called when some backoffice staff decides to award or
 * increase the refund on an existing contract.  This function
 * MUST be called from within a transaction scope setup by the
 * caller as it executes multiple SQL statements (NT).
 *
 * @param cls closure
 * @param h_contract_terms
 * @param merchant_pub merchant's instance public key
 * @param refund maximum refund to return to the customer for this contract
 * @param reason 0-terminated UTF-8 string giving the reason why the customer
 *               got a refund (free form, business-specific)
 * @return transaction status
 *         #GNUNET_DB_STATUS_SUCCESS_ONE_RESULT if the refund is accepted
 *         #GNUNET_DB_STATUS_SUCCESS_NO_RESULTS if the refund cannot be issued: this can happen for two
 *               reasons: the issued refund is not greater of the previous refund,
 *               or the coins don't have enough amount left to pay for this refund.
 */
static enum GNUNET_DB_QueryStatus
postgres_increase_refund_for_contract_NT (void *cls,
                                          const struct
                                          GNUNET_HashCode *h_contract_terms,
                                          const struct
                                          TALER_MerchantPublicKeyP *merchant_pub,
                                          const struct TALER_Amount *refund,
                                          const char *reason)
{
  struct PostgresClosure *pg = cls;
  struct InsertRefundContext ctx;
  enum GNUNET_DB_QueryStatus qs;
  struct GNUNET_PQ_QueryParam params[] = {
    GNUNET_PQ_query_param_auto_from_type (h_contract_terms),
    GNUNET_PQ_query_param_auto_from_type (merchant_pub),
    GNUNET_PQ_query_param_end
  };

  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Asked to refund %s on contract %s\n",
              TALER_amount2s (refund),
              GNUNET_h2s (h_contract_terms));
  ctx.pg = pg;
  ctx.qs = GNUNET_DB_STATUS_SUCCESS_ONE_RESULT;
  ctx.refund = refund;
  ctx.reason = reason;
  ctx.h_contract_terms = h_contract_terms;
  ctx.merchant_pub = merchant_pub;
  qs = GNUNET_PQ_eval_prepared_multi_select (pg->conn,
                                             "find_deposits",
                                             params,
                                             &process_deposits_for_refund_cb,
                                             &ctx);
  switch (qs)
  {
  case GNUNET_DB_STATUS_SUCCESS_NO_RESULTS:
    GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
                "Unknown contract: %s (merchant_pub: %s), no refund possible\n",
                GNUNET_h2s (h_contract_terms),
                TALER_B2S (merchant_pub));
    return qs;
  case GNUNET_DB_STATUS_SOFT_ERROR:
  case GNUNET_DB_STATUS_HARD_ERROR:
    return qs;
  default:
    /* Got one or more deposits */
    return ctx.qs;
  }
}


/**
 * Lookup proof information about a wire transfer.
 *
 * @param cls closure
 * @param exchange_url from which exchange are we looking for proof
 * @param wtid wire transfer identifier for the search
 * @param cb function to call with proof data
 * @param cb_cls closure for @a cb
 * @return transaction status
 */
static enum GNUNET_DB_QueryStatus
postgres_find_proof_by_wtid (void *cls,
                             const char *exchange_url,
                             const struct
                             TALER_WireTransferIdentifierRawP *wtid,
                             TALER_MERCHANTDB_ProofCallback cb,
                             void *cb_cls)
{
  struct PostgresClosure *pg = cls;
  struct GNUNET_PQ_QueryParam params[] = {
    GNUNET_PQ_query_param_auto_from_type (wtid),
    GNUNET_PQ_query_param_string (exchange_url),
    GNUNET_PQ_query_param_end
  };
  json_t *proof;
  struct GNUNET_PQ_ResultSpec rs[] = {
    TALER_PQ_result_spec_json ("proof",
                               &proof),
    GNUNET_PQ_result_spec_end
  };
  enum GNUNET_DB_QueryStatus qs;

  check_connection (pg);
  qs = GNUNET_PQ_eval_prepared_singleton_select (pg->conn,
                                                 "find_proof_by_wtid",
                                                 params,
                                                 rs);
  if (GNUNET_DB_STATUS_SUCCESS_ONE_RESULT == qs)
  {
    cb (cb_cls,
        proof);
    GNUNET_PQ_cleanup_result (rs);
  }
  return qs;
}


/**
 * Add @a credit to a reserve to be used for tipping.  Note that
 * this function does not actually perform any wire transfers to
 * credit the reserve, it merely tells the merchant backend that
 * a reserve was topped up.  This has to happen before tips can be
 * authorized.
 *
 * @param cls closure, typically a connection to the db
 * @param reserve_priv which reserve is topped up or created
 * @param credit_uuid unique identifier for the credit operation
 * @param credit how much money was added to the reserve
 * @param expiration when does the reserve expire?
 * @return transaction status, usually
 *      #GNUNET_DB_STATUS_SUCCESS_ONE_RESULT for success
 *      #GNUNET_DB_STATUS_SUCCESS_NO_RESULTS if @a credit_uuid already known
 */
static enum GNUNET_DB_QueryStatus
postgres_enable_tip_reserve_TR (void *cls,
                                const struct
                                TALER_ReservePrivateKeyP *reserve_priv,
                                const struct GNUNET_HashCode *credit_uuid,
                                const struct TALER_Amount *credit,
                                struct GNUNET_TIME_Absolute expiration)
{
  struct PostgresClosure *pg = cls;
  struct GNUNET_TIME_Absolute old_expiration;
  struct TALER_Amount old_balance;
  enum GNUNET_DB_QueryStatus qs;
  struct GNUNET_TIME_Absolute new_expiration;
  struct TALER_Amount new_balance;
  unsigned int retries;

  retries = 0;
  check_connection (pg);
RETRY:
  if (MAX_RETRIES < ++retries)
    return GNUNET_DB_STATUS_SOFT_ERROR;
  if (GNUNET_OK !=
      postgres_start (pg,
                      "enable tip reserve"))
  {
    GNUNET_break (0);
    return GNUNET_DB_STATUS_HARD_ERROR;
  }

  /* ensure that credit_uuid is new/unique */
  {
    struct GNUNET_PQ_QueryParam params[] = {
      GNUNET_PQ_query_param_auto_from_type (credit_uuid),
      GNUNET_PQ_query_param_auto_from_type (reserve_priv),
      GNUNET_PQ_query_param_end
    };

    struct GNUNET_PQ_ResultSpec rs[] = {
      GNUNET_PQ_result_spec_end
    };
    qs = GNUNET_PQ_eval_prepared_singleton_select (pg->conn,
                                                   "lookup_tip_credit_uuid",
                                                   params,
                                                   rs);
    if (0 > qs)
    {
      GNUNET_break (GNUNET_DB_STATUS_SOFT_ERROR == qs);
      postgres_rollback (pg);
      if (GNUNET_DB_STATUS_SOFT_ERROR == qs)
        goto RETRY;
      return qs;
    }
    if (GNUNET_DB_STATUS_SUCCESS_NO_RESULTS != qs)
    {
      /* UUID already exists, we are done! */
      postgres_rollback (pg);
      return GNUNET_DB_STATUS_SUCCESS_NO_RESULTS;
    }
  }

  {
    struct GNUNET_TIME_Absolute now;
    struct GNUNET_PQ_QueryParam params[] = {
      GNUNET_PQ_query_param_auto_from_type (reserve_priv),
      GNUNET_PQ_query_param_auto_from_type (credit_uuid),
      GNUNET_PQ_query_param_absolute_time (&now),
      TALER_PQ_query_param_amount (credit),
      GNUNET_PQ_query_param_end
    };

    now = GNUNET_TIME_absolute_get ();
    (void) GNUNET_TIME_round_abs (&now);
    qs = GNUNET_PQ_eval_prepared_non_select (pg->conn,
                                             "insert_tip_credit_uuid",
                                             params);
    if (0 > qs)
    {
      GNUNET_break (GNUNET_DB_STATUS_SOFT_ERROR == qs);
      postgres_rollback (pg);
      if (GNUNET_DB_STATUS_SOFT_ERROR == qs)
        goto RETRY;
      return qs;
    }
  }

  /* Obtain existing reserve balance */
  {
    struct GNUNET_PQ_QueryParam params[] = {
      GNUNET_PQ_query_param_auto_from_type (reserve_priv),
      GNUNET_PQ_query_param_end
    };
    struct GNUNET_PQ_ResultSpec rs[] = {
      GNUNET_PQ_result_spec_absolute_time ("expiration",
                                           &old_expiration),
      TALER_PQ_RESULT_SPEC_AMOUNT ("balance",
                                   &old_balance),
      GNUNET_PQ_result_spec_end
    };

    qs = GNUNET_PQ_eval_prepared_singleton_select (pg->conn,
                                                   "lookup_tip_reserve_balance",
                                                   params,
                                                   rs);
  }
  if (0 > qs)
  {
    GNUNET_break (GNUNET_DB_STATUS_SOFT_ERROR == qs);
    postgres_rollback (pg);
    if (GNUNET_DB_STATUS_SOFT_ERROR == qs)
      goto RETRY;
    return qs;
  }
  if ( (GNUNET_DB_STATUS_SUCCESS_ONE_RESULT == qs) &&
       (GNUNET_TIME_absolute_get_remaining (old_expiration).rel_value_us > 0) )
  {
    new_expiration = GNUNET_TIME_absolute_max (old_expiration,
                                               expiration);
    if (GNUNET_OK !=
        TALER_amount_add (&new_balance,
                          credit,
                          &old_balance))
    {
      GNUNET_break (0);
      postgres_rollback (pg);
      return GNUNET_DB_STATUS_HARD_ERROR;
    }
  }
  else
  {
    if (GNUNET_DB_STATUS_SUCCESS_ONE_RESULT == qs)
    {
      GNUNET_log (GNUNET_ERROR_TYPE_INFO,
                  "Old reserve balance of %s had expired at %s, not carrying it over!\n",
                  TALER_amount2s (&old_balance),
                  GNUNET_STRINGS_absolute_time_to_string (old_expiration));
    }
    new_expiration = expiration;
    new_balance = *credit;
  }

  {
    struct GNUNET_PQ_QueryParam params[] = {
      GNUNET_PQ_query_param_auto_from_type (reserve_priv),
      GNUNET_PQ_query_param_absolute_time (&new_expiration),
      TALER_PQ_query_param_amount (&new_balance),
      GNUNET_PQ_query_param_end
    };
    const char *stmt;

    stmt = (GNUNET_DB_STATUS_SUCCESS_ONE_RESULT == qs)
           ? "update_tip_reserve_balance"
           : "insert_tip_reserve_balance";
    qs = GNUNET_PQ_eval_prepared_non_select (pg->conn,
                                             stmt,
                                             params);
    if (0 > qs)
    {
      GNUNET_break (GNUNET_DB_STATUS_SOFT_ERROR == qs);
      postgres_rollback (pg);
      if (GNUNET_DB_STATUS_SOFT_ERROR == qs)
        goto RETRY;
      return qs;
    }
  }
  qs = postgres_commit (pg);
  if (GNUNET_DB_STATUS_SUCCESS_NO_RESULTS == qs)
    return GNUNET_DB_STATUS_SUCCESS_ONE_RESULT;
  GNUNET_break (GNUNET_DB_STATUS_SOFT_ERROR == qs);
  if (GNUNET_DB_STATUS_SOFT_ERROR == qs)
    goto RETRY;
  return qs;
}


/**
 * Authorize a tip over @a amount from reserve @a reserve_priv.  Remember
 * the authorization under @a tip_id for later, together with the
 * @a justification.
 *
 * @param cls closure, typically a connection to the db
 * @param justification why was the tip approved
 * @param extra extra data for the customer's wallet
 * @param amount how high is the tip (with fees)
 * @param reserve_priv which reserve is debited
 * @param exchange_url which exchange manages the tip
 * @param[out] expiration set to when the tip expires
 * @param[out] tip_id set to the unique ID for the tip
 * @return taler error code
 *      #TALER_EC_TIP_AUTHORIZE_RESERVE_EXPIRED if the reserve is known but has expired
 *      #TALER_EC_TIP_AUTHORIZE_RESERVE_UNKNOWN if the reserve is not known
 *      #TALER_EC_TIP_AUTHORIZE_INSUFFICIENT_FUNDS if the reserve has insufficient funds left
 *      #TALER_EC_TIP_AUTHORIZE_DB_HARD_ERROR on hard DB errors
 *      #TALER_EC_TIP_AUTHORIZE_DB_SOFT_ERROR on soft DB errors (client should retry)
 *      #TALER_EC_NONE upon success
 */
static enum TALER_ErrorCode
postgres_authorize_tip_TR (void *cls,
                           const char *justification,
                           const json_t *extra,
                           const struct TALER_Amount *amount,
                           const struct TALER_ReservePrivateKeyP *reserve_priv,
                           const char *exchange_url,
                           struct GNUNET_TIME_Absolute *expiration,
                           struct GNUNET_HashCode *tip_id)
{
  struct PostgresClosure *pg = cls;
  struct GNUNET_PQ_QueryParam params[] = {
    GNUNET_PQ_query_param_auto_from_type (reserve_priv),
    GNUNET_PQ_query_param_end
  };
  struct GNUNET_TIME_Absolute old_expiration;
  struct TALER_Amount old_balance;
  struct GNUNET_PQ_ResultSpec rs[] = {
    GNUNET_PQ_result_spec_absolute_time ("expiration",
                                         &old_expiration),
    TALER_PQ_RESULT_SPEC_AMOUNT ("balance",
                                 &old_balance),
    GNUNET_PQ_result_spec_end
  };
  enum GNUNET_DB_QueryStatus qs;
  struct TALER_Amount new_balance;
  unsigned int retries;

  retries = 0;
  check_connection (pg);
RETRY:
  if (MAX_RETRIES < ++retries)
    return TALER_EC_TIP_AUTHORIZE_DB_SOFT_ERROR;
  if (GNUNET_OK !=
      postgres_start (pg,
                      "authorize tip"))
  {
    GNUNET_break (0);
    return TALER_EC_TIP_AUTHORIZE_DB_HARD_ERROR;
  }
  qs = GNUNET_PQ_eval_prepared_singleton_select (pg->conn,
                                                 "lookup_tip_reserve_balance",
                                                 params,
                                                 rs);
  if (0 >= qs)
  {
    /* reserve unknown */
    postgres_rollback (pg);
    if (GNUNET_DB_STATUS_SOFT_ERROR == qs)
      goto RETRY;
    if (GNUNET_DB_STATUS_SUCCESS_NO_RESULTS == qs)
      return TALER_EC_TIP_AUTHORIZE_INSUFFICIENT_FUNDS;
    return TALER_EC_TIP_AUTHORIZE_DB_HARD_ERROR;
  }
  if (0 == GNUNET_TIME_absolute_get_remaining (old_expiration).rel_value_us)
  {
    /* reserve expired, can't be used */
    postgres_rollback (pg);
    return TALER_EC_TIP_AUTHORIZE_RESERVE_EXPIRED;
  }
  if (GNUNET_SYSERR ==
      TALER_amount_subtract (&new_balance,
                             &old_balance,
                             amount))
  {
    /* insufficient funds left in reserve */
    postgres_rollback (pg);
    return TALER_EC_TIP_AUTHORIZE_INSUFFICIENT_FUNDS;
  }
  /* Update reserve balance */
  {
    struct GNUNET_PQ_QueryParam params[] = {
      GNUNET_PQ_query_param_auto_from_type (reserve_priv),
      GNUNET_PQ_query_param_absolute_time (&old_expiration),
      TALER_PQ_query_param_amount (&new_balance),
      GNUNET_PQ_query_param_end
    };

    qs = GNUNET_PQ_eval_prepared_non_select (pg->conn,
                                             "update_tip_reserve_balance",
                                             params);
    if (0 > qs)
    {
      postgres_rollback (pg);
      if (GNUNET_DB_STATUS_SOFT_ERROR == qs)
        goto RETRY;
      return TALER_EC_TIP_AUTHORIZE_DB_HARD_ERROR;
    }
  }
  /* Generate and store tip ID */
  *expiration = old_expiration;
  GNUNET_CRYPTO_hash_create_random (GNUNET_CRYPTO_QUALITY_STRONG,
                                    tip_id);
  {
    struct GNUNET_TIME_Absolute now = GNUNET_TIME_absolute_get ();
    struct GNUNET_PQ_QueryParam params[] = {
      GNUNET_PQ_query_param_auto_from_type (reserve_priv),
      GNUNET_PQ_query_param_auto_from_type (tip_id),
      GNUNET_PQ_query_param_string (exchange_url),
      GNUNET_PQ_query_param_string (justification),
      TALER_PQ_query_param_json (extra),
      GNUNET_PQ_query_param_absolute_time (&now),
      TALER_PQ_query_param_amount (amount), /* overall amount */
      TALER_PQ_query_param_amount (amount), /* amount left */
      GNUNET_PQ_query_param_end
    };

    (void) GNUNET_TIME_round_abs (&now);
    qs = GNUNET_PQ_eval_prepared_non_select (pg->conn,
                                             "insert_tip_justification",
                                             params);
    if (0 > qs)
    {
      postgres_rollback (pg);
      if (GNUNET_DB_STATUS_SOFT_ERROR == qs)
        goto RETRY;
      return TALER_EC_TIP_AUTHORIZE_DB_HARD_ERROR;
    }
  }
  qs = postgres_commit (pg);
  if (0 <= qs)
    return TALER_EC_NONE; /* success! */
  if (GNUNET_DB_STATUS_SOFT_ERROR == qs)
    goto RETRY;
  return TALER_EC_TIP_AUTHORIZE_DB_HARD_ERROR;
}


/**
 * Find out tip authorization details associated with @a tip_id
 *
 * @param cls closure, typically a connection to the d
 * @param tip_id the unique ID for the tip
 * @param[out] exchange_url set to the URL of the exchange (unless NULL)
 * @param[out] extra extra data to pass to the wallet (unless NULL)
 * @param[out] amount set to the authorized amount (unless NULL)
 * @param[out] amount_left set to the amount left (unless NULL)
 * @param[out] timestamp set to the timestamp of the tip authorization (unless NULL)
 * @return transaction status, usually
 *      #GNUNET_DB_STATUS_SUCCESS_ONE_RESULT for success
 *      #GNUNET_DB_STATUS_SUCCESS_NO_RESULTS if @a credit_uuid already known
 */
static enum GNUNET_DB_QueryStatus
postgres_lookup_tip_by_id (void *cls,
                           const struct GNUNET_HashCode *tip_id,
                           char **exchange_url,
                           json_t **extra,
                           struct TALER_Amount *amount,
                           struct TALER_Amount *amount_left,
                           struct GNUNET_TIME_Absolute *timestamp)
{
  struct PostgresClosure *pg = cls;
  char *res_exchange_url;
  json_t *res_extra;
  struct TALER_Amount res_amount;
  struct TALER_Amount res_amount_left;
  struct GNUNET_TIME_Absolute res_timestamp;
  struct GNUNET_PQ_QueryParam params[] = {
    GNUNET_PQ_query_param_auto_from_type (tip_id),
    GNUNET_PQ_query_param_end
  };
  struct GNUNET_PQ_ResultSpec rs[] = {
    GNUNET_PQ_result_spec_string ("exchange_url",
                                  &res_exchange_url),
    GNUNET_PQ_result_spec_absolute_time ("timestamp",
                                         &res_timestamp),
    TALER_PQ_result_spec_json ("extra",
                               &res_extra),
    TALER_PQ_RESULT_SPEC_AMOUNT ("amount",
                                 &res_amount),
    TALER_PQ_RESULT_SPEC_AMOUNT ("left",
                                 &res_amount_left),
    GNUNET_PQ_result_spec_end
  };
  enum GNUNET_DB_QueryStatus qs;

  qs = GNUNET_PQ_eval_prepared_singleton_select (pg->conn,
                                                 "find_tip_by_id",
                                                 params,
                                                 rs);
  if (0 >= qs)
  {
    if (NULL != exchange_url)
      *exchange_url = NULL;
    return qs;
  }
  if (NULL != exchange_url)
    *exchange_url = strdup (res_exchange_url);
  if (NULL != amount)
    *amount = res_amount;
  if (NULL != amount_left)
    *amount_left = res_amount_left;
  if (NULL != timestamp)
    *timestamp = res_timestamp;
  if (NULL != extra)
  {
    json_incref (res_extra);
    *extra = res_extra;
  }
  GNUNET_PQ_cleanup_result (rs);
  return qs;
}


/**
 * Pickup a tip over @a amount using pickup id @a pickup_id.
 *
 * @param cls closure, typically a connection to the db
 * @param amount how high is the amount picked up (with fees)
 * @param tip_id the unique ID from the tip authorization
 * @param pickup_id the unique ID identifying the pick up operation
 *        (to allow replays, hash over the coin envelope and denomination key)
 * @param[out] reserve_priv which reserve key to use to sign
 * @return taler error code
 *      #TALER_EC_TIP_PICKUP_ID_UNKNOWN if @a tip_id is unknown
 *      #TALER_EC_TIP_PICKUP_NO_FUNDS if @a tip_id has insufficient funds left
 *      #TALER_EC_TIP_PICKUP_DB_ERROR_HARD on hard database errors
 *      #TALER_EC_TIP_PICKUP_AMOUNT_CHANGED if @a amount is different for known @a pickup_id
 *      #TALER_EC_TIP_PICKUP_DB_ERROR_SOFT on soft database errors (client should retry)
 *      #TALER_EC_NONE upon success (@a reserve_priv was set)
 */
static enum TALER_ErrorCode
postgres_pickup_tip_TR (void *cls,
                        const struct TALER_Amount *amount,
                        const struct GNUNET_HashCode *tip_id,
                        const struct GNUNET_HashCode *pickup_id,
                        struct TALER_ReservePrivateKeyP *reserve_priv)
{
  struct PostgresClosure *pg = cls;
  struct TALER_Amount left_amount;
  struct GNUNET_PQ_QueryParam params[] = {
    GNUNET_PQ_query_param_auto_from_type (tip_id),
    GNUNET_PQ_query_param_end
  };
  struct GNUNET_PQ_ResultSpec rs[] = {
    GNUNET_PQ_result_spec_auto_from_type ("reserve_priv",
                                          reserve_priv),
    TALER_PQ_RESULT_SPEC_AMOUNT ("left",
                                 &left_amount),
    GNUNET_PQ_result_spec_end
  };
  enum GNUNET_DB_QueryStatus qs;
  unsigned int retries;

  retries = 0;
  check_connection (pg);
RETRY:
  if (MAX_RETRIES < ++retries)
    return TALER_EC_TIP_PICKUP_DB_ERROR_SOFT;
  if (GNUNET_OK !=
      postgres_start (pg,
                      "pickup tip"))
  {
    GNUNET_break (0);
    return TALER_EC_TIP_PICKUP_DB_ERROR_HARD;
  }
  qs = GNUNET_PQ_eval_prepared_singleton_select (pg->conn,
                                                 "lookup_reserve_by_tip_id",
                                                 params,
                                                 rs);
  if (0 >= qs)
  {
    /* tip ID unknown */
    memset (reserve_priv,
            0,
            sizeof (*reserve_priv));
    postgres_rollback (pg);
    if (GNUNET_DB_STATUS_SUCCESS_NO_RESULTS == qs)
      return TALER_EC_TIP_PICKUP_TIP_ID_UNKNOWN;
    if (GNUNET_DB_STATUS_SOFT_ERROR == qs)
      goto RETRY;
    return TALER_EC_TIP_PICKUP_DB_ERROR_HARD;
  }

  /* Check if pickup_id already exists */
  {
    struct TALER_Amount existing_amount;
    struct GNUNET_PQ_QueryParam params[] = {
      GNUNET_PQ_query_param_auto_from_type (pickup_id),
      GNUNET_PQ_query_param_auto_from_type (tip_id),
      GNUNET_PQ_query_param_end
    };
    struct GNUNET_PQ_ResultSpec rs[] = {
      TALER_PQ_RESULT_SPEC_AMOUNT ("amount",
                                   &existing_amount),
      GNUNET_PQ_result_spec_end
    };

    qs = GNUNET_PQ_eval_prepared_singleton_select (pg->conn,
                                                   "lookup_amount_by_pickup",
                                                   params,
                                                   rs);
    if (0 > qs)
    {
      /* DB error */
      memset (reserve_priv,
              0,
              sizeof (*reserve_priv));
      postgres_rollback (pg);
      if (GNUNET_DB_STATUS_SOFT_ERROR == qs)
        goto RETRY;
      return TALER_EC_TIP_PICKUP_DB_ERROR_HARD;
    }
    if (GNUNET_DB_STATUS_SUCCESS_ONE_RESULT == qs)
    {
      if (0 !=
          TALER_amount_cmp (&existing_amount,
                            amount))
      {
        GNUNET_break_op (0);
        postgres_rollback (pg);
        return TALER_EC_TIP_PICKUP_AMOUNT_CHANGED;
      }
      postgres_commit (pg);
      return TALER_EC_NONE; /* we are done! */
    }
  }

  /* Calculate new balance */
  {
    struct TALER_Amount new_left;

    if (GNUNET_SYSERR ==
        TALER_amount_subtract (&new_left,
                               &left_amount,
                               amount))
    {
      /* attempt to take more tips than the tipping amount */
      GNUNET_break_op (0);
      memset (reserve_priv,
              0,
              sizeof (*reserve_priv));
      postgres_rollback (pg);
      return TALER_EC_TIP_PICKUP_NO_FUNDS;
    }

    /* Update DB: update balance */
    {
      struct GNUNET_PQ_QueryParam params[] = {
        GNUNET_PQ_query_param_auto_from_type (tip_id),
        TALER_PQ_query_param_amount (&new_left),
        GNUNET_PQ_query_param_end
      };

      qs = GNUNET_PQ_eval_prepared_non_select (pg->conn,
                                               "update_tip_balance",
                                               params);
      if (0 > qs)
      {
        postgres_rollback (pg);
        memset (reserve_priv,
                0,
                sizeof (*reserve_priv));
        if (GNUNET_DB_STATUS_SOFT_ERROR == qs)
          goto RETRY;
        return TALER_EC_TIP_PICKUP_DB_ERROR_HARD;
      }
    }

    /* Update DB: remember pickup_id */
    {
      struct GNUNET_PQ_QueryParam params[] = {
        GNUNET_PQ_query_param_auto_from_type (tip_id),
        GNUNET_PQ_query_param_auto_from_type (pickup_id),
        TALER_PQ_query_param_amount (amount),
        GNUNET_PQ_query_param_end
      };

      qs = GNUNET_PQ_eval_prepared_non_select (pg->conn,
                                               "insert_pickup_id",
                                               params);
      if (0 > qs)
      {
        postgres_rollback (pg);
        memset (reserve_priv,
                0,
                sizeof (*reserve_priv));
        if (GNUNET_DB_STATUS_SOFT_ERROR == qs)
          goto RETRY;
        return TALER_EC_TIP_PICKUP_DB_ERROR_HARD;
      }
    }
  }
  qs = postgres_commit (pg);
  if (0 <= qs)
    return TALER_EC_NONE; /* success  */
  if (GNUNET_DB_STATUS_SOFT_ERROR == qs)
    goto RETRY;
  return TALER_EC_TIP_PICKUP_DB_ERROR_HARD;
}


/**
 * Initialize Postgres database subsystem.
 *
 * @param cls a configuration instance
 * @return NULL on error, otherwise a `struct TALER_MERCHANTDB_Plugin`
 */
void *
libtaler_plugin_merchantdb_postgres_init (void *cls)
{
  struct GNUNET_CONFIGURATION_Handle *cfg = cls;
  struct PostgresClosure *pg;
  struct TALER_MERCHANTDB_Plugin *plugin;
  const char *ec;
  struct GNUNET_PQ_ExecuteStatement es[] = {
    /* Orders created by the frontend, not signed or given a nonce yet.
       The contract terms will change (nonce will be added) when moved to the
       contract terms table */
    GNUNET_PQ_make_execute ("CREATE TABLE IF NOT EXISTS merchant_orders ("
                            "order_id VARCHAR NOT NULL"
                            ",merchant_pub BYTEA NOT NULL CHECK (LENGTH(merchant_pub)=32)"
                            ",contract_terms BYTEA NOT NULL"
                            ",timestamp INT8 NOT NULL"
                            ",PRIMARY KEY (order_id, merchant_pub)"
                            ");"),
    /* Offers we made to customers */
    GNUNET_PQ_make_execute (
      "CREATE TABLE IF NOT EXISTS merchant_contract_terms ("
      "order_id VARCHAR NOT NULL"
      ",merchant_pub BYTEA NOT NULL CHECK (LENGTH(merchant_pub)=32)"
      ",contract_terms BYTEA NOT NULL"
      ",h_contract_terms BYTEA NOT NULL CHECK (LENGTH(h_contract_terms)=64)"
      ",timestamp INT8 NOT NULL"
      ",row_id BIGSERIAL UNIQUE"
      ",paid boolean DEFAULT FALSE NOT NULL"
      ",PRIMARY KEY (order_id, merchant_pub)"
      ",UNIQUE (h_contract_terms, merchant_pub)"
      ");"),
    /* Table with the proofs for each coin we deposited at the exchange */
    GNUNET_PQ_make_execute ("CREATE TABLE IF NOT EXISTS merchant_deposits ("
                            " h_contract_terms BYTEA NOT NULL"
                            ",merchant_pub BYTEA NOT NULL CHECK (LENGTH(merchant_pub)=32)"
                            ",coin_pub BYTEA NOT NULL CHECK (LENGTH(coin_pub)=32)"
                            ",exchange_url VARCHAR NOT NULL"
                            ",amount_with_fee_val INT8 NOT NULL"
                            ",amount_with_fee_frac INT4 NOT NULL"
                            ",deposit_fee_val INT8 NOT NULL"
                            ",deposit_fee_frac INT4 NOT NULL"
                            ",refund_fee_val INT8 NOT NULL"
                            ",refund_fee_frac INT4 NOT NULL"
                            ",wire_fee_val INT8 NOT NULL"
                            ",wire_fee_frac INT4 NOT NULL"
                            ",signkey_pub BYTEA NOT NULL CHECK (LENGTH(signkey_pub)=32)"
                            ",exchange_proof BYTEA NOT NULL"
                            ",PRIMARY KEY (h_contract_terms, coin_pub)"
                            ",FOREIGN KEY (h_contract_terms, merchant_pub) REFERENCES merchant_contract_terms (h_contract_terms, merchant_pub)"
                            ");"),
    GNUNET_PQ_make_execute ("CREATE TABLE IF NOT EXISTS merchant_proofs ("
                            " exchange_url VARCHAR NOT NULL"
                            ",wtid BYTEA CHECK (LENGTH(wtid)=32)"
                            ",execution_time INT8 NOT NULL"
                            ",signkey_pub BYTEA NOT NULL CHECK (LENGTH(signkey_pub)=32)"
                            ",proof BYTEA NOT NULL"
                            ",PRIMARY KEY (wtid, exchange_url)"
                            ");"),
    /* Note that h_contract_terms + coin_pub may actually be unknown to
       us, e.g. someone else deposits something for us at the exchange.
       Hence those cannot be foreign keys into deposits/transactions! */
    GNUNET_PQ_make_execute ("CREATE TABLE IF NOT EXISTS merchant_transfers ("
                            " h_contract_terms BYTEA NOT NULL"
                            ",coin_pub BYTEA NOT NULL CHECK (LENGTH(coin_pub)=32)"
                            ",wtid BYTEA NOT NULL CHECK (LENGTH(wtid)=32)"
                            ",PRIMARY KEY (h_contract_terms, coin_pub)"
                            ");"),
    GNUNET_PQ_make_try_execute (
      "CREATE INDEX IF NOT EXISTS merchant_transfers_by_coin"
      " ON merchant_transfers (h_contract_terms, coin_pub)"),
    GNUNET_PQ_make_try_execute (
      "CREATE INDEX IF NOT EXISTS merchant_transfers_by_wtid"
      " ON merchant_transfers (wtid)"),
    GNUNET_PQ_make_execute ("CREATE TABLE IF NOT EXISTS exchange_wire_fees ("
                            " exchange_pub BYTEA NOT NULL CHECK (length(exchange_pub)=32)"
                            ",h_wire_method BYTEA NOT NULL CHECK (length(h_wire_method)=64)"
                            ",wire_fee_val INT8 NOT NULL"
                            ",wire_fee_frac INT4 NOT NULL"
                            ",closing_fee_val INT8 NOT NULL"
                            ",closing_fee_frac INT4 NOT NULL"
                            ",start_date INT8 NOT NULL"
                            ",end_date INT8 NOT NULL"
                            ",exchange_sig BYTEA NOT NULL CHECK (length(exchange_sig)=64)"
                            ",PRIMARY KEY (exchange_pub,h_wire_method,start_date,end_date)"
                            ");"),
    GNUNET_PQ_make_execute ("CREATE TABLE IF NOT EXISTS merchant_refunds ("
                            " rtransaction_id BIGSERIAL UNIQUE"
                            ",merchant_pub BYTEA NOT NULL CHECK (LENGTH(merchant_pub)=32)"
                            ",h_contract_terms BYTEA NOT NULL"
                            ",coin_pub BYTEA NOT NULL CHECK (LENGTH(coin_pub)=32)"
                            ",reason VARCHAR NOT NULL"
                            ",refund_amount_val INT8 NOT NULL"
                            ",refund_amount_frac INT4 NOT NULL"
                            ",refund_fee_val INT8 NOT NULL"
                            ",refund_fee_frac INT4 NOT NULL"
                            ");"),
    /* balances of the reserves available for tips */
    GNUNET_PQ_make_execute ("CREATE TABLE IF NOT EXISTS merchant_tip_reserves ("
                            " reserve_priv BYTEA NOT NULL CHECK (LENGTH(reserve_priv)=32)"
                            ",expiration INT8 NOT NULL"
                            ",balance_val INT8 NOT NULL"
                            ",balance_frac INT4 NOT NULL"
                            ",PRIMARY KEY (reserve_priv)"
                            ");"),
    /* table where we remember when tipping reserves where established / enabled */
    GNUNET_PQ_make_execute (
      "CREATE TABLE IF NOT EXISTS merchant_tip_reserve_credits ("
      " reserve_priv BYTEA NOT NULL CHECK (LENGTH(reserve_priv)=32)"
      ",credit_uuid BYTEA UNIQUE NOT NULL CHECK (LENGTH(credit_uuid)=64)"
      ",timestamp INT8 NOT NULL"
      ",amount_val INT8 NOT NULL"
      ",amount_frac INT4 NOT NULL"
      ",PRIMARY KEY (credit_uuid)"
      ");"),
    /* tips that have been authorized */
    GNUNET_PQ_make_execute ("CREATE TABLE IF NOT EXISTS merchant_tips ("
                            " reserve_priv BYTEA NOT NULL CHECK (LENGTH(reserve_priv)=32)"
                            ",tip_id BYTEA NOT NULL CHECK (LENGTH(tip_id)=64)"
                            ",exchange_url VARCHAR NOT NULL"
                            ",justification VARCHAR NOT NULL"
                            ",extra BYTEA NOT NULL"
                            ",timestamp INT8 NOT NULL"
                            ",amount_val INT8 NOT NULL" /* overall tip amount */
                            ",amount_frac INT4 NOT NULL"
                            ",left_val INT8 NOT NULL" /* tip amount not yet picked up */
                            ",left_frac INT4 NOT NULL"
                            ",PRIMARY KEY (tip_id)"
                            ");"),
    /* tips that have been picked up */
    GNUNET_PQ_make_execute ("CREATE TABLE IF NOT EXISTS merchant_tip_pickups ("
                            " tip_id BYTEA NOT NULL REFERENCES merchant_tips (tip_id) ON DELETE CASCADE"
                            ",pickup_id BYTEA NOT NULL CHECK (LENGTH(pickup_id)=64)"
                            ",amount_val INT8 NOT NULL"
                            ",amount_frac INT4 NOT NULL"
                            ",PRIMARY KEY (pickup_id)"
                            ");"),
    /* sessions and their order_id/fulfillment_url mapping */
    GNUNET_PQ_make_execute ("CREATE TABLE IF NOT EXISTS merchant_session_info ("
                            " session_id VARCHAR NOT NULL"
                            ",fulfillment_url VARCHAR NOT NULL"
                            ",order_id VARCHAR NOT NULL"
                            ",merchant_pub BYTEA NOT NULL CHECK (LENGTH(merchant_pub)=32)"
                            ",timestamp INT8 NOT NULL"
                            ",PRIMARY KEY (session_id, fulfillment_url, merchant_pub)"
                            ",UNIQUE (session_id, fulfillment_url, order_id, merchant_pub)"
                            ");"),
    GNUNET_PQ_EXECUTE_STATEMENT_END
  };
  struct GNUNET_PQ_PreparedStatement ps[] = {
    GNUNET_PQ_make_prepare ("insert_deposit",
                            "INSERT INTO merchant_deposits"
                            "(h_contract_terms"
                            ",merchant_pub"
                            ",coin_pub"
                            ",exchange_url"
                            ",amount_with_fee_val"
                            ",amount_with_fee_frac"
                            ",deposit_fee_val"
                            ",deposit_fee_frac"
                            ",refund_fee_val"
                            ",refund_fee_frac"
                            ",wire_fee_val"
                            ",wire_fee_frac"
                            ",signkey_pub"
                            ",exchange_proof) VALUES "
                            "($1, $2, $3, $4, $5, $6, $7, $8, $9, $10, $11, $12, $13, $14)",
                            14),
    GNUNET_PQ_make_prepare ("insert_transfer",
                            "INSERT INTO merchant_transfers"
                            "(h_contract_terms"
                            ",coin_pub"
                            ",wtid) VALUES "
                            "($1, $2, $3)",
                            3),
    GNUNET_PQ_make_prepare ("insert_refund",
                            "INSERT INTO merchant_refunds"
                            "(merchant_pub"
                            ",h_contract_terms"
                            ",coin_pub"
                            ",reason"
                            ",refund_amount_val"
                            ",refund_amount_frac"
                            ",refund_fee_val"
                            ",refund_fee_frac"
                            ") VALUES"
                            "($1, $2, $3, $4, $5, $6, $7, $8)",
                            8),
    GNUNET_PQ_make_prepare ("insert_proof",
                            "INSERT INTO merchant_proofs"
                            "(exchange_url"
                            ",wtid"
                            ",execution_time"
                            ",signkey_pub"
                            ",proof) VALUES "
                            "($1, $2, $3, $4, $5)",
                            5),
    GNUNET_PQ_make_prepare ("insert_contract_terms",
                            "INSERT INTO merchant_contract_terms"
                            "(order_id"
                            ",merchant_pub"
                            ",timestamp"
                            ",contract_terms"
                            ",h_contract_terms)"
                            " VALUES "
                            "($1, $2, $3, $4, $5)",
                            5),
    GNUNET_PQ_make_prepare ("insert_order",
                            "INSERT INTO merchant_orders"
                            "(order_id"
                            ",merchant_pub"
                            ",timestamp"
                            ",contract_terms)"
                            " VALUES "
                            "($1, $2, $3, $4)",
                            4),
    GNUNET_PQ_make_prepare ("insert_session_info",
                            "INSERT INTO merchant_session_info"
                            "(session_id"
                            ",fulfillment_url"
                            ",order_id"
                            ",merchant_pub"
                            ",timestamp)"
                            " VALUES "
                            "($1, $2, $3, $4, $5)",
                            5),
    GNUNET_PQ_make_prepare ("mark_proposal_paid",
                            "UPDATE merchant_contract_terms SET"
                            " paid=TRUE"
                            " WHERE h_contract_terms=$1"
                            " AND merchant_pub=$2",
                            2),
    GNUNET_PQ_make_prepare ("insert_wire_fee",
                            "INSERT INTO exchange_wire_fees"
                            "(exchange_pub"
                            ",h_wire_method"
                            ",wire_fee_val"
                            ",wire_fee_frac"
                            ",closing_fee_val"
                            ",closing_fee_frac"
                            ",start_date"
                            ",end_date"
                            ",exchange_sig)"
                            " VALUES "
                            "($1, $2, $3, $4, $5, $6, $7, $8, $9)",
                            9),
    GNUNET_PQ_make_prepare ("lookup_wire_fee",
                            "SELECT"
                            " wire_fee_val"
                            ",wire_fee_frac"
                            ",closing_fee_val"
                            ",closing_fee_frac"
                            ",start_date"
                            ",end_date"
                            ",exchange_sig"
                            " FROM exchange_wire_fees"
                            " WHERE exchange_pub=$1"
                            "   AND h_wire_method=$2"
                            "   AND start_date <= $3"
                            "   AND end_date > $3",
                            1),
    GNUNET_PQ_make_prepare ("find_contract_terms_from_hash",
                            "SELECT"
                            " contract_terms"
                            " FROM merchant_contract_terms"
                            " WHERE h_contract_terms=$1"
                            "   AND merchant_pub=$2",
                            2),
    GNUNET_PQ_make_prepare ("find_paid_contract_terms_from_hash",
                            "SELECT"
                            " contract_terms"
                            " FROM merchant_contract_terms"
                            " WHERE h_contract_terms=$1"
                            "   AND merchant_pub=$2"
                            "   AND paid=TRUE",
                            2),
    GNUNET_PQ_make_prepare ("end_transaction",
                            "COMMIT",
                            0),

    GNUNET_PQ_make_prepare ("find_refunds",
                            "SELECT"
                            " refund_amount_val"
                            ",refund_amount_frac"
                            " FROM merchant_refunds"
                            " WHERE coin_pub=$1",
                            1),
    GNUNET_PQ_make_prepare ("find_contract_terms_history",
                            "SELECT"
                            " contract_terms"
                            " FROM merchant_contract_terms"
                            " WHERE"
                            " order_id=$1"
                            " AND merchant_pub=$2"
                            " AND paid=TRUE",
                            2),
    GNUNET_PQ_make_prepare ("find_contract_terms",
                            "SELECT"
                            " contract_terms"
                            " FROM merchant_contract_terms"
                            " WHERE"
                            " order_id=$1"
                            " AND merchant_pub=$2",
                            2),
    GNUNET_PQ_make_prepare ("find_order",
                            "SELECT"
                            " contract_terms"
                            " FROM merchant_orders"
                            " WHERE"
                            " order_id=$1"
                            " AND merchant_pub=$2",
                            2),
    GNUNET_PQ_make_prepare ("find_session_info",
                            "SELECT"
                            " order_id"
                            " FROM merchant_session_info"
                            " WHERE"
                            " fulfillment_url=$1"
                            " AND session_id=$2"
                            " AND merchant_pub=$3",
                            2),
    GNUNET_PQ_make_prepare ("find_contract_terms_by_date",
                            "SELECT"
                            " contract_terms"
                            ",order_id"
                            ",row_id"
                            " FROM merchant_contract_terms"
                            " WHERE"
                            " timestamp<$1"
                            " AND merchant_pub=$2"
                            " AND paid=TRUE"
                            " ORDER BY row_id DESC, timestamp DESC"
                            " LIMIT $3",
                            3),
    GNUNET_PQ_make_prepare ("find_refunds_from_contract_terms_hash",
                            "SELECT"
                            " coin_pub"
                            ",rtransaction_id"
                            ",refund_amount_val"
                            ",refund_amount_frac"
                            ",refund_fee_val"
                            ",refund_fee_frac"
                            ",reason"
                            " FROM merchant_refunds"
                            " WHERE merchant_pub=$1"
                            " AND h_contract_terms=$2",
                            2),
    GNUNET_PQ_make_prepare ("find_contract_terms_by_date_and_range_asc",
                            "SELECT"
                            " contract_terms"
                            ",order_id"
                            ",row_id"
                            " FROM merchant_contract_terms"
                            " WHERE"
                            " timestamp>$1"
                            " AND merchant_pub=$2"
                            " AND row_id>$3"
                            " AND paid=TRUE"
                            " ORDER BY row_id ASC, timestamp ASC"
                            " LIMIT $4",
                            4),
    GNUNET_PQ_make_prepare ("find_contract_terms_by_date_and_range",
                            "SELECT"
                            " contract_terms"
                            ",order_id"
                            ",row_id"
                            " FROM merchant_contract_terms"
                            " WHERE"
                            " timestamp>$1"
                            " AND merchant_pub=$2"
                            " AND row_id>$3"
                            " AND paid=TRUE"
                            " ORDER BY row_id DESC, timestamp DESC"
                            " LIMIT $4",
                            4),
    GNUNET_PQ_make_prepare ("find_contract_terms_by_date_and_range_past_asc",
                            "SELECT"
                            " contract_terms"
                            ",order_id"
                            ",row_id"
                            " FROM merchant_contract_terms"
                            " WHERE"
                            " timestamp<$1"
                            " AND merchant_pub=$2"
                            " AND row_id<$3"
                            " AND paid=TRUE"
                            " ORDER BY row_id ASC, timestamp ASC"
                            " LIMIT $4",
                            4),
    GNUNET_PQ_make_prepare ("find_contract_terms_by_date_and_range_past",
                            "SELECT"
                            " contract_terms"
                            ",order_id"
                            ",row_id"
                            " FROM merchant_contract_terms"
                            " WHERE"
                            " timestamp<$1"
                            " AND merchant_pub=$2"
                            " AND row_id<$3"
                            " AND paid=TRUE"
                            " ORDER BY row_id DESC, timestamp DESC"
                            " LIMIT $4",
                            4),
    GNUNET_PQ_make_prepare ("find_deposits",
                            "SELECT"
                            " coin_pub"
                            ",exchange_url"
                            ",amount_with_fee_val"
                            ",amount_with_fee_frac"
                            ",deposit_fee_val"
                            ",deposit_fee_frac"
                            ",refund_fee_val"
                            ",refund_fee_frac"
                            ",wire_fee_val"
                            ",wire_fee_frac"
                            ",exchange_proof"
                            " FROM merchant_deposits"
                            " WHERE h_contract_terms=$1"
                            " AND merchant_pub=$2",
                            2),
    GNUNET_PQ_make_prepare ("find_deposits_by_hash_and_coin",
                            "SELECT"
                            " amount_with_fee_val"
                            ",amount_with_fee_frac"
                            ",deposit_fee_val"
                            ",deposit_fee_frac"
                            ",refund_fee_val"
                            ",refund_fee_frac"
                            ",wire_fee_val"
                            ",wire_fee_frac"
                            ",exchange_url"
                            ",exchange_proof"
                            " FROM merchant_deposits"
                            " WHERE h_contract_terms=$1"
                            " AND merchant_pub=$2"
                            " AND coin_pub=$3",
                            3),
    GNUNET_PQ_make_prepare ("find_transfers_by_hash",
                            "SELECT"
                            " coin_pub"
                            ",wtid"
                            ",merchant_proofs.execution_time"
                            ",merchant_proofs.proof"
                            " FROM merchant_transfers"
                            "   JOIN merchant_proofs USING (wtid)"
                            " WHERE h_contract_terms=$1",
                            1),
    GNUNET_PQ_make_prepare ("find_deposits_by_wtid",
                            "SELECT"
                            " merchant_transfers.h_contract_terms"
                            ",merchant_transfers.coin_pub"
                            ",merchant_deposits.amount_with_fee_val"
                            ",merchant_deposits.amount_with_fee_frac"
                            ",merchant_deposits.deposit_fee_val"
                            ",merchant_deposits.deposit_fee_frac"
                            ",merchant_deposits.refund_fee_val"
                            ",merchant_deposits.refund_fee_frac"
                            ",merchant_deposits.wire_fee_val"
                            ",merchant_deposits.wire_fee_frac"
                            ",merchant_deposits.exchange_url"
                            ",merchant_deposits.exchange_proof"
                            " FROM merchant_transfers"
                            "   JOIN merchant_deposits"
                            "     ON (merchant_deposits.h_contract_terms = merchant_transfers.h_contract_terms"
                            "       AND"
                            "         merchant_deposits.coin_pub = merchant_transfers.coin_pub)"
                            " WHERE wtid=$1",
                            1),
    GNUNET_PQ_make_prepare ("find_proof_by_wtid",
                            "SELECT"
                            " proof"
                            " FROM merchant_proofs"
                            " WHERE wtid=$1"
                            "  AND exchange_url=$2",
                            2),
    GNUNET_PQ_make_prepare ("lookup_tip_reserve_balance",
                            "SELECT"
                            " expiration"
                            ",balance_val"
                            ",balance_frac"
                            " FROM merchant_tip_reserves"
                            " WHERE reserve_priv=$1",
                            1),
    GNUNET_PQ_make_prepare ("find_tip_authorizations",
                            "SELECT"
                            " amount_val"
                            ",amount_frac"
                            ",justification"
                            ",extra"
                            ",tip_id"
                            " FROM merchant_tips"
                            " WHERE reserve_priv=$1",
                            1),
    GNUNET_PQ_make_prepare ("update_tip_reserve_balance",
                            "UPDATE merchant_tip_reserves SET"
                            " expiration=$2"
                            ",balance_val=$3"
                            ",balance_frac=$4"
                            " WHERE reserve_priv=$1",
                            4),
    GNUNET_PQ_make_prepare ("insert_tip_reserve_balance",
                            "INSERT INTO merchant_tip_reserves"
                            "(reserve_priv"
                            ",expiration"
                            ",balance_val"
                            ",balance_frac"
                            ") VALUES "
                            "($1, $2, $3, $4)",
                            4),
    GNUNET_PQ_make_prepare ("insert_tip_justification",
                            "INSERT INTO merchant_tips"
                            "(reserve_priv"
                            ",tip_id"
                            ",exchange_url"
                            ",justification"
                            ",extra"
                            ",timestamp"
                            ",amount_val"
                            ",amount_frac"
                            ",left_val"
                            ",left_frac"
                            ") VALUES "
                            "($1, $2, $3, $4, $5, $6, $7, $8, $9, $10)",
                            10),
    GNUNET_PQ_make_prepare ("lookup_reserve_by_tip_id",
                            "SELECT"
                            " reserve_priv"
                            ",left_val"
                            ",left_frac"
                            " FROM merchant_tips"
                            " WHERE tip_id=$1",
                            1),
    GNUNET_PQ_make_prepare ("lookup_amount_by_pickup",
                            "SELECT"
                            " amount_val"
                            ",amount_frac"
                            " FROM merchant_tip_pickups"
                            " WHERE pickup_id=$1"
                            " AND tip_id=$2",
                            2),
    GNUNET_PQ_make_prepare ("find_tip_by_id",
                            "SELECT"
                            " exchange_url"
                            ",extra"
                            ",timestamp"
                            ",amount_val"
                            ",amount_frac"
                            ",left_val"
                            ",left_frac"
                            " FROM merchant_tips"
                            " WHERE tip_id=$1",
                            1),
    GNUNET_PQ_make_prepare ("update_tip_balance",
                            "UPDATE merchant_tips SET"
                            " left_val=$2"
                            ",left_frac=$3"
                            " WHERE tip_id=$1",
                            3),
    GNUNET_PQ_make_prepare ("insert_pickup_id",
                            "INSERT INTO merchant_tip_pickups"
                            "(tip_id"
                            ",pickup_id"
                            ",amount_val"
                            ",amount_frac"
                            ") VALUES "
                            "($1, $2, $3, $4)",
                            4),
    GNUNET_PQ_make_prepare ("insert_tip_credit_uuid",
                            "INSERT INTO merchant_tip_reserve_credits"
                            "(reserve_priv"
                            ",credit_uuid"
                            ",timestamp"
                            ",amount_val"
                            ",amount_frac"
                            ") VALUES "
                            "($1, $2, $3, $4, $5)",
                            5),
    GNUNET_PQ_make_prepare ("lookup_tip_credit_uuid",
                            "SELECT 1 "
                            "FROM merchant_tip_reserve_credits "
                            "WHERE credit_uuid=$1 AND reserve_priv=$2",
                            2),
    GNUNET_PQ_PREPARED_STATEMENT_END
  };

  pg = GNUNET_new (struct PostgresClosure);
  ec = getenv ("TALER_MERCHANTDB_POSTGRES_CONFIG");
  if (NULL != ec)
  {
    GNUNET_CONFIGURATION_set_value_string (cfg,
                                           "merchantdb-postgres",
                                           "CONFIG",
                                           ec);
  }
  else
  {
    if (GNUNET_OK !=
        GNUNET_CONFIGURATION_have_value (cfg,
                                         "merchantdb-postgres",
                                         "CONFIG"))
    {
      GNUNET_log_config_missing (GNUNET_ERROR_TYPE_ERROR,
                                 "merchantdb-postgres",
                                 "CONFIG");
      return NULL;
    }
  }
  pg->cfg = cfg;
  pg->conn = GNUNET_PQ_connect_with_cfg (cfg,
                                         "merchantdb-postgres",
                                         es,
                                         ps);
  if (NULL == pg->conn)
  {
    GNUNET_free (pg);
    return NULL;
  }
  if (GNUNET_OK !=
      GNUNET_CONFIGURATION_get_value_string (cfg,
                                             "taler",
                                             "CURRENCY",
                                             &pg->currency))
  {
    GNUNET_log_config_missing (GNUNET_ERROR_TYPE_ERROR,
                               "taler",
                               "CURRENCY");
    GNUNET_PQ_disconnect (pg->conn);
    GNUNET_free (pg);
    return NULL;
  }
  plugin = GNUNET_new (struct TALER_MERCHANTDB_Plugin);
  plugin->cls = pg;
  plugin->drop_tables = &postgres_drop_tables;
  plugin->store_deposit = &postgres_store_deposit;
  plugin->store_coin_to_transfer = &postgres_store_coin_to_transfer;
  plugin->store_transfer_to_proof = &postgres_store_transfer_to_proof;
  plugin->store_wire_fee_by_exchange = &postgres_store_wire_fee_by_exchange;
  plugin->find_payments_by_hash_and_coin =
    &postgres_find_payments_by_hash_and_coin;
  plugin->find_payments = &postgres_find_payments;
  plugin->find_transfers_by_hash = &postgres_find_transfers_by_hash;
  plugin->find_deposits_by_wtid = &postgres_find_deposits_by_wtid;
  plugin->find_proof_by_wtid = &postgres_find_proof_by_wtid;
  plugin->insert_contract_terms = &postgres_insert_contract_terms;
  plugin->insert_order = &postgres_insert_order;
  plugin->find_order = &postgres_find_order;
  plugin->find_contract_terms = &postgres_find_contract_terms;
  plugin->find_contract_terms_history = &postgres_find_contract_terms_history;
  plugin->find_contract_terms_by_date = &postgres_find_contract_terms_by_date;
  plugin->get_authorized_tip_amount = &postgres_get_authorized_tip_amount;
  plugin->find_contract_terms_by_date_and_range =
    &postgres_find_contract_terms_by_date_and_range;
  plugin->find_contract_terms_from_hash =
    &postgres_find_contract_terms_from_hash;
  plugin->find_paid_contract_terms_from_hash =
    &postgres_find_paid_contract_terms_from_hash;
  plugin->get_refunds_from_contract_terms_hash =
    &postgres_get_refunds_from_contract_terms_hash;
  plugin->lookup_wire_fee = &postgres_lookup_wire_fee;
  plugin->increase_refund_for_contract_NT =
    &postgres_increase_refund_for_contract_NT;
  plugin->mark_proposal_paid = &postgres_mark_proposal_paid;
  plugin->insert_session_info = &postgres_insert_session_info;
  plugin->find_session_info = &postgres_find_session_info;
  plugin->enable_tip_reserve_TR = &postgres_enable_tip_reserve_TR;
  plugin->authorize_tip_TR = &postgres_authorize_tip_TR;
  plugin->lookup_tip_by_id = &postgres_lookup_tip_by_id;
  plugin->pickup_tip_TR = &postgres_pickup_tip_TR;
  plugin->start = postgres_start;
  plugin->commit = postgres_commit;
  plugin->preflight = postgres_preflight;
  plugin->rollback = postgres_rollback;

  return plugin;
}


/**
 * Shutdown Postgres database subsystem.
 *
 * @param cls a `struct TALER_MERCHANTDB_Plugin`
 * @return NULL (always)
 */
void *
libtaler_plugin_merchantdb_postgres_done (void *cls)
{
  struct TALER_MERCHANTDB_Plugin *plugin = cls;
  struct PostgresClosure *pg = plugin->cls;

  GNUNET_PQ_disconnect (pg->conn);
  GNUNET_free (pg->currency);
  GNUNET_free (pg);
  GNUNET_free (plugin);
  return NULL;
}

/* end of plugin_merchantdb_postgres.c */