/*
  This file is part of TALER
  (C) 2017 Taler Systems SA

  TALER is free software; you can redistribute it and/or modify it under the
  terms of the GNU 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 backend/taler-merchant-httpd_check-payment.c
 * @brief implementation of /check-payment handler
 * @author Florian Dold
 */
#include "platform.h"
#include <string.h>
#include <microhttpd.h>
#include <jansson.h>
#include <taler/taler_json_lib.h>
#include <taler/taler_signatures.h>
#include "taler-merchant-httpd.h"
#include "taler-merchant-httpd_mhd.h"
#include "taler-merchant-httpd_parsing.h"
#include "taler-merchant-httpd_exchanges.h"
#include "taler-merchant-httpd_responses.h"
#include "taler-merchant-httpd_check-payment.h"

/**
 * Maximum number of retries for database operations.
 */
#define MAX_RETRIES 5


/**
 * Function called with information about a refund.
 * It is responsible for summing up the refund amount.
 *
 * @param cls closure
 * @param coin_pub public coin from which the refund comes from
 * @param rtransaction_id identificator of the refund
 * @param reason human-readable explaination of the refund
 * @param refund_amount refund amount which is being taken from coin_pub
 * @param refund_fee cost of this refund operation
 */
static void
process_refunds_cb (void *cls,
                    const struct TALER_CoinSpendPublicKeyP *coin_pub,
                    uint64_t rtransaction_id,
                    const char *reason,
                    const struct TALER_Amount *refund_amount,
                    const struct TALER_Amount *refund_fee)
{
  struct TALER_Amount *acc_amount = cls;

  GNUNET_assert (GNUNET_SYSERR !=
                 TALER_amount_add (acc_amount,
                                   acc_amount,
                                   refund_amount));
}


/**
 * Manages a /check-payment call, checking the status
 * of a payment and, if necessary, constructing the URL
 * for a payment redirect URL.
 *
 * @param rh context of the handler
 * @param connection the MHD connection to handle
 * @param[in,out] connection_cls the connection's closure (can be updated)
 * @param upload_data upload data
 * @param[in,out] upload_data_size number of bytes (left) in @a upload_data
 * @return MHD result code
 */
int
MH_handler_check_payment (struct TMH_RequestHandler *rh,
                          struct MHD_Connection *connection,
                          void **connection_cls,
                          const char *upload_data,
                          size_t *upload_data_size)
{
  const char *order_id;
  const char *contract_url;
  const char *session_id;
  const char *session_sig_str;
  const char *instance_str;
  const char *resource_url;
  char *final_contract_url = NULL;
  char *h_contract_terms_str = NULL;
  struct MerchantInstance *mi;
  enum GNUNET_DB_QueryStatus qs;
  json_t *contract_terms;
  struct GNUNET_HashCode h_contract_terms;
  struct TALER_Amount refund_amount;
  char *last_session_id;

  order_id = MHD_lookup_connection_value (connection,
                                          MHD_GET_ARGUMENT_KIND,
                                          "order_id");
  contract_url = MHD_lookup_connection_value (connection,
                                              MHD_GET_ARGUMENT_KIND,
                                              "contract_url");
  session_id = MHD_lookup_connection_value (connection,
                                                MHD_GET_ARGUMENT_KIND,
                                                "session_id");
  session_sig_str = MHD_lookup_connection_value (connection,
                                                MHD_GET_ARGUMENT_KIND,
                                                "session_sig");
  instance_str = MHD_lookup_connection_value (connection,
                                              MHD_GET_ARGUMENT_KIND,
                                              "instance");
  resource_url = MHD_lookup_connection_value (connection,
                                              MHD_GET_ARGUMENT_KIND,
                                              "resource_url");

  if (NULL == instance_str)
    instance_str = "default";

  mi = TMH_lookup_instance (instance_str);
  if (NULL == mi)
    return TMH_RESPONSE_reply_bad_request (connection,
                                           TALER_EC_CHECK_PAYMENT_INSTANCE_UNKNOWN,
                                           "merchant instance unknown");

  if (NULL == order_id)
  {
    if (NULL == contract_url)
      return TMH_RESPONSE_reply_bad_request (connection,
                                             TALER_EC_PARAMETER_MISSING,
                                             "either order_id or contract_url must be given");
    goto do_pay;
    // No order_id given, redirect to a page that gives the wallet a new
    // contract.
  }

  if (NULL == contract_url)
  {
    final_contract_url = TALER_url_absolute_mhd (connection,
						 "/public/proposal",
                                                 "instance", instance_str,
                                                 "order_id", order_id,
                                                 NULL);
    GNUNET_assert (NULL != final_contract_url);
  }
  else
  {
    final_contract_url = GNUNET_strdup (contract_url);
  }

  if (NULL != session_id)
  {
    struct GNUNET_CRYPTO_EddsaSignature sig;
    struct TALER_MerchantPaySessionSigPS mps;
    // If the session id is given, the frontend wants us
    // to verify the session signature.
    if (NULL == session_sig_str)
    {
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG, "pay session signature required but missing\n");
      goto do_pay;
    }

    if (GNUNET_OK !=
        GNUNET_STRINGS_string_to_data (session_sig_str,
                                       strlen (session_sig_str),
                                       &sig,
                                       sizeof (struct GNUNET_CRYPTO_EddsaSignature)))
    {
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG, "pay session signature malformed\n");
      goto do_pay;
    }
    mps.purpose.size = htonl (sizeof (struct TALER_MerchantPaySessionSigPS));
    mps.purpose.purpose = htonl (TALER_SIGNATURE_MERCHANT_PAY_SESSION);
    GNUNET_assert (NULL != order_id);
    GNUNET_assert (NULL != session_id);
    GNUNET_CRYPTO_hash (order_id, strlen (order_id), &mps.h_order_id);
    GNUNET_CRYPTO_hash (session_id, strlen (session_id), &mps.h_session_id);
    if (GNUNET_OK != GNUNET_CRYPTO_eddsa_verify (TALER_SIGNATURE_MERCHANT_PAY_SESSION,
                                                 &mps.purpose,
                                                 &sig,
                                                 &mi->pubkey.eddsa_pub))
    {
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG, "pay session signature invalid\n");
      goto do_pay;
    }
  }

  GNUNET_assert (NULL != order_id);

  db->preflight (db->cls);
  qs = db->find_contract_terms (db->cls,
                                &contract_terms,
                                &last_session_id,
                                order_id,
                                &mi->pubkey);
  if (0 > qs)
  {
    /* single, read-only SQL statements should never cause
       serialization problems */
    GNUNET_break (GNUNET_DB_STATUS_SOFT_ERROR != qs);
    /* Always report on hard error as well to enable diagnostics */
    GNUNET_break (GNUNET_DB_STATUS_HARD_ERROR == qs);
    return TMH_RESPONSE_reply_internal_error (connection,
					      TALER_EC_CHECK_PAYMENT_DB_FETCH_CONTRACT_TERMS_ERROR,
					      "db error fetching contract terms");
  }
  if (GNUNET_DB_STATUS_SUCCESS_NO_RESULTS == qs)
  {
    qs = db->find_order (db->cls,
                         &contract_terms,
                         order_id,
                         &mi->pubkey);
    if (0 > qs)
    {
      /* single, read-only SQL statements should never cause
         serialization problems */
      GNUNET_break (GNUNET_DB_STATUS_SOFT_ERROR != qs);
      /* Always report on hard error as well to enable diagnostics */
      GNUNET_break (GNUNET_DB_STATUS_HARD_ERROR == qs);
      return TMH_RESPONSE_reply_internal_error (connection,
                                                TALER_EC_CHECK_PAYMENT_DB_FETCH_ORDER_ERROR,
                                                "db error fetching order");
    }
    if (GNUNET_DB_STATUS_SUCCESS_NO_RESULTS == qs)
    {
      return TMH_RESPONSE_reply_not_found (connection,
                                           TALER_EC_CHECK_PAYMENT_ORDER_ID_UNKNOWN,
                                           "unknown order id");
    }
    /* Offer was not picked up yet, but we ensured that it exists */
    goto do_pay;
  }

  GNUNET_assert (NULL != contract_terms);
  GNUNET_assert (NULL != last_session_id);

  if (GNUNET_OK !=
      TALER_JSON_hash (contract_terms,
                       &h_contract_terms))
  {
    GNUNET_break (0);
    return TMH_RESPONSE_reply_internal_error (connection,
                                              TALER_EC_CHECK_PAYMENT_FAILED_COMPUTE_PROPOSAL_HASH,
                                              "Failed to hash proposal");
  }

  h_contract_terms_str = GNUNET_STRINGS_data_to_string_alloc (&h_contract_terms,
                                                              sizeof (struct GNUNET_HashCode));


  /* Check if paid */
  {
    json_t *xcontract_terms = NULL;

    qs = db->find_paid_contract_terms_from_hash (db->cls,
                                                 &xcontract_terms,
                                                 &h_contract_terms,
                                                 &mi->pubkey);
    if (0 > qs)
    {
      /* Always report on hard error as well to enable diagnostics */
      GNUNET_break (GNUNET_DB_STATUS_HARD_ERROR == qs);
      GNUNET_free_non_null (h_contract_terms_str);
      return TMH_RESPONSE_reply_internal_error (connection,
                                                TALER_EC_PAY_DB_FETCH_TRANSACTION_ERROR,
                                                "Merchant database error");
    }
    if (0 == qs)
    {
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG, "not paid yet\n");
      goto do_pay;
    }
    GNUNET_break (GNUNET_DB_STATUS_SUCCESS_ONE_RESULT == qs);
    GNUNET_assert (NULL != xcontract_terms);
    json_decref (xcontract_terms);
  }

  {
    struct TALER_Amount amount;
    struct GNUNET_JSON_Specification spec[] = {
      TALER_JSON_spec_amount ("amount", &amount),
      GNUNET_JSON_spec_end ()
    };
    if (GNUNET_OK != GNUNET_JSON_parse (contract_terms, spec, NULL, NULL))
      return TMH_RESPONSE_reply_internal_error (connection,
                                                TALER_EC_CHECK_PAYMENT_DB_FETCH_CONTRACT_TERMS_ERROR,
                                                "Merchant database error (contract terms corrupted)");
    TALER_amount_get_zero (amount.currency, &refund_amount);
  }

  for (unsigned int i=0;i<MAX_RETRIES;i++)
  {
    qs = db->get_refunds_from_contract_terms_hash (db->cls,
						   &mi->pubkey,
						   &h_contract_terms,
						   &process_refunds_cb,
						   &refund_amount);
    if (GNUNET_DB_STATUS_SOFT_ERROR != qs)
      break;
  }
  if (0 > qs)
  {
    GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
                "Database hard error on refunds_from_contract_terms_hash lookup: %s\n",
                GNUNET_h2s (&h_contract_terms));
    return TMH_RESPONSE_reply_internal_error (connection,
                                              TALER_EC_PAY_DB_FETCH_TRANSACTION_ERROR,
                                              "Merchant database error");
  }

  GNUNET_free_non_null (h_contract_terms_str);

  {
    int refunded = (0 != refund_amount.value) || (0 != refund_amount.fraction);
    int res;
    res = TMH_RESPONSE_reply_json_pack (connection,
                                        MHD_HTTP_OK,
                                        "{s:o s:b, s:b, s:o, s:s}",
                                        "contract_terms", contract_terms,
                                        "paid", 1,
                                        "refunded", refunded,
                                        "refund_amount", TALER_JSON_from_amount (&refund_amount),
                                        "last_session_id", last_session_id);
    GNUNET_free_non_null (final_contract_url);
    return res;
  }

do_pay:
  {
    char *url = TALER_url_absolute_mhd (connection, "public/trigger-pay",
                                        "contract_url", final_contract_url,
                                        "session_id", session_id,
                                        "resource_url", resource_url,
                                        "h_contract_terms", h_contract_terms_str,
                                        NULL);
    GNUNET_assert (NULL != url);
    int ret = TMH_RESPONSE_reply_json_pack (connection,
                                            MHD_HTTP_OK,
                                            "{s:s, s:b}",
                                            "payment_redirect_url",
                                            url,
                                            "paid",
                                            0);
    GNUNET_free_non_null (h_contract_terms_str);
    GNUNET_free_non_null (final_contract_url);
    json_decref (contract_terms);
    GNUNET_free (url);
    return ret;
  }
}