/*
  This file is part of TALER
  (C) 2020 Taler Systems SA

  TALER is free software; you can redistribute it and/or modify it under the
  terms of the GNU Affero 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 taler-merchant-httpd_reserves.c
 * @brief logic for initially tracking a reserve's status
 * @author Christian Grothoff
 */
#include "platform.h"
#include <taler/taler_json_lib.h>
#include "taler-merchant-httpd.h"
#include "taler-merchant-httpd_exchanges.h"
#include "taler-merchant-httpd_reserves.h"


/**
 * Our representation of a reserve that we are (still) checking the status of.
 */
struct Reserve
{

  /**
   * Kept in a DLL.
   */
  struct Reserve *next;

  /**
   * Kept in a DLL.
   */
  struct Reserve *prev;

  /**
   * Reserve's public key.
   */
  struct TALER_ReservePublicKeyP reserve_pub;

  /**
   * Amount the merchant expects to see in the reserve initially.
   * We log a warning if there is a mismatch.
   */
  struct TALER_Amount expected_amount;

  /**
   * URL of the exchange hosting this reserve.
   */
  char *exchange_url;

  /**
   * Instance this reserve belongs with.
   */
  char *instance_id;

  /**
   * Active find operation for this reserve.
   */
  struct TMH_EXCHANGES_FindOperation *fo;

  /**
   * Task scheduled waiting for a timeout for this reserve.
   */
  struct GNUNET_SCHEDULER_Task *tt;

  /**
   * Get operation with the exchange.
   */
  struct TALER_EXCHANGE_ReservesGetHandle *gh;

  /**
   * How long do we wait before trying this reserve again?
   */
  struct GNUNET_TIME_Relative delay;

};


/**
 * Head of DLL of pending reserves.
 */
static struct Reserve *reserves_head;

/**
 * Tail of DLL of pending reserves.
 */
static struct Reserve *reserves_tail;


/**
 * Function called to probe a reserve now.
 *
 * @param cls a `struct Reserve` to query
 */
static void
try_now (void *cls);


/**
 * Free reserve data structure.
 *
 * @param r reserve to free
 */
static void
free_reserve (struct Reserve *r)
{
  GNUNET_CONTAINER_DLL_remove (reserves_head,
                               reserves_tail,
                               r);
  if (NULL != r->fo)
  {
    TMH_EXCHANGES_find_exchange_cancel (r->fo);
    r->fo = NULL;
  }
  if (NULL != r->gh)
  {
    TALER_EXCHANGE_reserves_get_cancel (r->gh);
    r->gh = NULL;
  }
  if (NULL != r->tt)
  {
    GNUNET_SCHEDULER_cancel (r->tt);
    r->tt = NULL;
  }
  GNUNET_free (r->exchange_url);
  GNUNET_free (r->instance_id);
  GNUNET_free (r);
}


/**
 * Schedule a job to probe a reserve later again.
 *
 * @param r reserve to try again later
 */
static void
try_later (struct Reserve *r)
{
  r->delay = GNUNET_TIME_STD_BACKOFF (r->delay);
  r->tt = GNUNET_SCHEDULER_add_delayed (r->delay,
                                        &try_now,
                                        r);
}


/**
 * Callbacks of this type are used to serve the result of submitting a
 * reserve status request to a exchange.
 *
 * @param cls closure with a `struct Reserve *`
 * @param hr HTTP response data
 * @param balance current balance in the reserve, NULL on error
 * @param history_length number of entries in the transaction history, 0 on error
 * @param history detailed transaction history, NULL on error
 */
static void
reserve_cb (void *cls,
            const struct TALER_EXCHANGE_HttpResponse *hr,
            const struct TALER_Amount *balance,
            unsigned int history_length,
            const struct TALER_EXCHANGE_ReserveHistory *history)
{
  struct Reserve *r = cls;
  enum GNUNET_DB_QueryStatus qs;

  r->gh = NULL;
  if ( (NULL == hr) ||
       (MHD_HTTP_OK != hr->http_status) )
  {
    try_later (r);
    return;
  }
  if (GNUNET_OK !=
      TALER_amount_cmp_currency (&r->expected_amount,
                                 balance))
  {
    GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
                "Reserve currency disagreement: exchange `%s' has %s, expected %s\n",
                r->exchange_url,
                balance->currency,
                r->expected_amount.currency);
    free_reserve (r);
    return;
  }
  if (0 !=
      TALER_amount_cmp (&r->expected_amount,
                        balance))
  {
    GNUNET_log (GNUNET_ERROR_TYPE_WARNING,
                "Reserve initial balance disagreement: exchange `%s' received `%s'\n",
                r->exchange_url,
                TALER_amount2s (balance));
  }
  qs = TMH_db->activate_reserve (TMH_db->cls,
                                 r->instance_id,
                                 &r->reserve_pub,
                                 balance);
  if (qs <= 0)
  {
    GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
                "Failed to commit reserve activation to database (%d)\n",
                (int) qs);
  }
  else
  {
    GNUNET_log (GNUNET_ERROR_TYPE_INFO,
                "Reserve activated with initial balance %s\n",
                TALER_amount2s (balance));
  }
  free_reserve (r);
}


/**
 * Function called with the result of a #TMH_EXCHANGES_find_exchange()
 * operation.
 *
 * @param cls closure
 * @param hr HTTP response details
 * @param eh handle to the exchange context
 * @param payto_uri payto://-URI of the exchange
 * @param wire_fee current applicable wire fee for dealing with @a eh, NULL if not available
 * @param exchange_trusted true if this exchange is trusted by config
 */
static void
find_cb (void *cls,
         const struct TALER_EXCHANGE_HttpResponse *hr,
         struct TALER_EXCHANGE_Handle *eh,
         const char *payto_uri,
         const struct TALER_Amount *wire_fee,
         bool exchange_trusted)
{
  struct Reserve *r = cls;

  r->fo = NULL;
  if (NULL == eh)
  {
    try_later (r);
    return;
  }
  r->gh = TALER_EXCHANGE_reserves_get (eh,
                                       &r->reserve_pub,
                                       &reserve_cb,
                                       r);
  if (NULL == r->gh)
  {
    try_later (r);
    return;
  }
}


/**
 * Function called to probe a reserve now.
 *
 * @param cls a `struct Reserve` to query
 */
static void
try_now (void *cls)
{
  struct Reserve *r = cls;

  r->tt = NULL;
  r->fo = TMH_EXCHANGES_find_exchange (r->exchange_url,
                                       NULL,
                                       GNUNET_NO,
                                       &find_cb,
                                       r);
  if (NULL == r->fo)
  {
    try_later (r);
    return;
  }
}


/**
 * Function called with information about a reserve that we need
 * to check the status from at the exchange to see if/when it has
 * been filled (and with what amount).
 *
 * @param cls closure, NULL
 * @param instance_id for which instance is this reserve
 * @param exchange_url base URL of the exchange at which the reserve lives
 * @param reserve_pub public key of the reserve
 * @param expected_amount how much do we expect to see in the reserve
 */
static void
add_reserve (void *cls,
             const char *instance_id,
             const char *exchange_url,
             const struct TALER_ReservePublicKeyP *reserve_pub,
             const struct TALER_Amount *expected_amount)
{
  struct Reserve *r;

  (void) cls;
  r = GNUNET_new (struct Reserve);
  r->exchange_url = GNUNET_strdup (exchange_url);
  r->instance_id = GNUNET_strdup (instance_id);
  r->reserve_pub = *reserve_pub;
  r->expected_amount = *expected_amount;
  GNUNET_CONTAINER_DLL_insert (reserves_head,
                               reserves_tail,
                               r);
  try_now (r);
}


/**
 * Load information about reserves and start querying reserve status.
 * Must be called after the database is available.
 */
void
TMH_RESERVES_init (void)
{
  TMH_db->lookup_pending_reserves (TMH_db->cls,
                                   &add_reserve,
                                   NULL);
}


/**
 * Add a reserve to the list of reserves to check.
 *
 * @param instance_id which instance is the reserve for
 * @param exchange_url URL of the exchange with the reserve
 * @param reserve_pub public key of the reserve to check
 * @param expected_amount amount the merchant expects to see initially in the reserve
 */
void
TMH_RESERVES_check (const char *instance_id,
                    const char *exchange_url,
                    const struct TALER_ReservePublicKeyP *reserve_pub,
                    const struct TALER_Amount *expected_amount)
{
  add_reserve (NULL,
               instance_id,
               exchange_url,
               reserve_pub,
               expected_amount);
}


/**
 * Stop checking reserve status.
 */
void
TMH_RESERVES_done (void)
{
  while (NULL != reserves_head)
    free_reserve (reserves_head);
}


/* end of taler-merchant-httpd_reserves.c */