/*
  This file is part of TALER
  Copyright (C) 2023 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 Affero General Public License for more details.

  You should have received a copy of the GNU Affero General Public License along with
  TALER; see the file COPYING.  If not, see <http://www.gnu.org/licenses/>
*/
/**
 * @file taler-merchant-wirewatch.c
 * @brief Process that imports information about incoming bank transfers into the merchant backend
 * @author Christian Grothoff
 */
#include "platform.h"
#include <gnunet/gnunet_util_lib.h>
#include <jansson.h>
#include <pthread.h>
#include <taler/taler_dbevents.h>
#include "taler_merchant_bank_lib.h"
#include "taler_merchantdb_lib.h"
#include "taler_merchantdb_plugin.h"

/**
 * Timeout for the bank interaction.  Rather long as we should do long-polling
 * and do not want to wake up too often.
 */
#define BANK_TIMEOUT GNUNET_TIME_relative_multiply (GNUNET_TIME_UNIT_MINUTES, \
                                                    5)


/**
 * Information about a watch job.
 */
struct Watch
{
  /**
   * Kept in a DLL.
   */
  struct Watch *next;

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

  /**
   * Next task to run, if any.
   */
  struct GNUNET_SCHEDULER_Task *task;

  /**
   * Dynamically adjusted long polling time-out.
   */
  struct GNUNET_TIME_Relative bank_timeout;

  /**
   * For which instance are we importing bank transfers?
   */
  char *instance_id;

  /**
   * For which account are we importing bank transfers?
   */
  struct TALER_FullPayto payto_uri;

  /**
   * Bank history request.
   */
  struct TALER_MERCHANT_BANK_CreditHistoryHandle *hh;

  /**
   * Start row for the bank interaction. Exclusive.
   */
  uint64_t start_row;

  /**
   * Artificial delay to use between API calls. Used to
   * throttle on failures.
   */
  struct GNUNET_TIME_Relative delay;

  /**
   * When did we start our last HTTP request?
   */
  struct GNUNET_TIME_Absolute start_time;

  /**
   * How long should long-polling take at least?
   */
  struct GNUNET_TIME_Absolute long_poll_timeout;

  /**
   * Login data for the bank.
   */
  struct TALER_MERCHANT_BANK_AuthenticationData ad;

  /**
   * Set to true if we found a transaction in the last iteration.
   */
  bool found;

};


/**
 * Head of active watches.
 */
static struct Watch *w_head;

/**
 * Tail of active watches.
 */
static struct Watch *w_tail;

/**
 * The merchant's configuration.
 */
static const struct GNUNET_CONFIGURATION_Handle *cfg;

/**
 * Our database plugin.
 */
static struct TALER_MERCHANTDB_Plugin *db_plugin;

/**
 * Handle to the context for interacting with the bank.
 */
static struct GNUNET_CURL_Context *ctx;

/**
 * Scheduler context for running the @e ctx.
 */
static struct GNUNET_CURL_RescheduleContext *rc;

/**
 * Event handler to learn that the configuration changed
 * and we should shutdown (to be restarted).
 */
static struct GNUNET_DB_EventHandler *eh;

/**
 * Value to return from main(). 0 on success, non-zero on errors.
 */
static int global_ret;

/**
 * How many transactions should we fetch at most per batch?
 */
static unsigned int batch_size = 32;

/**
 * #GNUNET_YES if we are in test mode and should exit when idle.
 */
static int test_mode;

/**
 * #GNUNET_YES if we are in persistent mode and do
 * not exit on #config_changed.
 */
static int persist_mode;

/**
 * Set to true if we are shutting down due to a
 * configuration change.
 */
static bool config_changed_flag;

/**
 * Save progress in DB.
 */
static void
save (struct Watch *w)
{
  enum GNUNET_DB_QueryStatus qs;

  qs = db_plugin->update_wirewatch_progress (db_plugin->cls,
                                             w->instance_id,
                                             w->payto_uri,
                                             w->start_row);
  if (qs < 0)
  {
    GNUNET_log (GNUNET_ERROR_TYPE_WARNING,
                "Failed to persist wirewatch progress for %s/%s (%d)\n",
                w->instance_id,
                w->payto_uri.full_payto,
                qs);
    GNUNET_SCHEDULER_shutdown ();
    global_ret = EXIT_FAILURE;
  }
}


/**
 * Free resources of @a w.
 *
 * @param w watch job to terminate
 */
static void
end_watch (struct Watch *w)
{
  if (NULL != w->task)
  {
    GNUNET_SCHEDULER_cancel (w->task);
    w->task = NULL;
  }
  if (NULL != w->hh)
  {
    TALER_MERCHANT_BANK_credit_history_cancel (w->hh);
    w->hh = NULL;
  }
  GNUNET_free (w->instance_id);
  GNUNET_free (w->payto_uri.full_payto);
  TALER_MERCHANT_BANK_auth_free (&w->ad);
  GNUNET_CONTAINER_DLL_remove (w_head,
                               w_tail,
                               w);
  GNUNET_free (w);
}


/**
 * We're being aborted with CTRL-C (or SIGTERM). Shut down.
 *
 * @param cls closure
 */
static void
shutdown_task (void *cls)
{
  (void) cls;
  GNUNET_log (GNUNET_ERROR_TYPE_INFO,
              "Running shutdown\n");
  while (NULL != w_head)
  {
    struct Watch *w = w_head;

    save (w);
    end_watch (w);
  }
  if (NULL != eh)
  {
    db_plugin->event_listen_cancel (eh);
    eh = NULL;
  }
  TALER_MERCHANTDB_plugin_unload (db_plugin);
  db_plugin = NULL;
  cfg = NULL;
  if (NULL != ctx)
  {
    GNUNET_CURL_fini (ctx);
    ctx = NULL;
  }
  if (NULL != rc)
  {
    GNUNET_CURL_gnunet_rc_destroy (rc);
    rc = NULL;
  }
}


/**
 * Parse @a subject from wire transfer into @a wtid and @a exchange_url.
 *
 * @param subject wire transfer subject to parse;
 *        format is "$WTID $URL"
 * @param[out] wtid wire transfer ID to extract
 * @param[out] exchange_url set to exchange URL
 * @return #GNUNET_OK on success
 */
static enum GNUNET_GenericReturnValue
parse_subject (const char *subject,
               struct TALER_WireTransferIdentifierRawP *wtid,
               char **exchange_url)
{
  const char *space;

  space = strchr (subject, ' ');
  if (NULL == space)
    return GNUNET_NO;
  if (GNUNET_OK !=
      GNUNET_STRINGS_string_to_data (subject,
                                     space - subject,
                                     wtid,
                                     sizeof (*wtid)))
    return GNUNET_NO;
  space++;
  if (! TALER_url_valid_charset (space))
    return GNUNET_NO;
  if ( (0 != strncasecmp ("http://",
                          space,
                          strlen ("http://"))) &&
       (0 != strncasecmp ("https://",
                          space,
                          strlen ("https://"))) )
    return GNUNET_NO;
  *exchange_url = GNUNET_strdup (space);
  return GNUNET_OK;
}


/**
 * Run next iteration.
 *
 * @param cls a `struct Watch *`
 */
static void
do_work (void *cls);


/**
 * Callbacks of this type are used to serve the result of asking
 * the bank for the credit transaction history.
 *
 * @param cls a `struct Watch *`
 * @param http_status HTTP response code, #MHD_HTTP_OK (200) for successful status request
 *                    0 if the bank's reply is bogus (fails to follow the protocol),
 *                    #MHD_HTTP_NO_CONTENT if there are no more results; on success the
 *                    last callback is always of this status (even if `abs(num_results)` were
 *                    already returned).
 * @param ec detailed error code
 * @param serial_id monotonically increasing counter corresponding to the transaction
 * @param details details about the wire transfer
 * @return #GNUNET_OK to continue, #GNUNET_SYSERR to abort iteration
 */
static enum GNUNET_GenericReturnValue
credit_cb (
  void *cls,
  unsigned int http_status,
  enum TALER_ErrorCode ec,
  uint64_t serial_id,
  const struct TALER_MERCHANT_BANK_CreditDetails *details)
{
  struct Watch *w = cls;

  switch (http_status)
  {
  case 0:
    GNUNET_log (GNUNET_ERROR_TYPE_WARNING,
                "Invalid HTTP response (HTTP status: 0, %d) from bank\n",
                ec);
    w->delay = GNUNET_TIME_STD_BACKOFF (w->delay);
    break;
  case MHD_HTTP_OK:
    {
      enum GNUNET_DB_QueryStatus qs;
      char *exchange_url;
      struct TALER_WireTransferIdentifierRawP wtid;

      GNUNET_log (GNUNET_ERROR_TYPE_INFO,
                  "Received wire transfer `%s' over %s\n",
                  details->wire_subject,
                  TALER_amount2s (&details->amount));
      w->found = true;
      if (GNUNET_OK !=
          parse_subject (details->wire_subject,
                         &wtid,
                         &exchange_url))
      {
        GNUNET_log (GNUNET_ERROR_TYPE_INFO,
                    "Skipping transfer %llu (%s): not from exchange\n",
                    (unsigned long long) serial_id,
                    details->wire_subject);
        w->start_row = serial_id;
        return GNUNET_OK;
      }
      /* FIXME-Performance-Optimization: consider grouping multiple inserts
         into one bigger transaction with just one notify. */
      qs = db_plugin->insert_transfer (db_plugin->cls,
                                       w->instance_id,
                                       exchange_url,
                                       &wtid,
                                       &details->amount,
                                       details->credit_account_uri,
                                       true /* confirmed */);
      if (GNUNET_DB_STATUS_SUCCESS_NO_RESULTS == qs)
      {
        struct TALER_Amount total;
        struct TALER_Amount wfee;
        struct TALER_Amount eamount;
        struct GNUNET_TIME_Timestamp timestamp;
        bool have_esig;
        bool verified;

        qs = db_plugin->lookup_transfer (db_plugin->cls,
                                         w->instance_id,
                                         exchange_url,
                                         &wtid,
                                         &total,
                                         &wfee,
                                         &eamount,
                                         &timestamp,
                                         &have_esig,
                                         &verified);
        if (GNUNET_DB_STATUS_SUCCESS_NO_RESULTS == qs)
        {
          GNUNET_log (GNUNET_ERROR_TYPE_WARNING,
                      "Inserting transfer for %s into database failed. Is the credit account %s configured correctly?\n",
                      w->instance_id,
                      details->credit_account_uri.full_payto);
        }
        if (GNUNET_DB_STATUS_SUCCESS_ONE_RESULT == qs)
        {
          if (0 !=
              TALER_amount_cmp (&total,
                                &details->amount))
          {
            GNUNET_log (GNUNET_ERROR_TYPE_WARNING,
                        "Inserting transfer for %s into database failed. An entry exists for a different transfer amount (%s)!\n",
                        w->instance_id,
                        TALER_amount2s (&total));
          }
          else
          {
            GNUNET_log (GNUNET_ERROR_TYPE_INFO,
                        "Inserting transfer for %s into database failed. An equivalent entry already exists.\n",
                        w->instance_id);
          }
        }
      }
      GNUNET_free (exchange_url);
      if (qs < 0)
      {
        GNUNET_break (0);
        GNUNET_SCHEDULER_shutdown ();
        w->hh = NULL;
        return GNUNET_SYSERR;
      }
      /* Success => reset back-off timer! */
      w->delay = GNUNET_TIME_UNIT_ZERO;
      {
        struct GNUNET_DB_EventHeaderP es = {
          .size = htons (sizeof (es)),
          .type = htons (TALER_DBEVENT_MERCHANT_WIRE_TRANSFER_CONFIRMED)
        };

        db_plugin->event_notify (db_plugin->cls,
                                 &es,
                                 NULL,
                                 0);
      }
    }
    w->start_row = serial_id;
    return GNUNET_OK;
  case MHD_HTTP_NO_CONTENT:
    save (w);
    /* Delay artificially if server returned before long-poll timeout */
    if (! w->found)
      w->delay = GNUNET_TIME_absolute_get_remaining (w->long_poll_timeout);
    break;
  case MHD_HTTP_NOT_FOUND:
    /* configuration likely wrong, wait at least 1 minute, backoff up to 15 minutes! */
    w->delay = GNUNET_TIME_relative_max (GNUNET_TIME_UNIT_MINUTES,
                                         GNUNET_TIME_STD_BACKOFF (w->delay));
    GNUNET_log (GNUNET_ERROR_TYPE_WARNING,
                "Bank claims account is unknown, waiting for %s before trying again\n",
                GNUNET_TIME_relative2s (w->delay,
                                        true));
    break;
  case MHD_HTTP_GATEWAY_TIMEOUT:
    GNUNET_log (GNUNET_ERROR_TYPE_INFO,
                "Gateway timeout, adjusting long polling threshold\n");
    /* Limit new timeout at request delay */
    w->bank_timeout
      = GNUNET_TIME_relative_min (GNUNET_TIME_absolute_get_duration (
                                    w->start_time),
                                  w->bank_timeout);
    /* set the timeout a bit earlier */
    w->bank_timeout
      = GNUNET_TIME_relative_subtract (w->bank_timeout,
                                       GNUNET_TIME_UNIT_SECONDS);
    /* do not allow it to go to zero */
    w->bank_timeout
      = GNUNET_TIME_relative_max (w->bank_timeout,
                                  GNUNET_TIME_UNIT_SECONDS);
    w->delay = GNUNET_TIME_STD_BACKOFF (w->delay);
    break;
  default:
    /* Something went wrong, try again, but with back-off */
    w->delay = GNUNET_TIME_STD_BACKOFF (w->delay);
    GNUNET_log (GNUNET_ERROR_TYPE_WARNING,
                "Unexpected HTTP status code %u(%d) from bank\n",
                http_status,
                ec);
    break;
  }
  w->hh = NULL;
  if (test_mode && (! w->found))
  {
    GNUNET_log (GNUNET_ERROR_TYPE_INFO,
                "No transactions found and in test mode. Ending watch!\n");
    end_watch (w);
    if (NULL == w_head)
      GNUNET_SCHEDULER_shutdown ();
    return GNUNET_OK;
  }
  w->task = GNUNET_SCHEDULER_add_delayed (w->delay,
                                          &do_work,
                                          w);
  return GNUNET_OK;
}


static void
do_work (void *cls)
{
  struct Watch *w = cls;

  w->task = NULL;
  w->found = false;
  w->long_poll_timeout
    = GNUNET_TIME_relative_to_absolute (w->bank_timeout);
  w->start_time
    = GNUNET_TIME_absolute_get ();
  w->hh = TALER_MERCHANT_BANK_credit_history (ctx,
                                              &w->ad,
                                              w->start_row,
                                              batch_size,
                                              test_mode
                                              ? GNUNET_TIME_UNIT_ZERO
                                              : w->bank_timeout,
                                              &credit_cb,
                                              w);
  if (NULL == w->hh)
  {
    GNUNET_break (0);
    GNUNET_SCHEDULER_shutdown ();
    return;
  }
}


/**
 * Function called with information about a accounts
 * the wirewatcher should monitor.
 *
 * @param cls closure (NULL)
 * @param instance instance that owns the account
 * @param payto_uri account URI
 * @param credit_facade_url URL for the credit facade
 * @param credit_facade_credentials account access credentials
 * @param last_serial last transaction serial (inclusive) we have seen from this account
 */
static void
start_watch (
  void *cls,
  const char *instance,
  struct TALER_FullPayto payto_uri,
  const char *credit_facade_url,
  const json_t *credit_facade_credentials,
  uint64_t last_serial)
{
  struct Watch *w = GNUNET_new (struct Watch);

  (void) cls;
  w->bank_timeout = BANK_TIMEOUT;
  if (GNUNET_OK !=
      TALER_MERCHANT_BANK_auth_parse_json (credit_facade_credentials,
                                           credit_facade_url,
                                           &w->ad))
  {
    GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
                "Failed to parse authentication data of `%s/%s'\n",
                instance,
                payto_uri.full_payto);
    GNUNET_free (w);
    GNUNET_SCHEDULER_shutdown ();
    global_ret = EXIT_NOTCONFIGURED;
    return;
  }

  GNUNET_CONTAINER_DLL_insert (w_head,
                               w_tail,
                               w);
  w->instance_id = GNUNET_strdup (instance);
  w->payto_uri.full_payto = GNUNET_strdup (payto_uri.full_payto);
  w->start_row = last_serial;
  w->task = GNUNET_SCHEDULER_add_now (&do_work,
                                      w);
}


/**
 * Function called on configuration change events received from Postgres.  We
 * shutdown (and systemd should restart us).
 *
 * @param cls closure (NULL)
 * @param extra additional event data provided
 * @param extra_size number of bytes in @a extra
 */
static void
config_changed (void *cls,
                const void *extra,
                size_t extra_size)
{
  (void) cls;
  (void) extra;
  (void) extra_size;
  GNUNET_log (GNUNET_ERROR_TYPE_INFO,
              "Configuration changed, %s\n",
              0 == persist_mode
              ? "restarting"
              : "reinitializing");
  config_changed_flag = true;
  GNUNET_SCHEDULER_shutdown ();
}


/**
 * First task.
 *
 * @param cls closure, NULL
 * @param args remaining command-line arguments
 * @param cfgfile name of the configuration file used (for saving, can be NULL!)
 * @param c configuration
 */
static void
run (void *cls,
     char *const *args,
     const char *cfgfile,
     const struct GNUNET_CONFIGURATION_Handle *c)
{
  (void) args;
  (void) cfgfile;

  cfg = c;
  GNUNET_SCHEDULER_add_shutdown (&shutdown_task,
                                 NULL);
  ctx = GNUNET_CURL_init (&GNUNET_CURL_gnunet_scheduler_reschedule,
                          &rc);
  rc = GNUNET_CURL_gnunet_rc_create (ctx);
  if (NULL == ctx)
  {
    GNUNET_break (0);
    GNUNET_SCHEDULER_shutdown ();
    global_ret = EXIT_FAILURE;
    return;
  }
  if (NULL ==
      (db_plugin = TALER_MERCHANTDB_plugin_load (cfg)))
  {
    GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
                "Failed to initialize DB subsystem\n");
    GNUNET_SCHEDULER_shutdown ();
    global_ret = EXIT_NOTCONFIGURED;
    return;
  }
  if (GNUNET_OK !=
      db_plugin->connect (db_plugin->cls))
  {
    GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
                "Failed to connect to database\n");
    GNUNET_SCHEDULER_shutdown ();
    global_ret = EXIT_FAILURE;
    return;
  }
  {
    struct GNUNET_DB_EventHeaderP es = {
      .size = htons (sizeof (es)),
      .type = htons (TALER_DBEVENT_MERCHANT_ACCOUNTS_CHANGED)
    };

    eh = db_plugin->event_listen (db_plugin->cls,
                                  &es,
                                  GNUNET_TIME_UNIT_FOREVER_REL,
                                  &config_changed,
                                  NULL);
  }
  {
    enum GNUNET_DB_QueryStatus qs;

    qs = db_plugin->select_wirewatch_accounts (db_plugin->cls,
                                               &start_watch,
                                               NULL);
    if (qs < 0)
    {
      GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
                  "Failed to obtain wirewatch accounts from database\n");
      GNUNET_SCHEDULER_shutdown ();
      global_ret = EXIT_NO_RESTART;
      return;
    }
    if ( (NULL == w_head) &&
         (GNUNET_YES == test_mode) )
    {
      GNUNET_log (GNUNET_ERROR_TYPE_INFO,
                  "No active wirewatch accounts in database and in test mode. Exiting.\n");
      GNUNET_SCHEDULER_shutdown ();
      global_ret = EXIT_SUCCESS;
      return;
    }
  }
}


/**
 * The main function of taler-merchant-wirewatch
 *
 * @param argc number of arguments from the command line
 * @param argv command line arguments
 * @return 0 ok, 1 on error
 */
int
main (int argc,
      char *const *argv)
{
  struct GNUNET_GETOPT_CommandLineOption options[] = {
    GNUNET_GETOPT_option_flag ('p',
                               "persist",
                               "run in persist mode and do not exit on configuration changes",
                               &persist_mode),
    GNUNET_GETOPT_option_timetravel ('T',
                                     "timetravel"),
    GNUNET_GETOPT_option_flag ('t',
                               "test",
                               "run in test mode and exit when idle",
                               &test_mode),
    GNUNET_GETOPT_option_version (VERSION "-" VCS_VERSION),
    GNUNET_GETOPT_OPTION_END
  };
  enum GNUNET_GenericReturnValue ret;

  TALER_OS_init ();
  do {
    config_changed_flag = false;
    ret = GNUNET_PROGRAM_run (
      argc, argv,
      "taler-merchant-wirewatch",
      gettext_noop (
        "background process that watches for incoming wire transfers to the merchant bank account"),
      options,
      &run, NULL);
  } while ( (1 == persist_mode) &&
            config_changed_flag);
  if (GNUNET_SYSERR == ret)
    return EXIT_INVALIDARGUMENT;
  if (GNUNET_NO == ret)
    return EXIT_SUCCESS;
  return global_ret;
}


/* end of taler-exchange-wirewatch.c */