/*
   This file is part of TALER
   Copyright (C) 2022 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 backenddb/pg_increase_refund.c
 * @brief Implementation of the increase_refund function for Postgres
 * @author Christian Grothoff
 */
#include "platform.h"
#include <taler/taler_error_codes.h>
#include <taler/taler_dbevents.h>
#include <taler/taler_pq_lib.h>
#include "pg_increase_refund.h"
#include "pg_helper.h"


/**
 * 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 the largest refund transaction ID encountered.
   */
  uint64_t max_rtransaction_id;

  /**
   * Set to true on hard errors.
   */
  bool 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_results the number of results in @a result
 */
static void
process_refund_cb (void *cls,
                   PGresult *result,
                   unsigned int num_results)
{
  struct FindRefundContext *ictx = cls;

  for (unsigned int i = 0; i<num_results; i++)
  {
    /* Sum up existing refunds */
    struct TALER_Amount acc;
    uint64_t rtransaction_id;
    struct GNUNET_PQ_ResultSpec rs[] = {
      TALER_PQ_result_spec_amount_with_currency ("refund_amount",
                                                 &acc),
      GNUNET_PQ_result_spec_uint64 ("rtransaction_id",
                                    &rtransaction_id),
      GNUNET_PQ_result_spec_end
    };

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


/**
 * Closure for #process_deposits_for_refund_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;

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

  /**
   * Transaction status code.
   */
  enum TALER_MERCHANTDB_RefundStatus rs;
};


/**
 * Data extracted per coin.
 */
struct RefundCoinData
{

  /**
   * Public key of a coin.
   */
  struct TALER_CoinSpendPublicKeyP coin_pub;

  /**
   * Amount deposited for this coin.
   */
  struct TALER_Amount deposited_with_fee;

  /**
   * Amount refunded already for this coin.
   */
  struct TALER_Amount refund_amount;

  /**
   * Order serial (actually not really per-coin).
   */
  uint64_t order_serial;

  /**
   * Maximum rtransaction_id for this coin so far.
   */
  uint64_t max_rtransaction_id;

};


/**
 * 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_results 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 RefundCoinData rcd[GNUNET_NZL (num_results)];
  struct GNUNET_TIME_Timestamp now;

  now = GNUNET_TIME_timestamp_get ();
  GNUNET_assert (GNUNET_OK ==
                 TALER_amount_set_zero (ctx->refund->currency,
                                        &current_refund));
  memset (rcd, 0, sizeof (rcd));
  /* 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 GNUNET_PQ_ResultSpec rs[] = {
      GNUNET_PQ_result_spec_auto_from_type ("coin_pub",
                                            &rcd[i].coin_pub),
      GNUNET_PQ_result_spec_uint64 ("order_serial",
                                    &rcd[i].order_serial),
      TALER_PQ_result_spec_amount_with_currency ("amount_with_fee",
                                                 &rcd[i].deposited_with_fee),
      GNUNET_PQ_result_spec_end
    };
    struct FindRefundContext ictx = {
      .pg = pg
    };

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

    if (0 != strcmp (rcd[i].deposited_with_fee.currency,
                     ctx->refund->currency))
    {
      GNUNET_break_op (0);
      ctx->rs = TALER_MERCHANTDB_RS_BAD_CURRENCY;
      return;
    }

    {
      enum GNUNET_DB_QueryStatus ires;
      struct GNUNET_PQ_QueryParam params[] = {
        GNUNET_PQ_query_param_auto_from_type (&rcd[i].coin_pub),
        GNUNET_PQ_query_param_uint64 (&rcd[i].order_serial),
        GNUNET_PQ_query_param_end
      };

      GNUNET_assert (GNUNET_OK ==
                     TALER_amount_set_zero (ctx->refund->currency,
                                            &ictx.refunded_amount));
      ires = GNUNET_PQ_eval_prepared_multi_select (ctx->pg->conn,
                                                   "find_refunds_by_coin",
                                                   params,
                                                   &process_refund_cb,
                                                   &ictx);
      if ( (ictx.err) ||
           (GNUNET_DB_STATUS_HARD_ERROR == ires) )
      {
        GNUNET_break (0);
        ctx->rs = TALER_MERCHANTDB_RS_HARD_ERROR;
        return;
      }
      if (GNUNET_DB_STATUS_SOFT_ERROR == ires)
      {
        ctx->rs = TALER_MERCHANTDB_RS_SOFT_ERROR;
        return;
      }
    }
    if (0 >
        TALER_amount_add (&current_refund,
                          &current_refund,
                          &ictx.refunded_amount))
    {
      GNUNET_break (0);
      ctx->rs = TALER_MERCHANTDB_RS_HARD_ERROR;
      return;
    }
    rcd[i].refund_amount = ictx.refunded_amount;
    rcd[i].max_rtransaction_id = ictx.max_rtransaction_id;
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "Existing refund for coin %s is %s\n",
                TALER_B2S (&rcd[i].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))
  {
    GNUNET_log (GNUNET_ERROR_TYPE_INFO,
                "Existing refund of %s at or above requested refund. Finished early.\n",
                TALER_amount2s (&current_refund));
    ctx->rs = TALER_MERCHANTDB_RS_SUCCESS;
    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 (0 >
        TALER_amount_subtract (&left,
                               &rcd[i].deposited_with_fee,
                               &rcd[i].refund_amount))
    {
      GNUNET_break (0);
      ctx->rs = TALER_MERCHANTDB_RS_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 (&rcd[i].coin_pub));
      continue;
    }

    rcd[i].max_rtransaction_id++;
    /* How much of the refund is still to be paid back? */
    if (0 >
        TALER_amount_subtract (&remaining_refund,
                               ctx->refund,
                               &current_refund))
    {
      GNUNET_break (0);
      ctx->rs = TALER_MERCHANTDB_RS_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 (0 >
        TALER_amount_add (&current_refund,
                          &current_refund,
                          increment))
    {
      GNUNET_break (0);
      ctx->rs = TALER_MERCHANTDB_RS_HARD_ERROR;
      return;
    }

    /* actually run the refund */
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "Coin %s deposit amount is %s\n",
                TALER_B2S (&rcd[i].coin_pub),
                TALER_amount2s (&rcd[i].deposited_with_fee));
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "Coin %s refund will be incremented by %s\n",
                TALER_B2S (&rcd[i].coin_pub),
                TALER_amount2s (increment));
    {
      enum GNUNET_DB_QueryStatus qs;
      struct GNUNET_PQ_QueryParam params[] = {
        GNUNET_PQ_query_param_uint64 (&rcd[i].order_serial),
        GNUNET_PQ_query_param_uint64 (&rcd[i].max_rtransaction_id), /* already inc'ed */
        GNUNET_PQ_query_param_timestamp (&now),
        GNUNET_PQ_query_param_auto_from_type (&rcd[i].coin_pub),
        GNUNET_PQ_query_param_string (ctx->reason),
        TALER_PQ_query_param_amount_with_currency (pg->conn,
                                                   increment),
        GNUNET_PQ_query_param_end
      };

      check_connection (pg);
      qs = GNUNET_PQ_eval_prepared_non_select (pg->conn,
                                               "insert_refund",
                                               params);
      switch (qs)
      {
      case GNUNET_DB_STATUS_HARD_ERROR:
        GNUNET_break (0);
        ctx->rs = TALER_MERCHANTDB_RS_HARD_ERROR;
        return;
      case GNUNET_DB_STATUS_SOFT_ERROR:
        ctx->rs = TALER_MERCHANTDB_RS_SOFT_ERROR;
        return;
      default:
        ctx->rs = (enum TALER_MERCHANTDB_RefundStatus) qs;
        break;
      }
    }

    /* stop immediately if we are done */
    if (0 == TALER_amount_cmp (ctx->refund,
                               &current_refund))
    {
      ctx->rs = TALER_MERCHANTDB_RS_SUCCESS;
      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_WARNING,
              "The refund of %s is bigger than the order's value\n",
              TALER_amount2s (ctx->refund));
  ctx->rs = TALER_MERCHANTDB_RS_TOO_HIGH;
}


enum TALER_MERCHANTDB_RefundStatus
TMH_PG_increase_refund (void *cls,
                        const char *instance_id,
                        const char *order_id,
                        const struct TALER_Amount *refund,
                        const char *reason)
{
  struct PostgresClosure *pg = cls;
  enum GNUNET_DB_QueryStatus qs;
  struct GNUNET_PQ_QueryParam params[] = {
    GNUNET_PQ_query_param_string (instance_id),
    GNUNET_PQ_query_param_string (order_id),
    GNUNET_PQ_query_param_end
  };
  struct InsertRefundContext ctx = {
    .pg = pg,
    .refund = refund,
    .reason = reason
  };

  PREPARE (pg,
           "insert_refund",
           "INSERT INTO merchant_refunds"
           "(order_serial"
           ",rtransaction_id"
           ",refund_timestamp"
           ",coin_pub"
           ",reason"
           ",refund_amount"
           ") VALUES"
           "($1, $2, $3, $4, $5, $6)");
  PREPARE (pg,
           "find_refunds_by_coin",
           "SELECT"
           " refund_amount"
           ",rtransaction_id"
           " FROM merchant_refunds"
           " WHERE coin_pub=$1"
           "   AND order_serial=$2");
  PREPARE (pg,
           "find_deposits_for_refund",
           "SELECT"
           " dep.coin_pub"
           ",dco.order_serial"
           ",dep.amount_with_fee"
           " FROM merchant_deposits dep"
           " JOIN merchant_deposit_confirmations dco"
           "   USING (deposit_confirmation_serial)"
           " WHERE order_serial="
           "  (SELECT order_serial"
           "     FROM merchant_contract_terms"
           "    WHERE order_id=$2"
           "      AND paid"
           "      AND merchant_serial="
           "        (SELECT merchant_serial"
           "           FROM merchant_instances"
           "          WHERE merchant_id=$1))");
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Asked to refund %s on order %s\n",
              TALER_amount2s (refund),
              order_id);
  qs = GNUNET_PQ_eval_prepared_multi_select (pg->conn,
                                             "find_deposits_for_refund",
                                             params,
                                             &process_deposits_for_refund_cb,
                                             &ctx);
  switch (qs)
  {
  case GNUNET_DB_STATUS_SUCCESS_NO_RESULTS:
    /* never paid, means we clearly cannot refund anything */
    return TALER_MERCHANTDB_RS_NO_SUCH_ORDER;
  case GNUNET_DB_STATUS_SOFT_ERROR:
    return TALER_MERCHANTDB_RS_SOFT_ERROR;
  case GNUNET_DB_STATUS_HARD_ERROR:
    return TALER_MERCHANTDB_RS_HARD_ERROR;
  default:
    /* Got one or more deposits */
    return ctx.rs;
  }
}