/*
  This file is part of TALER
  Copyright (C) 2014-2020 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 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-exchange-httpd_refund.c
 * @brief Handle refund requests; parses the POST and JSON and
 *        verifies the coin signature before handing things off
 *        to the database.
 * @author Florian Dold
 * @author Benedikt Mueller
 * @author Christian Grothoff
 */
#include "platform.h"
#include <gnunet/gnunet_util_lib.h>
#include <gnunet/gnunet_json_lib.h>
#include <jansson.h>
#include <microhttpd.h>
#include <pthread.h>
#include "taler_json_lib.h"
#include "taler_mhd_lib.h"
#include "taler-exchange-httpd_refund.h"
#include "taler-exchange-httpd_responses.h"
#include "taler-exchange-httpd_keystate.h"


/**
 * Generate successful refund confirmation message.
 *
 * @param connection connection to the client
 * @param coin_pub public key of the coin
 * @param refund details about the successful refund
 * @return MHD result code
 */
static MHD_RESULT
reply_refund_success (struct MHD_Connection *connection,
                      const struct TALER_CoinSpendPublicKeyP *coin_pub,
                      const struct TALER_EXCHANGEDB_RefundListEntry *refund)
{
  struct TALER_ExchangePublicKeyP pub;
  struct TALER_ExchangeSignatureP sig;
  struct TALER_RefundConfirmationPS rc = {
    .purpose.purpose = htonl (TALER_SIGNATURE_EXCHANGE_CONFIRM_REFUND),
    .purpose.size = htonl (sizeof (rc)),
    .h_contract_terms = refund->h_contract_terms,
    .coin_pub = *coin_pub,
    .merchant = refund->merchant_pub,
    .rtransaction_id = GNUNET_htonll (refund->rtransaction_id)
  };

  TALER_amount_hton (&rc.refund_amount,
                     &refund->refund_amount);
  if (GNUNET_OK !=
      TEH_KS_sign (&rc,
                   &pub,
                   &sig))
  {
    return TALER_MHD_reply_with_error (connection,
                                       MHD_HTTP_INTERNAL_SERVER_ERROR,
                                       TALER_EC_EXCHANGE_BAD_CONFIGURATION,
                                       "no online signing key");
  }
  return TALER_MHD_reply_json_pack (
    connection,
    MHD_HTTP_OK,
    "{s:o, s:o}",
    "exchange_sig", GNUNET_JSON_from_data_auto (&sig),
    "exchange_pub", GNUNET_JSON_from_data_auto (&pub));
}


/**
 * Execute a "/refund" transaction.  Returns a confirmation that the
 * refund was successful, or a failure if we are not aware of a
 * matching /deposit or if it is too late to do the refund.
 *
 * IF it returns a non-error code, the transaction logic MUST
 * NOT queue a MHD response.  IF it returns an hard error, the
 * transaction logic MUST queue a MHD response and set @a mhd_ret.  IF
 * it returns the soft error code, the function MAY be called again to
 * retry and MUST not queue a MHD response.
 *
 * @param cls closure with a `const struct TALER_EXCHANGEDB_Refund *`
 * @param connection MHD request which triggered the transaction
 * @param session database session to use
 * @param[out] mhd_ret set to MHD response status for @a connection,
 *             if transaction failed (!)
 * @return transaction status
 */
static enum GNUNET_DB_QueryStatus
refund_transaction (void *cls,
                    struct MHD_Connection *connection,
                    struct TALER_EXCHANGEDB_Session *session,
                    MHD_RESULT *mhd_ret)
{
  const struct TALER_EXCHANGEDB_Refund *refund = cls;
  struct TALER_EXCHANGEDB_TransactionList *tl;
  const struct TALER_EXCHANGEDB_DepositListEntry *dep;
  const struct TALER_EXCHANGEDB_RefundListEntry *ref;
  enum GNUNET_DB_QueryStatus qs;
  int deposit_found;
  int refund_found;

  tl = NULL;
  qs = TEH_plugin->get_coin_transactions (TEH_plugin->cls,
                                          session,
                                          &refund->coin.coin_pub,
                                          GNUNET_NO,
                                          &tl);
  if (0 > qs)
  {
    if (GNUNET_DB_STATUS_HARD_ERROR == qs)
      *mhd_ret = TALER_MHD_reply_with_error (connection,
                                             MHD_HTTP_NOT_FOUND,
                                             TALER_EC_REFUND_COIN_NOT_FOUND,
                                             "database transaction failure");
    return qs;
  }
  dep = NULL;
  ref = NULL;
  deposit_found = GNUNET_NO;
  refund_found = GNUNET_NO;
  for (struct TALER_EXCHANGEDB_TransactionList *tlp = tl;
       NULL != tlp;
       tlp = tlp->next)
  {
    switch (tlp->type)
    {
    case TALER_EXCHANGEDB_TT_DEPOSIT:
      if (GNUNET_NO == deposit_found)
      {
        if ( (0 == memcmp (&tlp->details.deposit->merchant_pub,
                           &refund->details.merchant_pub,
                           sizeof (struct TALER_MerchantPublicKeyP))) &&
             (0 == memcmp (&tlp->details.deposit->h_contract_terms,
                           &refund->details.h_contract_terms,
                           sizeof (struct GNUNET_HashCode))) )
        {
          dep = tlp->details.deposit;
          deposit_found = GNUNET_YES;
          break;
        }
      }
      break;
    case TALER_EXCHANGEDB_TT_MELT:
      /* Melts cannot be refunded, ignore here */
      break;
    case TALER_EXCHANGEDB_TT_REFUND:
      if (GNUNET_NO == refund_found)
      {
        /* First, check if existing refund request is identical */
        if ( (0 == memcmp (&tlp->details.refund->merchant_pub,
                           &refund->details.merchant_pub,
                           sizeof (struct TALER_MerchantPublicKeyP))) &&
             (0 == memcmp (&tlp->details.refund->h_contract_terms,
                           &refund->details.h_contract_terms,
                           sizeof (struct GNUNET_HashCode))) &&
             (tlp->details.refund->rtransaction_id ==
              refund->details.rtransaction_id) )
        {
          ref = tlp->details.refund;
          refund_found = GNUNET_YES;
          break;
        }
        /* Second, check if existing refund request conflicts */
        if ( (0 == memcmp (&tlp->details.refund->merchant_pub,
                           &refund->details.merchant_pub,
                           sizeof (struct TALER_MerchantPublicKeyP))) &&
             (0 == memcmp (&tlp->details.refund->h_contract_terms,
                           &refund->details.h_contract_terms,
                           sizeof (struct GNUNET_HashCode))) &&
             (tlp->details.refund->rtransaction_id !=
              refund->details.rtransaction_id) )
        {
          refund_found = GNUNET_SYSERR;
          /* NOTE: Alternatively we could total up all existing
             refunds and check if the sum still permits the
             refund requested (thus allowing multiple, partial
             refunds). Fow now, we keep it simple. */
          break;
        }
      }
      break;
    case TALER_EXCHANGEDB_TT_OLD_COIN_RECOUP:
      /* Recoups cannot be refunded, ignore here */
      break;
    case TALER_EXCHANGEDB_TT_RECOUP:
      /* Recoups cannot be refunded, ignore here */
      break;
    case TALER_EXCHANGEDB_TT_RECOUP_REFRESH:
      /* Recoups cannot be refunded, ignore here */
      break;
    }
  }
  /* handle if deposit was NOT found */
  if (GNUNET_NO == deposit_found)
  {
    TALER_LOG_WARNING ("Deposit to /refund was not found\n");
    TEH_plugin->free_coin_transaction_list (TEH_plugin->cls,
                                            tl);
    *mhd_ret = TALER_MHD_reply_with_error (connection,
                                           MHD_HTTP_NOT_FOUND,
                                           TALER_EC_REFUND_DEPOSIT_NOT_FOUND,
                                           "deposit unknown");
    return GNUNET_DB_STATUS_HARD_ERROR;
  }
  /* handle if conflicting refund found */
  if (GNUNET_SYSERR == refund_found)
  {
    *mhd_ret = TALER_MHD_reply_json_pack (
      connection,
      MHD_HTTP_CONFLICT,
      "{s:s, s:I, s:o}",
      "hint", "conflicting refund",
      "code", (json_int_t) TALER_EC_REFUND_CONFLICT,
      "history", TEH_RESPONSE_compile_transaction_history (
        &refund->coin.coin_pub,
        tl));
    TEH_plugin->free_coin_transaction_list (TEH_plugin->cls,
                                            tl);
    return GNUNET_DB_STATUS_HARD_ERROR;
  }
  /* handle if identical refund found */
  if (GNUNET_YES == refund_found)
  {
    /* /refund already done, simply re-transmit confirmation */
    *mhd_ret = reply_refund_success (connection,
                                     &refund->coin.coin_pub,
                                     ref);
    TEH_plugin->free_coin_transaction_list (TEH_plugin->cls,
                                            tl);
    return GNUNET_DB_STATUS_HARD_ERROR;
  }

  /* check currency is compatible */
  if (GNUNET_YES !=
      TALER_amount_cmp_currency (&refund->details.refund_amount,
                                 &dep->amount_with_fee))
  {
    GNUNET_break_op (0); /* currency mismatch */
    TEH_plugin->free_coin_transaction_list (TEH_plugin->cls,
                                            tl);
    *mhd_ret = TALER_MHD_reply_with_error (connection,
                                           MHD_HTTP_BAD_REQUEST,
                                           TALER_EC_REFUND_CURRENCY_MISMATCH,
                                           "currencies involved do not match");
    return GNUNET_DB_STATUS_HARD_ERROR;
  }

  /* check if we already send the money for the /deposit */
  qs = TEH_plugin->test_deposit_done (TEH_plugin->cls,
                                      session,
                                      &refund->coin.coin_pub,
                                      &dep->merchant_pub,
                                      &dep->h_contract_terms,
                                      &dep->h_wire);
  if (GNUNET_DB_STATUS_HARD_ERROR == qs)
  {
    /* Internal error, we first had the deposit in the history,
       but now it is gone? */
    GNUNET_break (0);
    TEH_plugin->free_coin_transaction_list (TEH_plugin->cls,
                                            tl);
    *mhd_ret = TALER_MHD_reply_with_error (connection,
                                           MHD_HTTP_INTERNAL_SERVER_ERROR,
                                           TALER_EC_REFUND_DB_INCONSISTENT,
                                           "database inconsistent (deposit data became inaccessible during transaction)");
    return qs;
  }
  if (GNUNET_DB_STATUS_SOFT_ERROR == qs)
    return qs; /* go and retry */

  if (GNUNET_DB_STATUS_SUCCESS_ONE_RESULT == qs)
  {
    /* money was already transferred to merchant, can no longer refund */
    TEH_plugin->free_coin_transaction_list (TEH_plugin->cls,
                                            tl);
    *mhd_ret = TALER_MHD_reply_with_error (connection,
                                           MHD_HTTP_GONE,
                                           TALER_EC_REFUND_MERCHANT_ALREADY_PAID,
                                           "money already sent to merchant");
    return GNUNET_DB_STATUS_HARD_ERROR;
  }

  /* check refund amount is sufficiently low */
  if (1 == TALER_amount_cmp (&refund->details.refund_amount,
                             &dep->amount_with_fee) )
  {
    GNUNET_break_op (0); /* cannot refund more than original value */
    TEH_plugin->free_coin_transaction_list (TEH_plugin->cls,
                                            tl);
    *mhd_ret = TALER_MHD_reply_with_error (connection,
                                           MHD_HTTP_PRECONDITION_FAILED,
                                           TALER_EC_REFUND_INSUFFICIENT_FUNDS,
                                           "refund requested exceeds original value");
    return GNUNET_DB_STATUS_HARD_ERROR;
  }
  TEH_plugin->free_coin_transaction_list (TEH_plugin->cls,
                                          tl);

  /* Finally, store new refund data */
  qs = TEH_plugin->insert_refund (TEH_plugin->cls,
                                  session,
                                  refund);
  if (GNUNET_DB_STATUS_HARD_ERROR == qs)
  {
    TALER_LOG_WARNING ("Failed to store /refund information in database\n");
    *mhd_ret = TALER_MHD_reply_with_error (connection,
                                           MHD_HTTP_INTERNAL_SERVER_ERROR,
                                           TALER_EC_REFUND_STORE_DB_ERROR,
                                           "could not persist store information");
    return qs;
  }
  /* Success or soft failure */
  return qs;
}


/**
 * We have parsed the JSON information about the refund, do some basic
 * sanity checks (especially that the signature on the coin is valid)
 * and then execute the refund.  Note that we need the DB to check
 * the fee structure, so this is not done here.
 *
 * @param connection the MHD connection to handle
 * @param[in,out] refund information about the refund
 * @return MHD result code
 */
static MHD_RESULT
verify_and_execute_refund (struct MHD_Connection *connection,
                           struct TALER_EXCHANGEDB_Refund *refund)
{
  struct GNUNET_HashCode denom_hash;

  {
    struct TALER_RefundRequestPS rr = {
      .purpose.purpose = htonl (TALER_SIGNATURE_MERCHANT_REFUND),
      .purpose.size = htonl (sizeof (rr)),
      .h_contract_terms = refund->details.h_contract_terms,
      .coin_pub = refund->coin.coin_pub,
      .merchant = refund->details.merchant_pub,
      .rtransaction_id = GNUNET_htonll (refund->details.rtransaction_id)
    };

    TALER_amount_hton (&rr.refund_amount,
                       &refund->details.refund_amount);
    if (GNUNET_OK !=
        GNUNET_CRYPTO_eddsa_verify (TALER_SIGNATURE_MERCHANT_REFUND,
                                    &rr,
                                    &refund->details.merchant_sig.eddsa_sig,
                                    &refund->details.merchant_pub.eddsa_pub))
    {
      TALER_LOG_WARNING ("Invalid signature on refund request\n");
      return TALER_MHD_reply_with_error (connection,
                                         MHD_HTTP_FORBIDDEN,
                                         TALER_EC_REFUND_MERCHANT_SIGNATURE_INVALID,
                                         "merchant_sig");
    }
  }

  /* Fetch the coin's denomination (hash) */
  {
    enum GNUNET_DB_QueryStatus qs;

    qs = TEH_plugin->get_coin_denomination (TEH_plugin->cls,
                                            NULL,
                                            &refund->coin.coin_pub,
                                            &denom_hash);
    if (0 > qs)
    {
      GNUNET_break (GNUNET_DB_STATUS_HARD_ERROR == qs);
      return TALER_MHD_reply_with_error (connection,
                                         MHD_HTTP_NOT_FOUND,
                                         TALER_EC_REFUND_COIN_NOT_FOUND,
                                         "denomination of coin to be refunded not found in DB");
    }
  }

  {
    struct TEH_KS_StateHandle *key_state;

    key_state = TEH_KS_acquire (GNUNET_TIME_absolute_get ());
    if (NULL == key_state)
    {
      TALER_LOG_ERROR ("Lacking keys to operate\n");
      return TALER_MHD_reply_with_error (connection,
                                         MHD_HTTP_INTERNAL_SERVER_ERROR,
                                         TALER_EC_EXCHANGE_BAD_CONFIGURATION,
                                         "no keys");
    }
    /* Obtain information about the coin's denomination! */
    {
      struct TALER_EXCHANGEDB_DenominationKey *dki;
      unsigned int hc;
      enum TALER_ErrorCode ec;

      dki = TEH_KS_denomination_key_lookup_by_hash (key_state,
                                                    &denom_hash,
                                                    TEH_KS_DKU_DEPOSIT,
                                                    &ec,
                                                    &hc);
      if (NULL == dki)
      {
        /* DKI not found, but we do have a coin with this DK in our database;
           not good... */
        GNUNET_break (0);
        TEH_KS_release (key_state);
        return TALER_MHD_reply_with_error (connection,
                                           hc,
                                           ec,
                                           "denomination not found, but coin known");
      }
      TALER_amount_ntoh (&refund->details.refund_fee,
                         &dki->issue.properties.fee_refund);
    }
    TEH_KS_release (key_state);
  }

  /* Finally run the actual transaction logic */
  {
    MHD_RESULT mhd_ret;

    if (GNUNET_OK !=
        TEH_DB_run_transaction (connection,
                                "run refund",
                                &mhd_ret,
                                &refund_transaction,
                                (void *) refund))
    {
      return mhd_ret;
    }
  }
  return reply_refund_success (connection,
                               &refund->coin.coin_pub,
                               &refund->details);
}


/**
 * Handle a "/coins/$COIN_PUB/refund" request.  Parses the JSON, and, if
 * successful, passes the JSON data to #verify_and_execute_refund() to further
 * check the details of the operation specified.  If everything checks out,
 * this will ultimately lead to the refund being executed, or rejected.
 *
 * @param connection the MHD connection to handle
 * @param coin_pub public key of the coin
 * @param root uploaded JSON data
 * @return MHD result code
  */
MHD_RESULT
TEH_handler_refund (struct MHD_Connection *connection,
                    const struct TALER_CoinSpendPublicKeyP *coin_pub,
                    const json_t *root)
{
  struct TALER_EXCHANGEDB_Refund refund = {
    .details.refund_fee.currency = {0}                                        /* set to invalid, just to be sure */
  };
  struct GNUNET_JSON_Specification spec[] = {
    TALER_JSON_spec_amount ("refund_amount",
                            &refund.details.refund_amount),
    GNUNET_JSON_spec_fixed_auto ("h_contract_terms",
                                 &refund.details.h_contract_terms),
    GNUNET_JSON_spec_fixed_auto ("merchant_pub",
                                 &refund.details.merchant_pub),
    GNUNET_JSON_spec_uint64 ("rtransaction_id",
                             &refund.details.rtransaction_id),
    GNUNET_JSON_spec_fixed_auto ("merchant_sig",
                                 &refund.details.merchant_sig),
    GNUNET_JSON_spec_end ()
  };

  refund.coin.coin_pub = *coin_pub;
  {
    enum GNUNET_GenericReturnValue res;

    res = TALER_MHD_parse_json_data (connection,
                                     root,
                                     spec);
    if (GNUNET_SYSERR == res)
      return MHD_NO; /* hard failure */
    if (GNUNET_NO == res)
      return MHD_YES; /* failure */
  }
  {
    MHD_RESULT res;

    res = verify_and_execute_refund (connection,
                                     &refund);
    GNUNET_JSON_parse_free (spec);
    return res;
  }
}


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