/*
 * Copyright 2009-present MongoDB, Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */


#include "mongoc-aggregate-private.h"
#include "mongoc-client-private.h"
#include "mongoc-cursor-private.h"
#include "mongoc-read-prefs-private.h"
#include "mongoc-server-stream-private.h"
#include "mongoc-trace-private.h"
#include "mongoc-util-private.h"

#include <common-bson-dsl-private.h>

/*--------------------------------------------------------------------------
 *
 * _has_write_key --
 *
 *       Returns true if the aggregation pipeline's last stage is "$out"
 *       or "$merge"; otherwise returns false.
 *
 * Side effects:
 *       Advances @iter to the last element.
 *
 *--------------------------------------------------------------------------
 */

bool
_has_write_key (bson_iter_t *iter)
{
   bson_iter_t stage;
   bson_iter_t next;

   memcpy (&next, iter, sizeof (bson_iter_t));
   if (!bson_iter_next (&next)) {
      /* default to false when iter is emtpy */
      return false;
   }

   while (bson_iter_next (iter)) {
      if (!bson_iter_next (&next) && BSON_ITER_HOLDS_DOCUMENT (iter)) {
         bson_iter_recurse (iter, &stage);
         if (bson_iter_find (&stage, "$out")) {
            return true;
         }

         bson_iter_recurse (iter, &stage);
         if (bson_iter_find (&stage, "$merge")) {
            return true;
         }
      }
   }

   return false;
}


/*--------------------------------------------------------------------------
 *
 * _make_agg_cmd --
 *
 *       Constructs an aggregate command. If @ns does not include a collection
 *       name, 1 will be used in its place for the value of "aggregate" in the
 *       command document.
 *
 * Returns:
 *       true if successful; otherwise false and @error is set.
 *
 * Side effects:
 *       @command is always initialized.
 *       @error is set if there is a failure.
 *
 *--------------------------------------------------------------------------
 */

static bool
_make_agg_cmd (
   const char *ns, const bson_t *pipeline, mongoc_aggregate_opts_t *opts, bson_t *command, bson_error_t *err)
{
   const char *const dot = strstr (ns, ".");
   const char *error = NULL;
   const char *error_hint = NULL;

   bsonBuild (*command,
              kv ("aggregate",
                  if (dot,
                      /* Note: we're not validating that the collection name's length is
                         one or more characters, as functions such as
                         mongoc_client_get_collection also do not validate. */
                      // If 'ns' contains a dot, insert the string after the dot:
                      then (cstr (dot + 1)),
                      // Otherwise just an integer 1:
                      else (int32 (1)))));
   if ((error = bsonBuildError)) {
      error_hint = "append-aggregate";
      goto fail;
   }

   /*
    * The following will allow @pipeline to be either an array of
    * items for the pipeline, or {"pipeline": [...]}.
    */
   bsonParse (*pipeline,
              find (keyWithType ("pipeline", array),
                    // There is a "pipeline" array in the document
                    append (*command, kv ("pipeline", iterValue (bsonVisitIter)))),
              else ( // We did not find a "pipeline" array. copy the pipeline as
                     // an array into the command
                 append (*command, kv ("pipeline", array (insert (*pipeline, true))))));
   if ((error = bsonParseError)) {
      error_hint = "append-pipeline";
      goto fail;
   }

   // Check if there is a $merge or $out in the pipeline for the command
   bool has_write_key = false;
   bsonParse (*command,
              find (
                 // Find the "pipeline" array
                 keyWithType ("pipeline", array),
                 parse (
                    // Find the last element of the pipeline array
                    find (lastElement,
                          // If it has an "$out" or "$merge" key, it is a
                          // writing aggregate command.
                          parse (find (key ("$out", "$merge"), do (has_write_key = true)))))));

   if ((error = bsonParseError)) {
      error_hint = "parse-pipeline";
      goto fail;
   }

   bsonBuildAppend (*command,
                    kv ("cursor",
                        // If batchSize is set, and if we are not a writing command with zero
                        // batchSize, append 'batchSize' to the cursor, otherwise leave the
                        // 'cursor' as an empty subdocument.
                        doc (if (opts->batchSize_is_set && !(has_write_key && opts->batchSize == 0),
                                 then (kv ("batchSize", int32 (opts->batchSize)))))));
   if ((error = bsonBuildError)) {
      error_hint = "build-cursor";
      goto fail;
   }

   return true;

fail:
   bson_set_error (err,
                   MONGOC_ERROR_COMMAND,
                   MONGOC_ERROR_COMMAND_INVALID_ARG,
                   "Error while building aggregate command [%s]: %s",
                   error_hint,
                   error);
   return false;
}


/*
 *--------------------------------------------------------------------------
 *
 * _mongoc_aggregate --
 *
 *       Constructs a mongoc_cursor_t for an "aggregate" command.
 *
 *       This function will always return a new mongoc_cursor_t that should
 *       be freed with mongoc_cursor_destroy().
 *
 *       The cursor may fail once iterated upon, so check
 *       mongoc_cursor_error() if mongoc_cursor_next() returns false.
 *
 *       See https://www.mongodb.com/docs/manual/aggregation/ for more
 *       information on how to build aggregation pipelines.
 *
 * Parameters:
 *       @ns: Namespace (or database name for database-level aggregation).
 *       @flags: Bitwise or of mongoc_query_flags_t or 0.
 *       @pipeline: A bson_t containing the pipeline request. @pipeline
 *                  will be sent as an array type in the request.
 *       @opts: A bson_t containing aggregation options, such as
 *              bypassDocumentValidation (used with $out and $merge), maxTimeMS
 *              (declaring maximum server execution time) and explain (return
 *              information on the processing of the pipeline).
 *       @user_rp: Optional read preferences for the command.
 *       @default_rp: Default read preferences from the collection or database.
 *       @default_rc: Default read concern from the collection or database.
 *       @default_wc: Default write concern from the collection or database.
 *
 * Returns:
 *       A newly allocated mongoc_cursor_t that should be freed with
 *       mongoc_cursor_destroy().
 *
 * Side effects:
 *       None.
 *
 *--------------------------------------------------------------------------
 */

mongoc_cursor_t *
_mongoc_aggregate (mongoc_client_t *client,
                   const char *ns,
                   mongoc_query_flags_t flags,
                   const bson_t *pipeline,
                   const bson_t *opts,
                   const mongoc_read_prefs_t *user_rp,
                   const mongoc_read_prefs_t *default_rp,
                   const mongoc_read_concern_t *default_rc,
                   const mongoc_write_concern_t *default_wc)

{
   mongoc_server_stream_t *server_stream = NULL;
   bool has_write_key;
   bson_iter_t ar;
   mongoc_cursor_t *cursor;
   bson_iter_t iter;
   bson_t command = BSON_INITIALIZER;
   bson_t cursor_opts;
   bool created_command;
   bson_error_t create_cmd_err = {0};
   mongoc_aggregate_opts_t aggregate_opts;
   bson_error_t opts_err = {0};
   bool parsed_opts;

   ENTRY;

   BSON_ASSERT (client);
   BSON_ASSERT (ns);
   BSON_ASSERT (pipeline);

   bson_init (&cursor_opts);
   _mongoc_cursor_flags_to_opts (flags, &cursor_opts, NULL);
   if (opts) {
      bson_concat (&cursor_opts /* destination */, opts /* source */);
   }

   parsed_opts = _mongoc_aggregate_opts_parse (client, opts, &aggregate_opts, &opts_err);

   if (parsed_opts) {
      created_command = _make_agg_cmd (ns, pipeline, &aggregate_opts, &command, &create_cmd_err);
   } else {
      created_command = false;
   }

   cursor = _mongoc_cursor_cmd_new (
      client, ns, created_command ? &command : NULL, &cursor_opts, user_rp, default_rp, default_rc);

   bson_destroy (&command);
   bson_destroy (&cursor_opts);

   if (!parsed_opts) {
      memcpy (&cursor->error, &opts_err, sizeof (bson_error_t));
      GOTO (done);
   }

   if (!created_command) {
      /* copy error back to cursor. */
      memcpy (&cursor->error, &create_cmd_err, sizeof (bson_error_t));
      GOTO (done);
   }

   if (mongoc_cursor_error (cursor, NULL)) {
      GOTO (done);
   }

   if (!_mongoc_read_prefs_validate (cursor->read_prefs, &cursor->error)) {
      GOTO (done);
   }

   /* pipeline could be like {pipeline: [{$out: 'test'}]} or [{$out: 'test'}] */
   if (bson_iter_init_find (&iter, pipeline, "pipeline") && BSON_ITER_HOLDS_ARRAY (&iter) &&
       bson_iter_recurse (&iter, &ar)) {
      has_write_key = _has_write_key (&ar);
   } else {
      if (!bson_iter_init (&iter, pipeline)) {
         bson_set_error (&cursor->error, MONGOC_ERROR_BSON, MONGOC_ERROR_BSON_INVALID, "Pipeline is invalid BSON");
         GOTO (done);
      }
      has_write_key = _has_write_key (&iter);
   }

   /* This has an important effect on server selection when
    * readPreferences=secondary. Keep track of this fact for later use. */
   cursor->is_aggr_with_write_stage = has_write_key;

   /* server id isn't enough. ensure we're connected & know wire version */
   server_stream = _mongoc_cursor_fetch_stream (cursor);
   if (!server_stream) {
      GOTO (done);
   }

   /* Only inherit WriteConcern when aggregate has $out or $merge */
   if (!aggregate_opts.write_concern_owned && has_write_key) {
      mongoc_write_concern_destroy (cursor->write_concern);
      cursor->write_concern = mongoc_write_concern_copy (default_wc);
   }

done:
   _mongoc_aggregate_opts_cleanup (&aggregate_opts);
   mongoc_server_stream_cleanup (server_stream); /* null ok */

   /* we always return the cursor, even if it fails; users can detect the
    * failure on performing a cursor operation. see CDRIVER-880. */
   RETURN (cursor);
}
