text: 'use strict';
  
  const deprecate = require('util').deprecate;
  const deprecateOptions = require('./utils').deprecateOptions;
  const checkCollectionName = require('./utils').checkCollectionName;
  const ObjectID = require('mongodb-core').BSON.ObjectID;
  const MongoError = require('mongodb-core').MongoError;
  const toError = require('./utils').toError;
  const normalizeHintField = require('./utils').normalizeHintField;
  const handleCallback = require('./utils').handleCallback;
  const decorateCommand = require('./utils').decorateCommand;
  const decorateWithCollation = require('./utils').decorateWithCollation;
  const decorateWithReadConcern = require('./utils').decorateWithReadConcern;
  const formattedOrderClause = require('./utils').formattedOrderClause;
  const ReadPreference = require('mongodb-core').ReadPreference;
  const CommandCursor = require('./command_cursor');
  const unordered = require('./bulk/unordered');
  const ordered = require('./bulk/ordered');
  const ChangeStream = require('./change_stream');
  const executeOperation = require('./utils').executeOperation;
  const resolveReadPreference = require('./utils').resolveReadPreference;
  
  // Operations
  const aggregate = require('./operations/aggregate').aggregate;
  const bulkWrite = require('./operations/collection_ops').bulkWrite;
  const checkForAtomicOperators = require('./operations/collection_ops').checkForAtomicOperators;
  const count = require('./operations/collection_ops').count;
  const countDocuments = require('./operations/collection_ops').countDocuments;
  const createIndex = require('./operations/collection_ops').createIndex;
  const createIndexes = require('./operations/collection_ops').createIndexes;
  const deleteMany = require('./operations/collection_ops').deleteMany;
  const deleteOne = require('./operations/collection_ops').deleteOne;
  const distinct = require('./operations/collection_ops').distinct;
  const dropIndex = require('./operations/collection_ops').dropIndex;
  const dropIndexes = require('./operations/collection_ops').dropIndexes;
  const ensureIndex = require('./operations/collection_ops').ensureIndex;
  const findAndModify = require('./operations/collection_ops').findAndModify;
  const findAndRemove = require('./operations/collection_ops').findAndRemove;
  const findOne = require('./operations/collection_ops').findOne;
  const findOneAndDelete = require('./operations/collection_ops').findOneAndDelete;
  const findOneAndReplace = require('./operations/collection_ops').findOneAndReplace;
  const findOneAndUpdate = require('./operations/collection_ops').findOneAndUpdate;
  const geoHaystackSearch = require('./operations/collection_ops').geoHaystackSearch;
  const group = require('./operations/collection_ops').group;
  const indexes = require('./operations/collection_ops').indexes;
  const indexExists = require('./operations/collection_ops').indexExists;
  const indexInformation = require('./operations/collection_ops').indexInformation;
  const insertMany = require('./operations/collection_ops').insertMany;
  const insertOne = require('./operations/collection_ops').insertOne;
  const isCapped = require('./operations/collection_ops').isCapped;
  const mapReduce = require('./operations/collection_ops').mapReduce;
  const optionsOp = require('./operations/collection_ops').optionsOp;
  const parallelCollectionScan = require('./operations/collection_ops').parallelCollectionScan;
  const reIndex = require('./operations/collection_ops').reIndex;
  const removeDocuments = require('./operations/collection_ops').removeDocuments;
  const rename = require('./operations/collection_ops').rename;
  const replaceOne = require('./operations/collection_ops').replaceOne;
  const save = require('./operations/collection_ops').save;
  const stats = require('./operations/collection_ops').stats;
  const updateDocuments = require('./operations/collection_ops').updateDocuments;
  const updateMany = require('./operations/collection_ops').updateMany;
  const updateOne = require('./operations/collection_ops').updateOne;
  
  /**
   * @fileOverview The **Collection** class is an internal class that embodies a MongoDB collection
   * allowing for insert/update/remove/find and other command operation on that MongoDB collection.
   *
   * **COLLECTION Cannot directly be instantiated**
   * @example
   * const MongoClient = require('mongodb').MongoClient;
   * const test = require('assert');
   * // Connection url
   * const url = 'mongodb://localhost:27017';
   * // Database Name
   * const dbName = 'test';
   * // Connect using MongoClient
   * MongoClient.connect(url, function(err, client) {
   *   // Create a collection we want to drop later
   *   const col = client.db(dbName).collection('createIndexExample1');
   *   // Show that duplicate records got dropped
   *   col.find({}).toArray(function(err, items) {
   *     test.equal(null, err);
   *     test.equal(4, items.length);
   *     client.close();
   *   });
   * });
   */
  
  const mergeKeys = ['ignoreUndefined'];
  
  /**
   * Create a new Collection instance (INTERNAL TYPE, do not instantiate directly)
   * @class
   * @property {string} collectionName Get the collection name.
   * @property {string} namespace Get the full collection namespace.
   * @property {object} writeConcern The current write concern values.
   * @property {object} readConcern The current read concern values.
   * @property {object} hint Get current index hint for collection.
   * @return {Collection} a Collection instance.
   */
  function Collection(db, topology, dbName, name, pkFactory, options) {
    checkCollectionName(name);
  
    // Unpack variables
    const internalHint = null;
    const slaveOk = options == null || options.slaveOk == null ? db.slaveOk : options.slaveOk;
    const serializeFunctions =
      options == null || options.serializeFunctions == null
        ? db.s.options.serializeFunctions
        : options.serializeFunctions;
    const raw = options == null || options.raw == null ? db.s.options.raw : options.raw;
    const promoteLongs =
      options == null || options.promoteLongs == null
        ? db.s.options.promoteLongs
        : options.promoteLongs;
    const promoteValues =
      options == null || options.promoteValues == null
        ? db.s.options.promoteValues
        : options.promoteValues;
    const promoteBuffers =
      options == null || options.promoteBuffers == null
        ? db.s.options.promoteBuffers
        : options.promoteBuffers;
    let readPreference = null;
    const collectionHint = null;
    const namespace = `${dbName}.${name}`;
  
    // Get the promiseLibrary
    const promiseLibrary = options.promiseLibrary || Promise;
  
    // Assign the right collection level readPreference
    if (options && options.readPreference) {
      readPreference = options.readPreference;
    } else if (db.options.readPreference) {
      readPreference = db.options.readPreference;
    }
  
    // Set custom primary key factory if provided
    pkFactory = pkFactory == null ? ObjectID : pkFactory;
  
    // Internal state
    this.s = {
      // Set custom primary key factory if provided
      pkFactory: pkFactory,
      // Db
      db: db,
      // Topology
      topology: topology,
      // dbName
      dbName: dbName,
      // Options
      options: options,
      // Namespace
      namespace: namespace,
      // Read preference
      readPreference: readPreference,
      // SlaveOK
      slaveOk: slaveOk,
      // Serialize functions
      serializeFunctions: serializeFunctions,
      // Raw
      raw: raw,
      // promoteLongs
      promoteLongs: promoteLongs,
      // promoteValues
      promoteValues: promoteValues,
      // promoteBuffers
      promoteBuffers: promoteBuffers,
      // internalHint
      internalHint: internalHint,
      // collectionHint
      collectionHint: collectionHint,
      // Name
      name: name,
      // Promise library
      promiseLibrary: promiseLibrary,
      // Read Concern
      readConcern: options.readConcern,
      // Write Concern
      writeConcern: options.writeConcern
    };
  }
  
  Object.defineProperty(Collection.prototype, 'dbName', {
    enumerable: true,
    get: function() {
      return this.s.dbName;
    }
  });
  
  Object.defineProperty(Collection.prototype, 'collectionName', {
    enumerable: true,
    get: function() {
      return this.s.name;
    }
  });
  
  Object.defineProperty(Collection.prototype, 'namespace', {
    enumerable: true,
    get: function() {
      return this.s.namespace;
    }
  });
  
  Object.defineProperty(Collection.prototype, 'readConcern', {
    enumerable: true,
    get: function() {
      return this.s.readConcern || { level: 'local' };
    }
  });
  
  Object.defineProperty(Collection.prototype, 'writeConcern', {
    enumerable: true,
    get: function() {
      let ops = {};
      if (this.s.writeConcern) {
        return this.s.writeConcern;
      }
  
      if (this.s.options.w != null) ops.w = this.s.options.w;
      if (this.s.options.j != null) ops.j = this.s.options.j;
      if (this.s.options.fsync != null) ops.fsync = this.s.options.fsync;
      if (this.s.options.wtimeout != null) ops.wtimeout = this.s.options.wtimeout;
      return ops;
    }
  });
  
  /**
   * @ignore
   */
  Object.defineProperty(Collection.prototype, 'hint', {
    enumerable: true,
    get: function() {
      return this.s.collectionHint;
    },
    set: function(v) {
      this.s.collectionHint = normalizeHintField(v);
    }
  });
  
  const DEPRECATED_FIND_OPTIONS = ['maxScan', 'fields', 'snapshot'];
  
  /**
   * Creates a cursor for a query that can be used to iterate over results from MongoDB
   * @method
   * @param {object} [query={}] The cursor query object.
   * @param {object} [options] Optional settings.
   * @param {number} [options.limit=0] Sets the limit of documents returned in the query.
   * @param {(array|object)} [options.sort] Set to sort the documents coming back from the query. Array of indexes, [['a', 1]] etc.
   * @param {object} [options.projection] The fields to return in the query. Object of fields to include or exclude (not both), {'a':1}
   * @param {object} [options.fields] **Deprecated** Use `options.projection` instead
   * @param {number} [options.skip=0] Set to skip N documents ahead in your query (useful for pagination).
   * @param {Object} [options.hint] Tell the query to use specific indexes in the query. Object of indexes to use, {'_id':1}
   * @param {boolean} [options.explain=false] Explain the query instead of returning the data.
   * @param {boolean} [options.snapshot=false] DEPRECATED: Snapshot query.
   * @param {boolean} [options.timeout=false] Specify if the cursor can timeout.
   * @param {boolean} [options.tailable=false] Specify if the cursor is tailable.
   * @param {number} [options.batchSize=0] Set the batchSize for the getMoreCommand when iterating over the query results.
   * @param {boolean} [options.returnKey=false] Only return the index key.
   * @param {number} [options.maxScan] DEPRECATED: Limit the number of items to scan.
   * @param {number} [options.min] Set index bounds.
   * @param {number} [options.max] Set index bounds.
   * @param {boolean} [options.showDiskLoc=false] Show disk location of results.
   * @param {string} [options.comment] You can put a $comment field on a query to make looking in the profiler logs simpler.
   * @param {boolean} [options.raw=false] Return document results as raw BSON buffers.
   * @param {boolean} [options.promoteLongs=true] Promotes Long values to number if they fit inside the 53 bits resolution.
   * @param {boolean} [options.promoteValues=true] Promotes BSON values to native types where possible, set to false to only receive wrapper types.
   * @param {boolean} [options.promoteBuffers=false] Promotes Binary BSON values to native Node Buffers.
   * @param {(ReadPreference|string)} [options.readPreference] The preferred read preference (ReadPreference.PRIMARY, ReadPreference.PRIMARY_PREFERRED, ReadPreference.SECONDARY, ReadPreference.SECONDARY_PREFERRED, ReadPreference.NEAREST).
   * @param {boolean} [options.partial=false] Specify if the cursor should return partial results when querying against a sharded system
   * @param {number} [options.maxTimeMS] Number of milliseconds to wait before aborting the query.
   * @param {object} [options.collation] Specify collation (MongoDB 3.4 or higher) settings for update operation (see 3.4 documentation for available fields).
   * @param {ClientSession} [options.session] optional session to use for this operation
   * @throws {MongoError}
   * @return {Cursor}
   */
  Collection.prototype.find = deprecateOptions(
    {
      name: 'collection.find',
      deprecatedOptions: DEPRECATED_FIND_OPTIONS,
      optionsIndex: 1
    },
    function(query, options, callback) {
      if (typeof callback === 'object') {
        // TODO(MAJOR): throw in the future
        console.warn('Third parameter to `find()` must be a callback or undefined');
      }
  
      let selector = query;
      // figuring out arguments
      if (typeof callback !== 'function') {
        if (typeof options === 'function') {
          callback = options;
          options = undefined;
        } else if (options == null) {
          callback = typeof selector === 'function' ? selector : undefined;
          selector = typeof selector === 'object' ? selector : undefined;
        }
      }
  
      // Ensure selector is not null
      selector = selector == null ? {} : selector;
      // Validate correctness off the selector
      const object = selector;
      if (Buffer.isBuffer(object)) {
        const object_size = object[0] | (object[1] << 8) | (object[2] << 16) | (object[3] << 24);
        if (object_size !== object.length) {
          const error = new Error(
            'query selector raw message size does not match message header size [' +
              object.length +
              '] != [' +
              object_size +
              ']'
          );
          error.name = 'MongoError';
          throw error;
        }
      }
  
      // Check special case where we are using an objectId
      if (selector != null && selector._bsontype === 'ObjectID') {
        selector = { _id: selector };
      }
  
      if (!options) options = {};
  
      let projection = options.projection || options.fields;
  
      if (projection && !Buffer.isBuffer(projection) && Array.isArray(projection)) {
        projection = projection.length
          ? projection.reduce((result, field) => {
              result[field] = 1;
              return result;
            }, {})
          : { _id: 1 };
      }
  
      // Make a shallow copy of options
      let newOptions = Object.assign({}, options);
  
      // Make a shallow copy of the collection options
      for (let key in this.s.options) {
        if (mergeKeys.indexOf(key) !== -1) {
          newOptions[key] = this.s.options[key];
        }
      }
  
      // Unpack options
      newOptions.skip = options.skip ? options.skip : 0;
      newOptions.limit = options.limit ? options.limit : 0;
      newOptions.raw = typeof options.raw === 'boolean' ? options.raw : this.s.raw;
      newOptions.hint =
        options.hint != null ? normalizeHintField(options.hint) : this.s.collectionHint;
      newOptions.timeout = typeof options.timeout === 'undefined' ? undefined : options.timeout;
      // // If we have overridden slaveOk otherwise use the default db setting
      newOptions.slaveOk = options.slaveOk != null ? options.slaveOk : this.s.db.slaveOk;
  
      // Add read preference if needed
      newOptions.readPreference = resolveReadPreference(newOptions, {
        db: this.s.db,
        collection: this
      });
  
      // Set slave ok to true if read preference different from primary
      if (
        newOptions.readPreference != null &&
        (newOptions.readPreference !== 'primary' || newOptions.readPreference.mode !== 'primary')
      ) {
        newOptions.slaveOk = true;
      }
  
      // Ensure the query is an object
      if (selector != null && typeof selector !== 'object') {
        throw MongoError.create({ message: 'query selector must be an object', driver: true });
      }
  
      // Build the find command
      const findCommand = {
        find: this.s.namespace,
        limit: newOptions.limit,
        skip: newOptions.skip,
        query: selector
      };
  
      // Ensure we use the right await data option
      if (typeof newOptions.awaitdata === 'boolean') {
        newOptions.awaitData = newOptions.awaitdata;
      }
  
      // Translate to new command option noCursorTimeout
      if (typeof newOptions.timeout === 'boolean') newOptions.noCursorTimeout = newOptions.timeout;
  
      decorateCommand(findCommand, newOptions, ['session', 'collation']);
  
      if (projection) findCommand.fields = projection;
  
      // Add db object to the new options
      newOptions.db = this.s.db;
  
      // Add the promise library
      newOptions.promiseLibrary = this.s.promiseLibrary;
  
      // Set raw if available at collection level
      if (newOptions.raw == null && typeof this.s.raw === 'boolean') newOptions.raw = this.s.raw;
      // Set promoteLongs if available at collection level
      if (newOptions.promoteLongs == null && typeof this.s.promoteLongs === 'boolean')
        newOptions.promoteLongs = this.s.promoteLongs;
      if (newOptions.promoteValues == null && typeof this.s.promoteValues === 'boolean')
        newOptions.promoteValues = this.s.promoteValues;
      if (newOptions.promoteBuffers == null && typeof this.s.promoteBuffers === 'boolean')
        newOptions.promoteBuffers = this.s.promoteBuffers;
  
      // Sort options
      if (findCommand.sort) {
        findCommand.sort = formattedOrderClause(findCommand.sort);
      }
  
      // Set the readConcern
      decorateWithReadConcern(findCommand, this, options);
  
      // Decorate find command with collation options
      try {
        decorateWithCollation(findCommand, this, options);
      } catch (err) {
        if (typeof callback === 'function') return callback(err, null);
        throw err;
      }
  
      const cursor = this.s.topology.cursor(this.s.namespace, findCommand, newOptions);
  
      return typeof callback === 'function' ? handleCallback(callback, null, cursor) : cursor;
    }
  );
  
  /**
   * Inserts a single document into MongoDB. If documents passed in do not contain the **_id** field,
   * one will be added to each of the documents missing it by the driver, mutating the document. This behavior
   * can be overridden by setting the **forceServerObjectId** flag.
   *
   * @method
   * @param {object} doc Document to insert.
   * @param {object} [options] Optional settings.
   * @param {(number|string)} [options.w] The write concern.
   * @param {number} [options.wtimeout] The write concern timeout.
   * @param {boolean} [options.j=false] Specify a journal write concern.
   * @param {boolean} [options.serializeFunctions=false] Serialize functions on any object.
   * @param {boolean} [options.forceServerObjectId=false] Force server to assign _id values instead of driver.
   * @param {boolean} [options.bypassDocumentValidation=false] Allow driver to bypass schema validation in MongoDB 3.2 or higher.
   * @param {ClientSession} [options.session] optional session to use for this operation
   * @param {Collection~insertOneWriteOpCallback} [callback] The command result callback
   * @return {Promise} returns Promise if no callback passed
   */
  Collection.prototype.insertOne = function(doc, options, callback) {
    if (typeof options === 'function') (callback = options), (options = {});
    options = options || {};
  
    // Add ignoreUndefined
    if (this.s.options.ignoreUndefined) {
      options = Object.assign({}, options);
      options.ignoreUndefined = this.s.options.ignoreUndefined;
    }
  
    return executeOperation(this.s.topology, insertOne, [this, doc, options, callback]);
  };
  
  /**
   * Inserts an array of documents into MongoDB. If documents passed in do not contain the **_id** field,
   * one will be added to each of the documents missing it by the driver, mutating the document. This behavior
   * can be overridden by setting the **forceServerObjectId** flag.
   *
   * @method
   * @param {object[]} docs Documents to insert.
   * @param {object} [options] Optional settings.
   * @param {(number|string)} [options.w] The write concern.
   * @param {number} [options.wtimeout] The write concern timeout.
   * @param {boolean} [options.j=false] Specify a journal write concern.
   * @param {boolean} [options.serializeFunctions=false] Serialize functions on any object.
   * @param {boolean} [options.forceServerObjectId=false] Force server to assign _id values instead of driver.
   * @param {boolean} [options.bypassDocumentValidation=false] Allow driver to bypass schema validation in MongoDB 3.2 or higher.
   * @param {boolean} [options.ordered=true] If true, when an insert fails, don't execute the remaining writes. If false, continue with remaining inserts when one fails.
   * @param {ClientSession} [options.session] optional session to use for this operation
   * @param {Collection~insertWriteOpCallback} [callback] The command result callback
   * @return {Promise} returns Promise if no callback passed
   */
  Collection.prototype.insertMany = function(docs, options, callback) {
    if (typeof options === 'function') (callback = options), (options = {});
    options = options ? Object.assign({}, options) : { ordered: true };
  
    return executeOperation(this.s.topology, insertMany, [this, docs, options, callback]);
  };
  
  /**
   * @typedef {Object} Collection~BulkWriteOpResult
   * @property {number} insertedCount Number of documents inserted.
   * @property {number} matchedCount Number of documents matched for update.
   * @property {number} modifiedCount Number of documents modified.
   * @property {number} deletedCount Number of documents deleted.
   * @property {number} upsertedCount Number of documents upserted.
   * @property {object} insertedIds Inserted document generated Id's, hash key is the index of the originating operation
   * @property {object} upsertedIds Upserted document generated Id's, hash key is the index of the originating operation
   * @property {object} result The command result object.
   */
  
  /**
   * The callback format for inserts
   * @callback Collection~bulkWriteOpCallback
   * @param {BulkWriteError} error An error instance representing the error during the execution.
   * @param {Collection~BulkWriteOpResult} result The result object if the command was executed successfully.
   */
  
  /**
   * Perform a bulkWrite operation without a fluent API
   *
   * Legal operation types are
   *
   *  { insertOne: { document: { a: 1 } } }
   *
   *  { updateOne: { filter: {a:2}, update: {$set: {a:2}}, upsert:true } }
   *
   *  { updateMany: { filter: {a:2}, update: {$set: {a:2}}, upsert:true } }
   *
   *  { deleteOne: { filter: {c:1} } }
   *
   *  { deleteMany: { filter: {c:1} } }
   *
   *  { replaceOne: { filter: {c:3}, replacement: {c:4}, upsert:true}}
   *
   * If documents passed in do not contain the **_id** field,
   * one will be added to each of the documents missing it by the driver, mutating the document. This behavior
   * can be overridden by setting the **forceServerObjectId** flag.
   *
   * @method
   * @param {object[]} operations Bulk operations to perform.
   * @param {object} [options] Optional settings.
   * @param {(number|string)} [options.w] The write concern.
   * @param {number} [options.wtimeout] The write concern timeout.
   * @param {boolean} [options.j=false] Specify a journal write concern.
   * @param {boolean} [options.serializeFunctions=false] Serialize functions on any object.
   * @param {boolean} [options.ordered=true] Execute write operation in ordered or unordered fashion.
   * @param {boolean} [options.bypassDocumentValidation=false] Allow driver to bypass schema validation in MongoDB 3.2 or higher.
   * @param {ClientSession} [options.session] optional session to use for this operation
   * @param {Collection~bulkWriteOpCallback} [callback] The command result callback
   * @return {Promise} returns Promise if no callback passed
   */
  Collection.prototype.bulkWrite = function(operations, options, callback) {
    if (typeof options === 'function') (callback = options), (options = {});
    options = options || { ordered: true };
  
    if (!Array.isArray(operations)) {
      throw MongoError.create({ message: 'operations must be an array of documents', driver: true });
    }
  
    return executeOperation(this.s.topology, bulkWrite, [this, operations, options, callback]);
  };
  
  /**
   * @typedef {Object} Collection~WriteOpResult
   * @property {object[]} ops All the documents inserted using insertOne/insertMany/replaceOne. Documents contain the _id field if forceServerObjectId == false for insertOne/insertMany
   * @property {object} connection The connection object used for the operation.
   * @property {object} result The command result object.
   */
  
  /**
   * The callback format for inserts
   * @callback Collection~writeOpCallback
   * @param {MongoError} error An error instance representing the error during the execution.
   * @param {Collection~WriteOpResult} result The result object if the command was executed successfully.
   */
  
  /**
   * @typedef {Object} Collection~insertWriteOpResult
   * @property {Number} insertedCount The total amount of documents inserted.
   * @property {object[]} ops All the documents inserted using insertOne/insertMany/replaceOne. Documents contain the _id field if forceServerObjectId == false for insertOne/insertMany
   * @property {Object.<Number, ObjectId>} insertedIds Map of the index of the inserted document to the id of the inserted document.
   * @property {object} connection The connection object used for the operation.
   * @property {object} result The raw command result object returned from MongoDB (content might vary by server version).
   * @property {Number} result.ok Is 1 if the command executed correctly.
   * @property {Number} result.n The total count of documents inserted.
   */
  
  /**
   * @typedef {Object} Collection~insertOneWriteOpResult
   * @property {Number} insertedCount The total amount of documents inserted.
   * @property {object[]} ops All the documents inserted using insertOne/insertMany/replaceOne. Documents contain the _id field if forceServerObjectId == false for insertOne/insertMany
   * @property {ObjectId} insertedId The driver generated ObjectId for the insert operation.
   * @property {object} connection The connection object used for the operation.
   * @property {object} result The raw command result object returned from MongoDB (content might vary by server version).
   * @property {Number} result.ok Is 1 if the command executed correctly.
   * @property {Number} result.n The total count of documents inserted.
   */
  
  /**
   * The callback format for inserts
   * @callback Collection~insertWriteOpCallback
   * @param {MongoError} error An error instance representing the error during the execution.
   * @param {Collection~insertWriteOpResult} result The result object if the command was executed successfully.
   */
  
  /**
   * The callback format for inserts
   * @callback Collection~insertOneWriteOpCallback
   * @param {MongoError} error An error instance representing the error during the execution.
   * @param {Collection~insertOneWriteOpResult} result The result object if the command was executed successfully.
   */
  
  /**
   * Inserts a single document or a an array of documents into MongoDB. If documents passed in do not contain the **_id** field,
   * one will be added to each of the documents missing it by the driver, mutating the document. This behavior
   * can be overridden by setting the **forceServerObjectId** flag.
   *
   * @method
   * @param {(object|object[])} docs Documents to insert.
   * @param {object} [options] Optional settings.
   * @param {(number|string)} [options.w] The write concern.
   * @param {number} [options.wtimeout] The write concern timeout.
   * @param {boolean} [options.j=false] Specify a journal write concern.
   * @param {boolean} [options.serializeFunctions=false] Serialize functions on any object.
   * @param {boolean} [options.forceServerObjectId=false] Force server to assign _id values instead of driver.
   * @param {boolean} [options.bypassDocumentValidation=false] Allow driver to bypass schema validation in MongoDB 3.2 or higher.
   * @param {ClientSession} [options.session] optional session to use for this operation
   * @param {Collection~insertWriteOpCallback} [callback] The command result callback
   * @return {Promise} returns Promise if no callback passed
   * @deprecated Use insertOne, insertMany or bulkWrite
   */
  Collection.prototype.insert = deprecate(function(docs, options, callback) {
    if (typeof options === 'function') (callback = options), (options = {});
    options = options || { ordered: false };
    docs = !Array.isArray(docs) ? [docs] : docs;
  
    if (options.keepGoing === true) {
      options.ordered = false;
    }
  
    return this.insertMany(docs, options, callback);
  }, 'collection.insert is deprecated. Use insertOne, insertMany or bulkWrite instead.');
  
  /**
   * @typedef {Object} Collection~updateWriteOpResult
   * @property {Object} result The raw result returned from MongoDB. Will vary depending on server version.
   * @property {Number} result.ok Is 1 if the command executed correctly.
   * @property {Number} result.n The total count of documents scanned.
   * @property {Number} result.nModified The total count of documents modified.
   * @property {Object} connection The connection object used for the operation.
   * @property {Number} matchedCount The number of documents that matched the filter.
   * @property {Number} modifiedCount The number of documents that were modified.
   * @property {Number} upsertedCount The number of documents upserted.
   * @property {Object} upsertedId The upserted id.
   * @property {ObjectId} upsertedId._id The upserted _id returned from the server.
   * @property {Object} message
   * @property {Array} ops
   */
  
  /**
   * The callback format for inserts
   * @callback Collection~updateWriteOpCallback
   * @param {MongoError} error An error instance representing the error during the execution.
   * @param {Collection~updateWriteOpResult} result The result object if the command was executed successfully.
   */
  
  /**
   * Update a single document in a collection
   * @method
   * @param {object} filter The Filter used to select the document to update
   * @param {object} update The update operations to be applied to the document
   * @param {object} [options] Optional settings.
   * @param {boolean} [options.upsert=false] Update operation is an upsert.
   * @param {(number|string)} [options.w] The write concern.
   * @param {number} [options.wtimeout] The write concern timeout.
   * @param {boolean} [options.j=false] Specify a journal write concern.
   * @param {boolean} [options.bypassDocumentValidation=false] Allow driver to bypass schema validation in MongoDB 3.2 or higher.
   * @param {Array} [options.arrayFilters] optional list of array filters referenced in filtered positional operators
   * @param {ClientSession} [options.session] optional session to use for this operation
   * @param {Collection~updateWriteOpCallback} [callback] The command result callback
   * @return {Promise} returns Promise if no callback passed
   */
  Collection.prototype.updateOne = function(filter, update, options, callback) {
    if (typeof options === 'function') (callback = options), (options = {});
    options = options || {};
  
    const err = checkForAtomicOperators(update);
    if (err) {
      if (typeof callback === 'function') return callback(err);
      return this.s.promiseLibrary.reject(err);
    }
  
    options = Object.assign({}, options);
  
    // Add ignoreUndefined
    if (this.s.options.ignoreUndefined) {
      options = Object.assign({}, options);
      options.ignoreUndefined = this.s.options.ignoreUndefined;
    }
  
    return executeOperation(this.s.topology, updateOne, [this, filter, update, options, callback]);
  };
  
  /**
   * Replace a document in a collection with another document
   * @method
   * @param {object} filter The Filter used to select the document to replace
   * @param {object} doc The Document that replaces the matching document
   * @param {object} [options] Optional settings.
   * @param {boolean} [options.upsert=false] Update operation is an upsert.
   * @param {(number|string)} [options.w] The write concern.
   * @param {number} [options.wtimeout] The write concern timeout.
   * @param {boolean} [options.j=false] Specify a journal write concern.
   * @param {boolean} [options.bypassDocumentValidation=false] Allow driver to bypass schema validation in MongoDB 3.2 or higher.
   * @param {ClientSession} [options.session] optional session to use for this operation
   * @param {Collection~updateWriteOpCallback} [callback] The command result callback
   * @return {Promise<Collection~updatewriteOpResultObject>} returns Promise if no callback passed
   */
  Collection.prototype.replaceOne = function(filter, doc, options, callback) {
    if (typeof options === 'function') (callback = options), (options = {});
    options = Object.assign({}, options);
  
    // Add ignoreUndefined
    if (this.s.options.ignoreUndefined) {
      options = Object.assign({}, options);
      options.ignoreUndefined = this.s.options.ignoreUndefined;
    }
  
    return executeOperation(this.s.topology, replaceOne, [this, filter, doc, options, callback]);
  };
  
  /**
   * Update multiple documents in a collection
   * @method
   * @param {object} filter The Filter used to select the documents to update
   * @param {object} update The update operations to be applied to the documents
   * @param {object} [options] Optional settings.
   * @param {boolean} [options.upsert=false] Update operation is an upsert.
   * @param {(number|string)} [options.w] The write concern.
   * @param {number} [options.wtimeout] The write concern timeout.
   * @param {boolean} [options.j=false] Specify a journal write concern.
   * @param {Array} [options.arrayFilters] optional list of array filters referenced in filtered positional operators
   * @param {ClientSession} [options.session] optional session to use for this operation
   * @param {Collection~updateWriteOpCallback} [callback] The command result callback
   * @return {Promise<Collection~updateWriteOpResultObject>} returns Promise if no callback passed
   */
  Collection.prototype.updateMany = function(filter, update, options, callback) {
    if (typeof options === 'function') (callback = options), (options = {});
    options = options || {};
  
    const err = checkForAtomicOperators(update);
    if (err) {
      if (typeof callback === 'function') return callback(err);
      return this.s.promiseLibrary.reject(err);
    }
  
    options = Object.assign({}, options);
  
    // Add ignoreUndefined
    if (this.s.options.ignoreUndefined) {
      options = Object.assign({}, options);
      options.ignoreUndefined = this.s.options.ignoreUndefined;
    }
  
    return executeOperation(this.s.topology, updateMany, [this, filter, update, options, callback]);
  };
  
  /**
   * Updates documents.
   * @method
   * @param {object} selector The selector for the update operation.
   * @param {object} update The update operations to be applied to the documents
   * @param {object} [options] Optional settings.
   * @param {(number|string)} [options.w] The write concern.
   * @param {number} [options.wtimeout] The write concern timeout.
   * @param {boolean} [options.j=false] Specify a journal write concern.
   * @param {boolean} [options.upsert=false] Update operation is an upsert.
   * @param {boolean} [options.multi=false] Update one/all documents with operation.
   * @param {boolean} [options.bypassDocumentValidation=false] Allow driver to bypass schema validation in MongoDB 3.2 or higher.
   * @param {object} [options.collation] Specify collation (MongoDB 3.4 or higher) settings for update operation (see 3.4 documentation for available fields).
   * @param {Array} [options.arrayFilters] optional list of array filters referenced in filtered positional operators
   * @param {ClientSession} [options.session] optional session to use for this operation
   * @param {Collection~writeOpCallback} [callback] The command result callback
   * @throws {MongoError}
   * @return {Promise} returns Promise if no callback passed
   * @deprecated use updateOne, updateMany or bulkWrite
   */
  Collection.prototype.update = deprecate(function(selector, update, options, callback) {
    if (typeof options === 'function') (callback = options), (options = {});
    options = options || {};
  
    // Add ignoreUndefined
    if (this.s.options.ignoreUndefined) {
      options = Object.assign({}, options);
      options.ignoreUndefined = this.s.options.ignoreUndefined;
    }
  
    return executeOperation(this.s.topology, updateDocuments, [
      this,
      selector,
      update,
      options,
      callback
    ]);
  }, 'collection.update is deprecated. Use updateOne, updateMany, or bulkWrite instead.');
  
  /**
   * @typedef {Object} Collection~deleteWriteOpResult
   * @property {Object} result The raw result returned from MongoDB. Will vary depending on server version.
   * @property {Number} result.ok Is 1 if the command executed correctly.
   * @property {Number} result.n The total count of documents deleted.
   * @property {Object} connection The connection object used for the operation.
   * @property {Number} deletedCount The number of documents deleted.
   */
  
  /**
   * The callback format for inserts
   * @callback Collection~deleteWriteOpCallback
   * @param {MongoError} error An error instance representing the error during the execution.
   * @param {Collection~deleteWriteOpResult} result The result object if the command was executed successfully.
   */
  
  /**
   * Delete a document from a collection
   * @method
   * @param {object} filter The Filter used to select the document to remove
   * @param {object} [options] Optional settings.
   * @param {(number|string)} [options.w] The write concern.
   * @param {number} [options.wtimeout] The write concern timeout.
   * @param {boolean} [options.j=false] Specify a journal write concern.
   * @param {ClientSession} [options.session] optional session to use for this operation
   * @param {Collection~deleteWriteOpCallback} [callback] The command result callback
   * @return {Promise} returns Promise if no callback passed
   */
  Collection.prototype.deleteOne = function(filter, options, callback) {
    if (typeof options === 'function') (callback = options), (options = {});
    options = Object.assign({}, options);
  
    // Add ignoreUndefined
    if (this.s.options.ignoreUndefined) {
      options = Object.assign({}, options);
      options.ignoreUndefined = this.s.options.ignoreUndefined;
    }
  
    return executeOperation(this.s.topology, deleteOne, [this, filter, options, callback]);
  };
  
  Collection.prototype.removeOne = Collection.prototype.deleteOne;
  
  /**
   * Delete multiple documents from a collection
   * @method
   * @param {object} filter The Filter used to select the documents to remove
   * @param {object} [options] Optional settings.
   * @param {(number|string)} [options.w] The write concern.
   * @param {number} [options.wtimeout] The write concern timeout.
   * @param {boolean} [options.j=false] Specify a journal write concern.
   * @param {ClientSession} [options.session] optional session to use for this operation
   * @param {Collection~deleteWriteOpCallback} [callback] The command result callback
   * @return {Promise} returns Promise if no callback passed
   */
  Collection.prototype.deleteMany = function(filter, options, callback) {
    if (typeof options === 'function') (callback = options), (options = {});
    options = Object.assign({}, options);
  
    // Add ignoreUndefined
    if (this.s.options.ignoreUndefined) {
      options = Object.assign({}, options);
      options.ignoreUndefined = this.s.options.ignoreUndefined;
    }
  
    return executeOperation(this.s.topology, deleteMany, [this, filter, options, callback]);
  };
  
  Collection.prototype.removeMany = Collection.prototype.deleteMany;
  
  /**
   * Remove documents.
   * @method
   * @param {object} selector The selector for the update operation.
   * @param {object} [options] Optional settings.
   * @param {(number|string)} [options.w] The write concern.
   * @param {number} [options.wtimeout] The write concern timeout.
   * @param {boolean} [options.j=false] Specify a journal write concern.
   * @param {boolean} [options.single=false] Removes the first document found.
   * @param {ClientSession} [options.session] optional session to use for this operation
   * @param {Collection~writeOpCallback} [callback] The command result callback
   * @return {Promise} returns Promise if no callback passed
   * @deprecated use deleteOne, deleteMany or bulkWrite
   */
  Collection.prototype.remove = deprecate(function(selector, options, callback) {
    if (typeof options === 'function') (callback = options), (options = {});
    options = options || {};
  
    // Add ignoreUndefined
    if (this.s.options.ignoreUndefined) {
      options = Object.assign({}, options);
      options.ignoreUndefined = this.s.options.ignoreUndefined;
    }
  
    return executeOperation(this.s.topology, removeDocuments, [this, selector, options, callback]);
  }, 'collection.remove is deprecated. Use deleteOne, deleteMany, or bulkWrite instead.');
  
  /**
   * Save a document. Simple full document replacement function. Not recommended for efficiency, use atomic
   * operators and update instead for more efficient operations.
   * @method
   * @param {object} doc Document to save
   * @param {object} [options] Optional settings.
   * @param {(number|string)} [options.w] The write concern.
   * @param {number} [options.wtimeout] The write concern timeout.
   * @param {boolean} [options.j=false] Specify a journal write concern.
   * @param {ClientSession} [options.session] optional session to use for this operation
   * @param {Collection~writeOpCallback} [callback] The command result callback
   * @return {Promise} returns Promise if no callback passed
   * @deprecated use insertOne, insertMany, updateOne or updateMany
   */
  Collection.prototype.save = deprecate(function(doc, options, callback) {
    if (typeof options === 'function') (callback = options), (options = {});
    options = options || {};
  
    // Add ignoreUndefined
    if (this.s.options.ignoreUndefined) {
      options = Object.assign({}, options);
      options.ignoreUndefined = this.s.options.ignoreUndefined;
    }
  
    return executeOperation(this.s.topology, save, [this, doc, options, callback]);
  }, 'collection.save is deprecated. Use insertOne, insertMany, updateOne, or updateMany instead.');
  
  /**
   * The callback format for results
   * @callback Collection~resultCallback
   * @param {MongoError} error An error instance representing the error during the execution.
   * @param {object} result The result object if the command was executed successfully.
   */
  
  /**
   * The callback format for an aggregation call
   * @callback Collection~aggregationCallback
   * @param {MongoError} error An error instance representing the error during the execution.
   * @param {AggregationCursor} cursor The cursor if the aggregation command was executed successfully.
   */
  
  /**
   * Fetches the first document that matches the query
   * @method
   * @param {object} query Query for find Operation
   * @param {object} [options] Optional settings.
   * @param {number} [options.limit=0] Sets the limit of documents returned in the query.
   * @param {(array|object)} [options.sort] Set to sort the documents coming back from the query. Array of indexes, [['a', 1]] etc.
   * @param {object} [options.projection] The fields to return in the query. Object of fields to include or exclude (not both), {'a':1}
   * @param {object} [options.fields] **Deprecated** Use `options.projection` instead
   * @param {number} [options.skip=0] Set to skip N documents ahead in your query (useful for pagination).
   * @param {Object} [options.hint] Tell the query to use specific indexes in the query. Object of indexes to use, {'_id':1}
   * @param {boolean} [options.explain=false] Explain the query instead of returning the data.
   * @param {boolean} [options.snapshot=false] DEPRECATED: Snapshot query.
   * @param {boolean} [options.timeout=false] Specify if the cursor can timeout.
   * @param {boolean} [options.tailable=false] Specify if the cursor is tailable.
   * @param {number} [options.batchSize=0] Set the batchSize for the getMoreCommand when iterating over the query results.
   * @param {boolean} [options.returnKey=false] Only return the index key.
   * @param {number} [options.maxScan] DEPRECATED: Limit the number of items to scan.
   * @param {number} [options.min] Set index bounds.
   * @param {number} [options.max] Set index bounds.
   * @param {boolean} [options.showDiskLoc=false] Show disk location of results.
   * @param {string} [options.comment] You can put a $comment field on a query to make looking in the profiler logs simpler.
   * @param {boolean} [options.raw=false] Return document results as raw BSON buffers.
   * @param {boolean} [options.promoteLongs=true] Promotes Long values to number if they fit inside the 53 bits resolution.
   * @param {boolean} [options.promoteValues=true] Promotes BSON values to native types where possible, set to false to only receive wrapper types.
   * @param {boolean} [options.promoteBuffers=false] Promotes Binary BSON values to native Node Buffers.
   * @param {(ReadPreference|string)} [options.readPreference] The preferred read preference (ReadPreference.PRIMARY, ReadPreference.PRIMARY_PREFERRED, ReadPreference.SECONDARY, ReadPreference.SECONDARY_PREFERRED, ReadPreference.NEAREST).
   * @param {boolean} [options.partial=false] Specify if the cursor should return partial results when querying against a sharded system
   * @param {number} [options.maxTimeMS] Number of milliseconds to wait before aborting the query.
   * @param {object} [options.collation] Specify collation (MongoDB 3.4 or higher) settings for update operation (see 3.4 documentation for available fields).
   * @param {ClientSession} [options.session] optional session to use for this operation
   * @param {Collection~resultCallback} [callback] The command result callback
   * @return {Promise} returns Promise if no callback passed
   */
  Collection.prototype.findOne = deprecateOptions(
    {
      name: 'collection.find',
      deprecatedOptions: DEPRECATED_FIND_OPTIONS,
      optionsIndex: 1
    },
    function(query, options, callback) {
      if (typeof callback === 'object') {
        // TODO(MAJOR): throw in the future
        console.warn('Third parameter to `findOne()` must be a callback or undefined');
      }
  
      if (typeof query === 'function') (callback = query), (query = {}), (options = {});
      if (typeof options === 'function') (callback = options), (options = {});
      query = query || {};
      options = options || {};
  
      return executeOperation(this.s.topology, findOne, [this, query, options, callback]);
    }
  );
  
  /**
   * The callback format for the collection method, must be used if strict is specified
   * @callback Collection~collectionResultCallback
   * @param {MongoError} error An error instance representing the error during the execution.
   * @param {Collection} collection The collection instance.
   */
  
  /**
   * Rename the collection.
   *
   * @method
   * @param {string} newName New name of of the collection.
   * @param {object} [options] Optional settings.
   * @param {boolean} [options.dropTarget=false] Drop the target name collection if it previously exists.
   * @param {ClientSession} [options.session] optional session to use for this operation
   * @param {Collection~collectionResultCallback} [callback] The results callback
   * @return {Promise} returns Promise if no callback passed
   */
  Collection.prototype.rename = function(newName, options, callback) {
    if (typeof options === 'function') (callback = options), (options = {});
    options = Object.assign({}, options, { readPreference: ReadPreference.PRIMARY });
  
    return executeOperation(this.s.topology, rename, [this, newName, options, callback]);
  };
  
  /**
   * Drop the collection from the database, removing it permanently. New accesses will create a new collection.
   *
   * @method
   * @param {object} [options] Optional settings.
   * @param {ClientSession} [options.session] optional session to use for this operation
   * @param {Collection~resultCallback} [callback] The results callback
   * @return {Promise} returns Promise if no callback passed
   */
  Collection.prototype.drop = function(options, callback) {
    if (typeof options === 'function') (callback = options), (options = {});
    options = options || {};
  
    return executeOperation(this.s.topology, this.s.db.dropCollection.bind(this.s.db), [
      this.s.name,
      options,
      callback
    ]);
  };
  
  /**
   * Returns the options of the collection.
   *
   * @method
   * @param {Object} [options] Optional settings
   * @param {ClientSession} [options.session] optional session to use for this operation
   * @param {Collection~resultCallback} [callback] The results callback
   * @return {Promise} returns Promise if no callback passed
   */
  Collection.prototype.options = function(opts, callback) {
    if (typeof opts === 'function') (callback = opts), (opts = {});
    opts = opts || {};
  
    return executeOperation(this.s.topology, optionsOp, [this, opts, callback]);
  };
  
  /**
   * Returns if the collection is a capped collection
   *
   * @method
   * @param {Object} [options] Optional settings
   * @param {ClientSession} [options.session] optional session to use for this operation
   * @param {Collection~resultCallback} [callback] The results callback
   * @return {Promise} returns Promise if no callback passed
   */
  Collection.prototype.isCapped = function(options, callback) {
    if (typeof options === 'function') (callback = options), (options = {});
    options = options || {};
  
    return executeOperation(this.s.topology, isCapped, [this, options, callback]);
  };
  
  /**
   * Creates an index on the db and collection collection.
   * @method
   * @param {(string|object)} fieldOrSpec Defines the index.
   * @param {object} [options] Optional settings.
   * @param {(number|string)} [options.w] The write concern.
   * @param {number} [options.wtimeout] The write concern timeout.
   * @param {boolean} [options.j=false] Specify a journal write concern.
   * @param {boolean} [options.unique=false] Creates an unique index.
   * @param {boolean} [options.sparse=false] Creates a sparse index.
   * @param {boolean} [options.background=false] Creates the index in the background, yielding whenever possible.
   * @param {boolean} [options.dropDups=false] A unique index cannot be created on a key that has pre-existing duplicate values. If you would like to create the index anyway, keeping the first document the database indexes and deleting all subsequent documents that have duplicate value
   * @param {number} [options.min] For geospatial indexes set the lower bound for the co-ordinates.
   * @param {number} [options.max] For geospatial indexes set the high bound for the co-ordinates.
   * @param {number} [options.v] Specify the format version of the indexes.
   * @param {number} [options.expireAfterSeconds] Allows you to expire data on indexes applied to a data (MongoDB 2.2 or higher)
   * @param {string} [options.name] Override the autogenerated index name (useful if the resulting name is larger than 128 bytes)
   * @param {object} [options.partialFilterExpression] Creates a partial index based on the given filter object (MongoDB 3.2 or higher)
   * @param {object} [options.collation] Specify collation (MongoDB 3.4 or higher) settings for update operation (see 3.4 documentation for available fields).
   * @param {ClientSession} [options.session] optional session to use for this operation
   * @param {Collection~resultCallback} [callback] The command result callback
   * @return {Promise} returns Promise if no callback passed
   */
  Collection.prototype.createIndex = function(fieldOrSpec, options, callback) {
    if (typeof options === 'function') (callback = options), (options = {});
    options = options || {};
  
    return executeOperation(this.s.topology, createIndex, [this, fieldOrSpec, options, callback]);
  };
  
  /**
   * Creates multiple indexes in the collection, this method is only supported for
   * MongoDB 2.6 or higher. Earlier version of MongoDB will throw a command not supported
   * error. Index specifications are defined at http://docs.mongodb.org/manual/reference/command/createIndexes/.
   * @method
   * @param {array} indexSpecs An array of index specifications to be created
   * @param {Object} [options] Optional settings
   * @param {ClientSession} [options.session] optional session to use for this operation
   * @param {Collection~resultCallback} [callback] The command result callback
   * @return {Promise} returns Promise if no callback passed
   */
  Collection.prototype.createIndexes = function(indexSpecs, options, callback) {
    if (typeof options === 'function') (callback = options), (options = {});
  
    options = options ? Object.assign({}, options) : {};
    if (typeof options.maxTimeMS !== 'number') delete options.maxTimeMS;
  
    return executeOperation(this.s.topology, createIndexes, [this, indexSpecs, options, callback]);
  };
  
  /**
   * Drops an index from this collection.
   * @method
   * @param {string} indexName Name of the index to drop.
   * @param {object} [options] Optional settings.
   * @param {(number|string)} [options.w] The write concern.
   * @param {number} [options.wtimeout] The write concern timeout.
   * @param {boolean} [options.j=false] Specify a journal write concern.
   * @param {ClientSession} [options.session] optional session to use for this operation
   * @param {number} [options.maxTimeMS] Number of milliseconds to wait before aborting the query.
   * @param {Collection~resultCallback} [callback] The command result callback
   * @return {Promise} returns Promise if no callback passed
   */
  Collection.prototype.dropIndex = function(indexName, options, callback) {
    const args = Array.prototype.slice.call(arguments, 1);
    callback = typeof args[args.length - 1] === 'function' ? args.pop() : undefined;
  
    options = args.length ? args.shift() || {} : {};
    // Run only against primary
    options.readPreference = ReadPreference.PRIMARY;
  
    return executeOperation(this.s.topology, dropIndex, [this, indexName, options, callback]);
  };
  
  /**
   * Drops all indexes from this collection.
   * @method
   * @param {Object} [options] Optional settings
   * @param {ClientSession} [options.session] optional session to use for this operation
   * @param {number} [options.maxTimeMS] Number of milliseconds to wait before aborting the query.
   * @param {Collection~resultCallback} [callback] The command result callback
   * @return {Promise} returns Promise if no callback passed
   */
  Collection.prototype.dropIndexes = function(options, callback) {
    if (typeof options === 'function') (callback = options), (options = {});
    options = options ? Object.assign({}, options) : {};
  
    if (typeof options.maxTimeMS !== 'number') delete options.maxTimeMS;
  
    return executeOperation(this.s.topology, dropIndexes, [this, options, callback]);
  };
  
  /**
   * Drops all indexes from this collection.
   * @method
   * @deprecated use dropIndexes
   * @param {Collection~resultCallback} callback The command result callback
   * @return {Promise} returns Promise if no [callback] passed
   */
  Collection.prototype.dropAllIndexes = deprecate(
    Collection.prototype.dropIndexes,
    'collection.dropAllIndexes is deprecated. Use dropIndexes instead.'
  );
  
  /**
   * Reindex all indexes on the collection
   * Warning: reIndex is a blocking operation (indexes are rebuilt in the foreground) and will be slow for large collections.
   * @method
   * @param {Object} [options] Optional settings
   * @param {ClientSession} [options.session] optional session to use for this operation
   * @param {Collection~resultCallback} [callback] The command result callback
   * @return {Promise} returns Promise if no callback passed
   */
  Collection.prototype.reIndex = function(options, callback) {
    if (typeof options === 'function') (callback = options), (options = {});
    options = options || {};
  
    return executeOperation(this.s.topology, reIndex, [this, options, callback]);
  };
  
  /**
   * Get the list of all indexes information for the collection.
   *
   * @method
   * @param {object} [options] Optional settings.
   * @param {number} [options.batchSize] The batchSize for the returned command cursor or if pre 2.8 the systems batch collection
   * @param {(ReadPreference|string)} [options.readPreference] The preferred read preference (ReadPreference.PRIMARY, ReadPreference.PRIMARY_PREFERRED, ReadPreference.SECONDARY, ReadPreference.SECONDARY_PREFERRED, ReadPreference.NEAREST).
   * @param {ClientSession} [options.session] optional session to use for this operation
   * @return {CommandCursor}
   */
  Collection.prototype.listIndexes = function(options) {
    options = options || {};
    // Clone the options
    options = Object.assign({}, options);
    // Determine the read preference in the options.
    options.readPreference = resolveReadPreference(options, { db: this.s.db, collection: this });
    // Set the CommandCursor constructor
    options.cursorFactory = CommandCursor;
    // Set the promiseLibrary
    options.promiseLibrary = this.s.promiseLibrary;
  
    if (!this.s.topology.capabilities()) {
      throw new MongoError('cannot connect to server');
    }
  
    // Cursor options
    let cursor = options.batchSize ? { batchSize: options.batchSize } : {};
  
    // We have a list collections command
    if (this.s.topology.capabilities().hasListIndexesCommand) {
      // Build the command
      const command = { listIndexes: this.s.name, cursor: cursor };
      // Execute the cursor
      cursor = this.s.topology.cursor(`${this.s.dbName}.$cmd`, command, options);
      // Do we have a readPreference, apply it
      if (options.readPreference) cursor.setReadPreference(options.readPreference);
      // Return the cursor
      return cursor;
    }
  
    // Get the namespace
    const ns = `${this.s.dbName}.system.indexes`;
    // Get the query
    cursor = this.s.topology.cursor(ns, { find: ns, query: { ns: this.s.namespace } }, options);
    // Do we have a readPreference, apply it
    if (options.readPreference) cursor.setReadPreference(options.readPreference);
    // Set the passed in batch size if one was provided
    if (options.batchSize) cursor = cursor.batchSize(options.batchSize);
    // Return the cursor
    return cursor;
  };
  
  /**
   * Ensures that an index exists, if it does not it creates it
   * @method
   * @deprecated use createIndexes instead
   * @param {(string|object)} fieldOrSpec Defines the index.
   * @param {object} [options] Optional settings.
   * @param {(number|string)} [options.w] The write concern.
   * @param {number} [options.wtimeout] The write concern timeout.
   * @param {boolean} [options.j=false] Specify a journal write concern.
   * @param {boolean} [options.unique=false] Creates an unique index.
   * @param {boolean} [options.sparse=false] Creates a sparse index.
   * @param {boolean} [options.background=false] Creates the index in the background, yielding whenever possible.
   * @param {boolean} [options.dropDups=false] A unique index cannot be created on a key that has pre-existing duplicate values. If you would like to create the index anyway, keeping the first document the database indexes and deleting all subsequent documents that have duplicate value
   * @param {number} [options.min] For geospatial indexes set the lower bound for the co-ordinates.
   * @param {number} [options.max] For geospatial indexes set the high bound for the co-ordinates.
   * @param {number} [options.v] Specify the format version of the indexes.
   * @param {number} [options.expireAfterSeconds] Allows you to expire data on indexes applied to a data (MongoDB 2.2 or higher)
   * @param {number} [options.name] Override the autogenerated index name (useful if the resulting name is larger than 128 bytes)
   * @param {object} [options.collation] Specify collation (MongoDB 3.4 or higher) settings for update operation (see 3.4 documentation for available fields).
   * @param {ClientSession} [options.session] optional session to use for this operation
   * @param {Collection~resultCallback} [callback] The command result callback
   * @return {Promise} returns Promise if no callback passed
   */
  Collection.prototype.ensureIndex = deprecate(function(fieldOrSpec, options, callback) {
    if (typeof options === 'function') (callback = options), (options = {});
    options = options || {};
  
    return executeOperation(this.s.topology, ensureIndex, [this, fieldOrSpec, options, callback]);
  }, 'collection.ensureIndex is deprecated. Use createIndexes instead.');
  
  /**
   * Checks if one or more indexes exist on the collection, fails on first non-existing index
   * @method
   * @param {(string|array)} indexes One or more index names to check.
   * @param {Object} [options] Optional settings
   * @param {ClientSession} [options.session] optional session to use for this operation
   * @param {Collection~resultCallback} [callback] The command result callback
   * @return {Promise} returns Promise if no callback passed
   */
  Collection.prototype.indexExists = function(indexes, options, callback) {
    if (typeof options === 'function') (callback = options), (options = {});
    options = options || {};
  
    return executeOperation(this.s.topology, indexExists, [this, indexes, options, callback]);
  };
  
  /**
   * Retrieves this collections index info.
   * @method
   * @param {object} [options] Optional settings.
   * @param {boolean} [options.full=false] Returns the full raw index information.
   * @param {ClientSession} [options.session] optional session to use for this operation
   * @param {Collection~resultCallback} [callback] The command result callback
   * @return {Promise} returns Promise if no callback passed
   */
  Collection.prototype.indexInformation = function(options, callback) {
    const args = Array.prototype.slice.call(arguments, 0);
    callback = typeof args[args.length - 1] === 'function' ? args.pop() : undefined;
    options = args.length ? args.shift() || {} : {};
  
    return executeOperation(this.s.topology, indexInformation, [this, options, callback]);
  };
  
  /**
   * The callback format for results
   * @callback Collection~countCallback
   * @param {MongoError} error An error instance representing the error during the execution.
   * @param {number} result The count of documents that matched the query.
   */
  
  /**
   * Count number of matching documents in the db to a query.
   * @method
   * @param {object} [query={}] The query for the count.
   * @param {object} [options] Optional settings.
   * @param {boolean} [options.limit] The limit of documents to count.
   * @param {boolean} [options.skip] The number of documents to skip for the count.
   * @param {string} [options.hint] An index name hint for the query.
   * @param {(ReadPreference|string)} [options.readPreference] The preferred read preference (ReadPreference.PRIMARY, ReadPreference.PRIMARY_PREFERRED, ReadPreference.SECONDARY, ReadPreference.SECONDARY_PREFERRED, ReadPreference.NEAREST).
   * @param {number} [options.maxTimeMS] Number of milliseconds to wait before aborting the query.
   * @param {ClientSession} [options.session] optional session to use for this operation
   * @param {Collection~countCallback} [callback] The command result callback
   * @return {Promise} returns Promise if no callback passed
   * @deprecated use {@link Collection#countDocuments countDocuments} or {@link Collection#estimatedDocumentCount estimatedDocumentCount} instead
   */
  Collection.prototype.count = deprecate(function(query, options, callback) {
    const args = Array.prototype.slice.call(arguments, 0);
    callback = typeof args[args.length - 1] === 'function' ? args.pop() : undefined;
    query = args.length ? args.shift() || {} : {};
    options = args.length ? args.shift() || {} : {};
  
    return executeOperation(this.s.topology, count, [this, query, options, callback]);
  }, 'collection.count is deprecated, and will be removed in a future version.' +
    ' Use collection.countDocuments or collection.estimatedDocumentCount instead');
  
  /**
   * Gets an estimate of the count of documents in a collection using collection metadata.
   *
   * @method
   * @param {object} [options] Optional settings.
   * @param {number} [options.maxTimeMS] The maximum amount of time to allow the operation to run.
   * @param {Collection~countCallback} [callback] The command result callback.
   * @return {Promise} returns Promise if no callback passed.
   */
  Collection.prototype.estimatedDocumentCount = function(options, callback) {
    if (typeof options === 'function') (callback = options), (options = {});
    options = options || {};
  
    return executeOperation(this.s.topology, count, [this, null, options, callback]);
  };
  
  /**
   * Gets the number of documents matching the filter.
   *
   * **Note**: When migrating from {@link Collection#count count} to {@link Collection#countDocuments countDocuments}
   * the following query operators must be replaced:
   *
   * | Operator | Replacement |
   * | -------- | ----------- |
   * | `$where`   | [`$expr`][1] |
   * | `$near`    | [`$geoWithin`][2] with [`$center`][3] |
   * | `$nearSphere` | [`$geoWithin`][2] with [`$centerSphere`][4] |
   *
   * [1]: https://docs.mongodb.com/manual/reference/operator/query/expr/
   * [2]: https://docs.mongodb.com/manual/reference/operator/query/geoWithin/
   * [3]: https://docs.mongodb.com/manual/reference/operator/query/center/#op._S_center
   * [4]: https://docs.mongodb.com/manual/reference/operator/query/centerSphere/#op._S_centerSphere
   *
   * @param {object} [query] the query for the count
   * @param {object} [options] Optional settings.
   * @param {object} [options.collation] Specifies a collation.
   * @param {string|object} [options.hint] The index to use.
   * @param {number} [options.limit] The maximum number of document to count.
   * @param {number} [options.maxTimeMS] The maximum amount of time to allow the operation to run.
   * @param {number} [options.skip] The number of documents to skip before counting.
   * @param {Collection~countCallback} [callback] The command result callback.
   * @return {Promise} returns Promise if no callback passed.
   * @see https://docs.mongodb.com/manual/reference/operator/query/expr/
   * @see https://docs.mongodb.com/manual/reference/operator/query/geoWithin/
   * @see https://docs.mongodb.com/manual/reference/operator/query/center/#op._S_center
   * @see https://docs.mongodb.com/manual/reference/operator/query/centerSphere/#op._S_centerSphere
   */
  
  Collection.prototype.countDocuments = function(query, options, callback) {
    const args = Array.prototype.slice.call(arguments, 0);
    callback = typeof args[args.length - 1] === 'function' ? args.pop() : undefined;
    query = args.length ? args.shift() || {} : {};
    options = args.length ? args.shift() || {} : {};
  
    return executeOperation(this.s.topology, countDocuments, [this, query, options, callback]);
  };
  
  /**
   * The distinct command returns a list of distinct values for the given key across a collection.
   * @method
   * @param {string} key Field of the document to find distinct values for.
   * @param {object} query The query for filtering the set of documents to which we apply the distinct filter.
   * @param {object} [options] Optional settings.
   * @param {(ReadPreference|string)} [options.readPreference] The preferred read preference (ReadPreference.PRIMARY, ReadPreference.PRIMARY_PREFERRED, ReadPreference.SECONDARY, ReadPreference.SECONDARY_PREFERRED, ReadPreference.NEAREST).
   * @param {number} [options.maxTimeMS] Number of milliseconds to wait before aborting the query.
   * @param {ClientSession} [options.session] optional session to use for this operation
   * @param {Collection~resultCallback} [callback] The command result callback
   * @return {Promise} returns Promise if no callback passed
   */
  Collection.prototype.distinct = function(key, query, options, callback) {
    const args = Array.prototype.slice.call(arguments, 1);
    callback = typeof args[args.length - 1] === 'function' ? args.pop() : undefined;
    const queryOption = args.length ? args.shift() || {} : {};
    const optionsOption = args.length ? args.shift() || {} : {};
  
    return executeOperation(this.s.topology, distinct, [
      this,
      key,
      queryOption,
      optionsOption,
      callback
    ]);
  };
  
  /**
   * Retrieve all the indexes on the collection.
   * @method
   * @param {Object} [options] Optional settings
   * @param {ClientSession} [options.session] optional session to use for this operation
   * @param {Collection~resultCallback} [callback] The command result callback
   * @return {Promise} returns Promise if no callback passed
   */
  Collection.prototype.indexes = function(options, callback) {
    if (typeof options === 'function') (callback = options), (options = {});
    options = options || {};
  
    return executeOperation(this.s.topology, indexes, [this, options, callback]);
  };
  
  /**
   * Get all the collection statistics.
   *
   * @method
   * @param {object} [options] Optional settings.
   * @param {number} [options.scale] Divide the returned sizes by scale value.
   * @param {ClientSession} [options.session] optional session to use for this operation
   * @param {Collection~resultCallback} [callback] The collection result callback
   * @return {Promise} returns Promise if no callback passed
   */
  Collection.prototype.stats = function(options, callback) {
    const args = Array.prototype.slice.call(arguments, 0);
    callback = typeof args[args.length - 1] === 'function' ? args.pop() : undefined;
    options = args.length ? args.shift() || {} : {};
  
    return executeOperation(this.s.topology, stats, [this, options, callback]);
  };
  
  /**
   * @typedef {Object} Collection~findAndModifyWriteOpResult
   * @property {object} value Document returned from findAndModify command.
   * @property {object} lastErrorObject The raw lastErrorObject returned from the command.
   * @property {Number} ok Is 1 if the command executed correctly.
   */
  
  /**
   * The callback format for inserts
   * @callback Collection~findAndModifyCallback
   * @param {MongoError} error An error instance representing the error during the execution.
   * @param {Collection~findAndModifyWriteOpResult} result The result object if the command was executed successfully.
   */
  
  /**
   * Find a document and delete it in one atomic operation. Requires a write lock for the duration of the operation.
   *
   * @method
   * @param {object} filter The Filter used to select the document to remove
   * @param {object} [options] Optional settings.
   * @param {object} [options.projection] Limits the fields to return for all matching documents.
   * @param {object} [options.sort] Determines which document the operation modifies if the query selects multiple documents.
   * @param {number} [options.maxTimeMS] The maximum amount of time to allow the query to run.
   * @param {ClientSession} [options.session] optional session to use for this operation
   * @param {Collection~findAndModifyCallback} [callback] The collection result callback
   * @return {Promise<Collection~findAndModifyWriteOpResultObject>} returns Promise if no callback passed
   */
  Collection.prototype.findOneAndDelete = function(filter, options, callback) {
    if (typeof options === 'function') (callback = options), (options = {});
    options = options || {};
  
    // Basic validation
    if (filter == null || typeof filter !== 'object')
      throw toError('filter parameter must be an object');
  
    return executeOperation(this.s.topology, findOneAndDelete, [this, filter, options, callback]);
  };
  
  /**
   * Find a document and replace it in one atomic operation. Requires a write lock for the duration of the operation.
   *
   * @method
   * @param {object} filter The Filter used to select the document to replace
   * @param {object} replacement The Document that replaces the matching document
   * @param {object} [options] Optional settings.
   * @param {object} [options.projection] Limits the fields to return for all matching documents.
   * @param {object} [options.sort] Determines which document the operation modifies if the query selects multiple documents.
   * @param {number} [options.maxTimeMS] The maximum amount of time to allow the query to run.
   * @param {boolean} [options.upsert=false] Upsert the document if it does not exist.
   * @param {boolean} [options.returnOriginal=true] When false, returns the updated document rather than the original. The default is true.
   * @param {ClientSession} [options.session] optional session to use for this operation
   * @param {Collection~findAndModifyCallback} [callback] The collection result callback
   * @return {Promise<Collection~findAndModifyWriteOpResultObject>} returns Promise if no callback passed
   */
  Collection.prototype.findOneAndReplace = function(filter, replacement, options, callback) {
    if (typeof options === 'function') (callback = options), (options = {});
    options = options || {};
  
    // Basic validation
    if (filter == null || typeof filter !== 'object')
      throw toError('filter parameter must be an object');
    if (replacement == null || typeof replacement !== 'object')
      throw toError('replacement parameter must be an object');
  
    return executeOperation(this.s.topology, findOneAndReplace, [
      this,
      filter,
      replacement,
      options,
      callback
    ]);
  };
  
  /**
   * Find a document and update it in one atomic operation. Requires a write lock for the duration of the operation.
   *
   * @method
   * @param {object} filter The Filter used to select the document to update
   * @param {object} update Update operations to be performed on the document
   * @param {object} [options] Optional settings.
   * @param {object} [options.projection] Limits the fields to return for all matching documents.
   * @param {object} [options.sort] Determines which document the operation modifies if the query selects multiple documents.
   * @param {number} [options.maxTimeMS] The maximum amount of time to allow the query to run.
   * @param {boolean} [options.upsert=false] Upsert the document if it does not exist.
   * @param {boolean} [options.returnOriginal=true] When false, returns the updated document rather than the original. The default is true.
   * @param {ClientSession} [options.session] optional session to use for this operation
   * @param {Array} [options.arrayFilters] optional list of array filters referenced in filtered positional operators
   * @param {Collection~findAndModifyCallback} [callback] The collection result callback
   * @return {Promise<Collection~findAndModifyWriteOpResultObject>} returns Promise if no callback passed
   */
  Collection.prototype.findOneAndUpdate = function(filter, update, options, callback) {
    if (typeof options === 'function') (callback = options), (options = {});
    options = options || {};
  
    // Basic validation
    if (filter == null || typeof filter !== 'object')
      throw toError('filter parameter must be an object');
    if (update == null || typeof update !== 'object')
      throw toError('update parameter must be an object');
  
    const err = checkForAtomicOperators(update);
    if (err) {
      if (typeof callback === 'function') return callback(err);
      return this.s.promiseLibrary.reject(err);
    }
  
    return executeOperation(this.s.topology, findOneAndUpdate, [
      this,
      filter,
      update,
      options,
      callback
    ]);
  };
  
  /**
   * Find and update a document.
   * @method
   * @param {object} query Query object to locate the object to modify.
   * @param {array} sort If multiple docs match, choose the first one in the specified sort order as the object to manipulate.
   * @param {object} doc The fields/vals to be updated.
   * @param {object} [options] Optional settings.
   * @param {(number|string)} [options.w] The write concern.
   * @param {number} [options.wtimeout] The write concern timeout.
   * @param {boolean} [options.j=false] Specify a journal write concern.
   * @param {boolean} [options.remove=false] Set to true to remove the object before returning.
   * @param {boolean} [options.upsert=false] Perform an upsert operation.
   * @param {boolean} [options.new=false] Set to true if you want to return the modified object rather than the original. Ignored for remove.
   * @param {object} [options.projection] Object containing the field projection for the result returned from the operation.
   * @param {object} [options.fields] **Deprecated** Use `options.projection` instead
   * @param {ClientSession} [options.session] optional session to use for this operation
   * @param {Array} [options.arrayFilters] optional list of array filters referenced in filtered positional operators
   * @param {Collection~findAndModifyCallback} [callback] The command result callback
   * @return {Promise} returns Promise if no callback passed
   * @deprecated use findOneAndUpdate, findOneAndReplace or findOneAndDelete instead
   */
  Collection.prototype.findAndModify = deprecate(
    _findAndModify,
    'collection.findAndModify is deprecated. Use findOneAndUpdate, findOneAndReplace or findOneAndDelete instead.'
  );
  
  /**
   * @ignore
   */
  
  Collection.prototype._findAndModify = _findAndModify;
  
  function _findAndModify(query, sort, doc, options, callback) {
    const args = Array.prototype.slice.call(arguments, 1);
    callback = typeof args[args.length - 1] === 'function' ? args.pop() : undefined;
    sort = args.length ? args.shift() || [] : [];
    doc = args.length ? args.shift() : null;
    options = args.length ? args.shift() || {} : {};
  
    // Clone options
    options = Object.assign({}, options);
    // Force read preference primary
    options.readPreference = ReadPreference.PRIMARY;
  
    return executeOperation(this.s.topology, findAndModify, [
      this,
      query,
      sort,
      doc,
      options,
      callback
    ]);
  }
  
  /**
   * Find and remove a document.
   * @method
   * @param {object} query Query object to locate the object to modify.
   * @param {array} sort If multiple docs match, choose the first one in the specified sort order as the object to manipulate.
   * @param {object} [options] Optional settings.
   * @param {(number|string)} [options.w] The write concern.
   * @param {number} [options.wtimeout] The write concern timeout.
   * @param {boolean} [options.j=false] Specify a journal write concern.
   * @param {ClientSession} [options.session] optional session to use for this operation
   * @param {Collection~resultCallback} [callback] The command result callback
   * @return {Promise} returns Promise if no callback passed
   * @deprecated use findOneAndDelete instead
   */
  Collection.prototype.findAndRemove = deprecate(function(query, sort, options, callback) {
    const args = Array.prototype.slice.call(arguments, 1);
    callback = typeof args[args.length - 1] === 'function' ? args.pop() : undefined;
    sort = args.length ? args.shift() || [] : [];
    options = args.length ? args.shift() || {} : {};
  
    return executeOperation(this.s.topology, findAndRemove, [this, query, sort, options, callback]);
  }, 'collection.findAndRemove is deprecated. Use findOneAndDelete instead.');
  
  /**
   * Execute an aggregation framework pipeline against the collection, needs MongoDB >= 2.2
   * @method
   * @param {object} [pipeline=[]] Array containing all the aggregation framework commands for the execution.
   * @param {object} [options] Optional settings.
   * @param {(ReadPreference|string)} [options.readPreference] The preferred read preference (ReadPreference.PRIMARY, ReadPreference.PRIMARY_PREFERRED, ReadPreference.SECONDARY, ReadPreference.SECONDARY_PREFERRED, ReadPreference.NEAREST).
   * @param {object} [options.cursor] Return the query as cursor, on 2.6 > it returns as a real cursor on pre 2.6 it returns as an emulated cursor.
   * @param {number} [options.cursor.batchSize] The batchSize for the cursor
   * @param {boolean} [options.explain=false] Explain returns the aggregation execution plan (requires mongodb 2.6 >).
   * @param {boolean} [options.allowDiskUse=false] allowDiskUse lets the server know if it can use disk to store temporary results for the aggregation (requires mongodb 2.6 >).
   * @param {number} [options.maxTimeMS] maxTimeMS specifies a cumulative time limit in milliseconds for processing operations on the cursor. MongoDB interrupts the operation at the earliest following interrupt point.
   * @param {boolean} [options.bypassDocumentValidation=false] Allow driver to bypass schema validation in MongoDB 3.2 or higher.
   * @param {boolean} [options.raw=false] Return document results as raw BSON buffers.
   * @param {boolean} [options.promoteLongs=true] Promotes Long values to number if they fit inside the 53 bits resolution.
   * @param {boolean} [options.promoteValues=true] Promotes BSON values to native types where possible, set to false to only receive wrapper types.
   * @param {boolean} [options.promoteBuffers=false] Promotes Binary BSON values to native Node Buffers.
   * @param {object} [options.collation] Specify collation (MongoDB 3.4 or higher) settings for update operation (see 3.4 documentation for available fields).
   * @param {string} [options.comment] Add a comment to an aggregation command
   * @param {string|object} [options.hint] Add an index selection hint to an aggregation command
   * @param {ClientSession} [options.session] optional session to use for this operation
   * @param {Collection~aggregationCallback} callback The command result callback
   * @return {(null|AggregationCursor)}
   */
  Collection.prototype.aggregate = function(pipeline, options, callback) {
    if (Array.isArray(pipeline)) {
      // Set up callback if one is provided
      if (typeof options === 'function') {
        callback = options;
        options = {};
      }
  
      // If we have no options or callback we are doing
      // a cursor based aggregation
      if (options == null && callback == null) {
        options = {};
      }
    } else {
      // Aggregation pipeline passed as arguments on the method
      const args = Array.prototype.slice.call(arguments, 0);
      // Get the callback
      callback = args.pop();
      // Get the possible options object
      const opts = args[args.length - 1];
      // If it contains any of the admissible options pop it of the args
      options =
        opts &&
        (opts.readPreference ||
          opts.explain ||
          opts.cursor ||
          opts.out ||
          opts.maxTimeMS ||
          opts.hint ||
          opts.allowDiskUse)
          ? args.pop()
          : {};
      // Left over arguments is the pipeline
      pipeline = args;
    }
  
    return aggregate(this.s.db, this, pipeline, options, callback);
  };
  
  /**
   * Create a new Change Stream, watching for new changes (insertions, updates, replacements, deletions, and invalidations) in this collection.
   * @method
   * @since 3.0.0
   * @param {Array} [pipeline] An array of {@link https://docs.mongodb.com/manual/reference/operator/aggregation-pipeline/|aggregation pipeline stages} through which to pass change stream documents. This allows for filtering (using $match) and manipulating the change stream documents.
   * @param {object} [options] Optional settings
   * @param {string} [options.fullDocument='default'] Allowed values: ‘default’, ‘updateLookup’. When set to ‘updateLookup’, the change stream will include both a delta describing the changes to the document, as well as a copy of the entire document that was changed from some time after the change occurred.
   * @param {object} [options.resumeAfter] Specifies the logical starting point for the new change stream. This should be the _id field from a previously returned change stream document.
   * @param {number} [options.maxAwaitTimeMS] The maximum amount of time for the server to wait on new documents to satisfy a change stream query
   * @param {number} [options.batchSize] The number of documents to return per batch. See {@link https://docs.mongodb.com/manual/reference/command/aggregate|aggregation documentation}.
   * @param {object} [options.collation] Specify collation settings for operation. See {@link https://docs.mongodb.com/manual/reference/command/aggregate|aggregation documentation}.
   * @param {ReadPreference} [options.readPreference] The read preference. Defaults to the read preference of the database or collection. See {@link https://docs.mongodb.com/manual/reference/read-preference|read preference documentation}.
   * @param {Timestamp} [options.startAtClusterTime] receive change events that occur after the specified timestamp
   * @param {ClientSession} [options.session] optional session to use for this operation
   * @return {ChangeStream} a ChangeStream instance.
   */
  Collection.prototype.watch = function(pipeline, options) {
    pipeline = pipeline || [];
    options = options || {};
  
    // Allow optionally not specifying a pipeline
    if (!Array.isArray(pipeline)) {
      options = pipeline;
      pipeline = [];
    }
  
    return new ChangeStream(this, pipeline, options);
  };
  
  /**
   * The callback format for results
   * @callback Collection~parallelCollectionScanCallback
   * @param {MongoError} error An error instance representing the error during the execution.
   * @param {Cursor[]} cursors A list of cursors returned allowing for parallel reading of collection.
   */
  
  /**
   * Return N number of parallel cursors for a collection allowing parallel reading of entire collection. There are
   * no ordering guarantees for returned results.
   * @method
   * @param {object} [options] Optional settings.
   * @param {(ReadPreference|string)} [options.readPreference] The preferred read preference (ReadPreference.PRIMARY, ReadPreference.PRIMARY_PREFERRED, ReadPreference.SECONDARY, ReadPreference.SECONDARY_PREFERRED, ReadPreference.NEAREST).
   * @param {number} [options.batchSize] Set the batchSize for the getMoreCommand when iterating over the query results.
   * @param {number} [options.numCursors=1] The maximum number of parallel command cursors to return (the number of returned cursors will be in the range 1:numCursors)
   * @param {boolean} [options.raw=false] Return all BSON documents as Raw Buffer documents.
   * @param {Collection~parallelCollectionScanCallback} [callback] The command result callback
   * @return {Promise} returns Promise if no callback passed
   */
  Collection.prototype.parallelCollectionScan = deprecate(function(options, callback) {
    if (typeof options === 'function') (callback = options), (options = { numCursors: 1 });
    // Set number of cursors to 1
    options.numCursors = options.numCursors || 1;
    options.batchSize = options.batchSize || 1000;
  
    options = Object.assign({}, options);
    // Ensure we have the right read preference inheritance
    options.readPreference = resolveReadPreference(options, { db: this.s.db, collection: this });
  
    // Add a promiseLibrary
    options.promiseLibrary = this.s.promiseLibrary;
  
    if (options.session) {
      options.session = undefined;
    }
  
    return executeOperation(this.s.topology, parallelCollectionScan, [this, options, callback], {
      skipSessions: true
    });
  }, 'parallelCollectionScan is deprecated in MongoDB v4.1');
  
  /**
   * Execute a geo search using a geo haystack index on a collection.
   *
   * @method
   * @param {number} x Point to search on the x axis, ensure the indexes are ordered in the same order.
   * @param {number} y Point to search on the y axis, ensure the indexes are ordered in the same order.
   * @param {object} [options] Optional settings.
   * @param {(ReadPreference|string)} [options.readPreference] The preferred read preference (ReadPreference.PRIMARY, ReadPreference.PRIMARY_PREFERRED, ReadPreference.SECONDARY, ReadPreference.SECONDARY_PREFERRED, ReadPreference.NEAREST).
   * @param {number} [options.maxDistance] Include results up to maxDistance from the point.
   * @param {object} [options.search] Filter the results by a query.
   * @param {number} [options.limit=false] Max number of results to return.
   * @param {ClientSession} [options.session] optional session to use for this operation
   * @param {Collection~resultCallback} [callback] The command result callback
   * @return {Promise} returns Promise if no callback passed
   */
  Collection.prototype.geoHaystackSearch = function(x, y, options, callback) {
    const args = Array.prototype.slice.call(arguments, 2);
    callback = typeof args[args.length - 1] === 'function' ? args.pop() : undefined;
    options = args.length ? args.shift() || {} : {};
  
    return executeOperation(this.s.topology, geoHaystackSearch, [this, x, y, options, callback]);
  };
  
  /**
   * Run a group command across a collection
   *
   * @method
   * @param {(object|array|function|code)} keys An object, array or function expressing the keys to group by.
   * @param {object} condition An optional condition that must be true for a row to be considered.
   * @param {object} initial Initial value of the aggregation counter object.
   * @param {(function|Code)} reduce The reduce function aggregates (reduces) the objects iterated
   * @param {(function|Code)} finalize An optional function to be run on each item in the result set just before the item is returned.
   * @param {boolean} command Specify if you wish to run using the internal group command or using eval, default is true.
   * @param {object} [options] Optional settings.
   * @param {(ReadPreference|string)} [options.readPreference] The preferred read preference (ReadPreference.PRIMARY, ReadPreference.PRIMARY_PREFERRED, ReadPreference.SECONDARY, ReadPreference.SECONDARY_PREFERRED, ReadPreference.NEAREST).
   * @param {ClientSession} [options.session] optional session to use for this operation
   * @param {Collection~resultCallback} [callback] The command result callback
   * @return {Promise} returns Promise if no callback passed
   * @deprecated MongoDB 3.6 or higher no longer supports the group command. We recommend rewriting using the aggregation framework.
   */
  Collection.prototype.group = deprecate(function(
    keys,
    condition,
    initial,
    reduce,
    finalize,
    command,
    options,
    callback
  ) {
    const args = Array.prototype.slice.call(arguments, 3);
    callback = typeof args[args.length - 1] === 'function' ? args.pop() : undefined;
    reduce = args.length ? args.shift() : null;
    finalize = args.length ? args.shift() : null;
    command = args.length ? args.shift() : null;
    options = args.length ? args.shift() || {} : {};
  
    // Make sure we are backward compatible
    if (!(typeof finalize === 'function')) {
      command = finalize;
      finalize = null;
    }
  
    if (
      !Array.isArray(keys) &&
      keys instanceof Object &&
      typeof keys !== 'function' &&
      !(keys._bsontype === 'Code')
    ) {
      keys = Object.keys(keys);
    }
  
    if (typeof reduce === 'function') {
      reduce = reduce.toString();
    }
  
    if (typeof finalize === 'function') {
      finalize = finalize.toString();
    }
  
    // Set up the command as default
    command = command == null ? true : command;
  
    return executeOperation(this.s.topology, group, [
      this,
      keys,
      condition,
      initial,
      reduce,
      finalize,
      command,
      options,
      callback
    ]);
  },
  'MongoDB 3.6 or higher no longer supports the group command. We recommend rewriting using the aggregation framework.');
  
  /**
   * Run Map Reduce across a collection. Be aware that the inline option for out will return an array of results not a collection.
   *
   * @method
   * @param {(function|string)} map The mapping function.
   * @param {(function|string)} reduce The reduce function.
   * @param {object} [options] Optional settings.
   * @param {(ReadPreference|string)} [options.readPreference] The preferred read preference (ReadPreference.PRIMARY, ReadPreference.PRIMARY_PREFERRED, ReadPreference.SECONDARY, ReadPreference.SECONDARY_PREFERRED, ReadPreference.NEAREST).
   * @param {object} [options.out] Sets the output target for the map reduce job. *{inline:1} | {replace:'collectionName'} | {merge:'collectionName'} | {reduce:'collectionName'}*
   * @param {object} [options.query] Query filter object.
   * @param {object} [options.sort] Sorts the input objects using this key. Useful for optimization, like sorting by the emit key for fewer reduces.
   * @param {number} [options.limit] Number of objects to return from collection.
   * @param {boolean} [options.keeptemp=false] Keep temporary data.
   * @param {(function|string)} [options.finalize] Finalize function.
   * @param {object} [options.scope] Can pass in variables that can be access from map/reduce/finalize.
   * @param {boolean} [options.jsMode=false] It is possible to make the execution stay in JS. Provided in MongoDB > 2.0.X.
   * @param {boolean} [options.verbose=false] Provide statistics on job execution time.
   * @param {boolean} [options.bypassDocumentValidation=false] Allow driver to bypass schema validation in MongoDB 3.2 or higher.
   * @param {ClientSession} [options.session] optional session to use for this operation
   * @param {Collection~resultCallback} [callback] The command result callback
   * @throws {MongoError}
   * @return {Promise} returns Promise if no callback passed
   */
  Collection.prototype.mapReduce = function(map, reduce, options, callback) {
    if ('function' === typeof options) (callback = options), (options = {});
    // Out must allways be defined (make sure we don't break weirdly on pre 1.8+ servers)
    if (null == options.out) {
      throw new Error(
        'the out option parameter must be defined, see mongodb docs for possible values'
      );
    }
  
    if ('function' === typeof map) {
      map = map.toString();
    }
  
    if ('function' === typeof reduce) {
      reduce = reduce.toString();
    }
  
    if ('function' === typeof options.finalize) {
      options.finalize = options.finalize.toString();
    }
  
    return executeOperation(this.s.topology, mapReduce, [this, map, reduce, options, callback]);
  };
  
  /**
   * Initiate an Out of order batch write operation. All operations will be buffered into insert/update/remove commands executed out of order.
   *
   * @method
   * @param {object} [options] Optional settings.
   * @param {(number|string)} [options.w] The write concern.
   * @param {number} [options.wtimeout] The write concern timeout.
   * @param {boolean} [options.j=false] Specify a journal write concern.
   * @param {boolean} [options.ignoreUndefined=false] Specify if the BSON serializer should ignore undefined fields.
   * @param {ClientSession} [options.session] optional session to use for this operation
   * @return {UnorderedBulkOperation}
   */
  Collection.prototype.initializeUnorderedBulkOp = function(options) {
    options = options || {};
    // Give function's options precedence over session options.
    if (options.ignoreUndefined == null) {
      options.ignoreUndefined = this.s.options.ignoreUndefined;
    }
  
    options.promiseLibrary = this.s.promiseLibrary;
    return unordered(this.s.topology, this, options);
  };
  
  /**
   * Initiate an In order bulk write operation. Operations will be serially executed in the order they are added, creating a new operation for each switch in types.
   *
   * @method
   * @param {object} [options] Optional settings.
   * @param {(number|string)} [options.w] The write concern.
   * @param {number} [options.wtimeout] The write concern timeout.
   * @param {boolean} [options.j=false] Specify a journal write concern.
   * @param {ClientSession} [options.session] optional session to use for this operation
   * @param {boolean} [options.ignoreUndefined=false] Specify if the BSON serializer should ignore undefined fields.
   * @param {OrderedBulkOperation} callback The command result callback
   * @return {null}
   */
  Collection.prototype.initializeOrderedBulkOp = function(options) {
    options = options || {};
    // Give function's options precedence over session's options.
    if (options.ignoreUndefined == null) {
      options.ignoreUndefined = this.s.options.ignoreUndefined;
    }
    options.promiseLibrary = this.s.promiseLibrary;
    return ordered(this.s.topology, this, options);
  };
  
  /**
   * Return the db logger
   * @method
   * @return {Logger} return the db logger
   * @ignore
   */
  Collection.prototype.getLogger = function() {
    return this.s.db.s.logger;
  };
  
  module.exports = Collection;
  