text: 'use strict';
  
  const Logger = require('./connection/logger');
  const retrieveBSON = require('./connection/utils').retrieveBSON;
  const MongoError = require('./error').MongoError;
  const MongoNetworkError = require('./error').MongoNetworkError;
  const mongoErrorContextSymbol = require('./error').mongoErrorContextSymbol;
  const f = require('util').format;
  const collationNotSupported = require('./utils').collationNotSupported;
  
  const BSON = retrieveBSON();
  const Long = BSON.Long;
  
  /**
   * This is a cursor results callback
   *
   * @callback resultCallback
   * @param {error} error An error object. Set to null if no error present
   * @param {object} document
   */
  
  /**
   * @fileOverview The **Cursor** class is an internal class that embodies a cursor on MongoDB
   * allowing for iteration over the results returned from the underlying query.
   *
   * **CURSORS Cannot directly be instantiated**
   * @example
   * var Server = require('mongodb-core').Server
   *   , ReadPreference = require('mongodb-core').ReadPreference
   *   , assert = require('assert');
   *
   * var server = new Server({host: 'localhost', port: 27017});
   * // Wait for the connection event
   * server.on('connect', function(server) {
   *   assert.equal(null, err);
   *
   *   // Execute the write
   *   var cursor = _server.cursor('integration_tests.inserts_example4', {
   *       find: 'integration_tests.example4'
   *     , query: {a:1}
   *   }, {
   *     readPreference: new ReadPreference('secondary');
   *   });
   *
   *   // Get the first document
   *   cursor.next(function(err, doc) {
   *     assert.equal(null, err);
   *     server.destroy();
   *   });
   * });
   *
   * // Start connecting
   * server.connect();
   */
  
  /**
   * Creates a new Cursor, not to be used directly
   * @class
   * @param {object} bson An instance of the BSON parser
   * @param {string} ns The MongoDB fully qualified namespace (ex: db1.collection1)
   * @param {{object}|Long} cmd The selector (can be a command or a cursorId)
   * @param {object} [options=null] Optional settings.
   * @param {object} [options.batchSize=1000] Batchsize for the operation
   * @param {array} [options.documents=[]] Initial documents list for cursor
   * @param {object} [options.transforms=null] Transform methods for the cursor results
   * @param {function} [options.transforms.query] Transform the value returned from the initial query
   * @param {function} [options.transforms.doc] Transform each document returned from Cursor.prototype.next
   * @param {object} topology The server topology instance.
   * @param {object} topologyOptions The server topology options.
   * @return {Cursor} A cursor instance
   * @property {number} cursorBatchSize The current cursorBatchSize for the cursor
   * @property {number} cursorLimit The current cursorLimit for the cursor
   * @property {number} cursorSkip The current cursorSkip for the cursor
   */
  var Cursor = function(bson, ns, cmd, options, topology, topologyOptions) {
    options = options || {};
  
    // Cursor pool
    this.pool = null;
    // Cursor server
    this.server = null;
  
    // Do we have a not connected handler
    this.disconnectHandler = options.disconnectHandler;
  
    // Set local values
    this.bson = bson;
    this.ns = ns;
    this.cmd = cmd;
    this.options = options;
    this.topology = topology;
  
    // All internal state
    this.cursorState = {
      cursorId: null,
      cmd: cmd,
      documents: options.documents || [],
      cursorIndex: 0,
      dead: false,
      killed: false,
      init: false,
      notified: false,
      limit: options.limit || cmd.limit || 0,
      skip: options.skip || cmd.skip || 0,
      batchSize: options.batchSize || cmd.batchSize || 1000,
      currentLimit: 0,
      // Result field name if not a cursor (contains the array of results)
      transforms: options.transforms,
      raw: options.raw || (cmd && cmd.raw)
    };
  
    if (typeof options.session === 'object') {
      this.cursorState.session = options.session;
    }
  
    // Add promoteLong to cursor state
    if (typeof topologyOptions.promoteLongs === 'boolean') {
      this.cursorState.promoteLongs = topologyOptions.promoteLongs;
    } else if (typeof options.promoteLongs === 'boolean') {
      this.cursorState.promoteLongs = options.promoteLongs;
    }
  
    // Add promoteValues to cursor state
    if (typeof topologyOptions.promoteValues === 'boolean') {
      this.cursorState.promoteValues = topologyOptions.promoteValues;
    } else if (typeof options.promoteValues === 'boolean') {
      this.cursorState.promoteValues = options.promoteValues;
    }
  
    // Add promoteBuffers to cursor state
    if (typeof topologyOptions.promoteBuffers === 'boolean') {
      this.cursorState.promoteBuffers = topologyOptions.promoteBuffers;
    } else if (typeof options.promoteBuffers === 'boolean') {
      this.cursorState.promoteBuffers = options.promoteBuffers;
    }
  
    if (topologyOptions.reconnect) {
      this.cursorState.reconnect = topologyOptions.reconnect;
    }
  
    // Logger
    this.logger = Logger('Cursor', topologyOptions);
  
    //
    // Did we pass in a cursor id
    if (typeof cmd === 'number') {
      this.cursorState.cursorId = Long.fromNumber(cmd);
      this.cursorState.lastCursorId = this.cursorState.cursorId;
    } else if (cmd instanceof Long) {
      this.cursorState.cursorId = cmd;
      this.cursorState.lastCursorId = cmd;
    }
  };
  
  Cursor.prototype.setCursorBatchSize = function(value) {
    this.cursorState.batchSize = value;
  };
  
  Cursor.prototype.cursorBatchSize = function() {
    return this.cursorState.batchSize;
  };
  
  Cursor.prototype.setCursorLimit = function(value) {
    this.cursorState.limit = value;
  };
  
  Cursor.prototype.cursorLimit = function() {
    return this.cursorState.limit;
  };
  
  Cursor.prototype.setCursorSkip = function(value) {
    this.cursorState.skip = value;
  };
  
  Cursor.prototype.cursorSkip = function() {
    return this.cursorState.skip;
  };
  
  Cursor.prototype._endSession = function(options, callback) {
    if (typeof options === 'function') {
      callback = options;
      options = {};
    }
    options = options || {};
  
    const session = this.cursorState.session;
  
    if (session && (options.force || session.owner === this)) {
      this.cursorState.session = undefined;
      session.endSession(callback);
      return true;
    }
  
    if (callback) {
      callback();
    }
    return false;
  };
  
  //
  // Handle callback (including any exceptions thrown)
  var handleCallback = function(callback, err, result) {
    try {
      callback(err, result);
    } catch (err) {
      process.nextTick(function() {
        throw err;
      });
    }
  };
  
  // Internal methods
  Cursor.prototype._getmore = function(callback) {
    if (this.logger.isDebug())
      this.logger.debug(f('schedule getMore call for query [%s]', JSON.stringify(this.query)));
  
    // Set the current batchSize
    var batchSize = this.cursorState.batchSize;
    if (
      this.cursorState.limit > 0 &&
      this.cursorState.currentLimit + batchSize > this.cursorState.limit
    ) {
      batchSize = this.cursorState.limit - this.cursorState.currentLimit;
    }
  
    this.server.wireProtocolHandler.getMore(
      this.server,
      this.ns,
      this.cursorState,
      batchSize,
      this.options,
      callback
    );
  };
  
  /**
   * Clone the cursor
   * @method
   * @return {Cursor}
   */
  Cursor.prototype.clone = function() {
    return this.topology.cursor(this.ns, this.cmd, this.options);
  };
  
  /**
   * Checks if the cursor is dead
   * @method
   * @return {boolean} A boolean signifying if the cursor is dead or not
   */
  Cursor.prototype.isDead = function() {
    return this.cursorState.dead === true;
  };
  
  /**
   * Checks if the cursor was killed by the application
   * @method
   * @return {boolean} A boolean signifying if the cursor was killed by the application
   */
  Cursor.prototype.isKilled = function() {
    return this.cursorState.killed === true;
  };
  
  /**
   * Checks if the cursor notified it's caller about it's death
   * @method
   * @return {boolean} A boolean signifying if the cursor notified the callback
   */
  Cursor.prototype.isNotified = function() {
    return this.cursorState.notified === true;
  };
  
  /**
   * Returns current buffered documents length
   * @method
   * @return {number} The number of items in the buffered documents
   */
  Cursor.prototype.bufferedCount = function() {
    return this.cursorState.documents.length - this.cursorState.cursorIndex;
  };
  
  /**
   * Returns current buffered documents
   * @method
   * @return {Array} An array of buffered documents
   */
  Cursor.prototype.readBufferedDocuments = function(number) {
    var unreadDocumentsLength = this.cursorState.documents.length - this.cursorState.cursorIndex;
    var length = number < unreadDocumentsLength ? number : unreadDocumentsLength;
    var elements = this.cursorState.documents.slice(
      this.cursorState.cursorIndex,
      this.cursorState.cursorIndex + length
    );
  
    // Transform the doc with passed in transformation method if provided
    if (this.cursorState.transforms && typeof this.cursorState.transforms.doc === 'function') {
      // Transform all the elements
      for (var i = 0; i < elements.length; i++) {
        elements[i] = this.cursorState.transforms.doc(elements[i]);
      }
    }
  
    // Ensure we do not return any more documents than the limit imposed
    // Just return the number of elements up to the limit
    if (
      this.cursorState.limit > 0 &&
      this.cursorState.currentLimit + elements.length > this.cursorState.limit
    ) {
      elements = elements.slice(0, this.cursorState.limit - this.cursorState.currentLimit);
      this.kill();
    }
  
    // Adjust current limit
    this.cursorState.currentLimit = this.cursorState.currentLimit + elements.length;
    this.cursorState.cursorIndex = this.cursorState.cursorIndex + elements.length;
  
    // Return elements
    return elements;
  };
  
  /**
   * Kill the cursor
   * @method
   * @param {resultCallback} callback A callback function
   */
  Cursor.prototype.kill = function(callback) {
    // Set cursor to dead
    this.cursorState.dead = true;
    this.cursorState.killed = true;
    // Remove documents
    this.cursorState.documents = [];
  
    // If no cursor id just return
    if (
      this.cursorState.cursorId == null ||
      this.cursorState.cursorId.isZero() ||
      this.cursorState.init === false
    ) {
      if (callback) callback(null, null);
      return;
    }
  
    this.server.wireProtocolHandler.killCursor(this.server, this.ns, this.cursorState, callback);
  };
  
  /**
   * Resets the cursor
   * @method
   * @return {null}
   */
  Cursor.prototype.rewind = function() {
    if (this.cursorState.init) {
      if (!this.cursorState.dead) {
        this.kill();
      }
  
      this.cursorState.currentLimit = 0;
      this.cursorState.init = false;
      this.cursorState.dead = false;
      this.cursorState.killed = false;
      this.cursorState.notified = false;
      this.cursorState.documents = [];
      this.cursorState.cursorId = null;
      this.cursorState.cursorIndex = 0;
    }
  };
  
  /**
   * Validate if the pool is dead and return error
   */
  var isConnectionDead = function(self, callback) {
    if (self.pool && self.pool.isDestroyed()) {
      self.cursorState.killed = true;
      const err = new MongoNetworkError(
        f('connection to host %s:%s was destroyed', self.pool.host, self.pool.port)
      );
      _setCursorNotifiedImpl(self, () => callback(err));
      return true;
    }
  
    return false;
  };
  
  /**
   * Validate if the cursor is dead but was not explicitly killed by user
   */
  var isCursorDeadButNotkilled = function(self, callback) {
    // Cursor is dead but not marked killed, return null
    if (self.cursorState.dead && !self.cursorState.killed) {
      self.cursorState.killed = true;
      setCursorNotified(self, callback);
      return true;
    }
  
    return false;
  };
  
  /**
   * Validate if the cursor is dead and was killed by user
   */
  var isCursorDeadAndKilled = function(self, callback) {
    if (self.cursorState.dead && self.cursorState.killed) {
      handleCallback(callback, new MongoError('cursor is dead'));
      return true;
    }
  
    return false;
  };
  
  /**
   * Validate if the cursor was killed by the user
   */
  var isCursorKilled = function(self, callback) {
    if (self.cursorState.killed) {
      setCursorNotified(self, callback);
      return true;
    }
  
    return false;
  };
  
  /**
   * Mark cursor as being dead and notified
   */
  var setCursorDeadAndNotified = function(self, callback) {
    self.cursorState.dead = true;
    setCursorNotified(self, callback);
  };
  
  /**
   * Mark cursor as being notified
   */
  var setCursorNotified = function(self, callback) {
    _setCursorNotifiedImpl(self, () => handleCallback(callback, null, null));
  };
  
  var _setCursorNotifiedImpl = function(self, callback) {
    self.cursorState.notified = true;
    self.cursorState.documents = [];
    self.cursorState.cursorIndex = 0;
    if (self._endSession) {
      return self._endSession(undefined, () => callback());
    }
    return callback();
  };
  
  var nextFunction = function(self, callback) {
    // We have notified about it
    if (self.cursorState.notified) {
      return callback(new Error('cursor is exhausted'));
    }
  
    // Cursor is killed return null
    if (isCursorKilled(self, callback)) return;
  
    // Cursor is dead but not marked killed, return null
    if (isCursorDeadButNotkilled(self, callback)) return;
  
    // We have a dead and killed cursor, attempting to call next should error
    if (isCursorDeadAndKilled(self, callback)) return;
  
    // We have just started the cursor
    if (!self.cursorState.init) {
      return initializeCursor(self, callback);
    }
  
    if (self.cursorState.limit > 0 && self.cursorState.currentLimit >= self.cursorState.limit) {
      // Ensure we kill the cursor on the server
      self.kill();
      // Set cursor in dead and notified state
      return setCursorDeadAndNotified(self, callback);
    } else if (
      self.cursorState.cursorIndex === self.cursorState.documents.length &&
      !Long.ZERO.equals(self.cursorState.cursorId)
    ) {
      // Ensure an empty cursor state
      self.cursorState.documents = [];
      self.cursorState.cursorIndex = 0;
  
      // Check if topology is destroyed
      if (self.topology.isDestroyed())
        return callback(
          new MongoNetworkError('connection destroyed, not possible to instantiate cursor')
        );
  
      // Check if connection is dead and return if not possible to
      // execute a getmore on this connection
      if (isConnectionDead(self, callback)) return;
  
      // Execute the next get more
      self._getmore(function(err, doc, connection) {
        if (err) {
          if (err instanceof MongoError) {
            err[mongoErrorContextSymbol].isGetMore = true;
          }
  
          return handleCallback(callback, err);
        }
  
        if (self.cursorState.cursorId && self.cursorState.cursorId.isZero() && self._endSession) {
          self._endSession();
        }
  
        // Save the returned connection to ensure all getMore's fire over the same connection
        self.connection = connection;
  
        // Tailable cursor getMore result, notify owner about it
        // No attempt is made here to retry, this is left to the user of the
        // core module to handle to keep core simple
        if (
          self.cursorState.documents.length === 0 &&
          self.cmd.tailable &&
          Long.ZERO.equals(self.cursorState.cursorId)
        ) {
          // No more documents in the tailed cursor
          return handleCallback(
            callback,
            new MongoError({
              message: 'No more documents in tailed cursor',
              tailable: self.cmd.tailable,
              awaitData: self.cmd.awaitData
            })
          );
        } else if (
          self.cursorState.documents.length === 0 &&
          self.cmd.tailable &&
          !Long.ZERO.equals(self.cursorState.cursorId)
        ) {
          return nextFunction(self, callback);
        }
  
        if (self.cursorState.limit > 0 && self.cursorState.currentLimit >= self.cursorState.limit) {
          return setCursorDeadAndNotified(self, callback);
        }
  
        nextFunction(self, callback);
      });
    } else if (
      self.cursorState.documents.length === self.cursorState.cursorIndex &&
      self.cmd.tailable &&
      Long.ZERO.equals(self.cursorState.cursorId)
    ) {
      return handleCallback(
        callback,
        new MongoError({
          message: 'No more documents in tailed cursor',
          tailable: self.cmd.tailable,
          awaitData: self.cmd.awaitData
        })
      );
    } else if (
      self.cursorState.documents.length === self.cursorState.cursorIndex &&
      Long.ZERO.equals(self.cursorState.cursorId)
    ) {
      setCursorDeadAndNotified(self, callback);
    } else {
      if (self.cursorState.limit > 0 && self.cursorState.currentLimit >= self.cursorState.limit) {
        // Ensure we kill the cursor on the server
        self.kill();
        // Set cursor in dead and notified state
        return setCursorDeadAndNotified(self, callback);
      }
  
      // Increment the current cursor limit
      self.cursorState.currentLimit += 1;
  
      // Get the document
      var doc = self.cursorState.documents[self.cursorState.cursorIndex++];
  
      // Doc overflow
      if (!doc || doc.$err) {
        // Ensure we kill the cursor on the server
        self.kill();
        // Set cursor in dead and notified state
        return setCursorDeadAndNotified(self, function() {
          handleCallback(callback, new MongoError(doc ? doc.$err : undefined));
        });
      }
  
      // Transform the doc with passed in transformation method if provided
      if (self.cursorState.transforms && typeof self.cursorState.transforms.doc === 'function') {
        doc = self.cursorState.transforms.doc(doc);
      }
  
      // Return the document
      handleCallback(callback, null, doc);
    }
  };
  
  function initializeCursor(cursor, callback) {
    // Topology is not connected, save the call in the provided store to be
    // Executed at some point when the handler deems it's reconnected
    if (!cursor.topology.isConnected(cursor.options)) {
      // Only need this for single server, because repl sets and mongos
      // will always continue trying to reconnect
      if (cursor.topology._type === 'server' && !cursor.topology.s.options.reconnect) {
        // Reconnect is disabled, so we'll never reconnect
        return callback(new MongoError('no connection available'));
      }
  
      if (cursor.disconnectHandler != null) {
        if (cursor.topology.isDestroyed()) {
          // Topology was destroyed, so don't try to wait for it to reconnect
          return callback(new MongoError('Topology was destroyed'));
        }
  
        return cursor.disconnectHandler.addObjectAndMethod(
          'cursor',
          cursor,
          'next',
          [callback],
          callback
        );
      }
    }
  
    return cursor.topology.selectServer(cursor.options, (err, server) => {
      if (err) {
        const disconnectHandler = cursor.disconnectHandler;
        if (disconnectHandler != null) {
          return disconnectHandler.addObjectAndMethod('cursor', cursor, 'next', [callback], callback);
        }
  
        return callback(err);
      }
  
      cursor.server = server;
      cursor.cursorState.init = true;
      if (collationNotSupported(cursor.server, cursor.cmd)) {
        return callback(new MongoError(`server ${cursor.server.name} does not support collation`));
      }
  
      function done() {
        if (
          cursor.cursorState.cursorId &&
          cursor.cursorState.cursorId.isZero() &&
          cursor._endSession
        ) {
          cursor._endSession();
        }
  
        if (
          cursor.cursorState.documents.length === 0 &&
          cursor.cursorState.cursorId &&
          cursor.cursorState.cursorId.isZero() &&
          !cursor.cmd.tailable &&
          !cursor.cmd.awaitData
        ) {
          return setCursorNotified(cursor, callback);
        }
  
        nextFunction(cursor, callback);
      }
  
      // NOTE: this is a special internal method for cloning a cursor, consider removing
      if (cursor.cursorState.cursorId != null) {
        return done();
      }
  
      const queryCallback = (err, r) => {
        if (err) return callback(err);
  
        const result = r.message;
        if (result.queryFailure) {
          return callback(new MongoError(result.documents[0]), null);
        }
  
        // Check if we have a command cursor
        if (
          Array.isArray(result.documents) &&
          result.documents.length === 1 &&
          (!cursor.cmd.find || (cursor.cmd.find && cursor.cmd.virtual === false)) &&
          (typeof result.documents[0].cursor !== 'string' ||
            result.documents[0]['$err'] ||
            result.documents[0]['errmsg'] ||
            Array.isArray(result.documents[0].result))
        ) {
          // We have an error document, return the error
          if (result.documents[0]['$err'] || result.documents[0]['errmsg']) {
            return callback(new MongoError(result.documents[0]), null);
          }
  
          // We have a cursor document
          if (result.documents[0].cursor != null && typeof result.documents[0].cursor !== 'string') {
            var id = result.documents[0].cursor.id;
            // If we have a namespace change set the new namespace for getmores
            if (result.documents[0].cursor.ns) {
              cursor.ns = result.documents[0].cursor.ns;
            }
            // Promote id to long if needed
            cursor.cursorState.cursorId = typeof id === 'number' ? Long.fromNumber(id) : id;
            cursor.cursorState.lastCursorId = cursor.cursorState.cursorId;
            cursor.cursorState.operationTime = result.documents[0].operationTime;
            // If we have a firstBatch set it
            if (Array.isArray(result.documents[0].cursor.firstBatch)) {
              cursor.cursorState.documents = result.documents[0].cursor.firstBatch; //.reverse();
            }
  
            // Return after processing command cursor
            return done(result);
          }
  
          if (Array.isArray(result.documents[0].result)) {
            cursor.cursorState.documents = result.documents[0].result;
            cursor.cursorState.cursorId = Long.ZERO;
            return done(result);
          }
        }
  
        // Otherwise fall back to regular find path
        cursor.cursorState.cursorId = result.cursorId;
        cursor.cursorState.documents = result.documents;
        cursor.cursorState.lastCursorId = result.cursorId;
  
        // Transform the results with passed in transformation method if provided
        if (
          cursor.cursorState.transforms &&
          typeof cursor.cursorState.transforms.query === 'function'
        ) {
          cursor.cursorState.documents = cursor.cursorState.transforms.query(result);
        }
  
        // Return callback
        done(result);
      };
  
      if (cursor.logger.isDebug()) {
        cursor.logger.debug(
          `issue initial query [${JSON.stringify(cursor.cmd)}] with flags [${JSON.stringify(
            cursor.query
          )}]`
        );
      }
  
      if (cursor.cmd.find != null) {
        cursor.server.wireProtocolHandler.query(
          cursor.server,
          cursor.ns,
          cursor.cmd,
          cursor.cursorState,
          cursor.options,
          queryCallback
        );
  
        return;
      }
  
      cursor.query = cursor.server.wireProtocolHandler.command(
        cursor.server,
        cursor.ns,
        cursor.cmd,
        cursor.options,
        queryCallback
      );
    });
  }
  
  /**
   * Retrieve the next document from the cursor
   * @method
   * @param {resultCallback} callback A callback function
   */
  Cursor.prototype.next = function(callback) {
    nextFunction(this, callback);
  };
  
  module.exports = Cursor;
  