'use strict';
const EventEmitter = require('events');
const ServerDescription = require('./server_description').ServerDescription;
const TopologyDescription = require('./topology_description').TopologyDescription;
const TopologyType = require('./topology_description').TopologyType;
const monitoring = require('./monitoring');
const calculateDurationInMs = require('../utils').calculateDurationInMs;
const MongoTimeoutError = require('../error').MongoTimeoutError;
const MongoNetworkError = require('../error').MongoNetworkError;
const Server = require('./server');
const relayEvents = require('../utils').relayEvents;
const ReadPreference = require('../topologies/read_preference');
const readPreferenceServerSelector = require('./server_selectors').readPreferenceServerSelector;
const writableServerSelector = require('./server_selectors').writableServerSelector;
const isRetryableWritesSupported = require('../topologies/shared').isRetryableWritesSupported;
const Cursor = require('./cursor');
const deprecate = require('util').deprecate;
const BSON = require('../connection/utils').retrieveBSON();
const createCompressionInfo = require('../topologies/shared').createCompressionInfo;

// Global state
let globalTopologyCounter = 0;

// Constants
const TOPOLOGY_DEFAULTS = {
  localThresholdMS: 15,
  serverSelectionTimeoutMS: 10000,
  heartbeatFrequencyMS: 30000,
  minHeartbeatIntervalMS: 500
};

/**
 * A container of server instances representing a connection to a MongoDB topology.
 *
 * @fires Topology#serverOpening
 * @fires Topology#serverClosed
 * @fires Topology#serverDescriptionChanged
 * @fires Topology#topologyOpening
 * @fires Topology#topologyClosed
 * @fires Topology#topologyDescriptionChanged
 * @fires Topology#serverHeartbeatStarted
 * @fires Topology#serverHeartbeatSucceeded
 * @fires Topology#serverHeartbeatFailed
 */
class Topology extends EventEmitter {
  /**
   * Create a topology
   *
   * @param {Array|String} [seedlist] a string list, or array of Server instances to connect to
   * @param {Object} [options] Optional settings
   * @param {Number} [options.localThresholdMS=15] The size of the latency window for selecting among multiple suitable servers
   * @param {Number} [options.serverSelectionTimeoutMS=30000] How long to block for server selection before throwing an error
   * @param {Number} [options.heartbeatFrequencyMS=10000] The frequency with which topology updates are scheduled
   */
  constructor(seedlist, options) {
    super();
    if (typeof options === 'undefined') {
      options = seedlist;
      seedlist = [];

      // this is for legacy single server constructor support
      if (options.host) {
        seedlist.push({ host: options.host, port: options.port });
      }
    }

    seedlist = seedlist || [];
    options = Object.assign({}, TOPOLOGY_DEFAULTS, options);

    const topologyType = topologyTypeFromSeedlist(seedlist, options);
    const topologyId = globalTopologyCounter++;
    const serverDescriptions = seedlist.reduce((result, seed) => {
      const address = seed.port ? `${seed.host}:${seed.port}` : `${seed.host}:27017`;
      result.set(address, new ServerDescription(address));
      return result;
    }, new Map());

    this.s = {
      // the id of this topology
      id: topologyId,
      // passed in options
      options: Object.assign({}, options),
      // initial seedlist of servers to connect to
      seedlist: seedlist,
      // the topology description
      description: new TopologyDescription(
        topologyType,
        serverDescriptions,
        options.replicaSet,
        null,
        null,
        options
      ),
      serverSelectionTimeoutMS: options.serverSelectionTimeoutMS,
      heartbeatFrequencyMS: options.heartbeatFrequencyMS,
      minHeartbeatIntervalMS: options.minHeartbeatIntervalMS,
      // allow users to override the cursor factory
      Cursor: options.cursorFactory || Cursor,
      // the bson parser
      bson:
        options.bson ||
        new BSON([
          BSON.Binary,
          BSON.Code,
          BSON.DBRef,
          BSON.Decimal128,
          BSON.Double,
          BSON.Int32,
          BSON.Long,
          BSON.Map,
          BSON.MaxKey,
          BSON.MinKey,
          BSON.ObjectId,
          BSON.BSONRegExp,
          BSON.Symbol,
          BSON.Timestamp
        ])
    };

    // amend options for server instance creation
    this.s.options.compression = { compressors: createCompressionInfo(options) };
  }

  /**
   * @return A `TopologyDescription` for this topology
   */
  get description() {
    return this.s.description;
  }

  /**
   * All raw connections
   * @method
   * @return {Connection[]}
   */
  connections() {
    return Array.from(this.s.servers.values()).reduce((result, server) => {
      return result.concat(server.s.pool.allConnections());
    }, []);
  }

  /**
   * Initiate server connect
   *
   * @param {Object} [options] Optional settings
   * @param {Array} [options.auth=null] Array of auth options to apply on connect
   */
  connect(/* options */) {
    // emit SDAM monitoring events
    this.emit('topologyOpening', new monitoring.TopologyOpeningEvent(this.s.id));

    // emit an event for the topology change
    this.emit(
      'topologyDescriptionChanged',
      new monitoring.TopologyDescriptionChangedEvent(
        this.s.id,
        new TopologyDescription(TopologyType.Unknown), // initial is always Unknown
        this.s.description
      )
    );

    connectServers(this, Array.from(this.s.description.servers.values()));
    this.s.connected = true;
  }

  /**
   * Close this topology
   */
  close(callback) {
    // destroy all child servers
    this.s.servers.forEach(server => server.destroy());

    // emit an event for close
    this.emit('topologyClosed', new monitoring.TopologyClosedEvent(this.s.id));

    this.s.connected = false;

    if (typeof callback === 'function') {
      callback(null, null);
    }
  }

  /**
   * Selects a server according to the selection predicate provided
   *
   * @param {function} [selector] An optional selector to select servers by, defaults to a random selection within a latency window
   * @return {Server} An instance of a `Server` meeting the criteria of the predicate provided
   */
  selectServer(selector, options, callback) {
    if (typeof options === 'function') (callback = options), (options = {});
    options = Object.assign(
      {},
      { serverSelectionTimeoutMS: this.s.serverSelectionTimeoutMS },
      options
    );

    selectServers(
      this,
      selector,
      options.serverSelectionTimeoutMS,
      process.hrtime(),
      (err, servers) => {
        if (err) return callback(err, null);
        callback(null, randomSelection(servers));
      }
    );
  }

  /**
   * Update the internal TopologyDescription with a ServerDescription
   *
   * @param {object} serverDescription The server to update in the internal list of server descriptions
   */
  serverUpdateHandler(serverDescription) {
    if (!this.s.description.hasServer(serverDescription.address)) {
      return;
    }

    // these will be used for monitoring events later
    const previousTopologyDescription = this.s.description;
    const previousServerDescription = this.s.description.servers.get(serverDescription.address);

    // first update the TopologyDescription
    this.s.description = this.s.description.update(serverDescription);

    // emit monitoring events for this change
    this.emit(
      'serverDescriptionChanged',
      new monitoring.ServerDescriptionChangedEvent(
        this.s.id,
        serverDescription.address,
        previousServerDescription,
        this.s.description.servers.get(serverDescription.address)
      )
    );

    // update server list from updated descriptions
    updateServers(this, serverDescription);

    this.emit(
      'topologyDescriptionChanged',
      new monitoring.TopologyDescriptionChangedEvent(
        this.s.id,
        previousTopologyDescription,
        this.s.description
      )
    );
  }

  /**
   * Authenticate using a specified mechanism
   *
   * @param {String} mechanism The auth mechanism used for authentication
   * @param {String} db The db we are authenticating against
   * @param {Object} options Optional settings for the authenticating mechanism
   * @param {authResultCallback} callback A callback function
   */
  auth(mechanism, db, options, callback) {
    callback(null, null);
  }

  /**
   * Logout from a database
   *
   * @param {String} db The db we are logging out from
   * @param {authResultCallback} callback A callback function
   */
  logout(db, callback) {
    callback(null, null);
  }

  // Basic operation support. Eventually this should be moved into command construction
  // during the command refactor.

  /**
   * Insert one or more documents
   *
   * @param {String} ns The full qualified namespace for this operation
   * @param {Array} ops An array of documents to insert
   * @param {Boolean} [options.ordered=true] Execute in order or out of order
   * @param {Object} [options.writeConcern] Write concern for the operation
   * @param {Boolean} [options.serializeFunctions=false] Specify if functions on an object should be serialized
   * @param {Boolean} [options.ignoreUndefined=false] Specify if the BSON serializer should ignore undefined fields
   * @param {ClientSession} [options.session] Session to use for the operation
   * @param {boolean} [options.retryWrites] Enable retryable writes for this operation
   * @param {opResultCallback} callback A callback function
   */
  insert(ns, ops, options, callback) {
    executeWriteOperation({ topology: this, op: 'insert', ns, ops }, options, callback);
  }

  /**
   * Perform one or more update operations
   *
   * @param {string} ns The fully qualified namespace for this operation
   * @param {array} ops An array of updates
   * @param {boolean} [options.ordered=true] Execute in order or out of order
   * @param {object} [options.writeConcern] Write concern for the operation
   * @param {Boolean} [options.serializeFunctions=false] Specify if functions on an object should be serialized
   * @param {Boolean} [options.ignoreUndefined=false] Specify if the BSON serializer should ignore undefined fields
   * @param {ClientSession} [options.session] Session to use for the operation
   * @param {boolean} [options.retryWrites] Enable retryable writes for this operation
   * @param {opResultCallback} callback A callback function
   */
  update(ns, ops, options, callback) {
    executeWriteOperation({ topology: this, op: 'update', ns, ops }, options, callback);
  }

  /**
   * Perform one or more remove operations
   *
   * @param {string} ns The MongoDB fully qualified namespace (ex: db1.collection1)
   * @param {array} ops An array of removes
   * @param {boolean} [options.ordered=true] Execute in order or out of order
   * @param {object} [options.writeConcern={}] Write concern for the operation
   * @param {Boolean} [options.serializeFunctions=false] Specify if functions on an object should be serialized.
   * @param {Boolean} [options.ignoreUndefined=false] Specify if the BSON serializer should ignore undefined fields.
   * @param {ClientSession} [options.session=null] Session to use for the operation
   * @param {boolean} [options.retryWrites] Enable retryable writes for this operation
   * @param {opResultCallback} callback A callback function
   */
  remove(ns, ops, options, callback) {
    executeWriteOperation({ topology: this, op: 'remove', ns, ops }, options, callback);
  }

  /**
   * Execute a command
   *
   * @method
   * @param {string} ns The MongoDB fully qualified namespace (ex: db1.collection1)
   * @param {object} cmd The command hash
   * @param {ReadPreference} [options.readPreference] Specify read preference if command supports it
   * @param {Connection} [options.connection] Specify connection object to execute command against
   * @param {Boolean} [options.serializeFunctions=false] Specify if functions on an object should be serialized.
   * @param {Boolean} [options.ignoreUndefined=false] Specify if the BSON serializer should ignore undefined fields.
   * @param {ClientSession} [options.session=null] Session to use for the operation
   * @param {opResultCallback} callback A callback function
   */
  command(ns, cmd, options, callback) {
    if (typeof options === 'function') {
      (callback = options), (options = {}), (options = options || {});
    }

    const readPreference = options.readPreference ? options.readPreference : ReadPreference.primary;
    this.selectServer(readPreferenceServerSelector(readPreference), (err, server) => {
      if (err) {
        callback(err, null);
        return;
      }

      server.command(ns, cmd, options, callback);
    });
  }

  /**
   * Create a new cursor
   *
   * @method
   * @param {string} ns The MongoDB fully qualified namespace (ex: db1.collection1)
   * @param {object|Long} cmd Can be either a command returning a cursor or a cursorId
   * @param {object} [options] Options for the cursor
   * @param {object} [options.batchSize=0] Batchsize for the operation
   * @param {array} [options.documents=[]] Initial documents list for cursor
   * @param {ReadPreference} [options.readPreference] Specify read preference if command supports it
   * @param {Boolean} [options.serializeFunctions=false] Specify if functions on an object should be serialized.
   * @param {Boolean} [options.ignoreUndefined=false] Specify if the BSON serializer should ignore undefined fields.
   * @param {ClientSession} [options.session=null] Session to use for the operation
   * @param {object} [options.topology] The internal topology of the created cursor
   * @returns {Cursor}
   */
  cursor(ns, cmd, options) {
    options = options || {};
    const topology = options.topology || this;
    const CursorClass = options.cursorFactory || this.s.Cursor;

    return new CursorClass(this.s.bson, ns, cmd, options, topology, this.s.options);
  }
}

// legacy aliases
Topology.prototype.destroy = deprecate(
  Topology.prototype.close,
  'destroy() is deprecated, please use close() instead'
);

function topologyTypeFromSeedlist(seedlist, options) {
  if (seedlist.length === 1 && !options.replicaSet) return TopologyType.Single;
  if (options.replicaSet) return TopologyType.ReplicaSetNoPrimary;
  return TopologyType.Unknown;
}

function randomSelection(array) {
  return array[Math.floor(Math.random() * array.length)];
}

/**
 * Selects servers using the provided selector
 *
 * @private
 * @param {Topology} topology The topology to select servers from
 * @param {function} selector The actual predicate used for selecting servers
 * @param {Number} timeout The max time we are willing wait for selection
 * @param {Number} start A high precision timestamp for the start of the selection process
 * @param {function} callback The callback used to convey errors or the resultant servers
 */
function selectServers(topology, selector, timeout, start, callback) {
  const serverDescriptions = Array.from(topology.description.servers.values());
  let descriptions;

  try {
    descriptions = selector
      ? selector(topology.description, serverDescriptions)
      : serverDescriptions;
  } catch (e) {
    return callback(e, null);
  }

  if (descriptions.length) {
    const servers = descriptions.map(description => topology.s.servers.get(description.address));
    return callback(null, servers);
  }

  const duration = calculateDurationInMs(start);
  if (duration >= timeout) {
    return callback(new MongoTimeoutError(`Server selection timed out after ${timeout} ms`));
  }

  const retrySelection = () => {
    // ensure all server monitors attempt monitoring immediately
    topology.s.servers.forEach(server => server.monitor());

    const iterationTimer = setTimeout(() => {
      callback(new MongoTimeoutError('Server selection timed out due to monitoring'));
    }, topology.s.minHeartbeatIntervalMS);

    topology.once('topologyDescriptionChanged', () => {
      // successful iteration, clear the check timer
      clearTimeout(iterationTimer);

      // topology description has changed due to monitoring, reattempt server selection
      selectServers(topology, selector, timeout, start, callback);
    });
  };

  // ensure we are connected
  if (!topology.s.connected) {
    topology.connect();

    // we want to make sure we're still within the requested timeout window
    const failToConnectTimer = setTimeout(() => {
      callback(new MongoTimeoutError('Server selection timed out waiting to connect'));
    }, timeout - duration);

    topology.once('connect', () => {
      clearTimeout(failToConnectTimer);
      retrySelection();
    });

    return;
  }

  retrySelection();
}

/**
 * Create `Server` instances for all initially known servers, connect them, and assign
 * them to the passed in `Topology`.
 *
 * @param {Topology} topology The topology responsible for the servers
 * @param {ServerDescription[]} serverDescriptions A list of server descriptions to connect
 */
function connectServers(topology, serverDescriptions) {
  topology.s.servers = serverDescriptions.reduce((servers, serverDescription) => {
    // publish an open event for each ServerDescription created
    topology.emit(
      'serverOpening',
      new monitoring.ServerOpeningEvent(topology.s.id, serverDescription.address)
    );

    const server = new Server(serverDescription, topology.s.options);
    relayEvents(server, topology, [
      'serverHeartbeatStarted',
      'serverHeartbeatSucceeded',
      'serverHeartbeatFailed'
    ]);

    server.on('descriptionReceived', topology.serverUpdateHandler.bind(topology));
    server.on('connect', serverConnectEventHandler(server, topology));
    servers.set(serverDescription.address, server);
    server.connect();
    return servers;
  }, new Map());
}

function updateServers(topology, currentServerDescription) {
  // update the internal server's description
  if (topology.s.servers.has(currentServerDescription.address)) {
    const server = topology.s.servers.get(currentServerDescription.address);
    server.s.description = currentServerDescription;
  }

  // add new servers for all descriptions we currently don't know about locally
  for (const serverDescription of topology.description.servers.values()) {
    if (!topology.s.servers.has(serverDescription.address)) {
      topology.emit(
        'serverOpening',
        new monitoring.ServerOpeningEvent(topology.s.id, serverDescription.address)
      );

      const server = new Server(serverDescription, topology.s.options);
      relayEvents(server, topology, [
        'serverHeartbeatStarted',
        'serverHeartbeatSucceeded',
        'serverHeartbeatFailed'
      ]);

      server.on('descriptionReceived', topology.serverUpdateHandler.bind(topology));
      server.on('connect', serverConnectEventHandler(server, topology));
      topology.s.servers.set(serverDescription.address, server);
      server.connect();
    }
  }

  // for all servers no longer known, remove their descriptions and destroy their instances
  for (const entry of topology.s.servers) {
    const serverAddress = entry[0];
    if (topology.description.hasServer(serverAddress)) {
      continue;
    }

    const server = topology.s.servers.get(serverAddress);
    topology.s.servers.delete(serverAddress);

    server.destroy(() =>
      topology.emit('serverClosed', new monitoring.ServerClosedEvent(topology.s.id, serverAddress))
    );
  }
}

function serverConnectEventHandler(server, topology) {
  return function(/* ismaster */) {
    topology.emit('connect', topology);
  };
}

function executeWriteOperation(args, options, callback) {
  if (typeof options === 'function') (callback = options), (options = {});
  options = options || {};

  // TODO: once we drop Node 4, use destructuring either here or in arguments.
  const topology = args.topology;
  const op = args.op;
  const ns = args.ns;
  const ops = args.ops;

  const willRetryWrite =
    !args.retrying &&
    options.retryWrites &&
    options.session &&
    isRetryableWritesSupported(topology) &&
    !options.session.inTransaction();

  topology.selectServer(writableServerSelector(), (err, server) => {
    if (err) {
      callback(err, null);
      return;
    }

    const handler = (err, result) => {
      if (!err) return callback(null, result);
      if (!(err instanceof MongoNetworkError) && !err.message.match(/not master/)) {
        return callback(err);
      }

      if (willRetryWrite) {
        const newArgs = Object.assign({}, args, { retrying: true });
        return executeWriteOperation(newArgs, options, callback);
      }

      return callback(err);
    };

    if (callback.operationId) {
      handler.operationId = callback.operationId;
    }

    // increment and assign txnNumber
    if (willRetryWrite) {
      options.session.incrementTransactionNumber();
      options.willRetryWrite = willRetryWrite;
    }

    // execute the write operation
    server[op](ns, ops, options, handler);

    // we need to increment the statement id if we're in a transaction
    if (options.session && options.session.inTransaction()) {
      options.session.incrementStatementId(ops.length);
    }
  });
}

/**
 * A server opening SDAM monitoring event
 *
 * @event Topology#serverOpening
 * @type {ServerOpeningEvent}
 */

/**
 * A server closed SDAM monitoring event
 *
 * @event Topology#serverClosed
 * @type {ServerClosedEvent}
 */

/**
 * A server description SDAM change monitoring event
 *
 * @event Topology#serverDescriptionChanged
 * @type {ServerDescriptionChangedEvent}
 */

/**
 * A topology open SDAM event
 *
 * @event Topology#topologyOpening
 * @type {TopologyOpeningEvent}
 */

/**
 * A topology closed SDAM event
 *
 * @event Topology#topologyClosed
 * @type {TopologyClosedEvent}
 */

/**
 * A topology structure SDAM change event
 *
 * @event Topology#topologyDescriptionChanged
 * @type {TopologyDescriptionChangedEvent}
 */

/**
 * A topology serverHeartbeatStarted SDAM event
 *
 * @event Topology#serverHeartbeatStarted
 * @type {ServerHeartbeatStartedEvent}
 */

/**
 * A topology serverHeartbeatFailed SDAM event
 *
 * @event Topology#serverHeartbeatFailed
 * @type {ServerHearbeatFailedEvent}
 */

/**
 * A topology serverHeartbeatSucceeded SDAM change event
 *
 * @event Topology#serverHeartbeatSucceeded
 * @type {ServerHeartbeatSucceededEvent}
 */

module.exports = Topology;