text: var Promise = require('./Promise');
  var WorkerHandler = require('./WorkerHandler');
  var environment = require('./environment');
  var DebugPortAllocator = require('./debug-port-allocator');
  var DEBUG_PORT_ALLOCATOR = new DebugPortAllocator();
  /**
   * A pool to manage workers
   * @param {String} [script]   Optional worker script
   * @param {WorkerPoolOptions} [options]  See docs
   * @constructor
   */
  function Pool(script, options) {
    if (typeof script === 'string') {
      this.script = script || null;
    }
    else {
      this.script = null;
      options = script;
    }
  
    this.workers = [];  // queue with all workers
    this.tasks = [];    // queue with tasks awaiting execution
  
    options = options || {};
  
    this.forkArgs = options.forkArgs || [];
    this.forkOpts = options.forkOpts || {};
    this.debugPortStart = (options.debugPortStart || 43210);
    this.nodeWorker = options.nodeWorker;
    this.workerType = options.workerType || options.nodeWorker || 'auto'
    this.maxQueueSize = options.maxQueueSize || Infinity;
  
    // configuration
    if (options && 'maxWorkers' in options) {
      validateMaxWorkers(options.maxWorkers);
      this.maxWorkers = options.maxWorkers;
    }
    else {
      this.maxWorkers = Math.max((environment.cpus || 4) - 1, 1);
    }
  
    if (options && 'minWorkers' in options) {
      if(options.minWorkers === 'max') {
        this.minWorkers = this.maxWorkers;
      } else {
        validateMinWorkers(options.minWorkers);
        this.minWorkers = options.minWorkers;
        this.maxWorkers = Math.max(this.minWorkers, this.maxWorkers);     // in case minWorkers is higher than maxWorkers
      }
      this._ensureMinWorkers();
    }
  
    this._boundNext = this._next.bind(this);
  
  
    if (this.workerType === 'thread') {
      WorkerHandler.ensureWorkerThreads();
    }
  }
  
  
  /**
   * Execute a function on a worker.
   *
   * Example usage:
   *
   *   var pool = new Pool()
   *
   *   // call a function available on the worker
   *   pool.exec('fibonacci', [6])
   *
   *   // offload a function
   *   function add(a, b) {
   *     return a + b
   *   };
   *   pool.exec(add, [2, 4])
   *       .then(function (result) {
   *         console.log(result); // outputs 6
   *       })
   *       .catch(function(error) {
   *         console.log(error);
   *       });
   *
   * @param {String | Function} method  Function name or function.
   *                                    If `method` is a string, the corresponding
   *                                    method on the worker will be executed
   *                                    If `method` is a Function, the function
   *                                    will be stringified and executed via the
   *                                    workers built-in function `run(fn, args)`.
   * @param {Array} [params]  Function arguments applied when calling the function
   * @param {ExecOptions} [options]  Options object
   * @return {Promise.<*, Error>} result
   */
  Pool.prototype.exec = function (method, params, options) {
    // validate type of arguments
    if (params && !Array.isArray(params)) {
      throw new TypeError('Array expected as argument "params"');
    }
  
    if (typeof method === 'string') {
      var resolver = Promise.defer();
  
      if (this.tasks.length >= this.maxQueueSize) {
        throw new Error('Max queue size of ' + this.maxQueueSize + ' reached');
      }
  
      // add a new task to the queue
      var tasks = this.tasks;
      var task = {
        method:  method,
        params:  params,
        resolver: resolver,
        timeout: null,
        options: options
      };
      tasks.push(task);
  
      // replace the timeout method of the Promise with our own,
      // which starts the timer as soon as the task is actually started
      var originalTimeout = resolver.promise.timeout;
      resolver.promise.timeout = function timeout (delay) {
        if (tasks.indexOf(task) !== -1) {
          // task is still queued -> start the timer later on
          task.timeout = delay;
          return resolver.promise;
        }
        else {
          // task is already being executed -> start timer immediately
          return originalTimeout.call(resolver.promise, delay);
        }
      };
  
      // trigger task execution
      this._next();
  
      return resolver.promise;
    }
    else if (typeof method === 'function') {
      // send stringified function and function arguments to worker
      return this.exec('run', [String(method), params]);
    }
    else {
      throw new TypeError('Function or string expected as argument "method"');
    }
  };
  
  /**
   * Create a proxy for current worker. Returns an object containing all
   * methods available on the worker. The methods always return a promise.
   *
   * @return {Promise.<Object, Error>} proxy
   */
  Pool.prototype.proxy = function () {
    if (arguments.length > 0) {
      throw new Error('No arguments expected');
    }
  
    var pool = this;
    return this.exec('methods')
        .then(function (methods) {
          var proxy = {};
  
          methods.forEach(function (method) {
            proxy[method] = function () {
              return pool.exec(method, Array.prototype.slice.call(arguments));
            }
          });
  
          return proxy;
        });
  };
  
  /**
   * Creates new array with the results of calling a provided callback function
   * on every element in this array.
   * @param {Array} array
   * @param {function} callback  Function taking two arguments:
   *                             `callback(currentValue, index)`
   * @return {Promise.<Array>} Returns a promise which resolves  with an Array
   *                           containing the results of the callback function
   *                           executed for each of the array elements.
   */
  /* TODO: implement map
  Pool.prototype.map = function (array, callback) {
  };
  */
  
  /**
   * Grab the first task from the queue, find a free worker, and assign the
   * worker to the task.
   * @protected
   */
  Pool.prototype._next = function () {
    if (this.tasks.length > 0) {
      // there are tasks in the queue
  
      // find an available worker
      var worker = this._getWorker();
      if (worker) {
        // get the first task from the queue
        var me = this;
        var task = this.tasks.shift();
  
        // check if the task is still pending (and not cancelled -> promise rejected)
        if (task.resolver.promise.pending) {
          // send the request to the worker
          var promise = worker.exec(task.method, task.params, task.resolver, task.options)
            .then(me._boundNext)
            .catch(function () {
              // if the worker crashed and terminated, remove it from the pool
              if (worker.terminated) {
                return me._removeWorker(worker);
              }
            }).then(function() {
              me._next(); // trigger next task in the queue
            });
  
          // start queued timer now
          if (typeof task.timeout === 'number') {
            promise.timeout(task.timeout);
          }
        } else {
          // The task taken was already complete (either rejected or resolved), so just trigger next task in the queue
          me._next();
        }
      }
    }
  };
  
  /**
   * Get an available worker. If no worker is available and the maximum number
   * of workers isn't yet reached, a new worker will be created and returned.
   * If no worker is available and the maximum number of workers is reached,
   * null will be returned.
   *
   * @return {WorkerHandler | null} worker
   * @private
   */
  Pool.prototype._getWorker = function() {
    // find a non-busy worker
    var workers = this.workers;
    for (var i = 0; i < workers.length; i++) {
      var worker = workers[i];
      if (worker.busy() === false) {
        return worker;
      }
    }
  
    if (workers.length < this.maxWorkers) {
      // create a new worker
      worker = this._createWorkerHandler();
      workers.push(worker);
      return worker;
    }
  
    return null;
  };
  
  /**
   * Remove a worker from the pool.
   * Attempts to terminate worker if not already terminated, and ensures the minimum
   * pool size is met.
   * @param {WorkerHandler} worker
   * @return {Promise<WorkerHandler>}
   * @protected
   */
  Pool.prototype._removeWorker = function(worker) {
    DEBUG_PORT_ALLOCATOR.releasePort(worker.debugPort);
    // _removeWorker will call this, but we need it to be removed synchronously
    this._removeWorkerFromList(worker);
    // If minWorkers set, spin up new workers to replace the crashed ones
    this._ensureMinWorkers();
    // terminate the worker (if not already terminated)
    return new Promise(function(resolve, reject) {
      worker.terminate(false, function(err) {
        if (err) {
          reject(err);
        } else {
          resolve(worker);
        }
      });
    });
  };
  
  /**
   * Remove a worker from the pool list.
   * @param {WorkerHandler} worker
   * @protected
   */
  Pool.prototype._removeWorkerFromList = function(worker) {
    // remove from the list with workers
    var index = this.workers.indexOf(worker);
    if (index !== -1) {
      this.workers.splice(index, 1);
    }
  };
  
  /**
   * Close all active workers. Tasks currently being executed will be finished first.
   * @param {boolean} [force=false]   If false (default), the workers are terminated
   *                                  after finishing all tasks currently in
   *                                  progress. If true, the workers will be
   *                                  terminated immediately.
   * @param {number} [timeout]        If provided and non-zero, worker termination promise will be rejected
   *                                  after timeout if worker process has not been terminated.
   * @return {Promise.<void, Error>}
   */
  Pool.prototype.terminate = function (force, timeout) {
    // cancel any pending tasks
    this.tasks.forEach(function (task) {
      task.resolver.reject(new Error('Pool terminated'));
    });
    this.tasks.length = 0;
  
    var f = function (worker) {
      this._removeWorkerFromList(worker);
    };
    var removeWorker = f.bind(this);
  
    var promises = [];
    var workers = this.workers.slice();
    workers.forEach(function (worker) {
      var termPromise = worker.terminateAndNotify(force, timeout)
        .then(removeWorker);
      promises.push(termPromise);
    });
    return Promise.all(promises);
  };
  
  /**
   * Retrieve statistics on tasks and workers.
   * @return {{totalWorkers: number, busyWorkers: number, idleWorkers: number, pendingTasks: number, activeTasks: number}} Returns an object with statistics
   */
  Pool.prototype.stats = function () {
    var totalWorkers = this.workers.length;
    var busyWorkers = this.workers.filter(function (worker) {
      return worker.busy();
    }).length;
  
    return {
      totalWorkers:  totalWorkers,
      busyWorkers:   busyWorkers,
      idleWorkers:   totalWorkers - busyWorkers,
  
      pendingTasks:  this.tasks.length,
      activeTasks:   busyWorkers
    };
  };
  
  /**
   * Ensures that a minimum of minWorkers is up and running
   * @protected
   */
  Pool.prototype._ensureMinWorkers = function() {
    if (this.minWorkers) {
      for(var i = this.workers.length; i < this.minWorkers; i++) {
        this.workers.push(this._createWorkerHandler());
      }
    }
  };
  
  /**
   * Helper function to create a new WorkerHandler and pass all options.
   * @return {WorkerHandler}
   * @private
   */
  Pool.prototype._createWorkerHandler = function () {
    return new WorkerHandler(this.script, {
      forkArgs: this.forkArgs,
      forkOpts: this.forkOpts,
      debugPort: DEBUG_PORT_ALLOCATOR.nextAvailableStartingAt(this.debugPortStart),
      workerType: this.workerType
    });
  }
  
  /**
   * Ensure that the maxWorkers option is an integer >= 1
   * @param {*} maxWorkers
   * @returns {boolean} returns true maxWorkers has a valid value
   */
  function validateMaxWorkers(maxWorkers) {
    if (!isNumber(maxWorkers) || !isInteger(maxWorkers) || maxWorkers < 1) {
      throw new TypeError('Option maxWorkers must be an integer number >= 1');
    }
  }
  
  /**
   * Ensure that the minWorkers option is an integer >= 0
   * @param {*} minWorkers
   * @returns {boolean} returns true when minWorkers has a valid value
   */
  function validateMinWorkers(minWorkers) {
    if (!isNumber(minWorkers) || !isInteger(minWorkers) || minWorkers < 0) {
      throw new TypeError('Option minWorkers must be an integer number >= 0');
    }
  }
  
  /**
   * Test whether a variable is a number
   * @param {*} value
   * @returns {boolean} returns true when value is a number
   */
  function isNumber(value) {
    return typeof value === 'number';
  }
  
  /**
   * Test whether a number is an integer
   * @param {number} value
   * @returns {boolean} Returns true if value is an integer
   */
  function isInteger(value) {
    return Math.round(value) == value;
  }
  
  module.exports = Pool;
  