Constructs a promise manager.

@param {function(function)} nextTick Function for executing functions in the next turn.
@param {function(...*)} exceptionHandler Function into which unexpected exceptions are passed for
debugging purposes.
@param {boolean=} errorOnUnhandledRejections Whether an error should be generated on unhandled
promises rejections.
@returns {object} Promise manager.
function qFactory(nextTick, exceptionHandler, errorOnUnhandledRejections) {
  var $qMinErr = minErr('$q', TypeError);
  var queueSize = 0;
  var checkQueue = [];

  /**
   * @ngdoc method
   * @name ng.$q#defer
   * @kind function
   *
   * @description
   * Creates a `Deferred` object which represents a task which will finish in the future.
   *
   * @returns {Deferred} Returns a new instance of deferred.
   */
  function defer() {
    return new Deferred();
  }

  function Deferred() {
    var promise = this.promise = new Promise();
    //Non prototype methods necessary to support unbound execution :/
    this.resolve = function(val) { resolvePromise(promise, val); };
    this.reject = function(reason) { rejectPromise(promise, reason); };
    this.notify = function(progress) { notifyPromise(promise, progress); };
  }


  function Promise() {
    this.$$state = { status: 0 };
  }

  extend(Promise.prototype, {
    then: function(onFulfilled, onRejected, progressBack) {
      if (isUndefined(onFulfilled) && isUndefined(onRejected) && isUndefined(progressBack)) {
        return this;
      }
      var result = new Promise();

      this.$$state.pending = this.$$state.pending || [];
      this.$$state.pending.push([result, onFulfilled, onRejected, progressBack]);
      if (this.$$state.status > 0) scheduleProcessQueue(this.$$state);

      return result;
    },

    'catch': function(callback) {
      return this.then(null, callback);
    },

    'finally': function(callback, progressBack) {
      return this.then(function(value) {
        return handleCallback(value, resolve, callback);
      }, function(error) {
        return handleCallback(error, reject, callback);
      }, progressBack);
    }
  });

  function processQueue(state) {
    var fn, promise, pending;

    pending = state.pending;
    state.processScheduled = false;
    state.pending = undefined;
    try {
      for (var i = 0, ii = pending.length; i < ii; ++i) {
        markQStateExceptionHandled(state);
        promise = pending[i][0];
        fn = pending[i][state.status];
        try {
          if (isFunction(fn)) {
            resolvePromise(promise, fn(state.value));
          } else if (state.status === 1) {
            resolvePromise(promise, state.value);
          } else {
            rejectPromise(promise, state.value);
          }
        } catch (e) {
          rejectPromise(promise, e);
          // This error is explicitly marked for being passed to the $exceptionHandler
          if (e && e.$$passToExceptionHandler === true) {
            exceptionHandler(e);
          }
        }
      }
    } finally {
      --queueSize;
      if (errorOnUnhandledRejections && queueSize === 0) {
        nextTick(processChecks);
      }
    }
  }

  function processChecks() {
    // eslint-disable-next-line no-unmodified-loop-condition
    while (!queueSize && checkQueue.length) {
      var toCheck = checkQueue.shift();
      if (!isStateExceptionHandled(toCheck)) {
        markQStateExceptionHandled(toCheck);
        var errorMessage = 'Possibly unhandled rejection: ' + toDebugString(toCheck.value);
        if (isError(toCheck.value)) {
          exceptionHandler(toCheck.value, errorMessage);
        } else {
          exceptionHandler(errorMessage);
        }
      }
    }
  }

  function scheduleProcessQueue(state) {
    if (errorOnUnhandledRejections && !state.pending && state.status === 2 && !isStateExceptionHandled(state)) {
      if (queueSize === 0 && checkQueue.length === 0) {
        nextTick(processChecks);
      }
      checkQueue.push(state);
    }
    if (state.processScheduled || !state.pending) return;
    state.processScheduled = true;
    ++queueSize;
    nextTick(function() { processQueue(state); });
  }

  function resolvePromise(promise, val) {
    if (promise.$$state.status) return;
    if (val === promise) {
      $$reject(promise, $qMinErr(
        'qcycle',
        'Expected promise to be resolved with value other than itself \'{0}\'',
        val));
    } else {
      $$resolve(promise, val);
    }

  }

  function $$resolve(promise, val) {
    var then;
    var done = false;
    try {
      if (isObject(val) || isFunction(val)) then = val.then;
      if (isFunction(then)) {
        promise.$$state.status = -1;
        then.call(val, doResolve, doReject, doNotify);
      } else {
        promise.$$state.value = val;
        promise.$$state.status = 1;
        scheduleProcessQueue(promise.$$state);
      }
    } catch (e) {
      doReject(e);
    }

    function doResolve(val) {
      if (done) return;
      done = true;
      $$resolve(promise, val);
    }
    function doReject(val) {
      if (done) return;
      done = true;
      $$reject(promise, val);
    }
    function doNotify(progress) {
      notifyPromise(promise, progress);
    }
  }

  function rejectPromise(promise, reason) {
    if (promise.$$state.status) return;
    $$reject(promise, reason);
  }

  function $$reject(promise, reason) {
    promise.$$state.value = reason;
    promise.$$state.status = 2;
    scheduleProcessQueue(promise.$$state);
  }

  function notifyPromise(promise, progress) {
    var callbacks = promise.$$state.pending;

    if ((promise.$$state.status <= 0) && callbacks && callbacks.length) {
      nextTick(function() {
        var callback, result;
        for (var i = 0, ii = callbacks.length; i < ii; i++) {
          result = callbacks[i][0];
          callback = callbacks[i][3];
          try {
            notifyPromise(result, isFunction(callback) ? callback(progress) : progress);
          } catch (e) {
            exceptionHandler(e);
          }
        }
      });
    }
  }

  /**
   * @ngdoc method
   * @name $q#reject
   * @kind function
   *
   * @description
   * Creates a promise that is resolved as rejected with the specified `reason`. This api should be
   * used to forward rejection in a chain of promises. If you are dealing with the last promise in
   * a promise chain, you don't need to worry about it.
   *
   * When comparing deferreds/promises to the familiar behavior of try/catch/throw, think of
   * `reject` as the `throw` keyword in JavaScript. This also means that if you "catch" an error via
   * a promise error callback and you want to forward the error to the promise derived from the
   * current promise, you have to "rethrow" the error by returning a rejection constructed via
   * `reject`.
   *
   * ```js
   *   promiseB = promiseA.then(function(result) {
   *     // success: do something and resolve promiseB
   *     //          with the old or a new result
   *     return result;
   *   }, function(reason) {
   *     // error: handle the error if possible and
   *     //        resolve promiseB with newPromiseOrValue,
   *     //        otherwise forward the rejection to promiseB
   *     if (canHandle(reason)) {
   *      // handle the error and recover
   *      return newPromiseOrValue;
   *     }
   *     return $q.reject(reason);
   *   });
   * ```
   *
   * @param {*} reason Constant, message, exception or an object representing the rejection reason.
   * @returns {Promise} Returns a promise that was already resolved as rejected with the `reason`.
   */
  function reject(reason) {
    var result = new Promise();
    rejectPromise(result, reason);
    return result;
  }

  function handleCallback(value, resolver, callback) {
    var callbackOutput = null;
    try {
      if (isFunction(callback)) callbackOutput = callback();
    } catch (e) {
      return reject(e);
    }
    if (isPromiseLike(callbackOutput)) {
      return callbackOutput.then(function() {
        return resolver(value);
      }, reject);
    } else {
      return resolver(value);
    }
  }

  /**
   * @ngdoc method
   * @name $q#when
   * @kind function
   *
   * @description
   * Wraps an object that might be a value or a (3rd party) then-able promise into a $q promise.
   * This is useful when you are dealing with an object that might or might not be a promise, or if
   * the promise comes from a source that can't be trusted.
   *
   * @param {*} value Value or a promise
   * @param {Function=} successCallback
   * @param {Function=} errorCallback
   * @param {Function=} progressCallback
   * @returns {Promise} Returns a promise of the passed value or promise
   */


  function when(value, callback, errback, progressBack) {
    var result = new Promise();
    resolvePromise(result, value);
    return result.then(callback, errback, progressBack);
  }

  /**
   * @ngdoc method
   * @name $q#resolve
   * @kind function
   *
   * @description
   * Alias of {@link ng.$q#when when} to maintain naming consistency with ES6.
   *
   * @param {*} value Value or a promise
   * @param {Function=} successCallback
   * @param {Function=} errorCallback
   * @param {Function=} progressCallback
   * @returns {Promise} Returns a promise of the passed value or promise
   */
  var resolve = when;

  /**
   * @ngdoc method
   * @name $q#all
   * @kind function
   *
   * @description
   * Combines multiple promises into a single promise that is resolved when all of the input
   * promises are resolved.
   *
   * @param {Array.<Promise>|Object.<Promise>} promises An array or hash of promises.
   * @returns {Promise} Returns a single promise that will be resolved with an array/hash of values,
   *   each value corresponding to the promise at the same index/key in the `promises` array/hash.
   *   If any of the promises is resolved with a rejection, this resulting promise will be rejected
   *   with the same rejection value.
   */

  function all(promises) {
    var result = new Promise(),
        counter = 0,
        results = isArray(promises) ? [] : {};

    forEach(promises, function(promise, key) {
      counter++;
      when(promise).then(function(value) {
        results[key] = value;
        if (!(--counter)) resolvePromise(result, results);
      }, function(reason) {
        rejectPromise(result, reason);
      });
    });

    if (counter === 0) {
      resolvePromise(result, results);
    }

    return result;
  }

  /**
   * @ngdoc method
   * @name $q#race
   * @kind function
   *
   * @description
   * Returns a promise that resolves or rejects as soon as one of those promises
   * resolves or rejects, with the value or reason from that promise.
   *
   * @param {Array.<Promise>|Object.<Promise>} promises An array or hash of promises.
   * @returns {Promise} a promise that resolves or rejects as soon as one of the `promises`
   * resolves or rejects, with the value or reason from that promise.
   */

  function race(promises) {
    var deferred = defer();

    forEach(promises, function(promise) {
      when(promise).then(deferred.resolve, deferred.reject);
    });

    return deferred.promise;
  }

  function $Q(resolver) {
    if (!isFunction(resolver)) {
      throw $qMinErr('norslvr', 'Expected resolverFn, got \'{0}\'', resolver);
    }

    var promise = new Promise();

    function resolveFn(value) {
      resolvePromise(promise, value);
    }

    function rejectFn(reason) {
      rejectPromise(promise, reason);
    }

    resolver(resolveFn, rejectFn);

    return promise;
  }

  // Let's make the instanceof operator work for promises, so that
  // `new $q(fn) instanceof $q` would evaluate to true.
  $Q.prototype = Promise.prototype;

  $Q.defer = defer;
  $Q.reject = reject;
  $Q.when = when;
  $Q.resolve = resolve;
  $Q.all = all;
  $Q.race = race;

  return $Q;
}