(function(global: any) {
  interface ScheduledFunction {
    endTime: number;
    id: number,
    func: Function;
    args: any[];
    delay: number;
  }
  
  class Scheduler {
    // Next scheduler id.
    public nextId: number = 0;
    
    // Scheduler queue with the tuple of end time and callback function - sorted by end time.
    private _schedulerQueue: ScheduledFunction[] = [];
    // Current simulated time in millis.
    private _currentTime: number = 0;
    
    constructor() {}
    
    scheduleFunction(cb: Function, delay: number, args: any[] = [], id: number = -1) : number {
      let currentId: number = id < 0 ? this.nextId++ : id;
      let endTime = this._currentTime + delay;
            
      // Insert so that scheduler queue remains sorted by end time.
      let newEntry: ScheduledFunction = {
        endTime: endTime,
        id: currentId,
        func: cb,
        args: args,
        delay: delay
      }
      let i = 0;
      for (; i < this._schedulerQueue.length; i++) {
        let currentEntry = this._schedulerQueue[i];
        if (newEntry.endTime < currentEntry.endTime) {
          break;
        }
      }
      this._schedulerQueue.splice(i, 0, newEntry);
      return currentId;
    }
    
    removeScheduledFunctionWithId(id: number): void {
      for (let i = 0; i < this._schedulerQueue.length; i++) {
        if (this._schedulerQueue[i].id == id) {
          this._schedulerQueue.splice(i, 1);
          break;
        }
      }
    }
    
    tick(millis: number = 0): void {
      this._currentTime += millis;
      while (this._schedulerQueue.length > 0) {  
        let current = this._schedulerQueue[0];        
        if (this._currentTime < current.endTime) {
          // Done processing the queue since it's sorted by endTime.
          break;
        } else {
          // Time to run scheduled function. Remove it from the head of queue.
          let current = this._schedulerQueue.shift();
          let retval = current.func.apply(global, current.args);
          if (!retval) {
            // Uncaught exception in the current scheduled function. Stop processing the queue.
            break;
          }
        }
      }
    }
  }
  
  class FakeAsyncTestZoneSpec implements ZoneSpec {
    static assertInZone(): void {
      if (Zone.current.get('FakeAsyncTestZoneSpec') == null) {
        throw new Error('The code should be running in the fakeAsync zone to call this function');
      }
    }
    
    private _scheduler: Scheduler = new Scheduler();
    private _microtasks: Function[] = [];
    private _lastError: Error = null;
    private _uncaughtPromiseErrors: {rejection: any}[] = Promise[Zone['__symbol__']('uncaughtPromiseErrors')];
        
    pendingPeriodicTimers: number[] = [];
    pendingTimers: number[] = [];

    constructor(namePrefix: string) {
      this.name = 'fakeAsyncTestZone for ' + namePrefix;
    }

    private _fnAndFlush(fn: Function,
                        completers: {onSuccess?: Function, onError?: Function}): Function {
      return (...args): boolean => {
        fn.apply(global, args);
        
        if (this._lastError === null) { // Success
          if (completers.onSuccess != null) {
            completers.onSuccess.apply(global);
          }
          // Flush microtasks only on success.
          this.flushMicrotasks();
        } else { // Failure
          if (completers.onError != null) { 
            completers.onError.apply(global);
          }
        }
        // Return true if there were no errors, false otherwise. 
        return this._lastError === null;
      }
    }
    
    private static _removeTimer(timers: number[], id:number): void {
      let index = timers.indexOf(id);
        if (index > -1) {
          timers.splice(index, 1);
        }
    }
    
    private _dequeueTimer(id: number): Function {
      return () => {
        FakeAsyncTestZoneSpec._removeTimer(this.pendingTimers, id);
      };
    }
    
    private _requeuePeriodicTimer(
        fn: Function, interval: number, args: any[], id: number): Function {
      return () => {
        // Requeue the timer callback if it's not been canceled.
        if (this.pendingPeriodicTimers.indexOf(id) !== -1) {
          this._scheduler.scheduleFunction(fn, interval, args, id);
        }
      }
    }
    
    private _dequeuePeriodicTimer(id: number): Function {
      return () => {
        FakeAsyncTestZoneSpec._removeTimer(this.pendingPeriodicTimers, id);
      };
    }
    
    private _setTimeout(fn: Function, delay: number, args: any[]): number {
      let removeTimerFn = this._dequeueTimer(this._scheduler.nextId);
      // Queue the callback and dequeue the timer on success and error.
      let cb = this._fnAndFlush(fn, {onSuccess: removeTimerFn, onError: removeTimerFn});
      let id = this._scheduler.scheduleFunction(cb, delay, args);
      this.pendingTimers.push(id);
      return id;
    }
    
    private _clearTimeout(id: number): void {
      FakeAsyncTestZoneSpec._removeTimer(this.pendingTimers, id);
      this._scheduler.removeScheduledFunctionWithId(id);
    }
    
    private _setInterval(fn: Function, interval: number, ...args): number {
      let id = this._scheduler.nextId;
      let completers = {onSuccess: null, onError: this._dequeuePeriodicTimer(id)};
      let cb = this._fnAndFlush(fn, completers);
      
      // Use the callback created above to requeue on success. 
      completers.onSuccess = this._requeuePeriodicTimer(cb, interval, args, id);
      
      // Queue the callback and dequeue the periodic timer only on error.
      this._scheduler.scheduleFunction(cb, interval, args);
      this.pendingPeriodicTimers.push(id);
      return id;
    }

    private _clearInterval(id: number): void {
      FakeAsyncTestZoneSpec._removeTimer(this.pendingPeriodicTimers, id);
      this._scheduler.removeScheduledFunctionWithId(id);
    }

    private _resetLastErrorAndThrow(): void {
      let error = this._lastError || this._uncaughtPromiseErrors[0];
      this._uncaughtPromiseErrors.length = 0;
      this._lastError = null;
      throw error;
    }
    
    tick(millis: number = 0): void {
      FakeAsyncTestZoneSpec.assertInZone();
      this.flushMicrotasks();
      this._scheduler.tick(millis);
      if (this._lastError !== null) {
        this._resetLastErrorAndThrow();
      }
    }

    flushMicrotasks(): void {
      FakeAsyncTestZoneSpec.assertInZone();
      const flushErrors = () => {
        if (this._lastError !== null || this._uncaughtPromiseErrors.length) {
          // If there is an error stop processing the microtask queue and rethrow the error.
          this._resetLastErrorAndThrow();
        }
      }
      while (this._microtasks.length > 0) {
        let microtask = this._microtasks.shift();
        microtask();
      }
      flushErrors();
    }

    // ZoneSpec implementation below.

    name: string;

    properties: { [key: string]: any } = { 'FakeAsyncTestZoneSpec': this };

    onScheduleTask(delegate: ZoneDelegate, current: Zone, target: Zone, task: Task): Task {
      switch (task.type) {
        case 'microTask':
          this._microtasks.push(task.invoke);
          break;
        case 'macroTask':
          switch (task.source) {
            case 'setTimeout':
              task.data['handleId'] =
                this._setTimeout(task.invoke, task.data['delay'], task.data['args']);
              break;
            case 'setInterval':
              task.data['handleId'] =
                this._setInterval(task.invoke, task.data['delay'], task.data['args']);
              break;
            case 'XMLHttpRequest.send':
              throw new Error('Cannot make XHRs from within a fake async test.');
            default:
              task = delegate.scheduleTask(target, task);
          }
          break;
        case 'eventTask':
          task = delegate.scheduleTask(target, task);
          break;
      }
      return task;
    }

    onCancelTask(delegate: ZoneDelegate, current: Zone, target: Zone, task: Task): any {
      switch (task.source) {
        case 'setTimeout':
          return this._clearTimeout(task.data['handleId']);
        case 'setInterval':
          return this._clearInterval(task.data['handleId']);
        default:
          return delegate.cancelTask(target, task);
      }
    }
    
    onHandleError(parentZoneDelegate: ZoneDelegate, currentZone: Zone, targetZone: Zone,
        error: any): boolean {
      this._lastError = error; 
      return false; // Don't propagate error to parent zone.
    }
  }

  // Export the class so that new instances can be created with proper
  // constructor params.
  Zone['FakeAsyncTestZoneSpec'] = FakeAsyncTestZoneSpec;
})(typeof window === 'object' && window || typeof self === 'object' && self || global);
