Add finite execution count limit to timers

CHANGELOG.md

@@ -8,6 +8,7 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 ## Breaking Changes
 
 ## Added
+- Allow timers to limit repeats to a finite number of times ([#957](https://github.com/excaliburjs/Excalibur/pull/974))
 
 ## Changed
 

src/engine/Timer.ts

@@ -10,18 +10,27 @@ export class Timer {
    public interval: number = 10;
    public fcn: () => void = () => { return; };
    public repeats: boolean = false;
+   public maxNumberOfRepeats: number = -1;
    private _elapsedTime: number = 0;
    private _totalTimeAlive: number = 0;
    private _paused: boolean = false;
+   private _numberOfTicks: number = 0;
    public complete: boolean = false;
    public scene: Scene = null;
 
    /**
     * @param fcn        The callback to be fired after the interval is complete.
     * @param interval   Interval length
-    * @param repeats    Indicates whether this call back should be fired only once, or repeat after every interval as completed.    
+    * @param repeats    Indicates whether this call back should be fired only once, or repeat after every interval as completed.
+    * @param numberOfRepeats Specifies a maximum number of times that this timer will execute.   
     */
-   constructor(fcn: () => void, interval: number, repeats?: boolean) {
+   constructor(fcn: () => void, interval: number, repeats?: boolean, numberOfRepeats?: number) {
+      if (!!numberOfRepeats && numberOfRepeats >= 0) {
+         this.maxNumberOfRepeats = numberOfRepeats;
+         if (!repeats) {
+             throw new Error('repeats must be set to true if numberOfRepeats is set');
+         }
+      }
       this.id = Timer.id++;
       this.interval = interval || this.interval;
       this.fcn = fcn || this.fcn;
@@ -36,8 +45,14 @@ export class Timer {
       if (!this._paused) {   
          this._totalTimeAlive += delta;
          this._elapsedTime += delta;
+
+         if (this.maxNumberOfRepeats > -1 && this._numberOfTicks >= this.maxNumberOfRepeats) {
+            this.complete = true;
+         }
+
          if (!this.complete && this._elapsedTime >= this.interval) {
             this.fcn.call(this);
+            this._numberOfTicks++;
             if (this.repeats) {
                this._elapsedTime = 0;
             } else {
@@ -50,14 +65,27 @@ export class Timer {
    /**
     * Resets the timer so that it can be reused, and optionally reconfigure the timers interval.
     * @param newInterval If specified, sets a new non-negative interval in milliseconds to refire the callback
+    * @param newNumberOfRepeats If specified, sets a new non-negative upper limit to the number of time this timer executes
     */
-   public reset(newInterval?: number) {
+   public reset(newInterval?: number, newNumberOfRepeats?: number) {
       if (!!newInterval && newInterval >= 0) {
          this.interval = newInterval;
       }
+
+      if (!!this.maxNumberOfRepeats && this.maxNumberOfRepeats >= 0) {
+         this.maxNumberOfRepeats = newNumberOfRepeats;
+         if (!this.repeats) {
+            throw new Error('repeats must be set to true if numberOfRepeats is set');
+        }
+      }
+
       this.complete = false;
       this._elapsedTime = 0;
-
+      this._numberOfTicks = 0;
+   }
+
+   public get timesRepeated(): number {
+      return this._numberOfTicks;
    }
 
    public getTimeRunning(): number {

src/spec/TimerSpec.ts

@@ -35,7 +35,7 @@ describe('A Timer', () => {
       expect(timer.complete).toBeTruthy();
    });
 
-   it('can repeat itself multiple number of times', () => {
+   it('can repeat itself indefinitely at a specified interval', () => {
       // count the number of fires
       var count = 0;
       timer = new ex.Timer(function(){ count++; }, 500, true);
@@ -47,6 +47,17 @@ describe('A Timer', () => {
       expect(count).toBe(3);
    });
 
+   it('can repeat itself a finite number of times', () => {
+      // count the number of fires
+      timer = new ex.Timer(function(){ var dummy = 0; }, 500, true, 2);
+
+      timer.update(501);
+      timer.update(501);
+      timer.update(501);
+
+      expect(timer.timesRepeated).toBe(2);
+   });
+
    it('can return how long it has been running', () => {
       timer.update(372);
 
@@ -168,6 +179,32 @@ describe('A Timer', () => {
       }
    });
 
+   it('can be reset with a different number of maximum iterations', () => {
+      // non-repeating timer
+      timer = new ex.Timer(function(){ var dummy = 0; }, 500, true, 3);
+      scene.add(timer);
+
+      // tick the timer
+      scene.update(engine, 501);
+      scene.update(engine, 501);
+      scene.update(engine, 501);
+      expect(timer.timesRepeated).toBe(3);
+
+      // tick the timer again, but it shouldn't fire until reset
+      scene.update(engine, 501);
+      expect(timer.timesRepeated).toBe(3);
+      expect(timer.complete).toBe(true);
+
+      // once reset the timer should fire again
+      timer.reset(500, 4);
+      expect(timer.complete).toBe(false);
+      scene.update(engine, 501);
+      scene.update(engine, 501);
+      scene.update(engine, 501);
+      scene.update(engine, 501);
+      expect(timer.timesRepeated).toBe(4);
+   });
+
    it('can be paused', () => {
 
       var count = 0;