fix(mergeAll): merge all will properly handle async observables

spec/operators/merge-all-spec.js

@@ -33,4 +33,12 @@ describe('mergeAll', function () {
       done();
     });
   });
+
+  it('should handle merging a hot observable of observables', function (){
+    var x = cold(     'a---b---c---|');
+    var y = cold(        'd---e---f---|');
+    var e1 =    hot('--x--y--|', { x: x, y: y });
+    var expected =  '--a--db--ec--f---|';
+    expectObservable(e1.mergeAll()).toBe(expected);
+  });
 });

src/operators/mergeAll.ts

@@ -1,6 +1,68 @@
 import Observable from '../Observable';
-import { MergeOperator } from './merge-support';
+import Operator from '../Operator';
+import Subscriber from '../Subscriber';
+import Observer from '../Observer';
+import Subscription from '../Subscription';
 
-export default function mergeAll<R>(concurrent?: any): Observable<R> {
-  return this.lift(new MergeOperator(concurrent));
+export default function mergeAll<R>(concurrent: number = Number.POSITIVE_INFINITY): Observable<R> {
+  return this.lift(new MergeAllOperator(concurrent));
 }
+
+class MergeAllOperator<T, R> implements Operator<T, R> {
+  constructor(private concurrent: number) {
+
+  }
+
+  call(observer: Observer<T>) {
+    return new MergeAllSubscriber(observer, this.concurrent);
+  }
+}
+
+class MergeAllSubscriber<T> extends Subscriber<T> {
+  private hasCompleted: boolean = false;
+  private buffer: Observable<any>[] = [];
+  private active: number = 0;
+  constructor(destination: Observer<T>, private concurrent:number) {
+    super(destination);
+  }
+
+  _next(value: any) {
+    if(this.active < this.concurrent) {
+      const innerSub = new Subscription();
+      this.add(innerSub);
+      this.active++;
+      innerSub.add(value.subscribe(new MergeAllInnerSubscriber(this.destination, this, innerSub)));
+    } else {
+      this.buffer.push(value);
+    }
+  }
+
+  _complete() {
+    this.hasCompleted = true;
+    if(this.active === 0 && this.buffer.length === 0) {
+      this.destination.complete();
+    }
+  }
+
+  notifyComplete(innerSub: Subscription<T>) {
+    const buffer = this.buffer;
+    this.remove(innerSub);
+    this.active--;
+    if(buffer.length > 0) {
+      this._next(buffer.shift());
+    } else if (this.active === 0 && this.hasCompleted) {
+      this.destination.complete();
+    }
+  }
+}
+
+class MergeAllInnerSubscriber<T> extends Subscriber<T> {
+  constructor(destination: Observer<T>, private parent: MergeAllSubscriber<T>, 
+    private innerSub: Subscription<T> ) {
+    super(destination);
+  }
+
+  _complete() {
+    this.parent.notifyComplete(this.innerSub);
+  }
+}