fix(takeLast): fix takeLast behavior to emit correct order

closes #1407

spec/operators/takeLast-spec.ts

@@ -1,6 +1,6 @@
 import * as Rx from '../../dist/cjs/Rx';
 import {hot, cold, expectObservable, expectSubscriptions} from '../helpers/marble-testing';
-import {it, asDiagram} from '../helpers/test-helper';
+import {it, DoneSignature, asDiagram} from '../helpers/test-helper';
 
 const Observable = Rx.Observable;
 
@@ -14,6 +14,20 @@ describe('Observable.prototype.takeLast()', () => {
     expectSubscriptions(e1.subscriptions).toBe(e1subs);
   });
 
+  it('should take last three values', (done: DoneSignature) => {
+    const expected = [2, 3, 4];
+    Observable.of(0, 1, 2, 3, 4).takeLast(3).subscribe((x) => {
+      expect(x).toBe(expected.shift());
+    }, done.fail, done);
+  });
+
+  it('should not take any values', () => {
+    const e1 =  cold('--a-----b----c---d--|');
+    const expected = '|';
+
+    expectObservable(e1.takeLast(0)).toBe(expected);
+  });
+
   it('should work with empty', () => {
     const e1 =  cold('|');
     const e1subs =   '(^!)';

src/operator/takeLast.ts

@@ -31,50 +31,34 @@ class TakeLastOperator<T> implements Operator<T, T> {
 class TakeLastSubscriber<T> extends Subscriber<T> {
   private ring: T[];
   private count: number = 0;
-  private index: number = 0;
 
   constructor(destination: Subscriber<T>, private total: number) {
     super(destination);
     this.ring = new Array(total);
   }
 
   protected _next(value: T): void {
-
-    let index = this.index;
     const ring = this.ring;
     const total = this.total;
-    const count = this.count;
-
-    if (total > 1) {
-      if (count < total) {
-        this.count = count + 1;
-        this.index = index + 1;
-      } else if (index === 0) {
-        this.index = ++index;
-      } else if (index < total) {
-        this.index = index + 1;
-      } else  {
-        this.index = index = 0;
-      }
-    } else if (count < total) {
-      this.count = total;
-    }
+    const count = ++this.count;
 
+    const index = count % total;
     ring[index] = value;
   }
 
   protected _complete(): void {
+    const destination = this.destination;
+    let count = this.count;
 
-    let iter = -1;
-    const { ring, count, total, destination } = this;
-    let index = (total === 1 || count < total) ? 0 : this.index - 1;
+    if (count > 0) {
+      const { ring, total } = this;
 
-    while (++iter < count) {
-      if (iter + index === total) {
-        index = total - iter;
+      for (let i = 0; i < total; i++) {
+        const idx = (++count) % total;
+        destination.next(ring[idx]);
       }
-      destination.next(ring[iter + index]);
     }
+
     destination.complete();
   }
 }