feat(toggle): Add a toggle factory.

source/observable/index.ts

@@ -15,6 +15,7 @@ export * from "./mergeArray";
 export * from "./NotificationQueue";
 export * from "./queue";
 export * from "./separate";
+export * from "./toggle";
 export * from "./traverse";
 export * from "./zipArray";
 export * from "./zipPadded";

source/observable/toggle-spec.ts

@@ -0,0 +1,90 @@
+/**
+ * @license Use of this source code is governed by an MIT-style license that
+ * can be found in the LICENSE file at https://github.com/cartant/rxjs-etc
+ */
+/*tslint:disable:no-unused-expression*/
+
+import { bufferToggle, concatAll, switchMap, takeUntil, windowToggle } from "rxjs/operators";
+import { marbles } from "rxjs-marbles";
+import { toggle } from "./toggle";
+
+describe("toggle", () => {
+
+    it("should play nice with switchMap", marbles(m => {
+
+        const source =   m.hot("ab-cd-ef-gh");
+        const sourceSubs = [
+                               "--^--!-----",
+                               "--------^--"
+        ];
+        const notifier = m.hot("--x--x--x--");
+        const expected =       "---cd----gh";
+
+        const [on, off] = toggle(notifier);
+        const destination = on.pipe(
+            switchMap(() => source.pipe(takeUntil(off)))
+        );
+        m.expect(destination).toBeObservable(expected);
+        m.expect(source).toHaveSubscriptions(sourceSubs);
+    }));
+
+    it("should play nice with bufferToggle", marbles(m => {
+
+        const source =   m.hot("ab-cd-ef-gh");
+        const sourceSubs =     "^----------";
+        const notifier = m.hot("--x--x--x--");
+        const expected =       "-----(cd)--";
+
+        const [on, off] = toggle(notifier);
+        const destination = source.pipe(
+            bufferToggle(on, () => off),
+            concatAll()
+        );
+        m.expect(destination).toBeObservable(expected);
+        m.expect(source).toHaveSubscriptions(sourceSubs);
+    }));
+
+    it("should play nice with windowToggle", marbles(m => {
+
+        const source =   m.hot("ab-cd-ef-gh");
+        const sourceSubs =     "^----------";
+        const notifier = m.hot("--x--x--x--");
+        const expected =       "---cd----gh";
+
+        const [on, off] = toggle(notifier);
+        const destination = source.pipe(
+            windowToggle(on, () => off),
+            concatAll()
+        );
+        m.expect(destination).toBeObservable(expected);
+        m.expect(source).toHaveSubscriptions(sourceSubs);
+    }));
+
+    it("should support three states", marbles(m => {
+
+        const notifier = m.hot("abcdef");
+        const e1       =       "a--d--";
+        const e2       =       "-b--e-";
+        const e3       =       "--c--f";
+
+        const [t1, t2, t3] = toggle(notifier, 3);
+        m.expect(t1).toBeObservable(e1);
+        m.expect(t2).toBeObservable(e2);
+        m.expect(t3).toBeObservable(e3);
+    }));
+
+    it("should support four states", marbles(m => {
+
+        const notifier = m.hot("abcdef");
+        const e1       =       "a---e-";
+        const e2       =       "-b---f";
+        const e3       =       "--c---";
+        const e4       =       "---d--";
+
+        const [t1, t2, t3, t4] = toggle(notifier, 4);
+        m.expect(t1).toBeObservable(e1);
+        m.expect(t2).toBeObservable(e2);
+        m.expect(t3).toBeObservable(e3);
+        m.expect(t4).toBeObservable(e4);
+    }));
+});

source/observable/toggle.ts

@@ -0,0 +1,26 @@
+/**
+ * @license Use of this source code is governed by an MIT-style license that
+ * can be found in the LICENSE file at https://github.com/cartant/rxjs-etc
+ */
+
+import { Observable } from "rxjs";
+import { filter, map, share } from "rxjs/operators";
+
+export function toggle<T>(source: Observable<T>): [Observable<T>, Observable<T>];
+export function toggle<T>(source: Observable<T>, states: 2): [Observable<T>, Observable<T>];
+export function toggle<T>(source: Observable<T>, states: 3): [Observable<T>, Observable<T>, Observable<T>];
+export function toggle<T>(source: Observable<T>, states: number): Observable<T>[];
+export function toggle<T>(source: Observable<T>, states: number = 2): Observable<T>[] {
+    const result: Observable<T>[] = [];
+    const indexed = source.pipe(
+        map((value, index) => [index, value] as [number, T]),
+        share()
+    );
+    for (let state = 0; state < states; ++state) {
+        result.push(indexed.pipe(
+            filter(([index]) => (index % states) === state),
+            map(([, value]) => value)
+        ));
+    }
+    return result;
+}