Publishreplay(1) for all derive functions (#557)

* Add drr

* Transform all to publishreplay(1)

* Add comment in test

* Update headers

* Update headers

* Lint

packages/api-derive/src/util/cache.spec.ts

@@ -0,0 +1,30 @@
+// Copyright 2017-2019 @polkadot/api-derive authors & contributors
+// This software may be modified and distributed under the terms
+// of the Apache-2.0 license. See the LICENSE file for details.
+
+import ApiRx from '@polkadot/api/rx';
+
+import { cache } from './cache';
+
+describe('cache', () => {
+  const f = cache((api: ApiRx) => (a: number, b: number) => [api, a, b]);
+  const api = {} as ApiRx;
+
+  it('should hit cache when all arguments are the same', () => {
+    const first = f(api)(2, 3);
+    const second = f(api)(2, 3);
+
+    expect(first).toBe(second);
+  });
+
+  it('should not hit cache when some arguments are not the same', () => {
+    const first = f(api)(2, 3);
+    const second1 = f(api)(5, 3);
+    const second2 = f(api)(2, 5);
+    const second3 = f({} as ApiRx)(2, 3);
+
+    expect(first).not.toBe(second1);
+    expect(first).not.toBe(second2);
+    expect(first).not.toBe(second3);
+  });
+});

packages/api-derive/src/util/cache.ts

@@ -0,0 +1,30 @@
+// Copyright 2017-2019 @polkadot/api-derive authors & contributors
+// This software may be modified and distributed under the terms
+// of the Apache-2.0 license. See the LICENSE file for details.
+
+import memoizee from 'memoizee';
+import ApiRx from '@polkadot/api/rx';
+
+/**
+ * Create memoization for a 2-currified function.
+ *
+ * @param fn - The function to memoize.
+ * @param map - The Map used to cache function returns.
+ * @example
+ * ```javascript
+ * const f = (api: ApiRx) => (b: number) => a * b;
+ * const cached = cache(f);
+ * f(api)(1, 2);
+ * f(api)(1); // Cache not hit
+ * f({})(1, 2); // Cache not hit
+ * f(api)(1, 2); // Cache hit
+ * ```
+ */
+export const cache = (fn: Function, map = new WeakMap()) => (api: ApiRx) => {
+  if (!map.has(api)) {
+    const innerFn = fn(api);
+    map.set(api, memoizee(innerFn));
+  }
+
+  return map.get(api);
+};

packages/api-derive/src/util/drr.spec.ts

@@ -0,0 +1,32 @@
+// Copyright 2017-2019 @polkadot/api-derive authors & contributors
+// This software may be modified and distributed under the terms
+// of the Apache-2.0 license. See the LICENSE file for details.
+
+import { of, timer } from 'rxjs';
+
+import { drr } from './drr';
+
+describe('drr', () => {
+  it('should not fire twice the same value', (done) => {
+    let count = 0;
+    of(1, 1).pipe(drr()).subscribe(() => { ++count; });
+
+    setTimeout(() => {
+      expect(count).toBe(1);
+      done();
+    }, 50);
+  });
+
+  it('should be a ReplaySubject(1)', (done) => {
+    const obs = timer(0, 50).pipe(drr()); // Starts at 0, increments every 50ms
+    obs.subscribe(); // Fire the observable
+
+    // Subscribe another time after some time, i.e. after the observable has fired
+    setTimeout(() => {
+      obs.subscribe((value) => {
+        expect(value).toBe(2);
+        done();
+      });
+    }, 120);
+  });
+});

packages/api-derive/src/util/drr.ts

@@ -0,0 +1,18 @@
+// Copyright 2017-2019 @polkadot/api-derive authors & contributors
+// This software may be modified and distributed under the terms
+// of the Apache-2.0 license. See the LICENSE file for details.
+
+import { distinctUntilChanged, publishReplay, refCount } from 'rxjs/operators';
+import { Observable } from 'rxjs';
+
+/**
+ * Shorthand for distinctUntilChanged(), publishReplay(1) and refCount().
+ *
+ * @ignore
+ */
+export const drr = () => <T>(source$: Observable<T>): Observable<T> =>
+  source$.pipe(
+    distinctUntilChanged(),
+    publishReplay(1),
+    refCount()
+  );