Diagnostics: Add a fake observable helper

- Simplifies implementing fake observers
- Currently only supports a single observable value

Bug: 1125150
Test: browser_tests --gtest_filter=DiagnosticsApp*
Change-Id: Idcddbbe30e220ecab8e7218450630062fb69c8e1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2420769Reviewed-by: Bailey Berro <baileyberro@chromium.org>
Commit-Queue: Zentaro Kavanagh <zentaro@chromium.org>
Cr-Commit-Position: refs/heads/master@{#809588}

chrome/test/data/webui/chromeos/diagnostics/diagnostics_test.js

@@ -9,8 +9,10 @@ import 'chrome://diagnostics/diagnostics_app.js';
 import {SystemDataProviderInterface} from 'chrome://diagnostics/diagnostics_types.js';
 import {fakeBatteryInfo, fakeSystemInfo} from 'chrome://diagnostics/fake_data.js';
 import {FakeMethodResolver} from 'chrome://diagnostics/fake_method_resolver.js';
+import {FakeObservables} from 'chrome://diagnostics/fake_observables.js';
 import {FakeSystemDataProvider} from 'chrome://diagnostics/fake_system_data_provider.js';
 import {getSystemDataProvider, setSystemDataProviderForTesting} from 'chrome://diagnostics/mojo_interface_provider.js';
+import {PromiseResolver} from 'chrome://resources/js/promise_resolver.m.js';
 import {flush} from 'chrome://resources/polymer/v3_0/polymer/polymer_bundled.min.js';
 import {flushTasks} from 'chrome://test/test_util.m.js';
 
@@ -296,6 +298,36 @@ suite('FakeMojoProviderTest', () => {
   });
 });
 
+suite('FakeObservablesTest', () => {
+  /** @type {?FakeObservables} */
+  let observables = null;
+
+  setup(() => {
+    observables = new FakeObservables();
+  });
+
+  teardown(() => {
+    observables = null;
+  });
+
+  test('RegisterSimpleObservable', () => {
+    observables.register('ObserveFoo_OnFooUpdated');
+    /** @type !Array<string> */
+    const expected = ['bar'];
+    observables.setObservableData('ObserveFoo_OnFooUpdated', expected);
+
+    let resolver = new PromiseResolver();
+    observables.observe('ObserveFoo_OnFooUpdated', (foo) => {
+      assertEquals(expected[0], foo);
+      resolver.resolve();
+    });
+
+    observables.trigger('ObserveFoo_OnFooUpdated');
+    return resolver.promise;
+  });
+});
+
+
 suite('FakeSystemDataProviderTest', () => {
   /** @type {?FakeSystemDataProvider} */
   let provider = null;

chromeos/components/diagnostics_ui/resources/BUILD.gn

@@ -17,6 +17,7 @@ js_type_check("closure_compile_module") {
     ":diagnostics_types",
     ":fake_data",
     ":fake_method_resolver",
+    ":fake_observables",
     ":fake_system_data_provider",
     ":memory_card",
     ":mojo_interface_provider",
@@ -64,6 +65,10 @@ js_library("fake_method_resolver") {
   deps = [ "//ui/webui/resources/js:cr.m" ]
 }
 
+js_library("fake_observables") {
+  deps = [ "//ui/webui/resources/js:cr.m" ]
+}
+
 js_library("fake_system_data_provider") {
   deps = [ "//ui/webui/resources/js:cr.m" ]
 }

chromeos/components/diagnostics_ui/resources/diagnostics_app_resources.grd

@@ -21,6 +21,7 @@
       <include name="IDR_DIAGNOSTICS_CPU_CARD_JS" file="${root_gen_dir}/chromeos/components/diagnostics_ui/resources/cpu_card.js" use_base_dir="false" type="BINDATA"/>
       <include name="IDR_DIAGNOSTICS_FAKE_DATA_JS" file="fake_data.js" type="BINDATA"/>
       <include name="IDR_DIAGNOSTICS_FAKE_METHOD_RESOLVER_JS" file="fake_method_resolver.js" type="BINDATA"/>
+      <include name="IDR_DIAGNOSTICS_FAKE_OBSERVABLES_JS" file="fake_observables.js" type="BINDATA"/>
       <include name="IDR_DIAGNOSTICS_FAKE_SYSTEM_DATA_PROVIDER_JS" file="fake_system_data_provider.js" type="BINDATA"/>
       <include name="IDR_DIAGNOSTICS_FONTS_CSS_JS" file="${root_gen_dir}/chromeos/components/diagnostics_ui/resources/diagnostics_fonts_css.js" use_base_dir="false" type="BINDATA"/>
       <include name="IDR_DIAGNOSTICS_MEMORY_CARD_JS" file="${root_gen_dir}/chromeos/components/diagnostics_ui/resources/memory_card.js" use_base_dir="false" type="BINDATA"/>

chromeos/components/diagnostics_ui/resources/fake_observables.js

+// Copyright 2020 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import {assert} from 'chrome://resources/js/assert.m.js';
+
+/**
+ * @fileoverview
+ * Implements a helper class for faking asynchronous observables.
+ */
+
+/**
+ * Maintains state about an observable and the data it will produce.
+ * @template T
+ **/
+class FakeObservableState {
+  constructor() {
+    /**
+     * The list of functions that will be notified when the observable
+     * is triggered.
+     * @private {!Array<!function(!T)>}
+     **/
+    this.observers_ = [];
+
+    /**
+     * Array of observations to be supplied by the observer.
+     * @private {!Array<T>}
+     **/
+    this.observations_ = [];
+
+    /**
+     * The index of the next observation.
+     * @private {number}
+     **/
+    this.index_ = -1;
+  }
+
+  /** @param {!Array<!T>} observations */
+  setObservableData(observations) {
+    // TODO(zentaro): Fully support multiple observations.
+    assert(observations.length == 1);
+
+    this.observations_ = observations;
+    this.index_ = 0;
+  }
+
+  /** @param {!function(!T)} callback */
+  addObserver(callback) {
+    this.observers_.push(callback);
+  }
+
+  /**
+   * Causes the observable to trigger and notify all observers of the next
+   * observation value.
+   */
+  trigger() {
+    assert(this.observations_.length > 0);
+    assert(this.index_ >= 0);
+    assert(this.index_ < this.observations_.length);
+
+    // Get the value of this observation and update the index to point to the
+    // next one.
+    const value = this.observations_[this.index_];
+    this.index_ = (this.index_ + 1) % this.observations_.length;
+
+    // Fire all the callbacks that are observing this observable.
+    for (const fn of this.observers_) {
+      fn(value);
+    }
+  }
+}
+
+/**
+ * Manages a map of fake observables and the fake data they will produce
+ * when triggered.
+ * @template T
+ */
+export class FakeObservables {
+  constructor() {
+    /** @private {!Map<string, !FakeObservableState>} */
+    this.observables_ = new Map();
+  }
+
+  /**
+   * Register an observable. Other calls to this class will assert if the
+   * observable has not been registered.
+   * @param {string} methodName
+   */
+  register(methodName) {
+    this.observables_.set(methodName, new FakeObservableState());
+  }
+
+  /**
+   * Supply the callback for observing methodName.
+   * @param {string} methodName
+   * @param {!function(!T)} callback
+   */
+  observe(methodName, callback) {
+    this.getObservable_(methodName).addObserver(callback);
+  }
+
+  /**
+   * Sets the data that will be produced when the observable is triggered.
+   * Each observation produces the next value in the array and wraps around
+   * when all observations have been produced.
+   * @param {string} methodName
+   * @param {!Array<!T>} observations
+   */
+  setObservableData(methodName, observations) {
+    this.getObservable_(methodName).setObservableData(observations);
+  }
+
+  /**
+   * Causes the observable to trigger and notify all observers of the next
+   * observation value.
+   * @param {string} methodName
+   */
+  trigger(methodName) {
+    this.getObservable_(methodName).trigger();
+  }
+
+  /**
+   * Return the Observable for methodName.
+   * @param {string} methodName
+   * @return {!FakeObservableState}
+   * @private
+   */
+  getObservable_(methodName) {
+    let observable = this.observables_.get(methodName);
+    assert(!!observable, `Observable '${methodName}' not found.`);
+    return observable;
+  }
+}