add Counter utility

frontend/src/counter.js

@@ -0,0 +1,53 @@
+import * as logger from 'src/services/logger';
+
+export class Counter {
+ _counter = 0;
+
+ constructor({ onEnable, onDisable }) {
+ assert(onEnable);
+ this.onEnable = onEnable;
+ this.onDisable = onDisable;
+ }
+
+ enable = () => {
+ assert(counter >= 0);
+ if (counter <= 0) {
+ counter = 1;
+
+ const res = this.onEnable();
+ if (res) {
+ if (this.onDisable) {
+ logger.warn(new Error('both `onEnable` return value and `onDisable` callback were provided, giving priority to latter'));
+ } else {
+ this.onDisable = res;
+ }
+ } else {
+ if (this.onDisable) {
+ // nothing to do
+ } else {
+ logger.warn(new Error('both `onEnable` return value and `onDisable` callback were NOT provided'));
+ }
+ }
+ } else {
+ counter += 1;
+ }
+
+ return this.disable;
+ }
+
+ disable = () => {
+ assert(counter > 0);
+ if (counter > 1) {
+ counter -= 1;
+ } else if (counter < 1) {
+ logger.warn(new Error('trying to disable already disabled counter'));
+ counter = 0;
+ } else {
+ counter = 0;
+
+ if (this.onDisable) {
+ this.onDisable();
+ }
+ }
+ }
+}

frontend/test/counter.test.js

@@ -0,0 +1,49 @@
+import { Counter } from 'src/counter';
+import _ from 'lodash';
+
+describe("counter tests", function() {
+ it("should enable and disable", function() {
+ onEnable = jasmine.createSpy('onEnable');
+ onDisable = jasmine.createSpy('onDisable');
+ const counter = new Counter({ onEnable, onDisable });
+
+ counter.enable();
+ expect(onEnable).toHaveBeenCalledTimes(1);
+ expect(onDisable).not.toHaveBeenCalled();
+ counter.disable();
+ expect(onDisable).toHaveBeenCalledTimes(1);
+ });
+
+ it("should enable several times", function() {
+ onEnable = jasmine.createSpy('onEnable');
+ onDisable = jasmine.createSpy('onDisable');
+ const counter = new Counter({ onEnable, onDisable });
+
+ counter.enable();
+ counter.enable();
+ expect(onEnable).toHaveBeenCalledTimes(1);
+ counter.disable();
+ expect(onDisable).not.toHaveBeenCalled();
+ counter.disable();
+ expect(onDisable).toHaveBeenCalledTimes(1);
+ });
+
+ it("should chain enable and disable", function() {
+ onEnable = jasmine.createSpy('onEnable');
+ onDisable = jasmine.createSpy('onDisable');
+ const counter = new Counter({ onEnable, onDisable });
+
+ counter.enable();
+ counter.enable();
+ expect(onEnable).toHaveBeenCalledTimes(1);
+ counter.disable();
+ expect(onDisable).not.toHaveBeenCalled();
+ counter.disable();
+ expect(onDisable).toHaveBeenCalledTimes(1);
+
+ counter.enable();
+ expect(onEnable).toHaveBeenCalledTimes(2);
+ counter.disable();
+ expect(onDisable).toHaveBeenCalledTimes(2);
+ });
+});