[added] TokenGenerator

Summary: Closes #83

Reviewers: O2 Material Motion, markwei, featherless

Reviewed By: O2 Material Motion, markwei, featherless

Subscribers: shyndman, featherless, markwei

Tags: #material_motion

Differential Revision: http://codereview.cc/D1722

packages/runtime/src/TokenGenerator.ts

@@ -0,0 +1,55 @@
+/** @license
+ *  Copyright 2016 The Material Motion Authors. All Rights Reserved.
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License"); you may not
+ *  use this file except in compliance with the License. You may obtain a copy
+ *  of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ *  WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+ *  License for the specific language governing permissions and limitations
+ *  under the License.
+ */
+
+export default class TokenGenerator {
+  protected _tokenCount = 0;
+  protected _onTokenCountChange;
+
+  constructor({ onTokenCountChange }:{ onTokenCountChange:(_:{ count:number })=>void } = {}) {
+    if (!onTokenCountChange) {
+      throw new Error(`TokenGenerator requires an onTokenCountChange listener to be passed in`);
+    }
+
+    this._onTokenCountChange = onTokenCountChange;
+  }
+
+  /**
+   *  Generates a token, representing a task waiting to be completed.
+   *
+   *  Call the returned terminate function when the task is complete.
+   */
+  generateToken():{ terminate:()=>void } {
+    let terminated = false;
+    this._updateTokenCount(+1);
+
+    return {
+      terminate: () => {
+        if (terminated) {
+          throw new Error(`This token has already been terminated`);
+
+        } else {
+          terminated = true;
+          this._updateTokenCount(-1);
+        }
+      }
+    }
+  }
+
+  _updateTokenCount(delta:number):void {
+    this._tokenCount += delta;
+    this._onTokenCountChange({ count: this._tokenCount });
+  }
+}

packages/runtime/src/__tests__/TokenGenerator.test.ts

@@ -0,0 +1,76 @@
+/** @license
+ *  Copyright 2016 The Material Motion Authors. All Rights Reserved.
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License"); you may not
+ *  use this file except in compliance with the License. You may obtain a copy
+ *  of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ *  WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+ *  License for the specific language governing permissions and limitations
+ *  under the License.
+ */
+
+import { expect } from 'chai';
+
+import {
+  beforeEach,
+  describe,
+  it,
+} from 'mocha-sugar-free';
+
+import {
+  spy,
+} from 'sinon';
+
+import TokenGenerator from '../TokenGenerator';
+
+describe('TokenGenerator',
+  () => {
+    let tokenGenerator;
+
+    it(`should require a callback`,
+      () => {
+        expect(
+          () => {
+            new TokenGenerator();
+          }
+        ).to.throw(`onTokenCountChange`);
+      }
+    );
+
+    it(`should notify the callback when a new token is issued`,
+      () => {
+        const onTokenCountChange = spy();
+        new TokenGenerator({ onTokenCountChange }).generateToken();
+
+        expect(onTokenCountChange.lastCall.args[0].count).to.equal(1);
+      }
+    );
+
+    it(`should notify the callback when a token is terminated`,
+      () => {
+        const onTokenCountChange = spy();
+
+        new TokenGenerator({ onTokenCountChange }).generateToken().terminate();
+
+        expect(onTokenCountChange.lastCall.args[0].count).to.equal(0);
+      }
+    );
+
+    it(`should error if a token is terminated repeatedly`,
+      () => {
+        expect(
+          () => {
+            const token = new TokenGenerator({ onTokenCountChange: () => null }).generateToken();
+            token.terminate();
+            token.terminate();
+          }
+        ).to.throw(`terminated`);
+      }
+    );
+  }
+);