refactor: Move Async Storage Implementation to utils package (#503)

Summary:

This is first PR in an effort to implement support for Offline Events persistence for React Native Apps. Async Storage implementation was already done in datafile-manager package to support datafile caching. This PR moves the generic caching implementation to utils so that it can be used by both datafile-manager and event-processor.

Test plan:

All Existing tests should pass

Author: zashraf1985

packages/utils/CHANGELOG.MD

@@ -7,6 +7,9 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 ## [Unreleased]
 Changes that have landed but are not yet released.
 
+### New Features
+- Added `PersistentKeyValueCache` interface and its implementation for React Native under `ReactNativeAsyncStorageCahe`.
+
 ## [0.2.0] - August 7, 2019
 
 ### New Features

packages/utils/__mocks__/@react-native-community/async-storage.ts

@@ -0,0 +1,37 @@
+/**
+ * Copyright 2020, Optimizely
+ *
+ * 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 AsyncStorage {
+  static getItem(key: string, callback?: (error?: Error, result?: string) => void): Promise<string | null> {
+    return new Promise((resolve, reject) => {
+      switch (key) {
+        case 'keyThatExists':
+          resolve('{ "name": "Awesome Object" }')
+          break
+        case 'keyThatDoesNotExist':
+          resolve(null)
+          break
+        case 'keyWithInvalidJsonObject':
+          resolve('bad json }')
+          break
+      }
+    })
+  }
+
+  static setItem(key: string, value: string, callback?: (error?: Error) => void): Promise<void> {
+    return Promise.resolve()
+  }
+}

packages/utils/__tests__/reactNativeAsyncStorageCache.spec.ts

@@ -0,0 +1,70 @@
+/**
+ * Copyright 2020, Optimizely
+ *
+ * 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 ReactNativeAsyncStorageCache from '../src/reactNativeAsyncStorageCache';
+
+describe('reactNativeAsyncStorageCache', () => {
+  let cacheInstance: ReactNativeAsyncStorageCache;
+
+  beforeEach(() => {
+    cacheInstance = new ReactNativeAsyncStorageCache();
+  });
+
+  describe('get', function() {
+    it('should return correct object when item is found in cache', function() {
+      return cacheInstance.get('keyThatExists').then(v => expect(v).toEqual({ name: 'Awesome Object' }));
+    });
+
+    it('should return null if item is not found in cache', function() {
+      return cacheInstance.get('keyThatDoesNotExist').then(v => expect(v).toBeNull());
+    });
+
+    it('should reject promise error if string has an incorrect JSON format', function() {
+      return cacheInstance
+        .get('keyWithInvalidJsonObject')
+        .catch(() => 'exception caught')
+        .then(v => {
+          expect(v).toEqual('exception caught');
+        });
+    });
+  });
+
+  describe('set', function() {
+    it('should resolve promise if item was successfully set in the cache', function() {
+      const testObj = { name: 'Awesome Object' };
+      return cacheInstance.set('testKey', testObj);
+    });
+
+    it('should reject promise if item was not set in the cache because of json stringifying error', function() {
+      const testObj: any = { name: 'Awesome Object' };
+      testObj.myOwnReference = testObj;
+      return cacheInstance
+        .set('testKey', testObj)
+        .catch(() => 'exception caught')
+        .then(v => expect(v).toEqual('exception caught'));
+    });
+  });
+
+  describe('contains', function() {
+    it('should return true if object with key exists', function() {
+      return cacheInstance.contains('keyThatExists').then(v => expect(v).toBeTruthy());
+    });
+
+    it('should return false if object with key does not exist', function() {
+      return cacheInstance.contains('keyThatDoesNotExist').then(v => expect(v).toBeFalsy());
+    });
+  });
+});