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gaia/shared/js/smart-screen/piped_promise.js

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+(function(exports) {
+  'use strict';
+
+  /**
+   * The PipedPromise is a 'trait' or 'mixin' for other module to mix it in.
+   * Under certain situation, when we implement method that returns a Promise
+   * to callee, we don't want the method to be reentrant and instantiate another
+   * promise. We would like the request to be 'piped' in the same promise.
+   * This is the case where PipedPromise comes to our resque.
+   *
+   * @example
+   * SomeModule.prototype = {
+   *   ...
+   *   willReturnPromise: function willReturnPromise() {
+   *     return this._getPipedPromise('willReturnPromise',
+   *       function(resolve, reject) {
+   *         ...
+   *       });
+   *   },
+   *   ...
+   * };
+   * addMixin(SomeModule, PipedPromise);
+   *
+   */
+  var PipedPromise = {
+    _removePipedPromise: function pp_removePipedPromise(key) {
+      if (!this._piped_promises) {
+        this._piped_promises = {};
+      }
+
+      this._piped_promises[key] = undefined;
+    },
+
+    /**
+     * Get Promise object of specific key. It will generate a new Promise
+     * if Promise of the key is not existed yet.
+     *
+     * @param {String} key - key of the Promise
+     * @param {Function} executor - the executor once the Promise resolved
+     *                              or rejected
+     * @returns {Promise} - A Promise
+     *
+     */
+    _getPipedPromise: function pp_getOrCreatePromise(key, executor) {
+      if (!this._piped_promises) {
+        this._piped_promises = {};
+      }
+
+      var that = this;
+      var promise = this._piped_promises[key];
+      if (!promise) {
+        promise = new Promise(executor);
+        Promise.all([promise]).then(function onFulfill() {
+          that._removePipedPromise(key);
+        }, function onReject() {
+          that._removePipedPromise(key);
+        });
+        that._piped_promises[key] = promise;
+      }
+      return promise;
+    }
+  };
+
+  exports.PipedPromise = PipedPromise;
+
+}(window));