chrome/browser/resources/chromeos/accessibility/chromevox/injected/api_implementation.js

// Copyright 2014 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

/**
 * @fileoverview Implementation of ChromeVox's API for extnal apps.
 * Deprecated.
 * At this point, Google Docs is the only supported use case.
 */

goog.provide('ApiImplementation');

goog.require('ContentScriptBridge');
goog.require('ScriptInstaller');

ApiImplementation = class {
  /** Inject the API into the page and set up communication with it. */
  static init() {
    window.addEventListener('message', ApiImplementation.portSetup, true);
    const script = chrome.extension.getURL('chromevox/injected/api.js');

    const didInstall = ScriptInstaller.installScript(script, 'cvoxapi');
    if (!didInstall) {
      console.error('Unable to install api script');
    }

    ContentScriptBridge.addDisconnectListener(function() {
      ApiImplementation.port.postMessage(ApiImplementation.DISCONNECT_MSG);
      ScriptInstaller.uninstallScript('cvoxapi');
    });
  }

  /**
   * This method is called when the content script receives a message from
   * the page.
   * @param {Event} event The DOM event with the message data.
   * @return {boolean} True if default event processing should continue.
   */
  static portSetup(event) {
    if (event.data === 'cvox.PortSetup') {
      ApiImplementation.port = event.ports[0];
      ApiImplementation.port.onmessage = function(event) {
        ApiImplementation.dispatchApiMessage(JSON.parse(event.data));
      };

      // Stop propagation since it was our message.
      event.stopPropagation();
      return false;
    }
    return true;
  }

  /**
   * Call the appropriate API function given a message from the page.
   * @param {*} message The message.
   */
  static dispatchApiMessage(message) {
    if (message['cmd'] !== 'speak') {
      throw 'Unknown API call: ' + message['cmd'];
    }
    ApiImplementation.speak(...message['args']);
  }

  /**
   * Speaks the given string using the specified queueMode and properties.
   *
   * @param {number} callbackId The callback Id.
   * @param {string} textString The string of text to be spoken.
   * @param {number=} queueMode Valid modes are 0 for flush; 1 for queue.
   * @param {Object=} properties Speech properties to use for this utterance.
   */
  static speak(callbackId, textString, queueMode, properties) {
    if (!properties) {
      properties = {};
    }
    setupEndCallback_(properties, callbackId);
    const message = {
      'target': 'TTS',
      'action': 'speak',
      'text': textString,
      queueMode,
      properties,
    };

    ContentScriptBridge.send(message);
  }
};

/**
 * The message between content script and the page that indicates the
 * connection to the background page has been lost.
 * @type {string}
 * @const
 */
ApiImplementation.DISCONNECT_MSG = 'Disconnect';


/**
 * Sets endCallback in properties to call callbackId's function.
 * @param {!Object} properties Speech properties to use for this utterance.
 * @param {number} callbackId The callback Id.
 * @private
 */
function setupEndCallback_(properties, callbackId) {
  const endCallback = function() {
    ApiImplementation.port.postMessage(JSON.stringify({'id': callbackId}));
  };
  properties.endCallback = endCallback;
}