chrome/browser/resources/tts_engine/background.ts

// Copyright 2024 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

/**
 * @fileoverview The background script for the tts engine.
 */

// TODO(crbug.com/353972727): Download the web assembly file of the Google TTS
// engine.
console.info('TTS engine extension installed!');

const DOWNLOAD_BASE_URL = 'https://dl.google.com/android/tts/wasm/';

// This should be incremented each time there's a new upload of the TTS engine.
let CURRENT_VERSION_NUMBER = 1;

fetch(DOWNLOAD_BASE_URL + 'version.json')
    .then(response => response.json())
    .then(data => {
      const version = data.versionNumber;
      if (version && typeof version === 'number') {
        // If the version is valid and less than the current version number,
        // rollback.
        if (version < CURRENT_VERSION_NUMBER) {
          // If the version is valid, update the download version.
          CURRENT_VERSION_NUMBER = version;
        } else {
          if (!version) {
            console.info(
                'Found invalid version in version.json: ' +
                'versionNumber undefined');
          } else {
            console.info('Found invalid version in version.json: ' + version);
          }
        }
      }
    });

const CURRENT_VERSION = 'v' + CURRENT_VERSION_NUMBER;

const DOWNLOAD_URL = DOWNLOAD_BASE_URL + CURRENT_VERSION;


// TODO(crbug.com/353972727): Use of remotely fetched code is a temporary
// solution until updating to use component updater.
fetch(DOWNLOAD_URL + '/googletts_engine_js_bin.js')
    .then(response => response.text())
    .then(scriptContent => {
      const script = document.createElement('script');

      script.type = 'text/javascript';
      script.textContent = scriptContent;
      script.async = true;
      document.head.appendChild(script);
    })
    .catch(error => {
      console.info('Failed to fetch TTS engine: ' + error);
    });