packages/flutter_tools/lib/src/web/file_generators/flutter_service_worker_js.dart

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

import '../../globals.dart' as globals;

/// The caching strategy for the generated service worker.
enum ServiceWorkerStrategy {
  /// Download the app shell eagerly and all other assets lazily.
  /// Prefer the offline cached version.
  offlineFirst,

  /// Do not generate a service worker,
  none,
}

/// Generate a service worker with an app-specific cache name a map of
/// resource files.
///
/// The tool embeds file hashes directly into the worker so that the byte for byte
/// invalidation will automatically reactivate workers whenever a new
/// version is deployed.
String generateServiceWorker(
  String fileGeneratorsPath,
  Map<String, String> resources,
  List<String> coreBundle, {
  required ServiceWorkerStrategy serviceWorkerStrategy,
  required String baseHref,
}) {
  if (serviceWorkerStrategy == ServiceWorkerStrategy.none) {
    return '';
  }

  final String flutterServiceWorkerJsPath = globals.localFileSystem.path.join(
    fileGeneratorsPath,
    'js',
    'flutter_service_worker.js',
  );
  return globals.localFileSystem
      .file(flutterServiceWorkerJsPath)
      .readAsStringSync()
      .replaceAll(r'$$BASE_HREF', '"$baseHref"'),
      .replaceAll(
        r'$$RESOURCES_MAP',
        '{${resources.entries.map((MapEntry<String, String> entry) => '"${entry.key}": "${entry.value}"').join(",\n")}}',
      )
      .replaceAll(
        r'$$CORE_LIST',
        '[${coreBundle.map((String file) => '"$file"').join(',\n')}]',
      );
}