pkg/dartpad/asset/bootstrap_flutter.dart.tmpl

// Copyright (c) 2026, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

import 'dart:async';
import 'dart:js_interop';
import 'dart:typed_data';
import 'dart:ui_web' as ui_web;

import 'package:flutter/foundation.dart';
import 'package:flutter/services.dart';
import 'package:flutter/widgets.dart';
//import 'package:flutter_web_plugins/flutter_web_plugins.dart';

import '{{entrypoint}}' as entrypoint;

@JS('console.error')
external void _consoleError(JSString message);

@JS(r'$dartpadWorkspace')
external _DartPadWorkspace get _workspace;

extension type _DartPadWorkspace._(JSObject _) implements JSObject {
  external String? get packageRoot;
  external JSPromise<JSUint8Array> readFileAsBytes(String path);
  external JSPromise<_DartPadPackage?> resolvePackage(String package);
}

extension type _DartPadPackage._(JSObject _) implements JSObject {
  external String get name;
  external String get rootPath;
  external String get packagePath;
  external String get languageVersion;
}

final class _DartPadWidgetsFlutterBinding extends WidgetsFlutterBinding {
  final _DartPadAssetBundle _bundle = _DartPadAssetBundle();

  @override
  void attachRootWidget(Widget rootWidget) {
    super.attachRootWidget(
      DefaultAssetBundle(bundle: _bundle, child: rootWidget),
    );
  }

  @override
  Future<void> performReassemble() {
    _bundle.clear();
    imageCache.clear();
    imageCache.clearLiveImages();
    return super.performReassemble();
  }
}

final class _DartPadAssetBundle extends CachingAssetBundle {
  @override
  Future<ByteData> load(String key) async {
    final bytes = await _readAssetFromWorkspace(key);
    if (bytes != null) {
      return ByteData.sublistView(bytes);
    }
    return await rootBundle.load(key);
  }

  Future<Uint8List?> _readAssetFromWorkspace(String key) async {
    if (key.split('/') case [
      'packages',
      final pkgName,
      ...final rest,
    ] when pkgName.isNotEmpty && rest.isNotEmpty) {
      final subPath = rest.join('/');
      if (await _resolvePackage(pkgName) case final pkg?) {
        final bytes =
            await _readFileAsBytes('${pkg.rootPath}/$subPath') ??
            await _readFileAsBytes('${pkg.packagePath}/$subPath');
        if (bytes != null) {
          return bytes;
        }
      }
    }

    if (_workspace.packageRoot case final rootPath?) {
      return await _readFileAsBytes('$rootPath/$key');
    }

    return null;
  }
}

Future<Uint8List?> _readFileAsBytes(String path) async {
  try {
    return (await _workspace.readFileAsBytes(path).toDart).toDart;
  } catch (_, _) {
    return null;
  }
}

Future<_DartPadPackage?> _resolvePackage(String package) async {
  try {
    return await _workspace.resolvePackage(package).toDart;
  } catch (_, _) {
    return null;
  }
}

Future<void> main() async {
  // Disable URL strategy to prevent SecurityError in srcdoc iframes
  ui_web.urlStrategy = null;

  // Capture errors and pipe to console.error
  FlutterError.onError = (details) {
    _consoleError(details.toString().toJS);
  };

  await ui_web.bootstrapEngine(
    runApp: () {
      _DartPadWidgetsFlutterBinding();
      entrypoint.main();
    },
    registerPlugins: () {
      // pluginRegistrant.registerPlugins();
    },
  );
}