// 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 'dart:async';

import 'package:meta/meta.dart';
import 'package:package_config/package_config.dart';
import 'package:stream_channel/stream_channel.dart';
import 'package:test_api/src/backend/suite_platform.dart'; // ignore: implementation_imports
import 'package:test_core/src/runner/environment.dart'; // ignore: implementation_imports
import 'package:test_core/src/runner/plugin/platform_helpers.dart'; // ignore: implementation_imports
import 'package:test_core/src/runner/runner_suite.dart'; // ignore: implementation_imports
import 'package:test_core/src/runner/suite.dart'; // ignore: implementation_imports
import 'package:vm_service/vm_service.dart' as vm_service;

import '../base/common.dart';
import '../base/file_system.dart';
import '../base/io.dart';
import '../build_info.dart';
import '../compile.dart';
import '../convert.dart';
import '../dart/language_version.dart';
import '../dart/package_map.dart';
import '../globals.dart' as globals;
import '../project.dart';
import '../test/test_wrapper.dart';
import '../vmservice.dart';
import 'test_compiler.dart';
import 'test_config.dart';
import 'watcher.dart';

/// The address at which our WebSocket server resides and at which the sky_shell
/// processes will host the Observatory server.
final Map<InternetAddressType, InternetAddress> _kHosts = <InternetAddressType, InternetAddress>{
  InternetAddressType.IPv4: InternetAddress.loopbackIPv4,
  InternetAddressType.IPv6: InternetAddress.loopbackIPv6,
};

typedef PlatformPluginRegistration = void Function(FlutterPlatform platform);

/// Configure the `test` package to work with Flutter.
///
/// On systems where each [FlutterPlatform] is only used to run one test suite
/// (that is, one Dart file with a `*_test.dart` file name and a single `void
/// main()`), you can set an observatory port explicitly.
FlutterPlatform installHook({
  TestWrapper testWrapper = const TestWrapper(),
  @required String shellPath,
  TestWatcher watcher,
  bool enableObservatory = false,
  bool machine = false,
  bool startPaused = false,
  bool disableServiceAuthCodes = false,
  int port = 0,
  String precompiledDillPath,
  Map<String, String> precompiledDillFiles,
  @required BuildMode buildMode,
  bool trackWidgetCreation = false,
  bool updateGoldens = false,
  bool buildTestAssets = false,
  int observatoryPort,
  InternetAddressType serverType = InternetAddressType.IPv4,
  Uri projectRootDirectory,
  FlutterProject flutterProject,
  String icudtlPath,
  PlatformPluginRegistration platformPluginRegistration,
  List<String> extraFrontEndOptions,
  // Deprecated, use extraFrontEndOptions.
  List<String> dartExperiments,
  bool nullAssertions = false,
}) {
  assert(testWrapper != null);
  assert(enableObservatory || (!startPaused && observatoryPort == null));

  // registerPlatformPlugin can be injected for testing since it's not very mock-friendly.
  platformPluginRegistration ??= (FlutterPlatform platform) {
    testWrapper.registerPlatformPlugin(
      <Runtime>[Runtime.vm],
      () {
        return platform;
      },
    );
  };
  final FlutterPlatform platform = FlutterPlatform(
    shellPath: shellPath,
    watcher: watcher,
    machine: machine,
    enableObservatory: enableObservatory,
    startPaused: startPaused,
    disableServiceAuthCodes: disableServiceAuthCodes,
    explicitObservatoryPort: observatoryPort,
    host: _kHosts[serverType],
    port: port,
    precompiledDillPath: precompiledDillPath,
    precompiledDillFiles: precompiledDillFiles,
    buildMode: buildMode,
    trackWidgetCreation: trackWidgetCreation,
    updateGoldens: updateGoldens,
    buildTestAssets: buildTestAssets,
    projectRootDirectory: projectRootDirectory,
    flutterProject: flutterProject,
    icudtlPath: icudtlPath,
    extraFrontEndOptions: extraFrontEndOptions,
    nullAssertions: nullAssertions,
  );
  platformPluginRegistration(platform);
  return platform;
}

/// Generates the bootstrap entry point script that will be used to launch an
/// individual test file.
///
/// The [testUrl] argument specifies the path to the test file that is being
/// launched.
///
/// The [host] argument specifies the address at which the test harness is
/// running.
///
/// If [testConfigFile] is specified, it must follow the conventions of test
/// configuration files as outlined in the [flutter_test] library. By default,
/// the test file will be launched directly.
///
/// The [updateGoldens] argument will set the [autoUpdateGoldens] global
/// variable in the [flutter_test] package before invoking the test.
// NOTE: this API is used by the fuchsia source tree, do not add new
// required or position parameters.
String generateTestBootstrap({
  @required Uri testUrl,
  @required InternetAddress host,
  File testConfigFile,
  bool updateGoldens = false,
  String languageVersionHeader = '',
  bool nullSafety = false,
}) {
  assert(testUrl != null);
  assert(host != null);
  assert(updateGoldens != null);

  final String websocketUrl = host.type == InternetAddressType.IPv4
      ? 'ws://${host.address}'
      : 'ws://[${host.address}]';
  final String encodedWebsocketUrl = Uri.encodeComponent(websocketUrl);

  final StringBuffer buffer = StringBuffer();
  buffer.write('''
$languageVersionHeader
import 'dart:async';
import 'dart:convert';  // ignore: dart_convert_import
import 'dart:io';  // ignore: dart_io_import
import 'dart:isolate';

import 'package:flutter_test/flutter_test.dart';
import 'package:test_api/src/remote_listener.dart';
import 'package:stream_channel/stream_channel.dart';
import 'package:stack_trace/stack_trace.dart';

import '$testUrl' as test;
''');
  if (testConfigFile != null) {
    buffer.write('''
import '${Uri.file(testConfigFile.path)}' as test_config;
''');
  }
  buffer.write('''

/// Returns a serialized test suite.
StreamChannel<dynamic> serializeSuite(Function getMain()) {
  return RemoteListener.start(getMain);
}

/// Capture any top-level errors (mostly lazy syntax errors, since other are
/// caught below) and report them to the parent isolate.
void catchIsolateErrors() {
  final ReceivePort errorPort = ReceivePort();
  // Treat errors non-fatal because otherwise they'll be double-printed.
  Isolate.current.setErrorsFatal(false);
  Isolate.current.addErrorListener(errorPort.sendPort);
  errorPort.listen((dynamic message) {
    // Masquerade as an IsolateSpawnException because that's what this would
    // be if the error had been detected statically.
    final IsolateSpawnException error = IsolateSpawnException(
        message[0] as String);
    final Trace stackTrace = message[1] == null ?
        Trace(const <Frame>[]) : Trace.parse(message[1] as String);
    Zone.current.handleUncaughtError(error, stackTrace);
  });
}


void main() {
  String serverPort = Platform.environment['SERVER_PORT'] ?? '';
  String server = Uri.decodeComponent('$encodedWebsocketUrl:\$serverPort');
  StreamChannel<dynamic> channel = serializeSuite(() {
    catchIsolateErrors();
    goldenFileComparator = new LocalFileComparator(Uri.parse('$testUrl'));
    autoUpdateGoldenFiles = $updateGoldens;
''');
  if (testConfigFile != null) {
    buffer.write('''
    return () => test_config.main(test.main);
''');
  } else {
    buffer.write('''
    return test.main;
''');
  }
  buffer.write('''
  });
  WebSocket.connect(server).then((WebSocket socket) {
    socket.map((dynamic x) {
      return json.decode(x as String);
    }).pipe(channel.sink);
    socket.addStream(channel.stream.map(json.encode));
  });
}
''');
  return buffer.toString();
}

enum InitialResult { crashed, connected }

enum TestResult { crashed, harnessBailed, testBailed }

typedef Finalizer = Future<void> Function();

/// The flutter test platform used to integrate with package:test.
class FlutterPlatform extends PlatformPlugin {
  FlutterPlatform({
    @required this.shellPath,
    this.watcher,
    this.enableObservatory,
    this.machine,
    this.startPaused,
    this.disableServiceAuthCodes,
    this.explicitObservatoryPort,
    this.host,
    this.port,
    this.precompiledDillPath,
    this.precompiledDillFiles,
    @required this.buildMode,
    this.trackWidgetCreation,
    this.updateGoldens,
    this.buildTestAssets,
    this.projectRootDirectory,
    this.flutterProject,
    this.icudtlPath,
    this.nullAssertions = false,
    @required this.extraFrontEndOptions,
  }) : assert(shellPath != null);

  final String shellPath;
  final TestWatcher watcher;
  final bool enableObservatory;
  final bool machine;
  final bool startPaused;
  final bool disableServiceAuthCodes;
  final int explicitObservatoryPort;
  final InternetAddress host;
  final int port;
  final String precompiledDillPath;
  final Map<String, String> precompiledDillFiles;
  final BuildMode buildMode;
  final bool trackWidgetCreation;
  final bool updateGoldens;
  final bool buildTestAssets;
  final Uri projectRootDirectory;
  final FlutterProject flutterProject;
  final String icudtlPath;
  final List<String> extraFrontEndOptions;
  final bool nullAssertions;

  Directory fontsDirectory;

  /// The test compiler produces dill files for each test main.
  ///
  /// To speed up compilation, each compile is initialized from an existing
  /// dill file from previous runs, if possible.
  TestCompiler compiler;

  // Each time loadChannel() is called, we spin up a local WebSocket server,
  // then spin up the engine in a subprocess. We pass the engine a Dart file
  // that connects to our WebSocket server, then we proxy JSON messages from
  // the test harness to the engine and back again. If at any time the engine
  // crashes, we inject an error into that stream. When the process closes,
  // we clean everything up.

  int _testCount = 0;

  @override
  Future<RunnerSuite> load(
    String path,
    SuitePlatform platform,
    SuiteConfiguration suiteConfig,
    Object message,
  ) async {
    // loadChannel may throw an exception. That's fine; it will cause the
    // LoadSuite to emit an error, which will be presented to the user.
    // Except for the Declarer error, which is a specific test incompatibility
    // error we need to catch.
    try {
      final StreamChannel<dynamic> channel = loadChannel(path, platform);
      final RunnerSuiteController controller = deserializeSuite(path, platform,
        suiteConfig, const PluginEnvironment(), channel, message);
      return await controller.suite;
    } on Exception catch (err) {
      /// Rethrow a less confusing error if it is a test incompatibility.
      if (err.toString().contains("type 'Declarer' is not a subtype of type 'Declarer'")) {
        throw UnsupportedError('Package incompatibility between flutter and test packages:\n'
          '  * flutter is incompatible with test <1.4.0.\n'
          '  * flutter is incompatible with mockito <4.0.0\n'
          "To fix this error, update test to at least '^1.4.0' and mockito to at least '^4.0.0'\n"
        );
      }
      // Guess it was a different error.
      rethrow;
    }
  }

  @override
  StreamChannel<dynamic> loadChannel(String path, SuitePlatform platform) {
    if (_testCount > 0) {
      // Fail if there will be a port conflict.
      if (explicitObservatoryPort != null) {
        throwToolExit('installHook() was called with an observatory port or debugger mode enabled, but then more than one test suite was run.');
      }
      // Fail if we're passing in a precompiled entry-point.
      if (precompiledDillPath != null) {
        throwToolExit('installHook() was called with a precompiled test entry-point, but then more than one test suite was run.');
      }
    }
    final int ourTestCount = _testCount;
    _testCount += 1;
    final StreamController<dynamic> localController = StreamController<dynamic>();
    final StreamController<dynamic> remoteController = StreamController<dynamic>();
    final Completer<_AsyncError> testCompleteCompleter = Completer<_AsyncError>();
    final _FlutterPlatformStreamSinkWrapper<dynamic> remoteSink = _FlutterPlatformStreamSinkWrapper<dynamic>(
      remoteController.sink,
      testCompleteCompleter.future,
    );
    final StreamChannel<dynamic> localChannel = StreamChannel<dynamic>.withGuarantees(
      remoteController.stream,
      localController.sink,
    );
    final StreamChannel<dynamic> remoteChannel = StreamChannel<dynamic>.withGuarantees(
      localController.stream,
      remoteSink,
    );
    testCompleteCompleter.complete(_startTest(path, localChannel, ourTestCount));
    return remoteChannel;
  }

  Future<String> _compileExpressionService(
    String isolateId,
    String expression,
    List<String> definitions,
    List<String> typeDefinitions,
    String libraryUri,
    String klass,
    bool isStatic,
  ) async {
    if (compiler == null || compiler.compiler == null) {
      throw 'Compiler is not set up properly to compile $expression';
    }
    final CompilerOutput compilerOutput =
      await compiler.compiler.compileExpression(expression, definitions,
        typeDefinitions, libraryUri, klass, isStatic);
    if (compilerOutput != null && compilerOutput.outputFilename != null) {
      return base64.encode(globals.fs.file(compilerOutput.outputFilename).readAsBytesSync());
    }
    throw 'Failed to compile $expression';
  }

  /// Binds an [HttpServer] serving from `host` on `port`.
  ///
  /// Only intended to be overridden in tests for [FlutterPlatform].
  @protected
  @visibleForTesting
  Future<HttpServer> bind(InternetAddress host, int port) => HttpServer.bind(host, port);

  PackageConfig _packageConfig;

  Future<_AsyncError> _startTest(
    String testPath,
    StreamChannel<dynamic> controller,
    int ourTestCount,
  ) async {
    _packageConfig ??= await loadPackageConfigWithLogging(
      globals.fs.file(globalPackagesPath),
      logger: globals.logger,
    );
    globals.printTrace('test $ourTestCount: starting test $testPath');

    _AsyncError outOfBandError; // error that we couldn't send to the harness that we need to send via our future

    final List<Finalizer> finalizers = <Finalizer>[]; // Will be run in reverse order.
    bool subprocessActive = false;
    bool controllerSinkClosed = false;
    try {
      // Callback can't throw since it's just setting a variable.
      unawaited(controller.sink.done.whenComplete(() {
        controllerSinkClosed = true;
      }));

      // Prepare our WebSocket server to talk to the engine subproces.
      final HttpServer server = await bind(host, port);
      finalizers.add(() async {
        globals.printTrace('test $ourTestCount: shutting down test harness socket server');
        await server.close(force: true);
      });
      final Completer<WebSocket> webSocket = Completer<WebSocket>();
      server.listen(
        (HttpRequest request) {
          if (!webSocket.isCompleted) {
            webSocket.complete(WebSocketTransformer.upgrade(request));
          }
        },
        onError: (dynamic error, StackTrace stack) {
          // If you reach here, it's unlikely we're going to be able to really handle this well.
          globals.printTrace('test $ourTestCount: test harness socket server experienced an unexpected error: $error');
          if (!controllerSinkClosed) {
            controller.sink.addError(error, stack);
            controller.sink.close();
          } else {
            globals.printError('unexpected error from test harness socket server: $error');
          }
        },
        cancelOnError: true,
      );

      globals.printTrace('test $ourTestCount: starting shell process');

      // If a kernel file is given, then use that to launch the test.
      // If mapping is provided, look kernel file from mapping.
      // If all fails, create a "listener" dart that invokes actual test.
      String mainDart;
      if (precompiledDillPath != null) {
        mainDart = precompiledDillPath;
      } else if (precompiledDillFiles != null) {
        mainDart = precompiledDillFiles[testPath];
      }
      mainDart ??= _createListenerDart(finalizers, ourTestCount, testPath, server);

      if (precompiledDillPath == null && precompiledDillFiles == null) {
        // Lazily instantiate compiler so it is built only if it is actually used.
        compiler ??= TestCompiler(buildMode, trackWidgetCreation, flutterProject, extraFrontEndOptions);
        mainDart = await compiler.compile(globals.fs.file(mainDart).uri);

        if (mainDart == null) {
          controller.sink.addError(_getErrorMessage('Compilation failed', testPath, shellPath));
          return null;
        }
      }

      final Process process = await _startProcess(
        shellPath,
        mainDart,
        packages: globalPackagesPath,
        enableObservatory: enableObservatory,
        startPaused: startPaused,
        disableServiceAuthCodes: disableServiceAuthCodes,
        observatoryPort: explicitObservatoryPort,
        serverPort: server.port,
      );
      subprocessActive = true;
      finalizers.add(() async {
        if (subprocessActive) {
          globals.printTrace('test $ourTestCount: ensuring end-of-process for shell');
          process.kill();
          final int exitCode = await process.exitCode;
          subprocessActive = false;
          if (!controllerSinkClosed && exitCode != -15) {
            // ProcessSignal.SIGTERM
            // We expect SIGTERM (15) because we tried to terminate it.
            // It's negative because signals are returned as negative exit codes.
            final String message = _getErrorMessage(
                _getExitCodeMessage(exitCode, 'after tests finished'),
                testPath,
                shellPath);
            controller.sink.addError(message);
          }
        }
      });

      final Completer<void> gotProcessObservatoryUri = Completer<void>();
      if (!enableObservatory) {
        gotProcessObservatoryUri.complete();
      }

      // Pipe stdout and stderr from the subprocess to our printStatus console.
      // We also keep track of what observatory port the engine used, if any.
      Uri processObservatoryUri;
      _pipeStandardStreamsToConsole(
        process,
        reportObservatoryUri: (Uri detectedUri) async {
          assert(processObservatoryUri == null);
          assert(explicitObservatoryPort == null ||
              explicitObservatoryPort == detectedUri.port);
          if (startPaused && !machine) {
            globals.printStatus('The test process has been started.');
            globals.printStatus('You can now connect to it using observatory. To connect, load the following Web site in your browser:');
            globals.printStatus('  $detectedUri');
            globals.printStatus('You should first set appropriate breakpoints, then resume the test in the debugger.');
          } else {
            globals.printTrace('test $ourTestCount: using observatory uri $detectedUri from pid ${process.pid}');
          }
          processObservatoryUri = detectedUri;
          {
            globals.printTrace('Connecting to service protocol: $processObservatoryUri');
            final Future<vm_service.VmService> localVmService = connectToVmService(processObservatoryUri,
              compileExpression: _compileExpressionService);
            unawaited(localVmService.then((vm_service.VmService vmservice) {
              globals.printTrace('Successfully connected to service protocol: $processObservatoryUri');
            }));
          }
          gotProcessObservatoryUri.complete();
          watcher?.handleStartedProcess(
              ProcessEvent(ourTestCount, process, processObservatoryUri));
        },
      );

      // At this point, three things can happen next:
      // The engine could crash, in which case process.exitCode will complete.
      // The engine could connect to us, in which case webSocket.future will complete.
      // The local test harness could get bored of us.
      globals.printTrace('test $ourTestCount: awaiting initial result for pid ${process.pid}');
      final InitialResult initialResult = await Future.any<InitialResult>(<Future<InitialResult>>[
        process.exitCode.then<InitialResult>((int exitCode) => InitialResult.crashed),
        gotProcessObservatoryUri.future.then<InitialResult>((void value) {
          return webSocket.future.then<InitialResult>(
            (WebSocket webSocket) => InitialResult.connected,
          );
        }),
      ]);

      switch (initialResult) {
        case InitialResult.crashed:
          globals.printTrace('test $ourTestCount: process with pid ${process.pid} crashed before connecting to test harness');
          final int exitCode = await process.exitCode;
          subprocessActive = false;
          final String message = _getErrorMessage(
              _getExitCodeMessage(
                  exitCode, 'before connecting to test harness'),
              testPath,
              shellPath);
          controller.sink.addError(message);
          // Awaited for with 'sink.done' below.
          unawaited(controller.sink.close());
          globals.printTrace('test $ourTestCount: waiting for controller sink to close');
          await controller.sink.done;
          await watcher?.handleTestCrashed(ProcessEvent(ourTestCount, process));
          break;
        case InitialResult.connected:
          globals.printTrace('test $ourTestCount: process with pid ${process.pid} connected to test harness');
          final WebSocket testSocket = await webSocket.future;

          final Completer<void> harnessDone = Completer<void>();
          final StreamSubscription<dynamic> harnessToTest =
              controller.stream.listen(
            (dynamic event) {
              testSocket.add(json.encode(event));
            },
            onDone: harnessDone.complete,
            onError: (dynamic error, StackTrace stack) {
              // If you reach here, it's unlikely we're going to be able to really handle this well.
              globals.printError('test harness controller stream experienced an unexpected error\ntest: $testPath\nerror: $error');
              if (!controllerSinkClosed) {
                controller.sink.addError(error, stack);
                controller.sink.close();
              } else {
                globals.printError('unexpected error from test harness controller stream: $error');
              }
            },
            cancelOnError: true,
          );

          final Completer<void> testDone = Completer<void>();
          final StreamSubscription<dynamic> testToHarness = testSocket.listen(
            (dynamic encodedEvent) {
              assert(encodedEvent is String); // we shouldn't ever get binary messages
              controller.sink.add(json.decode(encodedEvent as String));
            },
            onDone: testDone.complete,
            onError: (dynamic error, StackTrace stack) {
              // If you reach here, it's unlikely we're going to be able to really handle this well.
              globals.printError('test socket stream experienced an unexpected error\ntest: $testPath\nerror: $error');
              if (!controllerSinkClosed) {
                controller.sink.addError(error, stack);
                controller.sink.close();
              } else {
                globals.printError('unexpected error from test socket stream: $error');
              }
            },
            cancelOnError: true,
          );

          globals.printTrace('test $ourTestCount: awaiting test result for pid ${process.pid}');
          final TestResult testResult = await Future.any<TestResult>(<Future<TestResult>>[
            process.exitCode.then<TestResult>((int exitCode) {
              return TestResult.crashed;
            }),
            harnessDone.future.then<TestResult>((void value) {
              return TestResult.harnessBailed;
            }),
            testDone.future.then<TestResult>((void value) {
              return TestResult.testBailed;
            }),
          ]);

          await Future.wait<void>(<Future<void>>[
            harnessToTest.cancel(),
            testToHarness.cancel(),
          ]);

          switch (testResult) {
            case TestResult.crashed:
              globals.printTrace('test $ourTestCount: process with pid ${process.pid} crashed');
              final int exitCode = await process.exitCode;
              subprocessActive = false;
              final String message = _getErrorMessage(
                  _getExitCodeMessage(
                      exitCode, 'before test harness closed its WebSocket'),
                  testPath,
                  shellPath);
              controller.sink.addError(message);
              // Awaited for with 'sink.done' below.
              unawaited(controller.sink.close());
              globals.printTrace('test $ourTestCount: waiting for controller sink to close');
              await controller.sink.done;
              break;
            case TestResult.harnessBailed:
            case TestResult.testBailed:
              if (testResult == TestResult.harnessBailed) {
                globals.printTrace('test $ourTestCount: process with pid ${process.pid} no longer needed by test harness');
              } else {
                assert(testResult == TestResult.testBailed);
                globals.printTrace('test $ourTestCount: process with pid ${process.pid} no longer needs test harness');
              }
              await watcher?.handleFinishedTest(
                  ProcessEvent(ourTestCount, process, processObservatoryUri));
              break;
          }
          break;
      }
    } on Exception catch (error, stack) {
      globals.printTrace('test $ourTestCount: error caught during test; ${controllerSinkClosed ? "reporting to console" : "sending to test framework"}');
      if (!controllerSinkClosed) {
        controller.sink.addError(error, stack);
      } else {
        globals.printError('unhandled error during test:\n$testPath\n$error\n$stack');
        outOfBandError ??= _AsyncError(error, stack);
      }
    } finally {
      globals.printTrace('test $ourTestCount: cleaning up...');
      // Finalizers are treated like a stack; run them in reverse order.
      for (final Finalizer finalizer in finalizers.reversed) {
        try {
          await finalizer();
        } on Exception catch (error, stack) {
          globals.printTrace('test $ourTestCount: error while cleaning up; ${controllerSinkClosed ? "reporting to console" : "sending to test framework"}');
          if (!controllerSinkClosed) {
            controller.sink.addError(error, stack);
          } else {
            globals.printError('unhandled error during finalization of test:\n$testPath\n$error\n$stack');
            outOfBandError ??= _AsyncError(error, stack);
          }
        }
      }
      if (!controllerSinkClosed) {
        // Waiting below with await.
        unawaited(controller.sink.close());
        globals.printTrace('test $ourTestCount: waiting for controller sink to close');
        await controller.sink.done;
      }
    }
    assert(!subprocessActive);
    assert(controllerSinkClosed);
    if (outOfBandError != null) {
      globals.printTrace('test $ourTestCount: finished with out-of-band failure');
    } else {
      globals.printTrace('test $ourTestCount: finished');
    }
    return outOfBandError;
  }

  String _createListenerDart(
    List<Finalizer> finalizers,
    int ourTestCount,
    String testPath,
    HttpServer server,
  ) {
    // Prepare a temporary directory to store the Dart file that will talk to us.
    final Directory tempDir = globals.fs.systemTempDirectory.createTempSync('flutter_test_listener.');
    finalizers.add(() async {
      globals.printTrace('test $ourTestCount: deleting temporary directory');
      tempDir.deleteSync(recursive: true);
    });

    // Prepare the Dart file that will talk to us and start the test.
    final File listenerFile = globals.fs.file('${tempDir.path}/listener.dart');
    listenerFile.createSync();
    listenerFile.writeAsStringSync(_generateTestMain(
      testUrl: globals.fs.path.toUri(globals.fs.path.absolute(testPath)),
    ));
    return listenerFile.path;
  }

  String _generateTestMain({
    Uri testUrl,
  }) {
    assert(testUrl.scheme == 'file');
    final File file = globals.fs.file(testUrl);
    return generateTestBootstrap(
      testUrl: testUrl,
      testConfigFile: findTestConfigFile(globals.fs.file(testUrl)),
      host: host,
      updateGoldens: updateGoldens,
      languageVersionHeader: determineLanguageVersion(
        file,
        _packageConfig[flutterProject?.manifest?.appName],
      ),
    );
  }


  File _cachedFontConfig;

  @override
  Future<dynamic> close() async {
    if (compiler != null) {
      await compiler.dispose();
      compiler = null;
    }
    if (fontsDirectory != null) {
      globals.printTrace('Deleting ${fontsDirectory.path}...');
      fontsDirectory.deleteSync(recursive: true);
      fontsDirectory = null;
    }
  }

  /// Returns a Fontconfig config file that limits font fallback to the
  /// artifact cache directory.
  File get _fontConfigFile {
    if (_cachedFontConfig != null) {
      return _cachedFontConfig;
    }

    final StringBuffer sb = StringBuffer();
    sb.writeln('<fontconfig>');
    sb.writeln('  <dir>${globals.cache.getCacheArtifacts().path}</dir>');
    sb.writeln('  <cachedir>/var/cache/fontconfig</cachedir>');
    sb.writeln('</fontconfig>');

    if (fontsDirectory == null) {
      fontsDirectory = globals.fs.systemTempDirectory.createTempSync('flutter_test_fonts.');
      globals.printTrace('Using this directory for fonts configuration: ${fontsDirectory.path}');
    }

    _cachedFontConfig = globals.fs.file('${fontsDirectory.path}/fonts.conf');
    _cachedFontConfig.createSync();
    _cachedFontConfig.writeAsStringSync(sb.toString());
    return _cachedFontConfig;
  }

  Future<Process> _startProcess(
    String executable,
    String testPath, {
    String packages,
    bool enableObservatory = false,
    bool startPaused = false,
    bool disableServiceAuthCodes = false,
    int observatoryPort,
    int serverPort,
  }) {
    assert(executable != null); // Please provide the path to the shell in the SKY_SHELL environment variable.
    assert(!startPaused || enableObservatory);
    final List<String> command = <String>[
      executable,
      if (enableObservatory) ...<String>[
        // Some systems drive the _FlutterPlatform class in an unusual way, where
        // only one test file is processed at a time, and the operating
        // environment hands out specific ports ahead of time in a cooperative
        // manner, where we're only allowed to open ports that were given to us in
        // advance like this. For those esoteric systems, we have this feature
        // whereby you can create _FlutterPlatform with a pair of ports.
        //
        // I mention this only so that you won't be tempted, as I was, to apply
        // the obvious simplification to this code and remove this entire feature.
        if (observatoryPort != null) '--observatory-port=$observatoryPort',
        if (startPaused) '--start-paused',
        if (disableServiceAuthCodes) '--disable-service-auth-codes',
      ]
      else
        '--disable-observatory',
      if (host.type == InternetAddressType.IPv6) '--ipv6',
      if (icudtlPath != null) '--icu-data-file-path=$icudtlPath',
      '--enable-checked-mode',
      '--verify-entry-points',
      '--enable-software-rendering',
      '--skia-deterministic-rendering',
      '--enable-dart-profiling',
      '--non-interactive',
      '--use-test-fonts',
      '--packages=$packages',
      if (nullAssertions)
        '--dart-flags=--null_assertions',
      testPath,
    ];

    globals.printTrace(command.join(' '));
    // If the FLUTTER_TEST environment variable has been set, then pass it on
    // for package:flutter_test to handle the value.
    //
    // If FLUTTER_TEST has not been set, assume from this context that this
    // call was invoked by the command 'flutter test'.
    final String flutterTest = globals.platform.environment.containsKey('FLUTTER_TEST')
        ? globals.platform.environment['FLUTTER_TEST']
        : 'true';
    final Map<String, String> environment = <String, String>{
      'FLUTTER_TEST': flutterTest,
      'FONTCONFIG_FILE': _fontConfigFile.path,
      'SERVER_PORT': serverPort.toString(),
      'APP_NAME': flutterProject?.manifest?.appName ?? '',
      if (buildTestAssets)
        'UNIT_TEST_ASSETS': globals.fs.path.join(flutterProject?.directory?.path ?? '', 'build', 'unit_test_assets'),
    };
    return globals.processManager.start(command, environment: environment);
  }

  void _pipeStandardStreamsToConsole(
    Process process, {
    Future<void> reportObservatoryUri(Uri uri),
  }) {

    const String observatoryString = 'Observatory listening on ';
    for (final Stream<List<int>> stream in <Stream<List<int>>>[
      process.stderr,
      process.stdout,
    ]) {
      stream
          .transform<String>(utf8.decoder)
          .transform<String>(const LineSplitter())
          .listen(
        (String line) async {
          if (line.startsWith("error: Unable to read Dart source 'package:test/")) {
            globals.printTrace('Shell: $line');
            globals.printError('\n\nFailed to load test harness. Are you missing a dependency on flutter_test?\n');
          } else if (line.startsWith(observatoryString)) {
            globals.printTrace('Shell: $line');
            try {
              final Uri uri = Uri.parse(line.substring(observatoryString.length));
              if (reportObservatoryUri != null) {
                await reportObservatoryUri(uri);
              }
            } on Exception catch (error) {
              globals.printError('Could not parse shell observatory port message: $error');
            }
          } else if (line != null) {
            globals.printStatus('Shell: $line');
          }
        },
        onError: (dynamic error) {
          globals. printError('shell console stream for process pid ${process.pid} experienced an unexpected error: $error');
        },
        cancelOnError: true,
      );
    }
  }

  String _getErrorMessage(String what, String testPath, String shellPath) {
    return '$what\nTest: $testPath\nShell: $shellPath\n\n';
  }

  String _getExitCodeMessage(int exitCode, String when) {
    switch (exitCode) {
      case 1:
        return 'Shell subprocess cleanly reported an error $when. Check the logs above for an error message.';
      case 0:
        return 'Shell subprocess ended cleanly $when. Did main() call exit()?';
      case -0x0f: // ProcessSignal.SIGTERM
        return 'Shell subprocess crashed with SIGTERM ($exitCode) $when.';
      case -0x0b: // ProcessSignal.SIGSEGV
        return 'Shell subprocess crashed with segmentation fault $when.';
      case -0x06: // ProcessSignal.SIGABRT
        return 'Shell subprocess crashed with SIGABRT ($exitCode) $when.';
      case -0x02: // ProcessSignal.SIGINT
        return 'Shell subprocess terminated by ^C (SIGINT, $exitCode) $when.';
      default:
        return 'Shell subprocess crashed with unexpected exit code $exitCode $when.';
    }
  }
}

// The [_shellProcessClosed] future can't have errors thrown on it because it
// crosses zones (it's fed in a zone created by the test package, but listened
// to by a parent zone, the same zone that calls [close] below).
//
// This is because Dart won't let errors that were fed into a Future in one zone
// propagate to listeners in another zone. (Specifically, the zone in which the
// future was completed with the error, and the zone in which the listener was
// registered, are what matters.)
//
// Because of this, the [_shellProcessClosed] future takes an [_AsyncError]
// object as a result. If it's null, it's as if it had completed correctly; if
// it's non-null, it contains the error and stack trace of the actual error, as
// if it had completed with that error.
class _FlutterPlatformStreamSinkWrapper<S> implements StreamSink<S> {
  _FlutterPlatformStreamSinkWrapper(this._parent, this._shellProcessClosed);

  final StreamSink<S> _parent;
  final Future<_AsyncError> _shellProcessClosed;

  @override
  Future<void> get done => _done.future;
  final Completer<void> _done = Completer<void>();

  @override
  Future<dynamic> close() {
    Future.wait<dynamic>(<Future<dynamic>>[
      _parent.close(),
      _shellProcessClosed,
    ]).then<void>(
      (List<dynamic> futureResults) {
        assert(futureResults.length == 2);
        assert(futureResults.first == null);
        final dynamic lastResult = futureResults.last;
        if (lastResult is _AsyncError) {
          _done.completeError(lastResult.error, lastResult.stack);
        } else {
          assert(lastResult == null);
          _done.complete();
        }
      },
      onError: _done.completeError,
    );
    return done;
  }

  @override
  void add(S event) => _parent.add(event);
  @override
  void addError(dynamic errorEvent, [ StackTrace stackTrace ]) => _parent.addError(errorEvent, stackTrace);
  @override
  Future<dynamic> addStream(Stream<S> stream) => _parent.addStream(stream);
}

@immutable
class _AsyncError {
  const _AsyncError(this.error, this.stack);
  final dynamic error;
  final StackTrace stack;
}