// Copyright (c) 2019, 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:collection';
import 'dart:convert';
// We need to use the 'io' prefix here, otherwise io.exitCode will shadow
// CommandOutput.exitCode in subclasses of CommandOutput.
import 'dart:io' as io;
import 'dart:math' as math;

import 'android.dart';
import 'browser_controller.dart';
import 'command.dart';
import 'command_output.dart';
import 'configuration.dart';
import 'dependency_graph.dart';
import 'output_log.dart';
import 'runtime_configuration.dart';
import 'test_case.dart';
import 'test_file.dart';
import 'test_progress.dart';
import 'test_suite.dart';
import 'utils.dart';

const unhandledCompilerExceptionExitCode = 253;
const parseFailExitCode = 245;

const _cannotOpenDisplayMessage = 'Gtk-WARNING **: cannot open display';
const _failedToRunCommandMessage = 'Failed to run command. return code=1';

typedef _StepFunction = Future<AdbCommandResult> Function();

class ProcessQueue {
  final TestConfiguration _globalConfiguration;
  final void Function() _allDone;
  final Graph<Command> _graph = Graph();
  final List<EventListener> _eventListener;

  ProcessQueue(
      this._globalConfiguration,
      int maxProcesses,
      int maxBrowserProcesses,
      List<TestSuite> testSuites,
      this._eventListener,
      this._allDone,
      [bool verbose = false,
      AdbDevicePool adbDevicePool]) {
    void setupForListing(TestCaseEnqueuer testCaseEnqueuer) {
      _graph.sealed.listen((_) {
        var testCases = testCaseEnqueuer.remainingTestCases.toList();
        testCases.sort((a, b) => a.displayName.compareTo(b.displayName));

        print("\nGenerating all matching test cases ....\n");

        for (var testCase in testCases) {
          eventFinishedTestCase(testCase);
          var outcomes = testCase.expectedOutcomes.map((o) => '$o').toList()
            ..sort();
          print("${testCase.displayName}   "
              "Expectations: ${outcomes.join(', ')}   "
              "Configuration: '${testCase.configurationString}'");
        }
        eventAllTestsKnown();
      });
    }

    TestCaseEnqueuer testCaseEnqueuer;
    CommandQueue commandQueue;

    void setupForRunning(TestCaseEnqueuer testCaseEnqueuer) {
      Timer _debugTimer;
      // If we haven't seen a single test finishing during a 10 minute period
      // something is definitely wrong, so we dump the debugging information.
      final debugTimerDuration = const Duration(minutes: 10);

      void cancelDebugTimer() {
        if (_debugTimer != null) {
          _debugTimer.cancel();
        }
      }

      void resetDebugTimer() {
        cancelDebugTimer();
        _debugTimer = Timer(debugTimerDuration, () {
          print("The debug timer of test.dart expired. Please report this issue"
              " to dart-engprod@ and provide the following information:");
          print("");
          print("Graph is sealed: ${_graph.isSealed}");
          print("");
          _graph.dumpCounts();
          print("");
          var unfinishedNodeStates = [
            NodeState.initialized,
            NodeState.waiting,
            NodeState.enqueuing,
            NodeState.processing
          ];

          for (var nodeState in unfinishedNodeStates) {
            if (_graph.stateCount(nodeState) > 0) {
              print("Commands in state '$nodeState':");
              print("=================================");
              print("");
              for (var node in _graph.nodes) {
                if (node.state == nodeState) {
                  var command = node.data;
                  var testCases = testCaseEnqueuer.command2testCases[command];
                  print("  Command: $command");
                  for (var testCase in testCases) {
                    print("    Enqueued by: ${testCase.configurationString} "
                        "-- ${testCase.displayName}");
                  }
                  print("");
                }
              }
              print("");
              print("");
            }
          }

          if (commandQueue != null) {
            commandQueue.dumpState();
          }
        });
      }

      // When the graph building is finished, notify event listeners.
      _graph.sealed.listen((_) {
        eventAllTestsKnown();
      });

      // Queue commands as they become "runnable"
      CommandEnqueuer(_graph);

      // CommandExecutor will execute commands
      var executor = CommandExecutorImpl(
          _globalConfiguration, maxProcesses, maxBrowserProcesses,
          adbDevicePool: adbDevicePool);

      // Run "runnable commands" using [executor] subject to
      // maxProcesses/maxBrowserProcesses constraint
      commandQueue = CommandQueue(_graph, testCaseEnqueuer, executor,
          maxProcesses, maxBrowserProcesses, verbose);

      // Finish test cases when all commands were run (or some failed)
      var testCaseCompleter =
          TestCaseCompleter(_graph, testCaseEnqueuer, commandQueue);
      testCaseCompleter.finishedTestCases.listen((TestCase finishedTestCase) {
        resetDebugTimer();

        eventFinishedTestCase(finishedTestCase);
      }, onDone: () {
        // Wait until the commandQueue/exectutor is done (it may need to stop
        // batch runners, browser controllers, ....)
        commandQueue.done.then((_) {
          cancelDebugTimer();
          eventAllTestsDone();
        });
      });

      resetDebugTimer();
    }

    // Build up the dependency graph
    testCaseEnqueuer = TestCaseEnqueuer(_graph, eventTestAdded);

    // Either list or run the tests
    if (_globalConfiguration.listTests) {
      setupForListing(testCaseEnqueuer);
    } else {
      setupForRunning(testCaseEnqueuer);
    }

    // Start enqueing all TestCases
    testCaseEnqueuer.enqueueTestSuites(testSuites);
  }

  void eventFinishedTestCase(TestCase testCase) {
    for (var listener in _eventListener) {
      listener.done(testCase);
    }
  }

  void eventTestAdded(TestCase testCase) {
    for (var listener in _eventListener) {
      listener.testAdded();
    }
  }

  void eventAllTestsKnown() {
    for (var listener in _eventListener) {
      listener.allTestsKnown();
    }
  }

  void eventAllTestsDone() {
    for (var listener in _eventListener) {
      listener.allDone();
    }
    _allDone();
  }
}

/// [TestCaseEnqueuer] takes a list of TestSuites, generates TestCases and
/// builds a dependency graph of all commands in every TestSuite.
///
/// It maintains three helper data structures:
///
/// - command2node: A mapping from a [Command] to a node in the dependency
///   graph.
///
/// - command2testCases: A mapping from [Command] to all TestCases that it is
///   part of.
///
/// - remainingTestCases: A set of TestCases that were enqueued but are not
///   finished.
///
/// [Command] and it's subclasses all have hashCode/operator== methods defined
/// on them, so we can safely use them as keys in Map/Set objects.
class TestCaseEnqueuer {
  final Graph<Command> graph;
  final Function _onTestCaseAdded;

  final command2node = <Command, Node<Command>>{};
  final command2testCases = <Command, List<TestCase>>{};
  final remainingTestCases = <TestCase>{};

  TestCaseEnqueuer(this.graph, this._onTestCaseAdded);

  void enqueueTestSuites(List<TestSuite> testSuites) {
    // Cache information about test cases per test suite. For multiple
    // configurations there is no need to repeatedly search the file
    // system, generate tests, and search test files for options.
    var testCache = <String, List<TestFile>>{};

    for (var suite in testSuites) {
      suite.findTestCases(_add, testCache);
    }

    // We're finished with building the dependency graph.
    graph.seal();
  }

  /// Adds a test case to the list of active test cases, and adds its commands
  /// to the dependency graph of commands.
  ///
  /// If the repeat flag is > 1, replicates the test case and its commands,
  /// adding an index field with a distinct value to each of the copies.
  ///
  /// Each copy of the test case depends on the previous copy of the test
  /// case completing, with its first command having a dependency on the last
  /// command of the previous copy of the test case. This dependency is
  /// marked as a "timingDependency", so that it doesn't depend on the previous
  /// test completing successfully, just on it completing.
  void _add(TestCase testCase) {
    Node<Command> lastNode;
    for (var i = 0; i < testCase.configuration.repeat; ++i) {
      if (i > 0) {
        testCase = testCase.indexedCopy(i);
      }
      remainingTestCases.add(testCase);
      var isFirstCommand = true;
      for (var command in testCase.commands) {
        // Make exactly *one* node in the dependency graph for every command.
        // This ensures that we never have two commands c1 and c2 in the graph
        // with "c1 == c2".
        var node = command2node[command];
        if (node == null) {
          var requiredNodes =
              (lastNode != null) ? [lastNode] : <Node<Command>>[];
          node = graph.add(command, requiredNodes,
              timingDependency: isFirstCommand);
          command2node[command] = node;
          command2testCases[command] = <TestCase>[];
        }
        // Keep mapping from command to all testCases that refer to it.
        command2testCases[command].add(testCase);

        lastNode = node;
        isFirstCommand = false;
      }
      _onTestCaseAdded(testCase);
    }
  }
}

/// [CommandEnqueuer] will:
///
/// - Change node.state to NodeState.enqueuing as soon as all dependencies have
///   a state of NodeState.Successful.
/// - Change node.state to NodeState.unableToRun if one or more dependencies
///   have a state of NodeState.failed/NodeState.unableToRun.
class CommandEnqueuer {
  static const _initStates = [NodeState.initialized, NodeState.waiting];

  static const _finishedStates = [
    NodeState.successful,
    NodeState.failed,
    NodeState.unableToRun
  ];

  final Graph<Command> _graph;

  CommandEnqueuer(this._graph) {
    _graph.added.listen(_changeNodeStateIfNecessary);

    _graph.changed.listen((event) {
      if (event.from == NodeState.waiting ||
          event.from == NodeState.processing) {
        if (_finishedStates.contains(event.to)) {
          for (var dependentNode in event.node.neededFor) {
            _changeNodeStateIfNecessary(dependentNode);
          }
        }
      }
    });
  }

  /// Called when either a new node was added or if one of it's dependencies
  /// changed it's state.
  void _changeNodeStateIfNecessary(Node<Command> node) {
    if (_initStates.contains(node.state)) {
      var allDependenciesFinished =
          node.dependencies.every((dep) => _finishedStates.contains(dep.state));
      var anyDependenciesUnsuccessful = node.dependencies.any((dep) =>
          [NodeState.failed, NodeState.unableToRun].contains(dep.state));
      var allDependenciesSuccessful =
          node.dependencies.every((dep) => dep.state == NodeState.successful);

      var newState = NodeState.waiting;
      if (allDependenciesSuccessful ||
          (allDependenciesFinished && node.timingDependency)) {
        newState = NodeState.enqueuing;
      } else if (anyDependenciesUnsuccessful) {
        newState = NodeState.unableToRun;
      }
      if (node.state != newState) {
        _graph.changeState(node, newState);
      }
    }
  }
}

/// [CommandQueue] will listen for nodes entering the NodeState.enqueuing state,
/// queue them up and run them. While nodes are processed they will be in the
/// NodeState.processing state. After running a command, the node will change
/// to a state of NodeState.Successful or NodeState.failed.
///
/// It provides a synchronous stream [completedCommands] which provides the
/// [CommandOutput]s for the finished commands.
///
/// It provides a [done] future, which will complete once there are no more
/// nodes left in the states Initialized/Waiting/Enqueing/Processing
/// and the [executor] has cleaned up its resources.
class CommandQueue {
  final Graph<Command> graph;
  final CommandExecutor executor;
  final TestCaseEnqueuer enqueuer;

  final _runQueue = Queue<Command>();
  final _commandOutputStream = StreamController<CommandOutput>(sync: true);
  final _completer = Completer<Null>();

  int _numProcesses = 0;
  final int _maxProcesses;
  int _numBrowserProcesses = 0;
  final int _maxBrowserProcesses;
  bool _finishing = false;
  final bool _verbose;

  CommandQueue(this.graph, this.enqueuer, this.executor, this._maxProcesses,
      this._maxBrowserProcesses, this._verbose) {
    graph.changed.listen((event) {
      if (event.to == NodeState.enqueuing) {
        assert(event.from == NodeState.initialized ||
            event.from == NodeState.waiting);
        graph.changeState(event.node, NodeState.processing);
        var command = event.node.data;
        if (event.node.dependencies.isNotEmpty) {
          _runQueue.addFirst(command);
        } else {
          _runQueue.add(command);
        }
        Timer.run(_tryRunNextCommand);
      } else if (event.to == NodeState.unableToRun) {
        _checkDone();
      }
    });

    // We're finished if the graph is sealed and all nodes are in a finished
    // state (Successful, Failed or UnableToRun).
    // So we're calling '_checkDone()' to check whether that condition is met
    // and we can cleanup.
    graph.sealed.listen((event) {
      _checkDone();
    });
  }

  Stream<CommandOutput> get completedCommands => _commandOutputStream.stream;

  Future get done => _completer.future;

  void _tryRunNextCommand() {
    _checkDone();

    if (_numProcesses < _maxProcesses && _runQueue.isNotEmpty) {
      var command = _runQueue.removeFirst();
      var isBrowserCommand = command is BrowserTestCommand;

      if (isBrowserCommand && _numBrowserProcesses == _maxBrowserProcesses) {
        // If there is no free browser runner, put it back into the queue.
        _runQueue.add(command);
        // Don't lose a process.
        Timer(const Duration(milliseconds: 100), _tryRunNextCommand);
        return;
      }

      _numProcesses++;
      if (isBrowserCommand) _numBrowserProcesses++;

      var node = enqueuer.command2node[command];
      Iterable<TestCase> testCases = enqueuer.command2testCases[command];
      // If a command is part of many TestCases we set the timeout to be
      // the maximum over all [TestCase.timeout]s. At some point, we might
      // eliminate [TestCase.timeout] completely and move it to [Command].
      var timeout =
          testCases.map((TestCase test) => test.timeout).fold(0, math.max);

      if (_verbose) {
        print('Running "${command.displayName}" command: $command');
      }

      executor.runCommand(node, command, timeout).then((CommandOutput output) {
        assert(command == output.command);

        _commandOutputStream.add(output);
        if (output.canRunDependendCommands) {
          graph.changeState(node, NodeState.successful);
        } else {
          graph.changeState(node, NodeState.failed);
        }

        _numProcesses--;
        if (isBrowserCommand) _numBrowserProcesses--;

        // Don't lose a process
        Timer.run(_tryRunNextCommand);
      });
    }
  }

  void _checkDone() {
    if (!_finishing &&
        _runQueue.isEmpty &&
        _numProcesses == 0 &&
        graph.isSealed &&
        graph.stateCount(NodeState.initialized) == 0 &&
        graph.stateCount(NodeState.waiting) == 0 &&
        graph.stateCount(NodeState.enqueuing) == 0 &&
        graph.stateCount(NodeState.processing) == 0) {
      _finishing = true;
      executor.cleanup().then((_) {
        _completer.complete();
        _commandOutputStream.close();
      });
    }
  }

  void dumpState() {
    print("");
    print("CommandQueue state:");
    print("  Processes: used: $_numProcesses max: $_maxProcesses");
    print("  BrowserProcesses: used: $_numBrowserProcesses "
        "max: $_maxBrowserProcesses");
    print("  Finishing: $_finishing");
    print("  Queue (length = ${_runQueue.length}):");
    for (var command in _runQueue) {
      print("      $command");
    }
  }
}

/// [CommandExecutor] is responsible for executing commands. It will make sure
/// that the following two constraints are satisfied
///  - `numberOfProcessesUsed <= maxProcesses`
///  - `numberOfBrowserProcessesUsed <= maxBrowserProcesses`
///
/// It provides a [runCommand] method which will complete with a
/// [CommandOutput] object.
///
/// It provides a [cleanup] method to free all the allocated resources.
abstract class CommandExecutor {
  Future cleanup();
  // TODO(kustermann): The [timeout] parameter should be a property of Command.
  Future<CommandOutput> runCommand(
      Node<Command> node, Command command, int timeout);
}

class CommandExecutorImpl implements CommandExecutor {
  final TestConfiguration globalConfiguration;
  final int maxProcesses;
  final int maxBrowserProcesses;
  AdbDevicePool adbDevicePool;

  /// For dart2js and analyzer batch processing,
  /// we keep a list of batch processes.
  final _batchProcesses = <String, List<BatchRunnerProcess>>{};

  /// We keep a BrowserTestRunner for every configuration.
  final _browserTestRunners = <TestConfiguration, BrowserTestRunner>{};

  bool _finishing = false;

  CommandExecutorImpl(
      this.globalConfiguration, this.maxProcesses, this.maxBrowserProcesses,
      {this.adbDevicePool});

  Future cleanup() {
    assert(!_finishing);
    _finishing = true;

    Future _terminateBatchRunners() {
      var futures = <Future>[];
      for (var runners in _batchProcesses.values) {
        futures.addAll(runners.map((runner) => runner.terminate()));
      }
      return Future.wait(futures);
    }

    Future _terminateBrowserRunners() {
      var futures =
          _browserTestRunners.values.map((runner) => runner.terminate());
      return Future.wait(futures);
    }

    return Future.wait([
      _terminateBatchRunners(),
      _terminateBrowserRunners(),
    ]);
  }

  Future<CommandOutput> runCommand(node, Command command, int timeout) {
    assert(!_finishing);

    Future<CommandOutput> runCommand(int retriesLeft) {
      return _runCommand(command, timeout).then((CommandOutput output) {
        if (retriesLeft > 0 && shouldRetryCommand(output)) {
          DebugLogger.warning("Rerunning Command: ($retriesLeft "
              "attempt(s) remains) [cmd: $command]");
          return runCommand(retriesLeft - 1);
        } else {
          return Future.value(output);
        }
      });
    }

    return runCommand(command.maxNumRetries);
  }

  Future<CommandOutput> _runCommand(Command command, int timeout) {
    if (command is BrowserTestCommand) {
      return _startBrowserControllerTest(command, timeout);
    } else if (command is VMKernelCompilationCommand) {
      // For now, we always run vm_compile_to_kernel in batch mode.
      var name = command.displayName;
      assert(name == 'vm_compile_to_kernel');
      return _getBatchRunner(name)
          .runCommand(name, command, timeout, command.arguments);
    } else if (command is CompilationCommand &&
        globalConfiguration.batchDart2JS &&
        command.displayName == 'dart2js') {
      return _getBatchRunner("dart2js")
          .runCommand("dart2js", command, timeout, command.arguments);
    } else if (command is AnalysisCommand && globalConfiguration.batch) {
      return _getBatchRunner(command.displayName)
          .runCommand(command.displayName, command, timeout, command.arguments);
    } else if (command is CompilationCommand &&
        (command.displayName == 'dartdevc' ||
            command.displayName == 'dartdevk' ||
            command.displayName == 'fasta') &&
        globalConfiguration.batch) {
      return _getBatchRunner(command.displayName)
          .runCommand(command.displayName, command, timeout, command.arguments);
    } else if (command is ScriptCommand) {
      return command.run();
    } else if (command is AdbPrecompilationCommand ||
        command is AdbDartkCommand) {
      assert(adbDevicePool != null);
      return adbDevicePool.acquireDevice().then((AdbDevice device) async {
        try {
          if (command is AdbPrecompilationCommand) {
            return await _runAdbPrecompilationCommand(device, command, timeout);
          } else {
            return await _runAdbDartkCommand(
                device, command as AdbDartkCommand, timeout);
          }
        } finally {
          adbDevicePool.releaseDevice(device);
        }
      });
    } else if (command is VMBatchCommand) {
      var name = command.displayName;
      return _getBatchRunner(command.displayName + command.dartFile)
          .runCommand(name, command, timeout, command.arguments);
    } else if (command is CompilationCommand &&
        command.displayName == 'babel') {
      return RunningProcess(command, timeout,
              configuration: globalConfiguration,
              outputFile: io.File(command.outputFile))
          .run();
    } else if (command is ProcessCommand) {
      return RunningProcess(command, timeout,
              configuration: globalConfiguration)
          .run();
    } else if (command is RRCommand) {
      return command.run(timeout);
    } else {
      throw ArgumentError("Unknown command type ${command.runtimeType}.");
    }
  }

  List<_StepFunction> _pushLibraries(AdbCommand command, AdbDevice device,
      String deviceDir, String deviceTestDir) {
    var steps = <_StepFunction>[];
    for (var lib in command.extraLibraries) {
      var libName = "lib$lib.so";
      steps.add(() => device.runAdbCommand([
            'push',
            '${command.buildPath}/$libName',
            '$deviceTestDir/$libName'
          ]));
    }
    return steps;
  }

  Future<CommandOutput> _runAdbPrecompilationCommand(
      AdbDevice device, AdbPrecompilationCommand command, int timeout) async {
    var buildPath = command.buildPath;
    var processTest = command.processTestFilename;
    var testdir = command.precompiledTestDirectory;
    var arguments = command.arguments;
    var devicedir = DartPrecompiledAdbRuntimeConfiguration.deviceDir;
    var deviceTestDir = DartPrecompiledAdbRuntimeConfiguration.deviceTestDir;

    // We copy all the files which the vm precompiler puts into the test
    // directory.
    var files = io.Directory(testdir)
        .listSync()
        .map((file) => file.path)
        .map((path) => path.substring(path.lastIndexOf('/') + 1))
        .toList();

    var timeoutDuration = Duration(seconds: timeout);

    var steps = <_StepFunction>[];

    steps.add(() => device.runAdbShellCommand(['rm', '-Rf', deviceTestDir]));
    steps.add(() => device.runAdbShellCommand(['mkdir', '-p', deviceTestDir]));
    steps.add(() => device.pushCachedData('$buildPath/dart_precompiled_runtime',
        '$devicedir/dart_precompiled_runtime'));
    steps.add(
        () => device.pushCachedData(processTest, '$devicedir/process_test'));
    steps.add(() => device.runAdbShellCommand([
          'chmod',
          '777',
          '$devicedir/dart_precompiled_runtime $devicedir/process_test'
        ]));

    steps.addAll(_pushLibraries(command, device, devicedir, deviceTestDir));

    for (var file in files) {
      steps.add(() => device
          .runAdbCommand(['push', '$testdir/$file', '$deviceTestDir/$file']));
    }

    steps.add(() => device.runAdbShellCommand(
        [
          'export LD_LIBRARY_PATH=\$LD_LIBRARY_PATH:$deviceTestDir;'
              '$devicedir/dart_precompiled_runtime',
          '--android-log-to-stderr'
        ]..addAll(arguments),
        timeout: timeoutDuration));

    var stopwatch = Stopwatch()..start();
    var writer = StringBuffer();

    await device.waitForBootCompleted();
    await device.waitForDevice();

    AdbCommandResult result;
    for (var i = 0; i < steps.length; i++) {
      var fun = steps[i];
      var commandStopwatch = Stopwatch()..start();
      result = await fun();

      writer.writeln("Executing ${result.command}");
      if (result.stdout.isNotEmpty) {
        writer.writeln("Stdout:\n${result.stdout.trim()}");
      }
      if (result.stderr.isNotEmpty) {
        writer.writeln("Stderr:\n${result.stderr.trim()}");
      }
      writer.writeln("ExitCode: ${result.exitCode}");
      writer.writeln("Time: ${commandStopwatch.elapsed}");
      writer.writeln("");

      // If one command fails, we stop processing the others and return
      // immediately.
      if (result.exitCode != 0) break;
    }
    return command.createOutput(result.exitCode, result.timedOut,
        utf8.encode('$writer'), [], stopwatch.elapsed, false);
  }

  Future<CommandOutput> _runAdbDartkCommand(
      AdbDevice device, AdbDartkCommand command, int timeout) async {
    var buildPath = command.buildPath;
    var hostKernelFile = command.kernelFile;
    var arguments = command.arguments;
    var devicedir = DartkAdbRuntimeConfiguration.deviceDir;
    var deviceTestDir = DartkAdbRuntimeConfiguration.deviceTestDir;

    var timeoutDuration = Duration(seconds: timeout);

    var steps = <_StepFunction>[];

    steps.add(() => device.runAdbShellCommand(['rm', '-Rf', deviceTestDir]));
    steps.add(() => device.runAdbShellCommand(['mkdir', '-p', deviceTestDir]));
    steps
        .add(() => device.pushCachedData("$buildPath/dart", '$devicedir/dart'));
    steps.add(() => device
        .runAdbCommand(['push', hostKernelFile, '$deviceTestDir/out.dill']));

    steps.addAll(_pushLibraries(command, device, devicedir, deviceTestDir));

    steps.add(() => device.runAdbShellCommand(
        [
          'export LD_LIBRARY_PATH=\$LD_LIBRARY_PATH:$deviceTestDir;'
              '$devicedir/dart',
          '--android-log-to-stderr'
        ]..addAll(arguments),
        timeout: timeoutDuration));

    var stopwatch = Stopwatch()..start();
    var writer = StringBuffer();

    await device.waitForBootCompleted();
    await device.waitForDevice();

    AdbCommandResult result;
    for (var i = 0; i < steps.length; i++) {
      var step = steps[i];
      var commandStopwatch = Stopwatch()..start();
      result = await step();

      writer.writeln("Executing ${result.command}");
      if (result.stdout.isNotEmpty) {
        writer.writeln("Stdout:\n${result.stdout.trim()}");
      }
      if (result.stderr.isNotEmpty) {
        writer.writeln("Stderr:\n${result.stderr.trim()}");
      }
      writer.writeln("ExitCode: ${result.exitCode}");
      writer.writeln("Time: ${commandStopwatch.elapsed}");
      writer.writeln("");

      // If one command fails, we stop processing the others and return
      // immediately.
      if (result.exitCode != 0) break;
    }
    return command.createOutput(result.exitCode, result.timedOut,
        utf8.encode('$writer'), [], stopwatch.elapsed, false);
  }

  BatchRunnerProcess _getBatchRunner(String identifier) {
    // Start batch processes if needed.
    var runners = _batchProcesses[identifier];
    if (runners == null) {
      runners = List<BatchRunnerProcess>(maxProcesses);
      for (var i = 0; i < maxProcesses; i++) {
        runners[i] = BatchRunnerProcess(useJson: identifier == "fasta");
      }
      _batchProcesses[identifier] = runners;
    }

    for (var runner in runners) {
      if (!runner._currentlyRunning) return runner;
    }
    throw Exception('Unable to find inactive batch runner.');
  }

  Future<CommandOutput> _startBrowserControllerTest(
      BrowserTestCommand browserCommand, int timeout) {
    var completer = Completer<CommandOutput>();

    callback(BrowserTestOutput output) {
      completer.complete(BrowserCommandOutput(browserCommand, output));
    }

    var browserTest = BrowserTest(browserCommand.url, callback, timeout);
    _getBrowserTestRunner(browserCommand.configuration).then((testRunner) {
      testRunner.enqueueTest(browserTest);
    });

    return completer.future;
  }

  Future<BrowserTestRunner> _getBrowserTestRunner(
      TestConfiguration configuration) async {
    if (_browserTestRunners[configuration] == null) {
      var testRunner = BrowserTestRunner(
          configuration, globalConfiguration.localIP, maxBrowserProcesses);
      if (globalConfiguration.isVerbose) {
        testRunner.logger = DebugLogger.info;
      }
      _browserTestRunners[configuration] = testRunner;
      await testRunner.start();
    }
    return _browserTestRunners[configuration];
  }
}

bool shouldRetryCommand(CommandOutput output) {
  if (!output.successful) {
    List<String> stdout, stderr;

    decodeOutput() {
      if (stdout == null && stderr == null) {
        stdout = decodeUtf8(output.stderr).split("\n");
        stderr = decodeUtf8(output.stderr).split("\n");
      }
    }

    final command = output.command;

    // The dartk batch compiler sometimes runs out of memory. In such a case we
    // will retry running it.
    if (command is VMKernelCompilationCommand) {
      if (output.hasCrashed) {
        bool containsOutOfMemoryMessage(String line) {
          return line.contains('Exhausted heap space, trying to allocat');
        }

        decodeOutput();
        if (stdout.any(containsOutOfMemoryMessage) ||
            stderr.any(containsOutOfMemoryMessage)) {
          return true;
        }
      }
    }

    if (io.Platform.operatingSystem == 'linux') {
      decodeOutput();
      // No matter which command we ran: If we get failures due to the
      // "xvfb-run" issue 7564, try re-running the test.
      bool containsFailureMsg(String line) {
        return line.contains(_cannotOpenDisplayMessage) ||
            line.contains(_failedToRunCommandMessage);
      }

      if (stdout.any(containsFailureMsg) || stderr.any(containsFailureMsg)) {
        return true;
      }
    }
  }
  return false;
}

/// [TestCaseCompleter] will listen for
/// NodeState.processing -> NodeState.{successful,failed} state changes and
/// will complete a TestCase if it is finished.
///
/// It provides a stream [finishedTestCases], which will stream all TestCases
/// once they're finished. After all TestCases are done, the stream will be
/// closed.
class TestCaseCompleter {
  static const _completedStates = [NodeState.failed, NodeState.successful];

  final Graph<Command> _graph;
  final TestCaseEnqueuer _enqueuer;
  final CommandQueue _commandQueue;

  final Map<Command, CommandOutput> _outputs = {};
  final StreamController<TestCase> _controller = StreamController();
  bool _closed = false;

  TestCaseCompleter(this._graph, this._enqueuer, this._commandQueue) {
    var finishedRemainingTestCases = false;

    // Store all the command outputs -- they will be delivered synchronously
    // (i.e. before state changes in the graph)
    _commandQueue.completedCommands.listen((CommandOutput output) {
      _outputs[output.command] = output;
    }, onDone: () {
      _completeTestCasesIfPossible(List.from(_enqueuer.remainingTestCases));
      finishedRemainingTestCases = true;
      assert(_enqueuer.remainingTestCases.isEmpty);
      _checkDone();
    });

    // Listen for NodeState.Processing -> NodeState.{Successful,Failed}
    // changes.
    _graph.changed.listen((event) {
      if (event.from == NodeState.processing && !finishedRemainingTestCases) {
        var command = event.node.data;

        assert(_completedStates.contains(event.to));
        assert(_outputs[command] != null);

        _completeTestCasesIfPossible(_enqueuer.command2testCases[command]);
        _checkDone();
      }
    });

    // Listen also for GraphSealedEvents. If there is not a single node in the
    // graph, we still want to finish after the graph was sealed.
    _graph.sealed.listen((_) {
      if (!_closed && _enqueuer.remainingTestCases.isEmpty) {
        _controller.close();
        _closed = true;
      }
    });
  }

  Stream<TestCase> get finishedTestCases => _controller.stream;

  void _checkDone() {
    if (!_closed && _graph.isSealed && _enqueuer.remainingTestCases.isEmpty) {
      _controller.close();
      _closed = true;
    }
  }

  void _completeTestCasesIfPossible(Iterable<TestCase> testCases) {
    // Update TestCases with command outputs.
    for (var test in testCases) {
      for (var icommand in test.commands) {
        var output = _outputs[icommand];
        if (output != null) {
          test.commandOutputs[icommand] = output;
        }
      }
    }

    void completeTestCase(TestCase testCase) {
      if (_enqueuer.remainingTestCases.contains(testCase)) {
        _controller.add(testCase);
        _enqueuer.remainingTestCases.remove(testCase);
      } else {
        DebugLogger.error("${testCase.displayName} would be finished twice");
      }
    }

    for (var testCase in testCases) {
      // Ask the [testCase] if it's done. Note that we assume, that
      // [TestCase.isFinished] will return true if all commands were executed
      // or if a previous one failed.
      if (testCase.isFinished) {
        completeTestCase(testCase);
      }
    }
  }
}

class BatchRunnerProcess {
  /// When true, the command line is passed to the test runner as a
  /// JSON-encoded list of strings.
  final bool _useJson;

  Completer<CommandOutput> _completer;
  ProcessCommand _command;
  List<String> _arguments;
  String _runnerType;

  io.Process _process;
  Map<String, String> _processEnvironmentOverrides;
  Completer<Null> _stdoutCompleter;
  Completer<Null> _stderrCompleter;
  StreamSubscription<String> _stdoutSubscription;
  StreamSubscription<String> _stderrSubscription;
  Function _processExitHandler;

  bool _currentlyRunning = false;
  OutputLog _testStdout;
  OutputLog _testStderr;
  String _status;
  DateTime _startTime;
  Timer _timer;
  int _testCount = 0;

  BatchRunnerProcess({bool useJson = true}) : _useJson = useJson;

  Future<CommandOutput> runCommand(String runnerType, ProcessCommand command,
      int timeout, List<String> arguments) {
    assert(_completer == null);
    assert(!_currentlyRunning);

    _completer = Completer();
    var sameRunnerType = _runnerType == runnerType &&
        _dictEquals(_processEnvironmentOverrides, command.environmentOverrides);
    _runnerType = runnerType;
    _currentlyRunning = true;
    _command = command;
    _arguments = arguments;
    _processEnvironmentOverrides = command.environmentOverrides;

    // TODO(jmesserly): this restarts `dartdevc --batch` to work around a
    // memory leak, see https://github.com/dart-lang/sdk/issues/30314.
    var clearMemoryLeak = command is CompilationCommand &&
        command.displayName == 'dartdevc' &&
        ++_testCount % 100 == 0;
    if (_process == null) {
      // Start process if not yet started.
      _startProcess(() {
        doStartTest(command, timeout);
      });
    } else if (!sameRunnerType || clearMemoryLeak) {
      // Restart this runner with the right executable for this test if needed.
      _processExitHandler = (_) {
        _startProcess(() {
          doStartTest(command, timeout);
        });
      };
      _process.kill();
      _stdoutSubscription.cancel();
      _stderrSubscription.cancel();
    } else {
      doStartTest(command, timeout);
    }
    return _completer.future;
  }

  Future<bool> terminate() {
    if (_process == null) return Future.value(true);
    var terminateCompleter = Completer<bool>();
    final sigkillTimer = Timer(const Duration(seconds: 5), () {
      _process.kill(io.ProcessSignal.sigkill);
    });
    _processExitHandler = (_) {
      sigkillTimer.cancel();
      terminateCompleter.complete(true);
    };
    _process.kill();
    _stdoutSubscription.cancel();
    _stderrSubscription.cancel();

    return terminateCompleter.future;
  }

  void doStartTest(Command command, int timeout) {
    _startTime = DateTime.now();
    _testStdout = OutputLog();
    _testStderr = OutputLog();
    _status = null;
    _stdoutCompleter = Completer();
    _stderrCompleter = Completer();
    _timer = Timer(Duration(seconds: timeout), _timeoutHandler);

    var line = _createArgumentsLine(_arguments, timeout);
    _process.stdin.write(line);
    _stdoutSubscription.resume();
    _stderrSubscription.resume();
    Future.wait([_stdoutCompleter.future, _stderrCompleter.future])
        .then((_) => _reportResult());
  }

  String _createArgumentsLine(List<String> arguments, int timeout) {
    if (_useJson) {
      return "${jsonEncode(arguments)}\n";
    } else {
      return arguments.join(' ') + '\n';
    }
  }

  void _reportResult() {
    if (!_currentlyRunning) return;

    var outcome = _status.split(" ")[2];
    var exitCode = 0;
    if (outcome == "CRASH") exitCode = unhandledCompilerExceptionExitCode;
    if (outcome == "PARSE_FAIL") exitCode = parseFailExitCode;
    if (outcome == "FAIL" || outcome == "TIMEOUT") exitCode = 1;
    var output = _command.createOutput(
        exitCode,
        outcome == "TIMEOUT",
        _testStdout.toList(),
        _testStderr.toList(),
        DateTime.now().difference(_startTime),
        false);
    assert(_completer != null);
    _completer.complete(output);
    _completer = null;
    _currentlyRunning = false;
  }

  void Function(int) makeExitHandler(String status) {
    return (int exitCode) {
      if (_currentlyRunning) {
        if (_timer != null) _timer.cancel();
        _status = status;
        _stdoutSubscription.cancel();
        _stderrSubscription.cancel();
        _startProcess(_reportResult);
      } else {
        // No active test case running.
        _process = null;
      }
    };
  }

  void _timeoutHandler() {
    _processExitHandler = makeExitHandler(">>> TEST TIMEOUT");
    _process.kill();
  }

  void _startProcess(void Function() callback) {
    assert(_command is ProcessCommand);
    var executable = _command.executable;
    var arguments = _command.batchArguments.toList();
    arguments.add('--batch');
    var environment = Map<String, String>.from(io.Platform.environment);
    if (_processEnvironmentOverrides != null) {
      for (var key in _processEnvironmentOverrides.keys) {
        environment[key] = _processEnvironmentOverrides[key];
      }
    }
    var processFuture =
        io.Process.start(executable, arguments, environment: environment);
    processFuture.then<dynamic>((io.Process p) {
      _process = p;

      var _stdoutStream = _process.stdout
          .transform(utf8.decoder)
          .transform(const LineSplitter());
      _stdoutSubscription = _stdoutStream.listen((String line) {
        if (line.startsWith('>>> TEST')) {
          _status = line;
        } else if (line.startsWith('>>> BATCH')) {
          // ignore
        } else if (line.startsWith('>>> ')) {
          throw Exception("Unexpected command from batch runner: '$line'.");
        } else {
          _testStdout.add(encodeUtf8(line));
          _testStdout.add("\n".codeUnits);
        }
        if (_status != null) {
          _stdoutSubscription.pause();
          _timer.cancel();
          _stdoutCompleter.complete(null);
        }
      });
      _stdoutSubscription.pause();

      var _stderrStream = _process.stderr
          .transform(utf8.decoder)
          .transform(const LineSplitter());
      _stderrSubscription = _stderrStream.listen((String line) {
        if (line.startsWith('>>> EOF STDERR')) {
          _stderrSubscription.pause();
          _stderrCompleter.complete(null);
        } else {
          _testStderr.add(encodeUtf8(line));
          _testStderr.add("\n".codeUnits);
        }
      });
      _stderrSubscription.pause();

      _processExitHandler = makeExitHandler(">>> TEST CRASH");
      _process.exitCode.then((exitCode) {
        _processExitHandler(exitCode);
      });

      _process.stdin.done.catchError((err) {
        print('Error on batch runner input stream stdin');
        print('  Previous test\'s status: $_status');
        print('  Error: $err');
        throw err;
      });
      callback();
    }).catchError((e) {
      // TODO(floitsch): should we try to report the stacktrace?
      print("Process error:");
      print("  Command: $executable ${arguments.join(' ')} ($_arguments)");
      print("  Error: $e");
      // If there is an error starting a batch process, chances are that
      // it will always fail. So rather than re-trying a 1000+ times, we
      // exit.
      io.exit(1);
    });
  }

  bool _dictEquals(Map a, Map b) {
    if (a == null) return b == null;
    if (b == null) return false;
    if (a.length != b.length) return false;
    for (var key in a.keys) {
      if (a[key] != b[key]) return false;
    }
    return true;
  }
}