// Copyright (c) 2018, 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:io';
import 'dart:isolate';
import 'dart:math';

import 'package:args/args.dart';

import 'dartfuzz.dart';

const debug = false;
const sigkill = 9;
const timeout = 60; // in seconds
const dartHeapSize = 128; // in Mb

// Status of divergence report.
enum ReportStatus { reported, ignored, rerun, no_divergence }

/// Result of running a test.
class TestResult {
  const TestResult(this.output, this.stderr, this.exitCode);
  final String output;
  final String stderr;
  final int exitCode;
}

/// Command runner.
TestResult runCommand(List<String> cmd, Map<String, String> env) {
  ProcessResult res = Process.runSync(
      'timeout', ['-s', '$sigkill', '$timeout', ...cmd],
      environment: env);
  if (debug) {
    print('\nrunning $cmd yields:\n'
        '${res.exitCode}\n${res.stdout}\n${res.stderr}\n');
  }
  return TestResult(res.stdout, res.stderr, res.exitCode);
}

/// Abstraction for running one test in a particular mode.
abstract class TestRunner {
  TestResult run();
  String description;

  // Factory.
  static TestRunner getTestRunner(String mode, String top, String tmp,
      Map<String, String> env, String fileName, Random rand) {
    String prefix = mode.substring(0, 3).toUpperCase();
    String tag = getTag(mode);
    List<String> extraFlags = [];
    // Required extra flags for kbc.
    if (mode.startsWith('kbc-int')) {
      prefix += '-INT';
      extraFlags += [
        '--enable-interpreter',
        '--compilation-counter-threshold=-1'
      ];
    } else if (mode.startsWith('kbc-mix')) {
      prefix += '-MIX';
      extraFlags += ['--enable-interpreter'];
    } else if (mode.startsWith('kbc-cmp')) {
      prefix += '-CMP';
      extraFlags += ['--use-bytecode-compiler'];
    }
    // Every once in a while, go directly from source for kbc.
    bool kbcSrc = false;
    if (mode.startsWith('kbc') && rand.nextInt(4) == 0) {
      prefix += '-SRC';
      kbcSrc = true;
    }
    // Every once in a while, stress test JIT.
    if (mode.startsWith('jit') && rand.nextInt(4) == 0) {
      final r = rand.nextInt(7);
      if (r == 0) {
        prefix += '-NOFIELDGUARDS';
        extraFlags += ['--use_field_guards=false'];
      } else if (r == 1) {
        prefix += '-NOINTRINSIFY';
        extraFlags += ['--intrinsify=false'];
      } else if (r == 2) {
        final freq = rand.nextInt(1000) + 500;
        prefix += '-COMPACTEVERY-${freq}';
        extraFlags += ['--gc_every=${freq}', '--use_compactor=true'];
      } else if (r == 3) {
        final freq = rand.nextInt(1000) + 500;
        prefix += '-MARKSWEEPEVERY-${freq}';
        extraFlags += ['--gc_every=${freq}', '--use_compactor=false'];
      } else if (r == 4) {
        final freq = rand.nextInt(100) + 50;
        prefix += '-DEPOPTEVERY-${freq}';
        extraFlags += ['--deoptimize_every=${freq}'];
      } else if (r == 5) {
        final freq = rand.nextInt(100) + 50;
        prefix += '-STACKTRACEEVERY-${freq}';
        extraFlags += ['--stacktrace_every=${freq}'];
      } else if (r == 6) {
        prefix += '-OPTCOUNTER';
        extraFlags += ['--optimization_counter_threshold=1'];
      }
    }
    // Every once in a while, disable VFP on arm32.
    if (mode.contains('arm32') && rand.nextInt(4) == 0) {
      prefix += '-noVFP';
      extraFlags += ['--no-use-vfp'];
    }
    // Every once in a while, use -O3 compiler.
    if (!mode.startsWith('djs') && rand.nextInt(4) == 0) {
      prefix += '-O3';
      extraFlags += ['--optimization_level=3'];
    }
    // Every once in a while, use the slowpath flag.
    if (!mode.startsWith('djs') && rand.nextInt(4) == 0) {
      prefix += '-SLOWPATH';
      extraFlags += ['--use-slow-path'];
    }
    // Every once in a while, use the deterministic flag.
    if (!mode.startsWith('djs') && rand.nextInt(4) == 0) {
      prefix += '-DET';
      extraFlags += ['--deterministic'];
    }
    // Construct runner.
    if (mode.startsWith('jit')) {
      return TestRunnerJIT(prefix, tag, top, tmp, env, fileName, extraFlags);
    } else if (mode.startsWith('aot')) {
      return TestRunnerAOT(prefix, tag, top, tmp, env, fileName, extraFlags);
    } else if (mode.startsWith('kbc')) {
      return TestRunnerKBC(
          prefix, tag, top, tmp, env, fileName, extraFlags, kbcSrc);
    } else if (mode.startsWith('djs')) {
      return TestRunnerDJS(prefix, tag, top, tmp, env, fileName);
    }
    throw ('unknown runner in mode: $mode');
  }

  // Convert mode to tag.
  static String getTag(String mode) {
    if (mode.endsWith('debug-ia32')) return 'DebugIA32';
    if (mode.endsWith('debug-x64')) return 'DebugX64';
    if (mode.endsWith('debug-arm32')) return 'DebugSIMARM';
    if (mode.endsWith('debug-arm64')) return 'DebugSIMARM64';
    if (mode.endsWith('ia32')) return 'ReleaseIA32';
    if (mode.endsWith('x64')) return 'ReleaseX64';
    if (mode.endsWith('arm32')) return 'ReleaseSIMARM';
    if (mode.endsWith('arm64')) return 'ReleaseSIMARM64';
    throw ('unknown tag in mode: $mode');
  }

  // Print steps to reproduce build and run.
  void printReproductionCommand();
}

/// Concrete test runner of Dart JIT.
class TestRunnerJIT implements TestRunner {
  TestRunnerJIT(String prefix, String tag, this.top, String tmp, this.env,
      this.fileName, List<String> extraFlags) {
    description = '$prefix-$tag';
    dart = '$top/out/$tag/dart';
    cmd = [
      dart,
      ...extraFlags,
      '--old_gen_heap_size=${dartHeapSize}',
      fileName
    ];
  }

  TestResult run() {
    return runCommand(cmd, env);
  }

  void printReproductionCommand() =>
      print(cmd.join(" ").replaceAll('$top/', ''));

  String description;
  String dart;
  String fileName;
  final String top;
  Map<String, String> env;
  List<String> cmd;
}

/// Concrete test runner of Dart AOT.
class TestRunnerAOT implements TestRunner {
  TestRunnerAOT(String prefix, String tag, this.top, this.tmp,
      Map<String, String> e, this.fileName, List<String> extraFlags) {
    description = '$prefix-$tag';
    precompiler = '$top/pkg/vm/tool/precompiler2';
    dart = '$top/pkg/vm/tool/dart_precompiled_runtime2';
    snapshot = '$tmp/snapshot';
    env = Map<String, String>.from(e);
    env['DART_CONFIGURATION'] = tag;
    env['DART_VM_FLAGS'] = '--enable-asserts';
    cmd = [precompiler, ...extraFlags, fileName, snapshot];
  }

  TestResult run() {
    TestResult result = runCommand(cmd, env);
    if (result.exitCode != 0) {
      return result;
    }
    return runCommand(
        [dart, '--old_gen_heap_size=${dartHeapSize}', snapshot], env);
  }

  void printReproductionCommand() {
    print([
      "DART_CONFIGURATION='${env['DART_CONFIGURATION']}'",
      "DART_VM_FLAGS='${env['DART_VM_FLAGS']}'",
      ...cmd
    ].join(" ").replaceAll('$top/', '').replaceAll('$tmp/', ''));
    print([dart, snapshot]
        .join(" ")
        .replaceAll('$top/', '')
        .replaceAll('$tmp/', ''));
  }

  String description;
  String precompiler;
  String dart;
  String fileName;
  String snapshot;
  final String top;
  final String tmp;
  Map<String, String> env;
  List<String> cmd;
}

/// Concrete test runner of bytecode.
class TestRunnerKBC implements TestRunner {
  TestRunnerKBC(String prefix, String tag, this.top, this.tmp, this.env,
      this.fileName, List<String> extraFlags, bool kbcSrc) {
    description = '$prefix-$tag';
    dart = '$top/out/$tag/dart';
    if (kbcSrc) {
      cmd = [
        dart,
        ...extraFlags,
        '--old_gen_heap_size=${dartHeapSize}',
        fileName
      ];
    } else {
      generate = '$top/pkg/vm/tool/gen_kernel';
      platform = '--platform=$top/out/$tag/vm_platform_strong.dill';
      dill = '$tmp/out.dill';
      cmd = [dart, ...extraFlags, '--old_gen_heap_size=${dartHeapSize}', dill];
    }
  }

  TestResult run() {
    if (generate != null) {
      TestResult result = runCommand(
          [generate, '--gen-bytecode', platform, '-o', dill, fileName], env);
      if (result.exitCode != 0) {
        return result;
      }
    }
    return runCommand(cmd, env);
  }

  void printReproductionCommand() {
    if (generate != null) {
      print([generate, '--gen-bytecode', platform, '-o', dill, fileName]
          .join(" ")
          .replaceAll('$top/', '')
          .replaceAll('$tmp/', ''));
    }
    print(cmd.join(" ").replaceAll('$top/', '').replaceAll('$tmp/', ''));
  }

  String description;
  String generate;
  String platform;
  String dill;
  String dart;
  String fileName;
  final String top;
  final String tmp;
  Map<String, String> env;
  List<String> cmd;
}

/// Concrete test runner of Dart2JS.
class TestRunnerDJS implements TestRunner {
  TestRunnerDJS(
      String prefix, String tag, this.top, this.tmp, this.env, this.fileName) {
    description = '$prefix-$tag';
    dart2js = '$top/sdk/bin/dart2js';
    js = '$tmp/out.js';
  }

  TestResult run() {
    TestResult result = runCommand([dart2js, fileName, '-o', js], env);
    if (result.exitCode != 0) {
      return result;
    }
    return runCommand(['nodejs', js], env);
  }

  void printReproductionCommand() {
    print([dart2js, fileName, '-o', js]
        .join(" ")
        .replaceAll('$top/', '')
        .replaceAll('$tmp/', ''));
    print('nodejs out.js');
  }

  String description;
  String dart2js;
  String fileName;
  String js;
  final String top;
  final String tmp;
  Map<String, String> env;
}

/// Class to run fuzz testing.
class DartFuzzTest {
  DartFuzzTest(
      this.env,
      this.repeat,
      this.time,
      this.numOutputLines,
      this.trueDivergence,
      this.showStats,
      this.top,
      this.mode1,
      this.mode2,
      this.rerun,
      this.dartSdkRevision);

  int run() {
    setup();

    print('\n${isolate}: start');
    if (showStats) {
      showStatistics();
    }

    for (int i = 0; i < repeat; i++) {
      numTests++;
      seed = rand.nextInt(1 << 32);
      generateTest();
      runTest();
      if (showStats) {
        showStatistics();
      }
      // Timeout?
      if (timeIsUp()) {
        break;
      }
    }

    print('\n${isolate}: done');
    showStatistics();
    print('');
    if (timeoutSeeds.isNotEmpty) {
      print('\n${isolate} timeout: ' + timeoutSeeds.join(", "));
      print('');
    }
    if (skippedSeeds.isNotEmpty) {
      print('\n${isolate} skipped: ' + skippedSeeds.join(", "));
      print('');
    }

    cleanup();
    return numDivergences;
  }

  void setup() {
    rand = Random();
    tmpDir = Directory.systemTemp.createTempSync('dart_fuzz');
    fileName = '${tmpDir.path}/fuzz.dart';

    // Testcase generation flags.

    // Only use FP when modes have the same architecture (to avoid false
    // divergences between 32-bit and 64-bit versions).
    fp = sameArchitecture(mode1, mode2);
    // Occasionally test FFI (if capable).
    ffi = ffiCapable(mode1, mode2) && (rand.nextInt(5) == 0);
    // Resort to flat types for the more expensive modes.
    flatTp = !nestedTypesAllowed(mode1, mode2);

    runner1 =
        TestRunner.getTestRunner(mode1, top, tmpDir.path, env, fileName, rand);
    runner2 =
        TestRunner.getTestRunner(mode2, top, tmpDir.path, env, fileName, rand);
    isolate =
        'Isolate (${tmpDir.path}) ${fp ? "" : "NO-"}FP ${ffi ? "" : "NO-"}FFI ${flatTp ? "" : "NO-"}FLAT : '
        '${runner1.description} - ${runner2.description}';

    start_time = DateTime.now().millisecondsSinceEpoch;
    current_time = start_time;
    report_time = start_time;
    end_time = start_time + max(0, time - timeout) * 1000;

    numTests = 0;
    numSuccess = 0;
    numSkipped = 0;
    numRerun = 0;
    numTimeout = 0;
    numDivergences = 0;
    timeoutSeeds = {};
    skippedSeeds = {};
  }

  bool sameArchitecture(String mode1, String mode2) =>
      ((mode1.contains('arm32') && mode2.contains('arm32')) ||
          (mode1.contains('arm64') && mode2.contains('arm64')) ||
          (mode1.contains('x64') && mode2.contains('x64')) ||
          (mode1.contains('ia32') && mode2.contains('ia32')));

  bool ffiCapable(String mode1, String mode2) =>
      (mode1.startsWith('jit') || mode1.startsWith('kbc')) &&
      (mode2.startsWith('jit') || mode2.startsWith('kbc')) &&
      (!mode1.contains('arm') && !mode2.contains('arm'));

  bool nestedTypesAllowed(String mode1, String mode2) =>
      (!mode1.contains('arm') && !mode2.contains('arm'));

  bool timeIsUp() {
    if (time > 0) {
      current_time = DateTime.now().millisecondsSinceEpoch;
      if (current_time > end_time) {
        return true;
      }
      // Report every 10 minutes.
      if ((current_time - report_time) > (10 * 60 * 1000)) {
        print(
            '\n${isolate}: busy @${numTests} ${current_time - start_time} seconds....');
        report_time = current_time;
      }
    }
    return false;
  }

  void cleanup() {
    tmpDir.delete(recursive: true);
  }

  void showStatistics() {
    stdout.write('\rTests: $numTests Success: $numSuccess (Rerun: $numRerun) '
        'Skipped: $numSkipped Timeout: $numTimeout '
        'Divergences: $numDivergences');
  }

  void generateTest() {
    final file = File(fileName).openSync(mode: FileMode.write);
    DartFuzz(seed, fp, ffi, flatTp, file).run();
    file.closeSync();
  }

  void runTest() {
    TestResult result1 = runner1.run();
    TestResult result2 = runner2.run();
    var report = checkDivergence(result1, result2);
    if (report == ReportStatus.rerun && rerun) {
      print("\nCommencing re-run .... \n");
      numDivergences--;
      result1 = runner1.run();
      result2 = runner2.run();
      report = checkDivergence(result1, result2);
      if (report == ReportStatus.no_divergence) {
        print("\nNo error on re-run\n");
        numRerun++;
      }
    }
    if (report == ReportStatus.reported ||
        (!rerun && report == ReportStatus.rerun)) {
      showReproduce();
    }
  }

  ReportStatus checkDivergence(TestResult result1, TestResult result2) {
    if (result1.exitCode == result2.exitCode) {
      // No divergence in result code.
      switch (result1.exitCode) {
        case 0:
          // Both were successful, inspect output.
          if (result1.output == result2.output) {
            numSuccess++;
          } else {
            reportDivergence(result1, result2);
            return ReportStatus.reported;
          }
          break;
        case -sigkill:
          // Both had a time out.
          numTimeout++;
          timeoutSeeds.add(seed);
          break;
        default:
          // Both had an error.
          numSkipped++;
          skippedSeeds.add(seed);
          break;
      }
    } else {
      // Divergence in result code.
      if (trueDivergence) {
        // When only true divergences are requested, any divergence
        // with at least one time out or out of memory error is
        // treated as a regular time out or skipped test, respectively.
        if (result1.exitCode == -sigkill || result2.exitCode == -sigkill) {
          numTimeout++;
          timeoutSeeds.add(seed);
          return ReportStatus.ignored;
        } else if (result1.exitCode == DartFuzz.oomExitCode ||
            result2.exitCode == DartFuzz.oomExitCode) {
          numSkipped++;
          skippedSeeds.add(seed);
          return ReportStatus.ignored;
        }
      }
      reportDivergence(result1, result2);
      // Exit codes outside [-255,255] are not due to Dart VM exits.
      if (result1.exitCode.abs() > 255 || result2.exitCode.abs() > 255) {
        return ReportStatus.rerun;
      } else {
        return ReportStatus.reported;
      }
    }
    return ReportStatus.no_divergence;
  }

  String generateReport(TestResult result1, TestResult result2) {
    if (result1.exitCode == result2.exitCode) {
      return "output";
    } else {
      return "${result1.exitCode} vs ${result2.exitCode}";
    }
  }

  void printDivergenceOutput(String string, int numLines) {
    final lines = string.split('\n');
    print(lines.sublist(0, min(lines.length, numLines)).join('\n'));
  }

  void reportDivergence(TestResult result1, TestResult result2) {
    numDivergences++;
    String report = generateReport(result1, result2);
    print('\n${isolate}: !DIVERGENCE! $version:$seed (${report})');
    if (result1.exitCode == result2.exitCode) {
      if (numOutputLines > 0) {
        // Only report the actual output divergence details up to
        // numOutputLines, since this output may be lengthy and should be
        // reproducable anyway.
        print('\nout1:\n');
        printDivergenceOutput(result1.output, numOutputLines);
        print('\nout2:\n');
        printDivergenceOutput(result2.output, numOutputLines);
      }
    } else {
      // For any other divergence, always report what went wrong.
      if (result1.exitCode != 0) {
        print(
            '\nfail1:\n${result1.exitCode}\n${result1.output}\n${result1.stderr}\n');
      }
      if (result2.exitCode != 0) {
        print(
            '\nfail2:\n${result2.exitCode}\n${result2.output}\n${result2.stderr}\n');
      }
    }
  }

  void showReproduce() {
    print("\n-- BEGIN REPRODUCE  --\n");
    print("DART SDK REVISION: $dartSdkRevision\n");
    print(
        "dart runtime/tools/dartfuzz/dartfuzz.dart --${fp ? "" : "no-"}fp --${ffi ? "" : "no-"}ffi "
        "--${flatTp ? "" : "no-"}flat "
        "--seed ${seed} fuzz.dart");
    print("\n-- RUN 1 --\n");
    runner1.printReproductionCommand();
    print("\n-- RUN 2 --\n");
    runner2.printReproductionCommand();
    print("\n-- END REPRODUCE  --\n");
  }

  // Context.
  final Map<String, String> env;
  final int repeat;
  final int time;
  final int numOutputLines;
  final bool trueDivergence;
  final bool showStats;
  final String top;
  final String mode1;
  final String mode2;
  final bool rerun;
  final String dartSdkRevision;

  // Test.
  Random rand;
  Directory tmpDir;
  String fileName;
  TestRunner runner1;
  TestRunner runner2;
  bool fp;
  bool ffi;
  bool flatTp;
  String isolate;
  int seed;

  // Timing
  int start_time;
  int current_time;
  int report_time;
  int end_time;

  // Stats.
  int numTests;
  int numSuccess;
  int numSkipped;
  int numRerun;
  int numTimeout;
  int numDivergences;
  Set<int> timeoutSeeds;
  Set<int> skippedSeeds;
}

/// Class to start fuzz testing session.
class DartFuzzTestSession {
  DartFuzzTestSession(
      this.isolates,
      this.repeat,
      this.time,
      this.numOutputLines,
      this.trueDivergence,
      this.showStats,
      String tp,
      this.mode1,
      this.mode2,
      this.rerun)
      : top = getTop(tp),
        dartSdkRevision = getDartSdkRevision(tp);

  start() async {
    print('\n**\n**** Dart Fuzz Testing Session\n**\n');
    print('Fuzz Version      : ${version}');
    print('Dart SDK Revision : ${dartSdkRevision}');
    print('Isolates          : ${isolates}');
    print('Tests             : ${repeat}');
    if (time > 0) {
      print('Time              : ${time} seconds');
    } else {
      print('Time              : unlimited');
    }
    print('True Divergence   : ${trueDivergence}');
    print('Show Stats        : ${showStats}');
    print('Dart Dev          : ${top}');
    // Fork.
    List<ReceivePort> ports = List();
    for (int i = 0; i < isolates; i++) {
      ReceivePort r = ReceivePort();
      ports.add(r);
      port = r.sendPort;
      await Isolate.spawn(run, this);
    }
    // Join.
    int divergences = 0;
    for (int i = 0; i < isolates; i++) {
      var d = await ports[i].first;
      divergences += d;
    }
    if (divergences == 0) {
      print('\nsuccess\n');
    } else {
      print('\nfailure ($divergences divergences)\n');
      exitCode = 1;
    }
  }

  static run(DartFuzzTestSession session) {
    int divergences = 0;
    try {
      final m1 = getMode(session.mode1, null);
      final m2 = getMode(session.mode2, m1);
      final fuzz = DartFuzzTest(
          Platform.environment,
          session.repeat,
          session.time,
          session.numOutputLines,
          session.trueDivergence,
          session.showStats,
          session.top,
          m1,
          m2,
          session.rerun,
          session.dartSdkRevision);
      divergences = fuzz.run();
    } catch (e) {
      print('Isolate: $e');
    }
    session.port.send(divergences);
  }

  // Picks a top directory (command line, environment, or current).
  static String getTop(String top) {
    if (top == null || top == '') {
      top = Platform.environment['DART_TOP'];
    }
    if (top == null || top == '') {
      top = Directory.current.path;
    }
    return top;
  }

  static String getDartSdkRevision(String top) {
    ProcessResult res =
        Process.runSync(Platform.resolvedExecutable, ['--version']);
    return res.stderr;
  }

  // Picks a mode (command line or random).
  static String getMode(String mode, String other) {
    // Random when not set.
    if (mode == null || mode == '') {
      // Pick a mode at random (cluster), different from other.
      Random rand = Random();
      do {
        mode = clusterModes[rand.nextInt(clusterModes.length)];
      } while (mode == other);
    }
    // Verify mode.
    if (modes.contains(mode)) {
      return mode;
    }
    throw ('unknown mode: $mode');
  }

  // Context.
  final int isolates;
  final int repeat;
  final int time;
  final int numOutputLines;
  final bool trueDivergence;
  final bool showStats;
  final bool rerun;
  final String top;
  final String mode1;
  final String mode2;
  final String dartSdkRevision;

  // Passes each port to isolate.
  SendPort port;

  // Modes used on cluster runs.
  static const List<String> clusterModes = [
    'jit-debug-ia32',
    'jit-debug-x64',
    'jit-debug-arm32',
    'jit-debug-arm64',
    'jit-ia32',
    'jit-x64',
    'jit-arm32',
    'jit-arm64',
    'aot-debug-x64',
    'aot-x64',
    'kbc-int-debug-ia32',
    'kbc-cmp-debug-ia32',
    'kbc-mix-debug-ia32',
    'kbc-int-debug-x64',
    'kbc-cmp-debug-x64',
    'kbc-mix-debug-x64',
    'kbc-int-debug-arm32',
    'kbc-cmp-debug-arm32',
    'kbc-mix-debug-arm32',
    'kbc-int-debug-arm64',
    'kbc-cmp-debug-arm64',
    'kbc-mix-debug-arm64',
    'kbc-int-ia32',
    'kbc-cmp-ia32',
    'kbc-mix-ia32',
    'kbc-int-x64',
    'kbc-cmp-x64',
    'kbc-mix-x64',
    'kbc-int-arm32',
    'kbc-cmp-arm32',
    'kbc-mix-arm32',
    'kbc-int-arm64',
    'kbc-cmp-arm64',
    'kbc-mix-arm64',
  ];

  // Modes not used on cluster runs because they have outstanding issues.
  static const List<String> nonClusterModes = [
    // Times out often:
    'aot-debug-arm32',
    'aot-debug-arm64',
    'aot-arm32',
    'aot-arm64',
    // Too many divergences (due to arithmetic):
    'js-x64',
  ];

  // All modes.
  static List<String> modes = clusterModes + nonClusterModes;
}

/// Main driver for a fuzz testing session.
main(List<String> arguments) {
  // Set up argument parser.
  final parser = ArgParser()
    ..addOption('isolates', help: 'number of isolates to use', defaultsTo: '1')
    ..addOption('repeat', help: 'number of tests to run', defaultsTo: '1000')
    ..addOption('time', help: 'time limit in seconds', defaultsTo: '0')
    ..addOption('num-output-lines',
        help:
            'number of output lines to be printed in the case of a divergence',
        defaultsTo: '200')
    ..addFlag('true-divergence',
        negatable: true, help: 'only report true divergences', defaultsTo: true)
    ..addFlag('show-stats',
        negatable: true, help: 'show session statistics', defaultsTo: true)
    ..addOption('dart-top', help: 'explicit value for \$DART_TOP')
    ..addOption('mode1', help: 'execution mode 1')
    ..addOption('mode2', help: 'execution mode 2')
    ..addFlag('rerun',
        negatable: true,
        help: 're-run if test only diverges on return code (not in the output)',
        defaultsTo: true)
    // Undocumented options for cluster runs.
    ..addOption('shards',
        help: 'number of shards used in cluster run', defaultsTo: '1')
    ..addOption('shard', help: 'shard id in cluster run', defaultsTo: '1')
    ..addOption('output_directory',
        help: 'path to output (ignored)', defaultsTo: null)
    ..addOption('output-directory',
        help: 'path to output (ignored)', defaultsTo: null);

  // Starts fuzz testing session.
  try {
    final results = parser.parse(arguments);
    final shards = int.parse(results['shards']);
    final shard = int.parse(results['shard']);
    if (shards > 1) {
      print('\nSHARD $shard OF $shards');
    }
    DartFuzzTestSession(
            int.parse(results['isolates']),
            int.parse(results['repeat']),
            int.parse(results['time']),
            int.parse(results['num-output-lines']),
            results['true-divergence'],
            results['show-stats'],
            results['dart-top'],
            results['mode1'],
            results['mode2'],
            results['rerun'])
        .start();
  } catch (e) {
    print('Usage: dart dartfuzz_test.dart [OPTIONS]\n${parser.usage}\n$e');
    exitCode = 255;
  }
}