// Copyright 2018 Google Inc. Use of this source code is governed by an
// MIT-style license that can be found in the LICENSE file or at
// https://opensource.org/licenses/MIT.

import 'dart:async';
import 'dart:io';
import 'dart:math' as math;

import 'package:grinder/grinder.dart';
import 'package:path/path.dart' as p;

import 'npm.dart';
import 'standalone.dart';
import 'utils.dart';

@Task('Generate benchmark files.')
Future<void> benchmarkGenerate() async {
  var sources = Directory("build/benchmark");
  if (!await sources.exists()) await sources.create(recursive: true);

  await _writeNTimes("${sources.path}/small_plain.scss", ".foo {a: b}", 4);
  await _writeNTimes(
      "${sources.path}/large_plain.scss", ".foo {a: b}", math.pow(2, 17));
  await _writeNTimes("${sources.path}/preceding_sparse_extend.scss",
      ".foo {a: b}", math.pow(2, 17),
      header: '.x {@extend .y}', footer: '.y {a: b}');
  await _writeNTimes("${sources.path}/following_sparse_extend.scss",
      ".foo {a: b}", math.pow(2, 17),
      header: '.y {a: b}', footer: '.x {@extend .y}');
  await _writeNTimes("${sources.path}/preceding_dense_extend.scss",
      ".foo {a: b}", math.pow(2, 17),
      header: '.bar {@extend .foo}');
  await _writeNTimes("${sources.path}/following_dense_extend.scss",
      ".foo {a: b}", math.pow(2, 17),
      footer: '.bar {@extend .foo}');

  await cloneOrCheckout("https://github.com/twbs/bootstrap", "v4.1.3");
  await _writeNTimes("${sources.path}/bootstrap.scss",
      "@import '../bootstrap/scss/bootstrap';", 16);

  await cloneOrCheckout("https://github.com/alex-page/sass-a11ycolor",
      "2e7ef93ec06f8bbec80b632863e4b2811618af89");
  File("${sources.path}/a11ycolor.scss").writeAsStringSync("""
    @import '../sass-a11ycolor/dist';

    x {
      // Adapted from a11ycolor's test1.scss, which at one point was much slower
      // in JS than in the Dart VM.
      y: AU-a11ycolor(red, blue)
         AU-a11ycolor(#646464, #E0E0E0)
         AU-a11ycolor(green, blue)
         AU-a11ycolor(pink, blue)
         AU-a11ycolor(blue, blue)
         AU-a11ycolor(#c0c0c0, #c0c0c0)
         AU-a11ycolor(#231284, #ccc)
         AU-a11ycolor(#fff, #fff);
    }
  """);

  var susy = await cloneOrCheckout("https://github.com/oddbird/susy", "v3.0.5");
  await runAsync("npm", arguments: ["install"], workingDirectory: susy);
  File("${sources.path}/susy.scss")
      .writeAsStringSync("@import '../susy/test/scss/test.scss'");
}

/// Writes [times] instances of [text] to [path].
///
/// If [header] is passed, it's written before [text]. If [footer] is passed,
/// it's written after [text]. If the file already exists and is the expected
/// length, it's not written.
Future<void> _writeNTimes(String path, String text, num times,
    {String header, String footer}) async {
  var file = File(path);
  var expectedLength = (header == null ? 0 : header.length + 1) +
      (text.length + 1) * times +
      (footer == null ? 0 : footer.length + 1);
  if (file.existsSync() && file.lengthSync() == expectedLength) {
    log("$path already exists.");
    return;
  }

  log("Generating $path...");
  var sink = file.openWrite();
  if (header != null) sink.writeln(header);
  for (var i = 0; i < times; i++) {
    sink.writeln(text);
  }
  if (footer != null) sink.writeln(footer);
  await sink.close();
}

@Task('Run benchmarks for Sass compilation speed.')
@Depends(benchmarkGenerate, snapshot, nativeExecutable, npmReleasePackage)
Future<void> benchmark() async {
  var libsass = await cloneOrPull('https://github.com/sass/libsass');
  var sassc = await cloneOrPull('https://github.com/sass/sassc');

  await runAsync("make",
      runOptions: RunOptions(
          workingDirectory: sassc,
          environment: {"SASS_LIBSASS_PATH": p.absolute(libsass)}));
  log("");

  var libsassRevision = await _revision(libsass);
  var sasscRevision = await _revision(sassc);
  var dartSassRevision = await _revision('.');
  var gPlusPlusVersion = await _version("g++");
  var nodeVersion = await _version("node");

  var perf = File("perf.md").readAsStringSync();
  perf = perf.replaceFirst(RegExp(r"This was tested against:\n\n[^]*?\n\n"), """
This was tested against:

* libsass $libsassRevision and sassc $sasscRevision compiled with $gPlusPlusVersion.
* Dart Sass $dartSassRevision on Dart $dartVersion and Node $nodeVersion.

""");

  var buffer = StringBuffer("""
# Measurements

I ran five instances of each configuration and recorded the fastest time.

""");

  var benchmarks = [
    ["small_plain.scss", "Small Plain CSS", "4 instances of `.foo {a: b}`"],
    ["large_plain.scss", "Large Plain CSS", "2^17 instances of `.foo {a: b}`"],
    [
      "preceding_sparse_extend.scss",
      "Preceding Sparse `@extend`",
      "`.x {@extend .y}`, 2^17 instances of `.foo {a: b}`, and then `.y {a: b}`"
    ],
    [
      "following_sparse_extend.scss",
      "Following Sparse `@extend`",
      "`.y {a: b}`, 2^17 instances of `.foo {a: b}`, and then `.x {@extend .y}`"
    ],
    [
      "preceding_dense_extend.scss",
      "Preceding Dense `@extend`",
      "`.bar {@extend .foo}` followed by 2^17 instances of `.foo {a: b}`"
    ],
    [
      "following_dense_extend.scss",
      "Following Dense `@extend`",
      "2^17 instances of `.foo {a: b}` followed by `.bar {@extend .foo}`"
    ],
    [
      "bootstrap.scss",
      "Bootstrap",
      "16 instances of importing the Bootstrap framework"
    ],
    [
      "a11ycolor.scss",
      "a11ycolor",
      "test cases for a computation-intensive color-processing library"
    ],
    [
      "susy.scss",
      "Susy",
      "test cases for the computation-intensive Susy grid framework"
    ],
  ];

  for (var info in benchmarks) {
    var path = p.join('build/benchmark', info[0]);
    var title = info[1];
    var description = info[2];

    buffer.writeln("## $title");
    buffer.writeln();
    buffer.writeln("Running on a file containing $description:");
    buffer.writeln();

    var sasscTime = await _benchmark(p.join(sassc, 'bin', 'sassc'), [path]);
    buffer.writeln("* sassc: ${_formatTime(sasscTime)}");

    var scriptSnapshotTime = await _benchmark(Platform.executable,
        ['--no-enable-asserts', p.join('build', 'sass.dart.snapshot'), path]);
    buffer.writeln("* Dart Sass from a script snapshot: "
        "${_formatTime(scriptSnapshotTime)}");

    var nativeExecutableTime = await _benchmark(
        p.join(sdkDir.path, 'bin/dartaotruntime'),
        [p.join('build', 'sass.dart.native'), path]);
    buffer.writeln("* Dart Sass native executable: "
        "${_formatTime(nativeExecutableTime)}");

    var nodeTime =
        await _benchmark("node", [p.join('build', 'npm', 'sass.js'), path]);
    buffer.writeln("* Dart Sass on Node.js: ${_formatTime(nodeTime)}");

    buffer.writeln();
    buffer.writeln('Based on these numbers, Dart Sass from a native executable '
        'is approximately:');
    buffer.writeln();
    buffer.writeln('* ${_compare(nativeExecutableTime, sasscTime)} libsass');
    buffer.writeln(
        '* ${_compare(nativeExecutableTime, nodeTime)} Dart Sass on Node');
    buffer.writeln();
    log('');
  }

  buffer.write("# Prior Measurements");
  perf = perf.replaceFirst(
      RegExp(r"# Measurements\n[^]*# Prior Measurements"), buffer.toString());

  File("perf.md").writeAsStringSync(perf);
}

/// Returns the revision of the Git repository at [path].
Future<String> _revision(String path) async => (await runAsync("git",
        arguments: ["rev-parse", "--short", "HEAD"],
        quiet: true,
        workingDirectory: path))
    .trim();

/// Returns the first line of output from `executable --version`.
Future<String> _version(String executable) async =>
    (await runAsync(executable, arguments: ["--version"], quiet: true))
        .split("\n")
        .first;

Future<Duration> _benchmark(String executable, List<String> arguments) async {
  log("$executable ${arguments.join(' ')}");

  // Run the benchmark once without recording output to give implementations a
  // chance to warm up at the OS level.
  await _benchmarkOnce(executable, arguments);

  Duration lowest;
  for (var i = 0; i < 5; i++) {
    var duration = await _benchmarkOnce(executable, arguments);
    if (lowest == null || duration < lowest) lowest = duration;
  }
  return lowest;
}

Future<Duration> _benchmarkOnce(
    String executable, List<String> arguments) async {
  var result = await Process.run(
      "sh", ["-c", "time $executable ${arguments.join(' ')}"]);

  if (result.exitCode != 0) {
    fail("Process failed with exit code ${result.exitCode}\n${result.stderr}");
  }

  var match =
      RegExp(r"(\d+)m(\d+)\.(\d+)s").firstMatch(result.stderr as String);
  return Duration(
      minutes: int.parse(match[1]),
      seconds: int.parse(match[2]),
      milliseconds: int.parse(match[3]));
}

String _formatTime(Duration duration) =>
    "${duration.inSeconds}." +
    (duration.inMilliseconds % 1000).toString().padLeft(3, '0') +
    's';

/// Returns an approximate, human-readable comparison between [duration1] and
/// [duration2].
String _compare(Duration duration1, Duration duration2) {
  var faster = duration1 < duration2;
  var ratio = faster
      ? duration2.inMilliseconds / duration1.inMilliseconds
      : duration1.inMilliseconds / duration2.inMilliseconds;
  var rounded = (ratio * 10).round().toString();
  var humanRatio = '${rounded.substring(0, rounded.length - 1)}.' +
      '${rounded.substring(rounded.length - 1)}x';
  if (humanRatio == '1.0x') return 'identical to';

  return humanRatio + (faster ? ' faster than' : ' slower than');
}