// Copyright (c) 2020, 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:convert';
import 'dart:io';
import 'dart:math';

import 'package:meta/meta.dart';
import 'package:pub_semver/pub_semver.dart';

import '../command.dart';
import '../entrypoint.dart';
import '../io.dart';
import '../log.dart' as log;
import '../package.dart';
import '../package_name.dart';
import '../pubspec.dart';
import '../pubspec_utils.dart';
import '../solver.dart';
import '../source/sdk.dart' show SdkSource;
import '../system_cache.dart';
import '../utils.dart';

class OutdatedCommand extends PubCommand {
  @override
  String get name => 'outdated';
  @override
  String get description =>
      'Analyze your dependencies to find which ones can be upgraded.';
  @override
  String get argumentsDescription => '[options]';
  @override
  String get docUrl => 'https://dart.dev/tools/pub/cmd/pub-outdated';

  /// Avoid showing spinning progress messages when not in a terminal, and
  /// when we are outputting machine-readable json.
  bool get _shouldShowSpinner => stdout.hasTerminal && !argResults['json'];

  OutdatedCommand() {
    argParser.addFlag('color',
        help: 'Whether to color the output.\n'
            'Defaults to color when connected to a '
            'terminal, and no-color otherwise.');

    argParser.addFlag(
      'dependency-overrides',
      defaultsTo: true,
      help: 'Show resolutions with `dependency_overrides`.',
    );

    argParser.addFlag(
      'dev-dependencies',
      defaultsTo: true,
      help: 'Take dev dependencies into account.',
    );

    argParser.addFlag(
      'transitive',
      help: 'Show transitive dependencies.\n'
          '(defaults to off in --mode=null-safety).',
    );

    argParser.addFlag('json',
        help: 'Output the results using a json format.', negatable: false);

    argParser.addOption('mode',
        help: 'Highlight versions with PROPERTY.\n'
            'Only packages currently missing that PROPERTY will be included unless '
            '--show-all.',
        valueHelp: 'PROPERTY',
        allowed: ['outdated', 'null-safety'],
        defaultsTo: 'outdated');

    argParser.addFlag('prereleases',
        help: 'Include prereleases in latest version.\n'
            '(defaults to on in --mode=null-safety).');

    // Preserve for backwards compatibility.
    argParser.addFlag('pre-releases',
        help: 'Alias of prereleases.', hide: true);

    argParser.addFlag('show-all',
        help: 'Include dependencies that are already fullfilling --mode.');

    // Preserve for backwards compatibility.
    argParser.addFlag('up-to-date',
        hide: true,
        help: 'Include dependencies that are already at the '
            'latest version. Alias of --show-all.');
  }

  @override
  Future<void> runProtected() async {
    final includeDevDependencies = argResults['dev-dependencies'];
    final includeDependencyOverrides = argResults['dependency-overrides'];

    final rootPubspec = includeDependencyOverrides
        ? entrypoint.root.pubspec
        : stripDependencyOverrides(entrypoint.root.pubspec);

    final upgradablePubspec = includeDevDependencies
        ? rootPubspec
        : stripDevDependencies(rootPubspec);

    final resolvablePubspec = stripVersionUpperBounds(upgradablePubspec);

    List<PackageId> upgradablePackages;
    List<PackageId> resolvablePackages;

    await log.spinner('Resolving', () async {
      upgradablePackages = await _tryResolve(upgradablePubspec, cache);
      resolvablePackages = await _tryResolve(resolvablePubspec, cache);
    }, condition: _shouldShowSpinner);

    // This list will be empty if there is no lock file.
    final currentPackages = entrypoint.lockFile.packages.values;

    /// The set of all dependencies (direct and transitive) that are in the
    /// closure of the non-dev dependencies from the root in at least one of
    /// the current, upgradable and resolvable resolutions.
    final nonDevDependencies = <String>{
      ...await _nonDevDependencyClosure(entrypoint.root, currentPackages),
      ...await _nonDevDependencyClosure(entrypoint.root, upgradablePackages),
      ...await _nonDevDependencyClosure(entrypoint.root, resolvablePackages),
    };

    Future<_PackageDetails> analyzeDependency(PackageRef packageRef) async {
      final name = packageRef.name;
      final current = (entrypoint.lockFile?.packages ?? {})[name];

      final upgradable = upgradablePackages.firstWhere((id) => id.name == name,
          orElse: () => null);
      final resolvable = resolvablePackages.firstWhere((id) => id.name == name,
          orElse: () => null);

      // Find the latest version, and if it's overridden.
      var latestIsOverridden = false;
      PackageId latest;
      // If not overridden in current resolution we can use this
      if (!entrypoint.root.pubspec.dependencyOverrides.containsKey(name)) {
        latest ??= await _getLatest(current);
      }
      // If present as a dependency or dev_dependency we use this
      latest ??= await _getLatest(rootPubspec.dependencies[name]);
      latest ??= await _getLatest(rootPubspec.devDependencies[name]);
      // If not overridden and present in either upgradable or resolvable we
      // use this reference to find the latest
      if (!upgradablePubspec.dependencyOverrides.containsKey(name)) {
        latest ??= await _getLatest(upgradable);
      }
      if (!resolvablePubspec.dependencyOverrides.containsKey(name)) {
        latest ??= await _getLatest(resolvable);
      }
      // Otherwise, we might simply not have a latest, when a transitive
      // dependency is overridden the source can depend on which versions we
      // are picking. This is not a problem on `pub.dev` because it does not
      // allow 3rd party pub servers, but other servers might. Hence, we choose
      // to fallback to using the overridden source for latest.
      if (latest == null) {
        latest ??= await _getLatest(current ?? upgradable ?? resolvable);
        latestIsOverridden = true;
      }

      return _PackageDetails(
        name,
        await _describeVersion(
          current,
          entrypoint.root.pubspec.dependencyOverrides.containsKey(name),
        ),
        await _describeVersion(
          upgradable,
          upgradablePubspec.dependencyOverrides.containsKey(name),
        ),
        await _describeVersion(
          resolvable,
          resolvablePubspec.dependencyOverrides.containsKey(name),
        ),
        await _describeVersion(
          latest,
          latestIsOverridden,
        ),
        _kind(name, entrypoint, nonDevDependencies),
      );
    }

    final rows = <_PackageDetails>[];

    final visited = <String>{
      entrypoint.root.name,
    };
    // Add all dependencies from the lockfile.
    for (final id in [
      ...currentPackages,
      ...upgradablePackages,
      ...resolvablePackages
    ]) {
      if (!visited.add(id.name) || id.source is SdkSource) continue;
      rows.add(await analyzeDependency(id.toRef()));
    }

    if (!includeDevDependencies) {
      rows.removeWhere((r) => r.kind == _DependencyKind.dev);
    }

    rows.sort();
    final mode = <String, Mode>{
      'outdated': _OutdatedMode(),
      'null-safety': _NullSafetyMode(cache, entrypoint,
          shouldShowSpinner: _shouldShowSpinner),
    }[argResults['mode']];
    final showAll = argResults['show-all'] || argResults['up-to-date'];
    if (argResults['json']) {
      await _outputJson(
        rows,
        mode,
        showAll: showAll,
        includeDevDependencies: includeDevDependencies,
      );
    } else {
      if (argResults.wasParsed('color')) {
        forceColors = argResults['color'];
      }
      final useColors =
          argResults.wasParsed('color') ? argResults['color'] : canUseAnsiCodes;

      await _outputHuman(
        rows,
        mode,
        useColors: useColors,
        showAll: showAll,
        includeDevDependencies: includeDevDependencies,
        lockFileExists: fileExists(entrypoint.lockFilePath),
        hasDirectDependencies: rootPubspec.dependencies.values.any(
          // Test if it contains non-SDK dependencies
          (c) => c.source is! SdkSource,
        ),
        hasDevDependencies: rootPubspec.devDependencies.values.any(
          // Test if it contains non-SDK dependencies
          (c) => c.source is! SdkSource,
        ),
        showTransitiveDependencies: showTransitiveDependencies,
      );
    }
  }

  bool get showTransitiveDependencies {
    if (argResults.wasParsed('transitive')) {
      return argResults['transitive'];
    }
    // We default to hidding transitive dependencies in --mode=null-safety
    return argResults['mode'] != 'null-safety';
  }

  bool _prereleases;

  bool get prereleases => _prereleases ??= () {
        // First check if 'prereleases' was passed as an argument.
        // If that was not the case, check for use of the legacy spelling
        // 'pre-releases'.
        // Otherwise fall back to the default implied by the mode.
        if (argResults.wasParsed('prereleases')) {
          return argResults['prereleases'];
        }
        if (argResults.wasParsed('pre-releases')) {
          return argResults['pre-releases'];
        }
        return argResults['mode'] == 'null-safety';
      }();

  /// Get the latest version of [package].
  ///
  /// Will include prereleases in the comparison if '--prereleases' was enabled
  /// by the arguments.
  ///
  /// If [package] is a [PackageId] with a prerelease version and there are no
  /// later stable version we return a prerelease version if it exists.
  ///
  /// Returns `null`, if unable to find the package.
  Future<PackageId> _getLatest(PackageName package) async {
    if (package == null) {
      return null;
    }
    final ref = package.toRef();
    final available = await cache.source(ref.source).getVersions(ref);
    if (available.isEmpty) {
      return null;
    }

    // TODO(sigurdm): Refactor this to share logic with report.dart.
    available.sort(prereleases
        ? (x, y) => x.version.compareTo(y.version)
        : (x, y) => Version.prioritize(x.version, y.version));
    if (package is PackageId &&
        package.version.isPreRelease &&
        package.version > available.last.version) {
      available.sort((x, y) => x.version.compareTo(y.version));
    }
    return available.last;
  }

  /// Retrieves the pubspec of package [name] in [version] from [source].
  ///
  /// Returns `null`, if given `null` as a convinience.
  Future<_VersionDetails> _describeVersion(
    PackageId id,
    bool isOverridden,
  ) async {
    if (id == null) {
      return null;
    }
    return _VersionDetails(
      await cache.source(id.source).describe(id),
      id,
      isOverridden,
    );
  }

  /// Computes the closure of the graph of dependencies (not including
  /// `dev_dependencies` from [root], given the package versions
  /// in [resolution].
  ///
  /// The [resolution] is allowed to be a partial (or empty) resolution not
  /// satisfying all the dependencies of [root].
  Future<Set<String>> _nonDevDependencyClosure(
    Package root,
    Iterable<PackageId> resolution,
  ) async {
    final nameToId = Map<String, PackageId>.fromIterable(
      resolution,
      key: (id) => id.name,
    );

    final nonDevDependencies = <String>{root.name};
    final queue = [...root.dependencies.keys];

    while (queue.isNotEmpty) {
      final name = queue.removeLast();
      if (!nonDevDependencies.add(name)) {
        continue;
      }

      final id = nameToId[name];
      if (id == null) {
        continue; // allow partial resolutions
      }
      final pubspec = await cache.source(id.source).describe(id);
      queue.addAll(pubspec.dependencies.keys);
    }

    return nonDevDependencies;
  }
}

/// Try to solve [pubspec] return [PackageId]s in the resolution or `[]`.
Future<List<PackageId>> _tryResolve(Pubspec pubspec, SystemCache cache) async {
  final solveResult = await tryResolveVersions(
      SolveType.UPGRADE, cache, Package.inMemory(pubspec));
  if (solveResult == null) {
    return [];
  }

  return solveResult.packages;
}

Future<void> _outputJson(
  List<_PackageDetails> rows,
  Mode mode, {
  @required bool showAll,
  @required bool includeDevDependencies,
}) async {
  final markedRows =
      Map.fromIterables(rows, await mode.markVersionDetails(rows));
  if (!showAll) {
    rows.removeWhere((row) => markedRows[row][0].asDesired);
  }
  if (!includeDevDependencies) {
    rows.removeWhere(
      (element) =>
          element.kind == _DependencyKind.dev ||
          element.kind == _DependencyKind.devTransitive,
    );
  }
  log.message(
    JsonEncoder.withIndent('  ').convert(
      {
        'packages': [
          ...(rows..sort((a, b) => a.name.compareTo(b.name)))
              .map((packageDetails) => {
                    'package': packageDetails.name,
                    'current': markedRows[packageDetails][0]?.toJson(),
                    'upgradable': markedRows[packageDetails][1]?.toJson(),
                    'resolvable': markedRows[packageDetails][2]?.toJson(),
                    'latest': markedRows[packageDetails][3]?.toJson(),
                  })
        ]
      },
    ),
  );
}

Future<void> _outputHuman(
  List<_PackageDetails> rows,
  Mode mode, {
  @required bool showAll,
  @required bool useColors,
  @required bool includeDevDependencies,
  @required bool lockFileExists,
  @required bool hasDirectDependencies,
  @required bool hasDevDependencies,
  @required bool showTransitiveDependencies,
}) async {
  final explanation = mode.explanation;
  if (explanation != null) {
    log.message(explanation + '\n');
  }
  final markedRows =
      Map.fromIterables(rows, await mode.markVersionDetails(rows));

  List<_FormattedString> formatted(_PackageDetails package) => [
        _FormattedString(package.name),
        ...markedRows[package].map((m) => m.toHuman()),
      ];

  if (!showAll) {
    rows.removeWhere((row) => markedRows[row][0].asDesired);
  }
  if (rows.isEmpty) {
    log.message(mode.foundNoBadText);
    return;
  }

  bool Function(_PackageDetails) hasKind(_DependencyKind kind) =>
      (row) => row.kind == kind;

  final directRows = rows.where(hasKind(_DependencyKind.direct)).map(formatted);
  final devRows = rows.where(hasKind(_DependencyKind.dev)).map(formatted);
  final transitiveRows =
      rows.where(hasKind(_DependencyKind.transitive)).map(formatted);
  final devTransitiveRows =
      rows.where(hasKind(_DependencyKind.devTransitive)).map(formatted);

  final formattedRows = <List<_FormattedString>>[
    ['Package Name', 'Current', 'Upgradable', 'Resolvable', 'Latest']
        .map((s) => _format(s, log.bold))
        .toList(),
    if (hasDirectDependencies) ...[
      [
        if (directRows.isEmpty)
          _format('\ndirect dependencies: ${mode.allGood}', log.bold)
        else
          _format('\ndirect dependencies:', log.bold)
      ],
      ...directRows,
    ],
    if (includeDevDependencies && hasDevDependencies) ...[
      [
        if (devRows.isEmpty)
          _format('\ndev_dependencies: ${mode.allGood}', log.bold)
        else
          _format('\ndev_dependencies:', log.bold)
      ],
      ...devRows,
    ],
    if (showTransitiveDependencies) ...[
      if (transitiveRows.isNotEmpty)
        [_format('\ntransitive dependencies:', log.bold)],
      ...transitiveRows,
      if (includeDevDependencies) ...[
        if (devTransitiveRows.isNotEmpty)
          [_format('\ntransitive dev_dependencies:', log.bold)],
        ...devTransitiveRows,
      ],
    ],
  ];

  final columnWidths = <int, int>{};
  for (var i = 0; i < formattedRows.length; i++) {
    if (formattedRows[i].length > 1) {
      for (var j = 0; j < formattedRows[i].length; j++) {
        final currentMaxWidth = columnWidths[j] ?? 0;
        columnWidths[j] = max(
            formattedRows[i][j].computeLength(useColors: useColors),
            currentMaxWidth);
      }
    }
  }

  for (final row in formattedRows) {
    final b = StringBuffer();
    for (var j = 0; j < row.length; j++) {
      b.write(row[j].formatted(useColors: useColors));
      b.write(' ' *
          ((columnWidths[j] + 2) - row[j].computeLength(useColors: useColors)));
    }
    log.message(b.toString());
  }

  var upgradable = rows
      .where((row) =>
          row.current != null &&
          row.upgradable != null &&
          row.current != row.upgradable &&
          // Include transitive only, if we show them
          (showTransitiveDependencies ||
              hasKind(_DependencyKind.direct)(row) ||
              hasKind(_DependencyKind.dev)(row)))
      .length;

  var notAtResolvable = rows
      .where((row) =>
          (row.current != null || !lockFileExists) &&
          row.resolvable != null &&
          row.upgradable != row.resolvable &&
          // Include transitive only, if we show them
          (showTransitiveDependencies ||
              hasKind(_DependencyKind.direct)(row) ||
              hasKind(_DependencyKind.dev)(row)))
      .length;

  if (lockFileExists) {
    if (upgradable != 0) {
      if (upgradable == 1) {
        log.message('\n1 upgradable dependency is locked (in pubspec.lock) to '
            'an older version.\n'
            'To update it, use `pub upgrade`.');
      } else {
        log.message(
            '\n$upgradable upgradable dependencies are locked (in pubspec.lock) '
            'to older versions.\n'
            'To update these dependencies, use `pub upgrade`.');
      }
    }
  } else {
    log.message('\nNo pubspec.lock found. There are no Current versions.\n'
        'Run `pub get` to create a pubspec.lock with versions matching your '
        'pubspec.yaml.');
  }

  if (lockFileExists &&
      notAtResolvable == 0 &&
      upgradable == 0 &&
      rows.isNotEmpty) {
    log.message(
        '\nCurrent dependencies are constrained to versions listed in Resolvable.'
        '\nA resolution compatible with the Latest versions doesn\'t exist, as they are not'
        '\nmutually compatible.');
  }

  if (notAtResolvable != 0) {
    if (notAtResolvable == 1) {
      log.message('\n1 dependency is constrained to a '
          'version that is older than a resolvable version.\n'
          'To update it, edit pubspec.yaml.');
    } else {
      log.message('\n$notAtResolvable  dependencies are constrained to '
          'versions that are older than a resolvable version.\n'
          'To update these dependencies, edit pubspec.yaml.');
    }
  }
}

abstract class Mode {
  /// Analyzes the [_PackageDetails] according to a --mode and outputs a
  /// corresponding list of the versions
  /// [current, upgradable, resolvable, latest].
  Future<List<List<_MarkedVersionDetails>>> markVersionDetails(
      List<_PackageDetails> packageDetails);

  String get explanation;
  String get foundNoBadText;
  String get allGood;
}

class _OutdatedMode implements Mode {
  @override
  String get explanation => '''
Showing outdated packages.
[${log.red('*')}] indicates versions that are not the latest available.
''';

  @override
  String get foundNoBadText => 'Found no outdated packages';

  @override
  String get allGood => 'all up-to-date.';

  @override
  Future<List<List<_MarkedVersionDetails>>> markVersionDetails(
      List<_PackageDetails> packages) async {
    final rows = <List<_MarkedVersionDetails>>[];
    for (final packageDetails in packages) {
      final cols = <_MarkedVersionDetails>[];
      _VersionDetails previous;
      for (final versionDetails in [
        packageDetails.current,
        packageDetails.upgradable,
        packageDetails.resolvable,
        packageDetails.latest
      ]) {
        String Function(String) color;
        String prefix;
        var asDesired = false;
        if (versionDetails != null) {
          final isLatest = versionDetails == packageDetails.latest;
          if (isLatest) {
            color = versionDetails == previous ? color = log.gray : null;
            asDesired = true;
          } else {
            color = log.red;
          }
          prefix = isLatest ? '' : '*';
        }
        cols.add(
          _MarkedVersionDetails(
            versionDetails,
            asDesired: asDesired,
            format: color,
            prefix: prefix,
          ),
        );
        previous = versionDetails;
      }
      rows.add(cols);
    }
    return rows;
  }
}

class _NullSafetyMode implements Mode {
  final SystemCache cache;
  final Entrypoint entrypoint;
  final bool shouldShowSpinner;

  final _compliantEmoji = emoji('✓', '+');
  final _notCompliantEmoji = emoji('✗', 'x');

  _NullSafetyMode(this.cache, this.entrypoint,
      {@required this.shouldShowSpinner});

  @override
  String get explanation => '''
Showing dependencies that are currently not opted in to null-safety.
[${log.red(_notCompliantEmoji)}] indicates versions without null safety support.
[${log.green(_compliantEmoji)}] indicates versions opting in to null safety.
''';

  @override
  String get foundNoBadText =>
      'All your dependencies declare support for null-safety.';

  @override
  String get allGood => 'all support null safety.';

  @override
  Future<List<List<_MarkedVersionDetails>>> markVersionDetails(
      List<_PackageDetails> packages) async {
    final nullSafetyMap =
        await log.spinner('Computing null safety support', () async {
      /// Find all unique ids.
      final ids = {
        for (final packageDetails in packages) ...[
          packageDetails.current?._id,
          packageDetails.upgradable?._id,
          packageDetails.resolvable?._id,
          packageDetails.latest?._id,
        ]
      }.where((id) => id != null);

      return Map.fromEntries(
        await Future.wait(
          ids.map(
            (id) async => MapEntry(
                id,
                (await id.source.bind(cache).describe(id))
                    .languageVersion
                    .supportsNullSafety),
          ),
        ),
      );
    }, condition: shouldShowSpinner);
    return [
      for (final packageDetails in packages)
        [
          packageDetails.current,
          packageDetails.upgradable,
          packageDetails.resolvable,
          packageDetails.latest
        ].map(
          (versionDetails) {
            String Function(String) color;
            String prefix;
            bool nullSafetyJson;
            var asDesired = false;
            if (versionDetails != null) {
              if (nullSafetyMap[versionDetails._id]) {
                color = log.green;
                prefix = _compliantEmoji;
                nullSafetyJson = true;
                asDesired = true;
              } else {
                color = log.red;
                prefix = _notCompliantEmoji;
                nullSafetyJson = false;
              }
            }
            return _MarkedVersionDetails(
              versionDetails,
              asDesired: asDesired,
              format: color,
              prefix: prefix,
              jsonExplanation: MapEntry('nullSafety', nullSafetyJson),
            );
          },
        ).toList()
    ];
  }
}

/// Details about a single version of a package.
class _VersionDetails {
  final Pubspec _pubspec;

  /// True if this version is overridden.
  final bool _overridden;
  final PackageId _id;
  _VersionDetails(this._pubspec, this._id, this._overridden);

  /// A string representation of this version to include in the outdated report.
  String get describe {
    final version = _pubspec.version;
    final suffix = _overridden ? ' (overridden)' : '';
    return '$version$suffix';
  }

  Map<String, Object> toJson() => {
        'version': _pubspec.version.toString(),
        if (_overridden) 'overridden': true,
      };

  @override
  bool operator ==(Object other) =>
      identical(this, other) ||
      other is _VersionDetails &&
          _overridden == other._overridden &&
          _id.source == other._id.source &&
          _pubspec.version == other._pubspec.version;
}

class _PackageDetails implements Comparable<_PackageDetails> {
  final String name;
  final _VersionDetails current;
  final _VersionDetails upgradable;
  final _VersionDetails resolvable;
  final _VersionDetails latest;
  final _DependencyKind kind;

  _PackageDetails(this.name, this.current, this.upgradable, this.resolvable,
      this.latest, this.kind);

  @override
  int compareTo(_PackageDetails other) {
    if (kind != other.kind) {
      return kind.index.compareTo(other.kind.index);
    }
    return name.compareTo(other.name);
  }

  Map<String, Object> toJson() {
    return {
      'package': name,
      'current': current?.toJson(),
      'upgradable': upgradable?.toJson(),
      'resolvable': resolvable?.toJson(),
      'latest': latest?.toJson(),
    };
  }
}

_DependencyKind _kind(
    String name, Entrypoint entrypoint, Set<String> nonDevTransitive) {
  if (entrypoint.root.dependencies.containsKey(name)) {
    return _DependencyKind.direct;
  } else if (entrypoint.root.devDependencies.containsKey(name)) {
    return _DependencyKind.dev;
  } else {
    if (nonDevTransitive.contains(name)) {
      return _DependencyKind.transitive;
    } else {
      return _DependencyKind.devTransitive;
    }
  }
}

enum _DependencyKind {
  /// Direct non-dev dependencies.
  direct,

  /// Direct dev dependencies.
  dev,

  /// Transitive dependencies of direct dependencies.
  transitive,

  /// Transitive dependencies needed only by dev_dependencies.
  devTransitive,
}

_FormattedString _format(String value, Function(String) format, {prefix = ''}) {
  return _FormattedString(value, format: format, prefix: prefix);
}

class _MarkedVersionDetails {
  final MapEntry<String, Object> _jsonExplanation;
  final _VersionDetails _versionDetails;
  final String Function(String) _format;
  final String _prefix;

  /// This should be true if the mode creating this consideres the version as
  /// "good".
  ///
  /// By default only packages with a current version that is not as desired
  /// will be shown in the report.
  final bool asDesired;

  _MarkedVersionDetails(
    this._versionDetails, {
    @required this.asDesired,
    format,
    prefix = '',
    jsonExplanation,
  })  : _format = format,
        _prefix = prefix,
        _jsonExplanation = jsonExplanation;

  _FormattedString toHuman() => _FormattedString(
        _versionDetails?.describe ?? '-',
        format: _format,
        prefix: _prefix,
      );

  Object toJson() {
    if (_versionDetails == null) return null;

    return _jsonExplanation == null
        ? _versionDetails.toJson()
        : (_versionDetails.toJson()..addEntries([_jsonExplanation]));
  }
}

class _FormattedString {
  final String value;

  /// Should apply the ansi codes to present this string.
  final String Function(String) _format;

  /// A prefix for marking this string if colors are not used.
  final String _prefix;

  _FormattedString(this.value, {String Function(String) format, prefix})
      : _format = format ?? _noFormat,
        _prefix = prefix ?? '';

  String formatted({@required bool useColors}) {
    return useColors ? _format(_prefix + value) : _prefix + value;
  }

  int computeLength({@required bool useColors}) {
    return _prefix.length + value.length;
  }

  static String _noFormat(String x) => x;
}