// Copyright 2014 The Flutter Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

import 'package:meta/meta.dart';
import 'package:uuid/uuid.dart';
import 'package:yaml/yaml.dart';

import '../android/gradle_utils.dart' as gradle;
import '../base/common.dart';
import '../base/file_system.dart';
import '../base/utils.dart';
import '../cache.dart';
import '../convert.dart';
import '../flutter_project_metadata.dart';
import '../globals.dart' as globals;
import '../project.dart';
import '../runner/flutter_command.dart';
import '../template.dart';

const _kAvailablePlatforms = <String>['ios', 'android', 'windows', 'linux', 'macos', 'web'];

/// A list of all possible create platforms, even those that may not be enabled
/// with the current config.
const kAllCreatePlatforms = <String>[
  'ios',
  'android',
  'windows',
  'linux',
  'macos',
  'web',
  'darwin',
];

const _kDefaultPlatformArgumentHelp =
    '(required) The platforms supported by this project. '
    'Platform folders (e.g. android/) will be generated in the target project. '
    'Adding desktop platforms requires the corresponding desktop config setting to be enabled.';

/// Common behavior for `flutter create` and `flutter widget-preview start` commands.
mixin CreateBase on FlutterCommand {
  /// Pattern for a Windows file system drive (e.g. "D:").
  ///
  /// `dart:io` does not recognize strings matching this pattern as absolute
  /// paths, as they have no top level back-slash; however, users often specify
  /// this
  @visibleForTesting
  @protected
  static final kWindowsDrivePattern = RegExp(r'^[a-zA-Z]:$');

  /// The output directory of the command.
  @protected
  @visibleForTesting
  Directory get projectDir {
    final String argProjectDir = argResults!.rest.first;
    if (globals.platform.isWindows && kWindowsDrivePattern.hasMatch(argProjectDir)) {
      throwToolExit(
        'You attempted to create a flutter project at the path "$argProjectDir", which is the name of a drive. This '
        'is usually a mistake--you probably want to specify a containing directory, like "$argProjectDir\\app_name". '
        'If you really want it at the drive root, re-run the command with the root directory after the drive, like '
        '"$argProjectDir\\".',
      );
    }
    return globals.fs.directory(argResults!.rest.first);
  }

  /// The normalized absolute path of [projectDir].
  @protected
  String get projectDirPath {
    return globals.fs.path.normalize(projectDir.absolute.path);
  }

  @protected
  bool get shouldCallPubGet {
    return boolArg('pub');
  }

  @protected
  bool get offline {
    return boolArg('offline');
  }

  /// Adds `--pub` and `--offline` options.
  @protected
  void addPubOptions() {
    argParser
      ..addFlag(
        'pub',
        defaultsTo: true,
        help: 'Whether to run "flutter pub get" after the project has been created.',
      )
      ..addFlag(
        'offline',
        help:
            'When "flutter pub get" is run by the create command, this indicates '
            'whether to run it in offline mode or not. In offline mode, it will need to '
            'have all dependencies already available in the pub cache to succeed.',
      );
  }

  /// Adds a `--platforms` argument.
  ///
  /// The help message of the argument is replaced with `customHelp` if `customHelp` is not null.
  @protected
  void addPlatformsOptions({String? customHelp, required Map<String, String> allowedHelp}) {
    argParser.addMultiOption(
      'platforms',
      help: customHelp ?? _kDefaultPlatformArgumentHelp,
      aliases: <String>['platform'],
      defaultsTo: <String>[..._kAvailablePlatforms],
      allowed: <String>[...kAllCreatePlatforms],
      allowedHelp: allowedHelp,
    );
  }

  /// Throw with exit code 2 if the output directory is invalid.
  @protected
  void validateOutputDirectoryArg() {
    final List<String>? rest = argResults?.rest;
    if (rest == null || rest.isEmpty) {
      throwToolExit('No option specified for the output directory.\n$usage', exitCode: 2);
    }

    if (rest.length > 1) {
      var message = 'Multiple output directories specified.';
      for (final String arg in rest) {
        if (arg.startsWith('-')) {
          message += '\nTry moving $arg to be immediately following $name';
          break;
        }
      }
      throwToolExit(message, exitCode: 2);
    }
  }

  /// Gets the flutter root directory.
  @protected
  String get flutterRoot => Cache.flutterRoot!;

  /// Determines the project type in an existing flutter project.
  ///
  /// If it has a .metadata file with the project_type in it, use that.
  /// If it has an android dir and an android/app dir, it's a legacy app
  /// If it has an ios dir and an ios/Flutter dir, it's a legacy app
  /// Otherwise, we don't presume to know what type of project it could be, since
  /// many of the files could be missing, and we can't really tell definitively.
  ///
  /// Throws assertion if [projectDir] does not exist or empty.
  /// Returns null if no project type can be determined.
  @protected
  FlutterTemplateType? determineTemplateType() {
    assert(projectDir.existsSync() && projectDir.listSync().isNotEmpty);
    final File metadataFile = globals.fs.file(
      globals.fs.path.join(projectDir.absolute.path, '.metadata'),
    );
    final projectMetadata = FlutterProjectMetadata(metadataFile, globals.logger);
    final FlutterTemplateType? projectType = projectMetadata.projectType;
    if (projectType != null) {
      return projectType;
    }

    bool exists(List<String> path) {
      return globals.fs
          .directory(globals.fs.path.joinAll(<String>[projectDir.absolute.path, ...path]))
          .existsSync();
    }

    // There either wasn't any metadata, or it didn't contain the project type,
    // so try and figure out what type of project it is from the existing
    // directory structure.
    if (exists(<String>['android', 'app']) ||
        exists(<String>['ios', 'Runner']) ||
        exists(<String>['ios', 'Flutter'])) {
      return FlutterTemplateType.app;
    }
    // Since we can't really be definitive on nearly-empty directories, err on
    // the side of prudence and just say we don't know.
    return null;
  }

  /// Determines the organization.
  ///
  /// If `--org` is specified in the command, returns that directly.
  /// If `--org` is not specified, returns the organization from the existing project.
  @protected
  Future<String> getOrganization() async {
    String? organization = stringArg('org');
    if (!argResults!.wasParsed('org')) {
      final FlutterProject project = FlutterProject.fromDirectory(projectDir);
      final Set<String> existingOrganizations = await project.organizationNames;
      if (existingOrganizations.length == 1) {
        organization = existingOrganizations.first;
      } else if (existingOrganizations.length > 1) {
        throwToolExit(
          'Ambiguous organization in existing files: $existingOrganizations. '
          'The --org command line argument must be specified to recreate project.',
        );
      }
    }
    if (organization == null) {
      throwToolExit('The --org command line argument must be specified to create a project.');
    }
    return organization;
  }

  /// Throws with exit 2 if the project directory is illegal.
  @protected
  void validateProjectDir({bool overwrite = false}) {
    if (globals.fs.path.isWithin(flutterRoot, projectDirPath)) {
      // Make exception for dev and examples to facilitate example project development.
      final String examplesDirectory = globals.fs.path.join(flutterRoot, 'examples');
      final String devDirectory = globals.fs.path.join(flutterRoot, 'dev');
      if (!globals.fs.path.isWithin(examplesDirectory, projectDirPath) &&
          !globals.fs.path.isWithin(devDirectory, projectDirPath)) {
        throwToolExit(
          'Cannot create a project within the Flutter SDK. '
          "Target directory '$projectDirPath' is within the Flutter SDK at '$flutterRoot'.",
          exitCode: 2,
        );
      }
    }

    // If the destination directory is actually a file, then we refuse to
    // overwrite, on the theory that the user probably didn't expect it to exist.
    if (globals.fs.isFileSync(projectDirPath)) {
      final message = "Invalid project name: '$projectDirPath' - refers to an existing file.";
      throwToolExit(
        overwrite ? '$message Refusing to overwrite a file with a directory.' : message,
        exitCode: 2,
      );
    }

    if (overwrite) {
      return;
    }

    final FileSystemEntityType type = globals.fs.typeSync(projectDirPath);

    // ignore: exhaustive_cases, https://github.com/dart-lang/linter/issues/3017
    switch (type) {
      case FileSystemEntityType.file:
        // Do not overwrite files.
        throwToolExit("Invalid project name: '$projectDirPath' - file exists.", exitCode: 2);
      case FileSystemEntityType.link:
        // Do not overwrite links.
        throwToolExit("Invalid project name: '$projectDirPath' - refers to a link.", exitCode: 2);
      case FileSystemEntityType.directory:
      case FileSystemEntityType.notFound:
        break;
    }
  }

  /// Gets the project name.
  ///
  /// If the `--project-name` is not specified explicitly,
  /// the `name` field from the pubspec.yaml file is used.
  ///
  /// If the pubspec.yaml file does not exist,
  /// the current directory path name is used.
  @protected
  String get projectName {
    String? projectName = stringArg('project-name');

    if (projectName == null) {
      final File pubspec = globals.fs.directory(projectDirPath).childFile('pubspec.yaml');

      if (pubspec.existsSync()) {
        final String pubspecContents = pubspec.readAsStringSync();

        try {
          final Object? pubspecYaml = loadYaml(pubspecContents);

          if (pubspecYaml is YamlMap) {
            final Object? pubspecName = pubspecYaml['name'];

            if (pubspecName is String) {
              projectName = pubspecName;
            }
          }
        } on YamlException {
          // If the pubspec is malformed, fallback to using the directory name.
        }
      }

      final String projectDirName = globals.fs.path.basename(projectDirPath);

      projectName ??= projectDirName;
    }

    if (!boolArg('skip-name-checks')) {
      final String? error = _validateProjectName(projectName);
      if (error != null) {
        throwToolExit(error);
      }
    }
    return projectName;
  }

  /// Creates a template to use for [renderTemplate].
  @protected
  Map<String, Object?> createTemplateContext({
    required String organization,
    required String projectName,
    required String titleCaseProjectName,
    String? projectDescription,
    String? androidLanguage,
    String? iosDevelopmentTeam,
    required String flutterRoot,
    required String dartSdkVersionBounds,
    String? agpVersion,
    String? kotlinVersion,
    String? gradleVersion,
    bool withPlatformChannelPluginHook = false,
    bool withSwiftPackageManager = false,
    bool withFfiPluginHook = false,
    bool withFfiPackage = false,
    bool withEmptyMain = false,
    bool ios = false,
    bool android = false,
    bool web = false,
    bool linux = false,
    bool macos = false,
    bool windows = false,
    bool darwin = false,
    bool implementationTests = false,
  }) {
    final String pluginDartClass = _createPluginClassName(projectName);
    final pluginClass = pluginDartClass.endsWith('Plugin')
        ? pluginDartClass
        : '${pluginDartClass}Plugin';
    final String pluginClassSnakeCase = snakeCase(pluginClass);
    final String pluginClassCapitalSnakeCase = pluginClassSnakeCase.toUpperCase();
    final String pluginClassLowerCamelCase =
        pluginClass[0].toLowerCase() + pluginClass.substring(1);
    final String appleIdentifier = createUTIIdentifier(organization, projectName);
    final String androidIdentifier = createAndroidIdentifier(organization, projectName);
    final String windowsIdentifier = createWindowsIdentifier(organization, projectName);
    // Linux uses the same scheme as the Android identifier.
    // https://developer.gnome.org/gio/stable/GApplication.html#g-application-id-is-valid
    final linuxIdentifier = androidIdentifier;

    return <String, Object?>{
      'organization': organization,
      'projectName': projectName,
      'titleCaseProjectName': titleCaseProjectName,
      'androidIdentifier': androidIdentifier,
      'iosIdentifier': appleIdentifier,
      'macosIdentifier': appleIdentifier,
      'darwinIdentifier': appleIdentifier,
      'linuxIdentifier': linuxIdentifier,
      'windowsIdentifier': windowsIdentifier,
      'description': projectDescription,
      'dartSdk': '$flutterRoot/bin/cache/dart-sdk',
      'androidMinApiLevel': gradle.minSdkVersion,
      'androidSdkVersion': gradle.minSdkVersion,
      'pluginClass': pluginClass,
      'pluginClassSnakeCase': pluginClassSnakeCase,
      'pluginClassLowerCamelCase': pluginClassLowerCamelCase,
      'pluginClassCapitalSnakeCase': pluginClassCapitalSnakeCase,
      'pluginDartClass': pluginDartClass,
      'pluginProjectUUID': const Uuid().v4().toUpperCase(),
      'withFfi': withFfiPluginHook || withFfiPackage,
      'withFfiPackage': withFfiPackage,
      'withFfiPluginHook': withFfiPluginHook,
      'withPlatformChannelPluginHook': withPlatformChannelPluginHook,
      'withSwiftPackageManager': withSwiftPackageManager,
      'withPluginHook': withFfiPluginHook || withFfiPackage || withPlatformChannelPluginHook,
      'withEmptyMain': withEmptyMain,
      'androidLanguage': androidLanguage,
      'hasIosDevelopmentTeam': iosDevelopmentTeam != null && iosDevelopmentTeam.isNotEmpty,
      'iosDevelopmentTeam': iosDevelopmentTeam ?? '',
      'flutterRevision': escapeYamlString(globals.flutterVersion.frameworkRevision),
      'flutterChannel': escapeYamlString(globals.flutterVersion.getBranchName()), // may contain PII
      'ios': ios,
      'android': android,
      'web': web,
      'linux': linux,
      'macos': macos,
      'darwin': darwin,
      'sharedDarwinSource': darwin,
      'windows': windows,
      'year': DateTime.now().year,
      'dartSdkVersionBounds': dartSdkVersionBounds,
      'implementationTests': implementationTests,
      'agpVersion': agpVersion,
      'agpVersionForModule': gradle.templateAndroidGradlePluginVersionForModule,
      'kotlinVersion': kotlinVersion,
      'gradleVersion': gradleVersion,
      'compileSdkVersion': gradle.compileSdkVersion,
      'minSdkVersion': gradle.minSdkVersion,
      'ndkVersion': gradle.ndkVersion,
      'targetSdkVersion': gradle.targetSdkVersion,
    };
  }

  /// Renders the template, generate files into `directory`.
  ///
  /// `templateName` should match one of directory names under flutter_tools/template/.
  /// If `overwrite` is true, overwrites existing files, `overwrite` defaults to `false`.
  @protected
  Future<int> renderTemplate(
    String templateName,
    Directory directory,
    Map<String, Object?> context, {
    bool overwrite = false,
    bool printStatusWhenWriting = true,
  }) async {
    final Template template = await Template.fromName(
      templateName,
      fileSystem: globals.fs,
      logger: globals.logger,
      templateRenderer: globals.templateRenderer,
      templateManifest: _templateManifest,
    );
    return template.render(
      directory,
      context,
      overwriteExisting: overwrite,
      printStatusWhenWriting: printStatusWhenWriting,
    );
  }

  /// Merges named templates into a single template, output to `directory`.
  ///
  /// `names` should match directory names under flutter_tools/template/.
  ///
  /// If `overwrite` is true, overwrites existing files, `overwrite` defaults to `false`.
  @protected
  Future<int> renderMerged(
    List<String> names,
    Directory directory,
    Map<String, Object?> context, {
    bool overwrite = false,
    bool printStatusWhenWriting = true,
  }) async {
    final Template template = await Template.merged(
      names,
      directory,
      fileSystem: globals.fs,
      logger: globals.logger,
      templateRenderer: globals.templateRenderer,
      templateManifest: _templateManifest,
    );
    return template.render(
      directory,
      context,
      overwriteExisting: overwrite,
      printStatusWhenWriting: printStatusWhenWriting,
    );
  }

  /// Generate application project in the `directory` using `templateContext`.
  ///
  /// If `overwrite` is true, overwrites existing files, `overwrite` defaults to `false`.
  @protected
  Future<int> generateApp(
    List<String> templateNames,
    Directory directory,
    Map<String, Object?> templateContext, {
    bool overwrite = false,
    bool pluginExampleApp = false,
    bool printStatusWhenWriting = true,
    bool generateMetadata = true,
    FlutterTemplateType? projectType,
  }) async {
    var generatedCount = 0;
    generatedCount += await renderMerged(
      <String>[...templateNames],
      directory,
      templateContext,
      overwrite: overwrite,
      printStatusWhenWriting: printStatusWhenWriting,
    );
    final FlutterProject project = FlutterProject.fromDirectory(directory);
    if (templateContext['android'] == true) {
      generatedCount += _injectGradleWrapper(project);
    }

    final bool androidPlatform = templateContext['android'] as bool? ?? false;
    final bool iosPlatform = templateContext['ios'] as bool? ?? false;
    final bool linuxPlatform = templateContext['linux'] as bool? ?? false;
    final bool macOSPlatform = templateContext['macos'] as bool? ?? false;
    final bool windowsPlatform = templateContext['windows'] as bool? ?? false;
    final bool webPlatform = templateContext['web'] as bool? ?? false;
    final bool darwinPlatform = templateContext['darwin'] as bool? ?? false;

    final platformsForMigrateConfig = <SupportedPlatform>[SupportedPlatform.root];
    if (androidPlatform) {
      gradle.updateLocalProperties(project: project, requireAndroidSdk: false);
      platformsForMigrateConfig.add(SupportedPlatform.android);
    }
    if (iosPlatform) {
      platformsForMigrateConfig.add(SupportedPlatform.ios);
    }
    if (linuxPlatform) {
      platformsForMigrateConfig.add(SupportedPlatform.linux);
    }
    if (macOSPlatform) {
      platformsForMigrateConfig.add(SupportedPlatform.macos);
    }
    if (darwinPlatform) {
      if (!platformsForMigrateConfig.contains(SupportedPlatform.ios)) {
        platformsForMigrateConfig.add(SupportedPlatform.ios);
      }
      if (!platformsForMigrateConfig.contains(SupportedPlatform.macos)) {
        platformsForMigrateConfig.add(SupportedPlatform.macos);
      }
    }
    if (webPlatform) {
      platformsForMigrateConfig.add(SupportedPlatform.web);
    }
    if (windowsPlatform) {
      platformsForMigrateConfig.add(SupportedPlatform.windows);
    }
    if (templateContext['fuchsia'] == true) {
      platformsForMigrateConfig.add(SupportedPlatform.fuchsia);
    }
    if (generateMetadata) {
      final File metadataFile = globals.fs.file(
        globals.fs.path.join(projectDir.absolute.path, '.metadata'),
      );
      final metadata = FlutterProjectMetadata.explicit(
        file: metadataFile,
        versionRevision: globals.flutterVersion.frameworkRevision,
        versionChannel: globals.flutterVersion.getBranchName(), // may contain PII
        projectType: projectType,
        migrateConfig: MigrateConfig(),
        logger: globals.logger,
      );
      metadata.populate(
        platforms: platformsForMigrateConfig,
        projectDirectory: directory,
        update: false,
        currentRevision:
            stringArg('initial-create-revision') ?? globals.flutterVersion.frameworkRevision,
        createRevision: globals.flutterVersion.frameworkRevision,
        logger: globals.logger,
      );
      metadata.writeFile();
    }

    return generatedCount;
  }

  /// Creates an android identifier.
  ///
  /// Android application ID is specified in: https://developer.android.com/studio/build/application-id
  /// All characters must be alphanumeric or an underscore [a-zA-Z0-9_].
  static String createAndroidIdentifier(String organization, String name) {
    var tmpIdentifier = '$organization.$name';
    final disallowed = RegExp(r'[^\w\.]');
    tmpIdentifier = tmpIdentifier.replaceAll(disallowed, '');

    // It must have at least two segments (one or more dots).
    final List<String> segments = tmpIdentifier
        .split('.')
        .where((String segment) => segment.isNotEmpty)
        .toList();
    while (segments.length < 2) {
      segments.add('untitled');
    }

    // Each segment must start with a letter.
    final segmentPatternRegex = RegExp(r'^[a-zA-Z][\w]*$');
    final List<String> prefixedSegments = segments.map((String segment) {
      if (!segmentPatternRegex.hasMatch(segment)) {
        return 'u$segment';
      }
      return segment;
    }).toList();
    return prefixedSegments.join('.');
  }

  /// Creates a Windows package name.
  ///
  /// Package names must be a globally unique, commonly a GUID.
  static String createWindowsIdentifier(String organization, String name) {
    return const Uuid().v4().toUpperCase();
  }

  String _createPluginClassName(String name) {
    final String camelizedName = camelCase(name);
    return camelizedName[0].toUpperCase() + camelizedName.substring(1);
  }

  /// Create a UTI (https://en.wikipedia.org/wiki/Uniform_Type_Identifier) from a base name
  static String createUTIIdentifier(String organization, String name) {
    name = camelCase(name);
    var tmpIdentifier = '$organization.$name';
    final disallowed = RegExp(r'[^a-zA-Z0-9\-\.\u0080-\uffff]+');
    tmpIdentifier = tmpIdentifier.replaceAll(disallowed, '');

    // It must have at least two segments (one or more dots).
    final List<String> segments = tmpIdentifier
        .split('.')
        .where((String segment) => segment.isNotEmpty)
        .toList();
    while (segments.length < 2) {
      segments.add('untitled');
    }

    return segments.join('.');
  }

  late final Set<Uri> _templateManifest = _computeTemplateManifest();
  Set<Uri> _computeTemplateManifest() {
    final String flutterToolsAbsolutePath = globals.fs.path.join(
      Cache.flutterRoot!,
      'packages',
      'flutter_tools',
    );
    final String manifestPath = globals.fs.path.join(
      flutterToolsAbsolutePath,
      'templates',
      'template_manifest.json',
    );
    final String manifestFileContents;
    try {
      manifestFileContents = globals.fs.file(manifestPath).readAsStringSync();
    } on FileSystemException catch (e) {
      throwToolExit(
        'Unable to read the template manifest at path "$manifestPath".\n'
        'Make sure that your user account has sufficient permissions to read this file.\n'
        'Exception details: $e',
      );
    }
    final manifest = json.decode(manifestFileContents) as Map<String, Object?>;
    return Set<Uri>.from(
      (manifest['files']! as List<Object?>).cast<String>().map<Uri>(
        (String path) => Uri.file(globals.fs.path.join(flutterToolsAbsolutePath, path)),
      ),
    );
  }

  int _injectGradleWrapper(FlutterProject project) {
    var filesCreated = 0;
    copyDirectory(
      globals.cache.getArtifactDirectory('gradle_wrapper'),
      project.android.hostAppGradleRoot,
      onFileCopied: (File sourceFile, File destinationFile) {
        filesCreated++;
        final String modes = sourceFile.statSync().modeString();
        if (modes.contains('x')) {
          globals.os.makeExecutable(destinationFile);
        }
      },
    );
    return filesCreated;
  }
}

// A valid Dart identifier that can be used for a package, i.e. no
// capital letters.
// https://dart.dev/language#important-concepts
final _identifierRegExp = RegExp('[a-z_][a-z0-9_]*');

// non-contextual dart keywords.
// https://dart.dev/language/keywords
const _keywords = <String>{
  'abstract',
  'as',
  'assert',
  'async',
  'await',
  'break',
  'case',
  'catch',
  'class',
  'const',
  'continue',
  'covariant',
  'default',
  'deferred',
  'do',
  'dynamic',
  'else',
  'enum',
  'export',
  'extends',
  'extension',
  'external',
  'factory',
  'false',
  'final',
  'finally',
  'for',
  'function',
  'get',
  'hide',
  'if',
  'implements',
  'import',
  'in',
  'inout',
  'interface',
  'is',
  'late',
  'library',
  'mixin',
  'native',
  'new',
  'null',
  'of',
  'on',
  'operator',
  'out',
  'part',
  'patch',
  'required',
  'rethrow',
  'return',
  'set',
  'show',
  'source',
  'static',
  'super',
  'switch',
  'sync',
  'this',
  'throw',
  'true',
  'try',
  'typedef',
  'var',
  'void',
  'while',
  'with',
  'yield',
};

const _packageDependencies = <String>{'collection', 'flutter', 'flutter_test', 'meta'};

/// Whether [name] is a valid Pub package.
@visibleForTesting
bool isValidPackageName(String name) {
  final Match? match = _identifierRegExp.matchAsPrefix(name);
  return match != null && match.end == name.length && !_keywords.contains(name);
}

/// Returns a potential valid name from the given [name].
///
/// If a valid name cannot be found, returns `null`.
@visibleForTesting
String? potentialValidPackageName(String name) {
  String newName = name.toLowerCase();
  if (newName.startsWith(RegExp(r'[0-9]'))) {
    newName = '_$newName';
  }
  newName = newName.replaceAll('-', '_');
  if (isValidPackageName(newName)) {
    return newName;
  } else {
    return null;
  }
}

// Return null if the project name is legal. Return a validation message if
// we should disallow the project name.
String? _validateProjectName(String projectName) {
  if (!isValidPackageName(projectName)) {
    final String? potentialValidName = potentialValidPackageName(projectName);
    return '"$projectName" is not a valid Dart package name.'
        '${potentialValidName != null ? ' Try "$potentialValidName" instead.' : ''}\n'
        '\n'
        'The name should consist of lowercase words separated by underscores, "like_this". '
        'Use only basic Latin letters and Arabic digits: [a-z0-9_], and '
        'ensure the name is a valid Dart identifier '
        '(i.e. it does not start with a digit and is not a reserved word).\n'
        '\n'
        'See https://dart.dev/tools/pub/pubspec#name for more information.';
  }
  if (_packageDependencies.contains(projectName)) {
    return "Invalid project name: '$projectName' - this will conflict with Flutter "
        'package dependencies.';
  }
  return null;
}