// 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 'package:analyzer/dart/analysis/analysis_context.dart';
import 'package:analyzer/dart/ast/ast.dart';
import 'package:analyzer/error/listener.dart';
import 'package:analyzer/file_system/file_system.dart';
import 'package:analyzer/source/line_info.dart';
import 'package:analyzer/src/dart/analysis/byte_store.dart';
import 'package:analyzer/src/dart/scanner/reader.dart';
import 'package:analyzer/src/dart/scanner/scanner.dart';
import 'package:analyzer/src/generated/parser.dart';
import 'package:analyzer/src/generated/utilities_dart.dart';
import 'package:analyzer/src/string_source.dart';
import 'package:analyzer/src/summary/api_signature.dart';
import 'package:analyzer/src/summary/format.dart' as idl;
import 'package:analyzer/src/summary/idl.dart' as idl;
import 'package:analyzer/src/summary/link.dart' as graph
    show DependencyWalker, Node;
import 'package:analyzer/src/util/comment.dart';
import 'package:convert/convert.dart';
import 'package:meta/meta.dart';
import 'package:yaml/yaml.dart';

/// A top-level public declaration.
class Declaration {
  final String defaultArgumentListString;
  final List<int> defaultArgumentListTextRanges;
  final String docComplete;
  final String docSummary;
  final bool isAbstract;
  final bool isConst;
  final bool isDeprecated;
  final bool isFinal;
  final DeclarationKind kind;
  final int locationOffset;
  final String locationPath;
  final int locationStartColumn;
  final int locationStartLine;

  /// The name of the declaration.
  /// For enum constants, the name of the constant.
  final String name;

  /// Usually `null`.
  /// For enum constants, the name of the enum.
  final String name2;

  final String parameters;
  final List<String> parameterNames;
  final List<String> parameterTypes;
  final int requiredParameterCount;
  final String returnType;
  final String typeParameters;

  List<String> _relevanceTags;

  Declaration({
    @required this.defaultArgumentListString,
    @required this.defaultArgumentListTextRanges,
    @required this.docComplete,
    @required this.docSummary,
    @required this.isAbstract,
    @required this.isConst,
    @required this.isDeprecated,
    @required this.isFinal,
    @required this.kind,
    @required this.locationOffset,
    @required this.locationPath,
    @required this.locationStartColumn,
    @required this.locationStartLine,
    @required this.name,
    @required this.name2,
    @required this.parameters,
    @required this.parameterNames,
    @required this.parameterTypes,
    @required List<String> relevanceTags,
    @required this.requiredParameterCount,
    @required this.returnType,
    @required this.typeParameters,
  }) : _relevanceTags = relevanceTags;

  List<String> get relevanceTags => _relevanceTags;

  @override
  String toString() {
    if (name2 == null) {
      return '($kind, $name)';
    } else {
      return '($kind, $name, $name2)';
    }
  }
}

/// A kind of a top-level declaration.
enum DeclarationKind {
  CLASS,
  CLASS_TYPE_ALIAS,
  ENUM,
  ENUM_CONSTANT,
  FUNCTION,
  FUNCTION_TYPE_ALIAS,
  GETTER,
  MIXIN,
  SETTER,
  VARIABLE
}

/// The context in which completions happens, so declarations are collected.
class DeclarationsContext {
  final DeclarationsTracker _tracker;

  /// The analysis context for this context.  Declarations from all files in
  /// the root are included into completion, even in 'lib/src' folders.
  final AnalysisContext _analysisContext;

  /// Packages in the analysis context.
  ///
  /// Packages are sorted so that inner packages are before outer.
  final List<_Package> _packages = [];

  /// The list of paths of all files inside the context.
  final List<String> _contextPathList = [];

  /// The list of paths of all SDK libraries.
  final List<String> _sdkLibraryPathList = [];

  /// Map of path prefixes to lists of paths of files from dependencies
  /// (both libraries and parts, we don't know at the time when we fill this
  /// map) that libraries with paths starting with these prefixes can access.
  ///
  /// The path prefix keys are sorted so that the longest keys are first.
  final Map<String, List<String>> _pathPrefixToDependencyPathList = {};

  DeclarationsContext(this._tracker, this._analysisContext);

  /// Return libraries that are available to the file with the given [path].
  ///
  /// With `Pub`, files below the `pubspec.yaml` file can access libraries
  /// of packages listed as `dependencies`, and files in the `test` directory
  /// can in addition access libraries of packages listed as `dev_dependencies`.
  ///
  /// With `Bazel` sets of accessible libraries are specified explicitly by
  /// the client using [setDependencies].
  Libraries getLibraries(String path) {
    var sdkLibraries = <Library>[];
    _addLibrariesWithPaths(sdkLibraries, _sdkLibraryPathList);

    var dependencyLibraries = <Library>[];
    for (var pathPrefix in _pathPrefixToDependencyPathList.keys) {
      if (path.startsWith(pathPrefix)) {
        var pathList = _pathPrefixToDependencyPathList[pathPrefix];
        _addLibrariesWithPaths(dependencyLibraries, pathList);
        break;
      }
    }

    _Package package;
    for (var candidatePackage in _packages) {
      if (candidatePackage.contains(path)) {
        package = candidatePackage;
        break;
      }
    }

    var contextPathList = <String>[];
    if (package != null) {
      var containingFolder = package.folderInRootContaining(path);
      if (containingFolder != null) {
        for (var contextPath in _contextPathList) {
          // `lib/` can see only libraries in `lib/`.
          // `test/` can see libraries in `lib/` and in `test/`.
          if (package.containsInLib(contextPath) ||
              containingFolder.contains(contextPath)) {
            contextPathList.add(contextPath);
          }
        }
      }
    } else {
      // Not in a package, include all libraries of the context.
      contextPathList = _contextPathList;
    }

    var contextLibraries = <Library>[];
    _addLibrariesWithPaths(
      contextLibraries,
      contextPathList,
      excludingLibraryOfPath: path,
    );

    return Libraries(sdkLibraries, dependencyLibraries, contextLibraries);
  }

  /// Set dependencies for path prefixes in this context.
  ///
  /// The map [pathPrefixToPathList] specifies the list of paths of libraries
  /// and directories with libraries that are accessible to the files with
  /// paths that start with the path that is the key in the map.  The longest
  /// (so most specific) key will be used, each list of paths is complete, and
  /// is not combined with any enclosing locations.
  ///
  /// For `Pub` packages this method is invoked automatically, because their
  /// dependencies, described in `pubspec.yaml` files, and can be automatically
  /// included.  This method is useful for `Bazel` contexts, where dependencies
  /// are specified externally, in form of `BUILD` files.
  ///
  /// New dependencies will replace any previously set dependencies for this
  /// context.
  ///
  /// Every path in the list must be absolute and normalized.
  void setDependencies(Map<String, List<String>> pathPrefixToPathList) {
    var rootFolder = _analysisContext.contextRoot.root;
    _pathPrefixToDependencyPathList.removeWhere((pathPrefix, _) {
      return rootFolder.isOrContains(pathPrefix);
    });

    var sortedPrefixes = pathPrefixToPathList.keys.toList();
    sortedPrefixes.sort((a, b) {
      return b.compareTo(a);
    });

    for (var pathPrefix in sortedPrefixes) {
      var pathList = pathPrefixToPathList[pathPrefix];
      var files = <String>[];
      for (var path in pathList) {
        var resource = _tracker._resourceProvider.getResource(path);
        _scheduleDependencyResource(files, resource);
      }
      _pathPrefixToDependencyPathList[pathPrefix] = files;
    }
  }

  void _addContextFile(String path) {
    if (!_contextPathList.contains(path)) {
      _contextPathList.add(path);
    }
  }

  void _addLibrariesWithPaths(List<Library> libraries, List<String> pathList,
      {String excludingLibraryOfPath}) {
    var excludedFile = _tracker._pathToFile[excludingLibraryOfPath];
    var excludedLibraryPath = (excludedFile?.library ?? excludedFile)?.path;

    for (var path in pathList) {
      if (path == excludedLibraryPath) continue;

      var file = _tracker._pathToFile[path];
      if (file != null && file.isLibrary) {
        var library = _tracker._idToLibrary[file.id];
        if (library != null) {
          libraries.add(library);
        }
      }
    }
  }

  /// Traverse the folders of this context and fill [_packages];  use
  /// `pubspec.yaml` files to set `Pub` dependencies.
  void _findPackages() {
    var pathContext = _tracker._resourceProvider.pathContext;
    var pubPathPrefixToPathList = <String, List<String>>{};

    void visitFolder(Folder folder) {
      var buildFile = folder.getChildAssumingFile('BUILD');
      var pubspecFile = folder.getChildAssumingFile('pubspec.yaml');
      if (buildFile.exists) {
        _packages.add(_Package(folder));
      } else if (pubspecFile.exists) {
        var dependencies = _parsePubspecDependencies(pubspecFile);
        var libPaths = _resolvePackageNamesToLibPaths(dependencies.lib);
        var devPaths = _resolvePackageNamesToLibPaths(dependencies.dev);

        var packagePath = folder.path;
        pubPathPrefixToPathList[packagePath] = <String>[]
          ..addAll(libPaths)
          ..addAll(devPaths);

        var libPath = pathContext.join(packagePath, 'lib');
        pubPathPrefixToPathList[libPath] = libPaths;

        _packages.add(_Package(folder));
      }

      try {
        for (var resource in folder.getChildren()) {
          if (resource is Folder) {
            visitFolder(resource);
          }
        }
      } on FileSystemException {}
    }

    visitFolder(_analysisContext.contextRoot.root);
    setDependencies(pubPathPrefixToPathList);

    _packages.sort((a, b) {
      var aRoot = a.root.path;
      var bRoot = b.root.path;
      return bRoot.compareTo(aRoot);
    });
  }

  bool _isLibSrcPath(String path) {
    var parts = _tracker._resourceProvider.pathContext.split(path);
    for (var i = 0; i < parts.length - 1; ++i) {
      if (parts[i] == 'lib' && parts[i + 1] == 'src') return true;
    }
    return false;
  }

  List<String> _resolvePackageNamesToLibPaths(List<String> packageNames) {
    return packageNames
        .map(_resolvePackageNameToLibPath)
        .where((path) => path != null)
        .toList();
  }

  String _resolvePackageNameToLibPath(String packageName) {
    try {
      var uri = Uri.parse('package:$packageName/ref.dart');

      var path = _resolveUri(uri);
      if (path == null) return null;

      return _tracker._resourceProvider.pathContext.dirname(path);
    } on FormatException {
      return null;
    }
  }

  String _resolveUri(Uri uri) {
    var uriConverter = _analysisContext.currentSession.uriConverter;
    return uriConverter.uriToPath(uri);
  }

  Uri _restoreUri(String path) {
    var uriConverter = _analysisContext.currentSession.uriConverter;
    return uriConverter.pathToUri(path);
  }

  void _scheduleContextFiles() {
    var contextFiles = _analysisContext.contextRoot.analyzedFiles();
    for (var path in contextFiles) {
      _contextPathList.add(path);
      _tracker._addFile(this, path);
    }
  }

  void _scheduleDependencyFolder(List<String> files, Folder folder) {
    if (_isLibSrcPath(folder.path)) return;
    try {
      for (var resource in folder.getChildren()) {
        _scheduleDependencyResource(files, resource);
      }
    } on FileSystemException catch (_) {}
  }

  void _scheduleDependencyResource(List<String> files, Resource resource) {
    if (resource is File) {
      files.add(resource.path);
      _tracker._addFile(this, resource.path);
    } else if (resource is Folder) {
      _scheduleDependencyFolder(files, resource);
    }
  }

  void _scheduleSdkLibraries() {
    // ignore: deprecated_member_use_from_same_package
    var sdk = _analysisContext.currentSession.sourceFactory.dartSdk;
    for (var uriStr in sdk.uris) {
      if (!uriStr.startsWith('dart:_')) {
        var uri = Uri.parse(uriStr);
        var path = _resolveUri(uri);
        if (path != null) {
          _sdkLibraryPathList.add(path);
          _tracker._addFile(this, path);
        }
      }
    }
  }

  static _PubspecDependencies _parsePubspecDependencies(File pubspecFile) {
    var dependencies = <String>[];
    var devDependencies = <String>[];
    try {
      var fileContent = pubspecFile.readAsStringSync();
      var document = loadYamlDocument(fileContent);
      var contents = document.contents;
      if (contents is YamlMap) {
        var dependenciesNode = contents.nodes['dependencies'];
        if (dependenciesNode is YamlMap) {
          dependencies = dependenciesNode.keys.whereType<String>().toList();
        }

        var devDependenciesNode = contents.nodes['dev_dependencies'];
        if (devDependenciesNode is YamlMap) {
          devDependencies =
              devDependenciesNode.keys.whereType<String>().toList();
        }
      }
    } catch (e) {}
    return _PubspecDependencies(dependencies, devDependencies);
  }
}

/// Tracker for top-level declarations across multiple analysis contexts
/// and their dependencies.
class DeclarationsTracker {
  final ByteStore _byteStore;
  final ResourceProvider _resourceProvider;

  final Map<AnalysisContext, DeclarationsContext> _contexts = {};
  final Map<String, _File> _pathToFile = {};
  final Map<Uri, _File> _uriToFile = {};
  final Map<int, Library> _idToLibrary = {};

  final _changesController = _StreamController<LibraryChange>();

  /// The list of changed file paths.
  final List<String> _changedPaths = [];

  /// The list of files scheduled for processing.  It may include parts and
  /// libraries, but parts are ignored when we detect them.
  final List<_ScheduledFile> _scheduledFiles = [];

  DeclarationsTracker(this._byteStore, this._resourceProvider);

  /// The stream of changes to the set of libraries used by the added contexts.
  Stream<LibraryChange> get changes => _changesController.stream;

  /// Return `true` if there is scheduled work to do, as a result of adding
  /// new contexts, or changes to files.
  bool get hasWork {
    return _changedPaths.isNotEmpty || _scheduledFiles.isNotEmpty;
  }

  /// Add the [analysisContext], so that its libraries are reported via the
  /// [changes] stream, and return the [DeclarationsContext] that can be used
  /// to set additional dependencies and request libraries available to this
  /// context.
  DeclarationsContext addContext(AnalysisContext analysisContext) {
    if (_contexts.containsKey(analysisContext)) {
      throw StateError('The analysis context has already been added.');
    }

    var declarationsContext = DeclarationsContext(this, analysisContext);
    _contexts[analysisContext] = declarationsContext;

    declarationsContext._scheduleContextFiles();
    declarationsContext._scheduleSdkLibraries();
    declarationsContext._findPackages();
    return declarationsContext;
  }

  /// The file with the given [path] was changed - added, updated, or removed.
  ///
  /// The [path] must be absolute and normalized.
  ///
  /// Usually causes [hasWork] to return `true`, so that [doWork] should
  /// be invoked to send updates to [changes] that reflect changes to the
  /// library of the file, and other libraries that export it.
  void changeFile(String path) {
    if (!path.endsWith('.dart')) return;

    _changedPaths.add(path);
  }

  /// Discard all contexts and libraries, notify the [changes] stream that
  /// these libraries are removed.
  void discardContexts() {
    var libraryIdList = _idToLibrary.keys.toList();
    _changesController.add(LibraryChange._([], libraryIdList));

    _contexts.clear();
    _pathToFile.clear();
    _uriToFile.clear();
    _idToLibrary.clear();
    _changedPaths.clear();
    _scheduledFiles.clear();
  }

  /// Do a single piece of work.
  ///
  /// The client should call this method until [hasWork] returns `false`.
  /// This would mean that all previous changes have been processed, and
  /// updates scheduled to be delivered via the [changes] stream.
  void doWork() {
    if (_changedPaths.isNotEmpty) {
      var path = _changedPaths.removeLast();
      _performChangeFile(path);
      return;
    }

    if (_scheduledFiles.isNotEmpty) {
      var scheduledFile = _scheduledFiles.removeLast();
      var file = _getFileByPath(scheduledFile.context, scheduledFile.path);

      if (!file.isLibrary) return;

      if (file.isSent) {
        return;
      } else {
        file.isSent = true;
      }

      if (file.exportedDeclarations == null) {
        new _LibraryWalker().walkLibrary(file);
        assert(file.exportedDeclarations != null);
      }

      var library = Library._(
        file.id,
        file.path,
        file.uri,
        file.isLibraryDeprecated,
        file.exportedDeclarations,
      );
      _idToLibrary[file.id] = library;
      _changesController.add(
        LibraryChange._([library], []),
      );
    }
  }

  /// Return the context associated with the given [analysisContext], or `null`
  /// if there is none.
  DeclarationsContext getContext(AnalysisContext analysisContext) {
    return _contexts[analysisContext];
  }

  /// Return the library with the given [id], or `null` if there is none.
  Library getLibrary(int id) {
    return _idToLibrary[id];
  }

  void _addFile(DeclarationsContext context, String path) {
    if (path.endsWith('.dart')) {
      _scheduledFiles.add(_ScheduledFile(context, path));
    }
  }

  /// Compute exported declarations for the given [libraries].
  void _computeExportedDeclarations(Set<_File> libraries) {
    var walker = new _LibraryWalker();
    for (var library in libraries) {
      if (library.isLibrary && library.exportedDeclarations == null) {
        walker.walkLibrary(library);
        assert(library.exportedDeclarations != null);
      }
    }
  }

  DeclarationsContext _findContextOfPath(String path) {
    // Prefer the context in which the path is analyzed.
    for (var context in _contexts.values) {
      if (context._analysisContext.contextRoot.isAnalyzed(path)) {
        context._addContextFile(path);
        return context;
      }
    }

    // The path must have the URI with one of the supported URI schemes.
    for (var context in _contexts.values) {
      var uri = context._restoreUri(path);
      if (uri != null) {
        if (uri.isScheme('dart') || uri.isScheme('package')) {
          return context;
        }
      }
    }

    return null;
  }

  _File _getFileByPath(DeclarationsContext context, String path) {
    var file = _pathToFile[path];
    if (file == null) {
      var uri = context._restoreUri(path);
      if (uri != null) {
        file = _File(this, path, uri);
        _pathToFile[path] = file;
        _uriToFile[uri] = file;
        file.refresh(context);
      }
    }
    return file;
  }

  _File _getFileByUri(DeclarationsContext context, Uri uri) {
    var file = _uriToFile[uri];
    if (file == null) {
      var path = context._resolveUri(uri);
      if (path != null) {
        file = _File(this, path, uri);
        _pathToFile[path] = file;
        _uriToFile[uri] = file;
        file.refresh(context);
      }
    }
    return file;
  }

  /// Recursively invalidate exported declarations of the given [library]
  /// and libraries that export it.
  void _invalidateExportedDeclarations(Set<_File> libraries, _File library) {
    if (libraries.add(library)) {
      library.exportedDeclarations = null;
      for (var exporter in library.directExporters) {
        _invalidateExportedDeclarations(libraries, exporter);
      }
    }
  }

  void _performChangeFile(String path) {
    var containingContext = _findContextOfPath(path);
    if (containingContext == null) return;

    var file = _getFileByPath(containingContext, path);
    if (file == null) return;

    var isLibrary = file.isLibrary;
    var library = isLibrary ? file : file.library;

    if (isLibrary) {
      file.refresh(containingContext);
    } else {
      file.refresh(containingContext);
      library.refresh(containingContext);
    }

    var invalidatedLibraries = Set<_File>();
    _invalidateExportedDeclarations(invalidatedLibraries, library);
    _computeExportedDeclarations(invalidatedLibraries);

    var changedLibraries = <Library>[];
    var removedLibraries = <int>[];
    for (var libraryFile in invalidatedLibraries) {
      if (libraryFile.exists) {
        var library = Library._(
          libraryFile.id,
          libraryFile.path,
          libraryFile.uri,
          libraryFile.isLibraryDeprecated,
          libraryFile.exportedDeclarations,
        );
        _idToLibrary[library.id] = library;
        changedLibraries.add(library);
      } else {
        _idToLibrary.remove(libraryFile.id);
        removedLibraries.add(libraryFile.id);
      }
    }
    _changesController.add(
      LibraryChange._(changedLibraries, removedLibraries),
    );
  }
}

class Libraries {
  final List<Library> sdk;
  final List<Library> dependencies;
  final List<Library> context;

  Libraries(this.sdk, this.dependencies, this.context);
}

/// A library with declarations.
class Library {
  /// The unique identifier of a library with the given [path].
  final int id;

  /// The path to the file that defines this library.
  final String path;

  /// The URI of the library.
  final Uri uri;

  /// Is `true` if the library has `@deprecated` annotation, so it probably
  /// deprecated.  But we don't actually resolve the annotation, so it might be
  /// a false positive.
  final bool isDeprecated;

  /// All public declaration that the library declares or (re)exports.
  final List<Declaration> declarations;

  Library._(this.id, this.path, this.uri, this.isDeprecated, this.declarations);

  String get uriStr => '$uri';

  @override
  String toString() {
    return '(id: $id, uri: $uri, path: $path)';
  }
}

/// A change to the set of libraries and their declarations.
class LibraryChange {
  /// The list of new or changed libraries.
  final List<Library> changed;

  /// The list of identifier of libraries that are removed, either because
  /// the corresponding files were removed, or because none of the contexts
  /// has these libraries as dependencies, so that they cannot be used anymore.
  final List<int> removed;

  LibraryChange._(this.changed, this.removed);
}

class RelevanceTags {
  static List<String> _forDeclaration(String uriStr, Declaration declaration) {
    switch (declaration.kind) {
      case DeclarationKind.CLASS:
      case DeclarationKind.CLASS_TYPE_ALIAS:
      case DeclarationKind.ENUM:
      case DeclarationKind.MIXIN:
      case DeclarationKind.FUNCTION_TYPE_ALIAS:
        var name = declaration.name;
        return <String>['$uriStr::$name'];
      case DeclarationKind.ENUM_CONSTANT:
        var name2 = declaration.name2;
        return <String>['$uriStr::$name2'];
      default:
        return null;
    }
  }

  static List<String> _forExpression(Expression expression) {
    if (expression is BooleanLiteral) {
      return const ['dart:core::bool'];
    } else if (expression is DoubleLiteral) {
      return const ['dart:core::double'];
    } else if (expression is IntegerLiteral) {
      return const ['dart:core::int'];
    } else if (expression is StringLiteral) {
      return const ['dart:core::String'];
    } else if (expression is ListLiteral) {
      return const ['dart:core::List'];
    } else if (expression is SetOrMapLiteral) {
      if (expression.isMap) {
        return const ['dart:core::Map'];
      } else if (expression.isSet) {
        return const ['dart:core::Set'];
      }
    }

    return null;
  }
}

class _DeclarationStorage {
  static const fieldDocMask = 1 << 0;
  static const fieldName2Mask = 1 << 1;
  static const fieldParametersMask = 1 << 2;
  static const fieldReturnTypeMask = 1 << 3;
  static const fieldTypeParametersMask = 1 << 4;

  static Declaration fromIdl(String path, idl.AvailableDeclaration d) {
    var fieldMask = d.fieldMask;
    var hasDoc = fieldMask & fieldDocMask != 0;
    var hasName2 = fieldMask & fieldName2Mask != 0;
    var hasParameters = fieldMask & fieldParametersMask != 0;
    var hasReturnType = fieldMask & fieldReturnTypeMask != 0;
    var hasTypeParameters = fieldMask & fieldTypeParametersMask != 0;

    var kind = kindFromIdl(d.kind);

    var relevanceTags = d.relevanceTags.toList();
    if (relevanceTags.isEmpty) {
      relevanceTags = null;
    }

    return Declaration(
      defaultArgumentListString: d.defaultArgumentListString.isNotEmpty
          ? d.defaultArgumentListString
          : null,
      defaultArgumentListTextRanges: d.defaultArgumentListTextRanges.isNotEmpty
          ? d.defaultArgumentListTextRanges
          : null,
      docComplete: hasDoc ? d.docComplete : null,
      docSummary: hasDoc ? d.docSummary : null,
      isAbstract: d.isAbstract,
      isConst: d.isConst,
      isDeprecated: d.isDeprecated,
      isFinal: d.isFinal,
      kind: kind,
      locationOffset: d.locationOffset,
      locationPath: path,
      locationStartColumn: d.locationStartColumn,
      locationStartLine: d.locationStartLine,
      name: d.name,
      name2: hasName2 ? d.name2 : null,
      parameters: hasParameters ? d.parameters : null,
      parameterNames: hasParameters ? d.parameterNames : null,
      parameterTypes: hasParameters ? d.parameterTypes.toList() : null,
      relevanceTags: relevanceTags,
      requiredParameterCount: hasParameters ? d.requiredParameterCount : null,
      returnType: hasReturnType ? d.returnType : null,
      typeParameters: hasTypeParameters ? d.typeParameters : null,
    );
  }

  static DeclarationKind kindFromIdl(idl.AvailableDeclarationKind kind) {
    switch (kind) {
      case idl.AvailableDeclarationKind.CLASS:
        return DeclarationKind.CLASS;
      case idl.AvailableDeclarationKind.CLASS_TYPE_ALIAS:
        return DeclarationKind.CLASS_TYPE_ALIAS;
      case idl.AvailableDeclarationKind.ENUM:
        return DeclarationKind.ENUM;
      case idl.AvailableDeclarationKind.ENUM_CONSTANT:
        return DeclarationKind.ENUM_CONSTANT;
      case idl.AvailableDeclarationKind.FUNCTION:
        return DeclarationKind.FUNCTION;
      case idl.AvailableDeclarationKind.FUNCTION_TYPE_ALIAS:
        return DeclarationKind.FUNCTION_TYPE_ALIAS;
      case idl.AvailableDeclarationKind.GETTER:
        return DeclarationKind.GETTER;
      case idl.AvailableDeclarationKind.MIXIN:
        return DeclarationKind.MIXIN;
      case idl.AvailableDeclarationKind.SETTER:
        return DeclarationKind.SETTER;
      case idl.AvailableDeclarationKind.VARIABLE:
        return DeclarationKind.VARIABLE;
      default:
        throw StateError('Unknown kind: $kind');
    }
  }

  static idl.AvailableDeclarationKind kindToIdl(DeclarationKind kind) {
    switch (kind) {
      case DeclarationKind.CLASS:
        return idl.AvailableDeclarationKind.CLASS;
      case DeclarationKind.CLASS_TYPE_ALIAS:
        return idl.AvailableDeclarationKind.CLASS_TYPE_ALIAS;
      case DeclarationKind.ENUM:
        return idl.AvailableDeclarationKind.ENUM;
      case DeclarationKind.ENUM_CONSTANT:
        return idl.AvailableDeclarationKind.ENUM_CONSTANT;
      case DeclarationKind.FUNCTION:
        return idl.AvailableDeclarationKind.FUNCTION;
      case DeclarationKind.FUNCTION_TYPE_ALIAS:
        return idl.AvailableDeclarationKind.FUNCTION_TYPE_ALIAS;
      case DeclarationKind.GETTER:
        return idl.AvailableDeclarationKind.GETTER;
      case DeclarationKind.MIXIN:
        return idl.AvailableDeclarationKind.MIXIN;
      case DeclarationKind.SETTER:
        return idl.AvailableDeclarationKind.SETTER;
      case DeclarationKind.VARIABLE:
        return idl.AvailableDeclarationKind.VARIABLE;
      default:
        throw StateError('Unknown kind: $kind');
    }
  }

  static idl.AvailableDeclarationBuilder toIdl(Declaration d) {
    var fieldMask = 0;
    if (d.docComplete != null) {
      fieldMask |= fieldDocMask;
    }
    if (d.name2 != null) {
      fieldMask |= fieldName2Mask;
    }
    if (d.parameters != null) {
      fieldMask |= fieldParametersMask;
    }
    if (d.returnType != null) {
      fieldMask |= fieldReturnTypeMask;
    }
    if (d.typeParameters != null) {
      fieldMask |= fieldTypeParametersMask;
    }

    var idlKind = kindToIdl(d.kind);
    return idl.AvailableDeclarationBuilder(
      defaultArgumentListString: d.defaultArgumentListString,
      defaultArgumentListTextRanges: d.defaultArgumentListTextRanges,
      docComplete: d.docComplete,
      docSummary: d.docSummary,
      fieldMask: fieldMask,
      isAbstract: d.isAbstract,
      isConst: d.isConst,
      isDeprecated: d.isDeprecated,
      isFinal: d.isFinal,
      kind: idlKind,
      locationOffset: d.locationOffset,
      locationStartColumn: d.locationStartColumn,
      locationStartLine: d.locationStartLine,
      name: d.name,
      name2: d.name2,
      parameters: d.parameters,
      parameterNames: d.parameterNames,
      parameterTypes: d.parameterTypes,
      relevanceTags: d.relevanceTags,
      requiredParameterCount: d.requiredParameterCount,
      returnType: d.returnType,
      typeParameters: d.typeParameters,
    );
  }
}

class _DefaultArguments {
  final String text;
  final List<int> ranges;

  _DefaultArguments(this.text, this.ranges);
}

class _Export {
  final Uri uri;
  final List<_ExportCombinator> combinators;

  _File file;

  _Export(this.uri, this.combinators);

  Iterable<Declaration> filter(List<Declaration> declarations) {
    return declarations.where((d) {
      var name = d.name2 ?? d.name;
      for (var combinator in combinators) {
        if (combinator.shows.isNotEmpty) {
          if (!combinator.shows.contains(name)) return false;
        }
        if (combinator.hides.isNotEmpty) {
          if (combinator.hides.contains(name)) return false;
        }
      }
      return true;
    });
  }
}

class _ExportCombinator {
  final List<String> shows;
  final List<String> hides;

  _ExportCombinator(this.shows, this.hides);
}

class _File {
  /// The version of data format, should be incremented on every format change.
  static const int DATA_VERSION = 8;

  /// The next value for [id].
  static int _nextId = 0;

  final DeclarationsTracker tracker;

  final int id = _nextId++;
  final String path;
  final Uri uri;

  bool exists = false;
  bool isLibrary = false;
  bool isLibraryDeprecated = false;
  List<_Export> exports = [];
  List<_Part> parts = [];

  /// If this file is a part, the containing library.
  _File library;

  /// If this file is a library, libraries that export it.
  List<_File> directExporters = [];

  List<Declaration> fileDeclarations = [];
  List<Declaration> libraryDeclarations = [];
  List<Declaration> exportedDeclarations;

  /// If `true`, then this library has already been sent to the client.
  bool isSent = false;

  _File(this.tracker, this.path, this.uri);

  String get uriStr => uri.toString();

  void refresh(DeclarationsContext context) {
    var resource = tracker._resourceProvider.getFile(path);

    int modificationStamp;
    try {
      modificationStamp = resource.modificationStamp;
      exists = true;
    } catch (e) {
      modificationStamp = -1;
      exists = false;
    }

    // When a file changes, its modification stamp changes.
    String pathKey;
    {
      var pathKeyBuilder = ApiSignature();
      pathKeyBuilder.addInt(DATA_VERSION);
      pathKeyBuilder.addString(path);
      pathKeyBuilder.addInt(modificationStamp);
      pathKey = pathKeyBuilder.toHex() + '.declarations_content';
    }

    // With Bazel multiple workspaces might be copies of the same workspace,
    // and have files with the same content, but with different paths.
    // So, we use the content hash to reuse their declarations without parsing.
    String content;
    String contentKey;
    {
      var contentHashBytes = tracker._byteStore.get(pathKey);
      if (contentHashBytes == null) {
        content = _readContent(resource);

        var contentHashBuilder = ApiSignature();
        contentHashBuilder.addInt(DATA_VERSION);
        contentHashBuilder.addString(content);
        contentHashBytes = contentHashBuilder.toByteList();

        tracker._byteStore.put(pathKey, contentHashBytes);
      }

      contentKey = hex.encode(contentHashBytes) + '.declarations';
    }

    var bytes = tracker._byteStore.get(contentKey);
    if (bytes == null) {
      content ??= _readContent(resource);

      CompilationUnit unit = _parse(content);
      _buildFileDeclarations(unit);
      _putFileDeclarationsToByteStore(contentKey);
    } else {
      _readFileDeclarationsFromBytes(bytes);
    }

    // Resolve exports and parts.
    for (var export in exports) {
      export.file = _fileForRelativeUri(context, export.uri);
    }
    for (var part in parts) {
      part.file = _fileForRelativeUri(context, part.uri);
    }
    exports.removeWhere((e) => e.file == null);
    parts.removeWhere((e) => e.file == null);

    // Set back pointers.
    for (var export in exports) {
      export.file.directExporters.add(this);
    }
    for (var part in parts) {
      part.file.library = this;
      part.file.isLibrary = false;
    }

    // Compute library declarations.
    if (isLibrary) {
      libraryDeclarations = <Declaration>[];
      libraryDeclarations.addAll(fileDeclarations);
      for (var part in parts) {
        libraryDeclarations.addAll(part.file.fileDeclarations);
      }
      _computeRelevanceTagsForLibraryDeclarations();
    }
  }

  void _buildFileDeclarations(CompilationUnit unit) {
    isLibrary = true;
    exports = [];
    fileDeclarations = [];
    libraryDeclarations = null;
    exportedDeclarations = null;

    for (var astDirective in unit.directives) {
      if (astDirective is ExportDirective) {
        var uri = _uriFromAst(astDirective.uri);
        if (uri == null) continue;

        var combinators = <_ExportCombinator>[];
        for (var astCombinator in astDirective.combinators) {
          if (astCombinator is ShowCombinator) {
            combinators.add(_ExportCombinator(
              astCombinator.shownNames.map((id) => id.name).toList(),
              const [],
            ));
          } else if (astCombinator is HideCombinator) {
            combinators.add(_ExportCombinator(
              const [],
              astCombinator.hiddenNames.map((id) => id.name).toList(),
            ));
          }
        }

        exports.add(_Export(uri, combinators));
      } else if (astDirective is LibraryDirective) {
        isLibraryDeprecated = _hasDeprecatedAnnotation(astDirective);
      } else if (astDirective is PartDirective) {
        var uri = _uriFromAst(astDirective.uri);
        if (uri == null) continue;

        parts.add(_Part(uri));
      } else if (astDirective is PartOfDirective) {
        isLibrary = false;
      }
    }

    var lineInfo = unit.lineInfo;

    String docComplete = null;
    String docSummary = null;

    void setDartDoc(AnnotatedNode node) {
      if (node.documentationComment != null) {
        var rawText = getCommentNodeRawText(node.documentationComment);
        docComplete = getDartDocPlainText(rawText);
        docSummary = getDartDocSummary(docComplete);
      } else {
        docComplete = null;
        docSummary = null;
      }
    }

    void addDeclaration({
      String defaultArgumentListString,
      List<int> defaultArgumentListTextRanges,
      bool isAbstract = false,
      bool isConst = false,
      bool isDeprecated = false,
      bool isFinal = false,
      @required DeclarationKind kind,
      @required Identifier name,
      Identifier name2,
      String parameters,
      List<String> parameterNames,
      List<String> parameterTypes,
      List<String> relevanceTags,
      int requiredParameterCount,
      String returnType,
      String typeParameters,
    }) {
      if (Identifier.isPrivateName(name.name) ||
          name2 != null && Identifier.isPrivateName(name2.name)) {
        return;
      }

      var locationOffset = name.offset;
      var lineLocation = lineInfo.getLocation(locationOffset);
      fileDeclarations.add(Declaration(
        defaultArgumentListString: defaultArgumentListString,
        defaultArgumentListTextRanges: defaultArgumentListTextRanges,
        docComplete: docComplete,
        docSummary: docSummary,
        isAbstract: isAbstract,
        isConst: isConst,
        isDeprecated: isDeprecated,
        isFinal: isFinal,
        kind: kind,
        locationOffset: locationOffset,
        locationPath: path,
        name: name.name,
        name2: name2?.name,
        locationStartColumn: lineLocation.columnNumber,
        locationStartLine: lineLocation.lineNumber,
        parameters: parameters,
        parameterNames: parameterNames,
        parameterTypes: parameterTypes,
        relevanceTags: relevanceTags,
        requiredParameterCount: requiredParameterCount,
        returnType: returnType,
        typeParameters: typeParameters,
      ));
    }

    for (var node in unit.declarations) {
      setDartDoc(node);
      var isDeprecated = _hasDeprecatedAnnotation(node);

      if (node is ClassDeclaration) {
        addDeclaration(
          isAbstract: node.isAbstract,
          isDeprecated: isDeprecated,
          kind: DeclarationKind.CLASS,
          name: node.name,
        );
      } else if (node is ClassTypeAlias) {
        addDeclaration(
          isDeprecated: isDeprecated,
          kind: DeclarationKind.CLASS_TYPE_ALIAS,
          name: node.name,
        );
      } else if (node is EnumDeclaration) {
        addDeclaration(
          isDeprecated: isDeprecated,
          kind: DeclarationKind.ENUM,
          name: node.name,
        );
        for (var constant in node.constants) {
          setDartDoc(constant);
          var isDeprecated = _hasDeprecatedAnnotation(constant);
          addDeclaration(
            isDeprecated: isDeprecated,
            kind: DeclarationKind.ENUM_CONSTANT,
            name: constant.name,
            name2: node.name,
          );
        }
      } else if (node is FunctionDeclaration) {
        var functionExpression = node.functionExpression;
        var parameters = functionExpression.parameters;
        if (node.isGetter) {
          addDeclaration(
            isDeprecated: isDeprecated,
            kind: DeclarationKind.GETTER,
            name: node.name,
            returnType: _getTypeAnnotationString(node.returnType),
          );
        } else if (node.isSetter) {
          addDeclaration(
            isDeprecated: isDeprecated,
            kind: DeclarationKind.SETTER,
            name: node.name,
            parameters: parameters.toSource(),
            parameterNames: _getFormalParameterNames(parameters),
            parameterTypes: _getFormalParameterTypes(parameters),
            requiredParameterCount:
                _getFormalParameterRequiredCount(parameters),
          );
        } else {
          var defaultArguments = _computeDefaultArguments(parameters);
          addDeclaration(
            defaultArgumentListString: defaultArguments?.text,
            defaultArgumentListTextRanges: defaultArguments?.ranges,
            isDeprecated: isDeprecated,
            kind: DeclarationKind.FUNCTION,
            name: node.name,
            parameters: parameters.toSource(),
            parameterNames: _getFormalParameterNames(parameters),
            parameterTypes: _getFormalParameterTypes(parameters),
            requiredParameterCount:
                _getFormalParameterRequiredCount(parameters),
            returnType: _getTypeAnnotationString(node.returnType),
            typeParameters: functionExpression.typeParameters?.toSource(),
          );
        }
      } else if (node is GenericTypeAlias) {
        var functionType = node.functionType;
        var parameters = functionType.parameters;
        addDeclaration(
          isDeprecated: isDeprecated,
          kind: DeclarationKind.FUNCTION_TYPE_ALIAS,
          name: node.name,
          parameters: parameters.toSource(),
          parameterNames: _getFormalParameterNames(parameters),
          parameterTypes: _getFormalParameterTypes(parameters),
          requiredParameterCount: _getFormalParameterRequiredCount(parameters),
          returnType: _getTypeAnnotationString(functionType.returnType),
          typeParameters: functionType.typeParameters?.toSource(),
        );
      } else if (node is MixinDeclaration) {
        addDeclaration(
          isDeprecated: isDeprecated,
          kind: DeclarationKind.MIXIN,
          name: node.name,
        );
      } else if (node is TopLevelVariableDeclaration) {
        var isConst = node.variables.isConst;
        var isFinal = node.variables.isFinal;
        for (var variable in node.variables.variables) {
          addDeclaration(
            isConst: isConst,
            isDeprecated: isDeprecated,
            isFinal: isFinal,
            kind: DeclarationKind.VARIABLE,
            name: variable.name,
            relevanceTags: RelevanceTags._forExpression(variable.initializer),
            returnType: _getTypeAnnotationString(node.variables.type),
          );
        }
      }
    }
  }

  void _computeRelevanceTagsForLibraryDeclarations() {
    for (var declaration in libraryDeclarations) {
      declaration._relevanceTags ??=
          RelevanceTags._forDeclaration(uriStr, declaration);
    }
  }

  /// Return the [_File] for the given [relative] URI, maybe `null`.
  _File _fileForRelativeUri(DeclarationsContext context, Uri relative) {
    var absoluteUri = resolveRelativeUri(uri, relative);
    return tracker._getFileByUri(context, absoluteUri);
  }

  void _putFileDeclarationsToByteStore(String contentKey) {
    var builder = idl.AvailableFileBuilder(
      isLibrary: isLibrary,
      isLibraryDeprecated: isLibraryDeprecated,
      exports: exports.map((e) {
        return idl.AvailableFileExportBuilder(
          uri: e.uri.toString(),
          combinators: e.combinators.map((c) {
            return idl.AvailableFileExportCombinatorBuilder(
                shows: c.shows, hides: c.hides);
          }).toList(),
        );
      }).toList(),
      parts: parts.map((p) => p.uri.toString()).toList(),
      declarations: fileDeclarations.map((d) {
        return _DeclarationStorage.toIdl(d);
      }).toList(),
    );
    var bytes = builder.toBuffer();
    tracker._byteStore.put(contentKey, bytes);
  }

  void _readFileDeclarationsFromBytes(List<int> bytes) {
    var idlFile = idl.AvailableFile.fromBuffer(bytes);

    isLibrary = idlFile.isLibrary;
    isLibraryDeprecated = idlFile.isLibraryDeprecated;

    exports = idlFile.exports.map((e) {
      return _Export(
        Uri.parse(e.uri),
        e.combinators.map((c) {
          return _ExportCombinator(c.shows.toList(), c.hides.toList());
        }).toList(),
      );
    }).toList();

    parts = idlFile.parts.map((e) {
      var uri = Uri.parse(e);
      return _Part(uri);
    }).toList();

    fileDeclarations = idlFile.declarations.map((e) {
      return _DeclarationStorage.fromIdl(path, e);
    }).toList();
  }

  static _DefaultArguments _computeDefaultArguments(
      FormalParameterList parameters) {
    var buffer = StringBuffer();
    var ranges = <int>[];
    for (var parameter in parameters.parameters) {
      if (parameter.isRequired) {
        if (buffer.isNotEmpty) {
          buffer.write(', ');
        }
        var valueOffset = buffer.length;
        buffer.write(parameter.identifier.name);
        var valueLength = buffer.length - valueOffset;
        ranges.add(valueOffset);
        ranges.add(valueLength);
      } else if (parameter.isNamed && _hasRequiredAnnotation(parameter)) {
        if (buffer.isNotEmpty) {
          buffer.write(', ');
        }
        buffer.write(parameter.identifier.name);
        buffer.write(': ');

        var valueOffset = buffer.length;
        buffer.write('null');
        var valueLength = buffer.length - valueOffset;

        ranges.add(valueOffset);
        ranges.add(valueLength);
      }
    }
    if (buffer.isEmpty) return null;
    return _DefaultArguments(buffer.toString(), ranges);
  }

  static List<String> _getFormalParameterNames(FormalParameterList parameters) {
    if (parameters == null) return const <String>[];

    var names = <String>[];
    for (var parameter in parameters.parameters) {
      var name = parameter.identifier?.name ?? '';
      names.add(name);
    }
    return names;
  }

  static int _getFormalParameterRequiredCount(FormalParameterList parameters) {
    if (parameters == null) return null;

    return parameters.parameters
        .takeWhile((parameter) => parameter.isRequired)
        .length;
  }

  static String _getFormalParameterType(FormalParameter parameter) {
    if (parameter is DefaultFormalParameter) {
      DefaultFormalParameter defaultFormalParameter = parameter;
      parameter = defaultFormalParameter.parameter;
    }
    if (parameter is SimpleFormalParameter) {
      return _getTypeAnnotationString(parameter.type);
    }
    return '';
  }

  static List<String> _getFormalParameterTypes(FormalParameterList parameters) {
    if (parameters == null) return null;

    var types = <String>[];
    for (var parameter in parameters.parameters) {
      var type = _getFormalParameterType(parameter);
      types.add(type);
    }
    return types;
  }

  static String _getTypeAnnotationString(TypeAnnotation typeAnnotation) {
    return typeAnnotation?.toSource() ?? '';
  }

  /// Return `true` if the [node] is probably deprecated.
  static bool _hasDeprecatedAnnotation(AnnotatedNode node) {
    for (var annotation in node.metadata) {
      var name = annotation.name;
      if (name is SimpleIdentifier) {
        if (name.name == 'deprecated' || name.name == 'Deprecated') {
          return true;
        }
      }
    }
    return false;
  }

  /// Return `true` if the [node] probably has `@required` annotation.
  static bool _hasRequiredAnnotation(FormalParameter node) {
    for (var annotation in node.metadata) {
      var name = annotation.name;
      if (name is SimpleIdentifier) {
        if (name.name == 'required') {
          return true;
        }
      }
    }
    return false;
  }

  static CompilationUnit _parse(String content) {
    var errorListener = AnalysisErrorListener.NULL_LISTENER;
    var source = StringSource(content, '');

    var reader = new CharSequenceReader(content);
    var scanner = new Scanner(null, reader, errorListener);
    var token = scanner.tokenize();

    var parser = new Parser(source, errorListener, useFasta: true);
    var unit = parser.parseCompilationUnit(token);
    unit.lineInfo = LineInfo(scanner.lineStarts);

    return unit;
  }

  static String _readContent(File resource) {
    try {
      return resource.readAsStringSync();
    } catch (e) {
      return '';
    }
  }

  static Uri _uriFromAst(StringLiteral astUri) {
    if (astUri is SimpleStringLiteral) {
      var uriStr = astUri.value.trim();
      if (uriStr.isEmpty) return null;
      try {
        return Uri.parse(uriStr);
      } catch (_) {}
    }
    return null;
  }
}

class _LibraryNode extends graph.Node<_LibraryNode> {
  final _LibraryWalker walker;
  final _File file;

  _LibraryNode(this.walker, this.file);

  @override
  bool get isEvaluated => file.exportedDeclarations != null;

  @override
  List<_LibraryNode> computeDependencies() {
    return file.exports.map((e) => e.file).map(walker.getNode).toList();
  }
}

class _LibraryWalker extends graph.DependencyWalker<_LibraryNode> {
  final Map<_File, _LibraryNode> nodesOfFiles = {};

  @override
  void evaluate(_LibraryNode node) {
    var file = node.file;
    var resultSet = _newDeclarationSet();
    resultSet.addAll(file.libraryDeclarations);

    for (var export in file.exports) {
      var exportedDeclarations = export.file.exportedDeclarations;
      resultSet.addAll(export.filter(exportedDeclarations));
    }

    file.exportedDeclarations = resultSet.toList();
  }

  @override
  void evaluateScc(List<_LibraryNode> scc) {
    for (var node in scc) {
      var visitedFiles = Set<_File>();

      List<Declaration> computeExported(_File file) {
        if (file.exportedDeclarations != null) {
          return file.exportedDeclarations;
        }

        if (!visitedFiles.add(file)) {
          return const [];
        }

        var resultSet = _newDeclarationSet();
        resultSet.addAll(file.libraryDeclarations);

        for (var export in file.exports) {
          var exportedDeclarations = computeExported(export.file);
          resultSet.addAll(export.filter(exportedDeclarations));
        }

        return resultSet.toList();
      }

      var file = node.file;
      file.exportedDeclarations = computeExported(file);
    }
  }

  _LibraryNode getNode(_File file) {
    return nodesOfFiles.putIfAbsent(file, () => new _LibraryNode(this, file));
  }

  void walkLibrary(_File file) {
    var node = getNode(file);
    walk(node);
  }

  static Set<Declaration> _newDeclarationSet() {
    return HashSet<Declaration>(
      hashCode: (e) => e.name.hashCode,
      equals: (a, b) => a.name == b.name && a.name2 == b.name2,
    );
  }
}

/// Information about a package: `Pub` or `Bazel`.
class _Package {
  final Folder root;
  final Folder lib;

  _Package(this.root) : lib = root.getChildAssumingFolder('lib');

  /// Return `true` if the [path] is anywhere in the [root] of the package.
  ///
  /// Note, that this method does not check if the are nested packages, that
  /// might actually contain the [path].
  bool contains(String path) {
    return root.contains(path);
  }

  /// Return `true` if the [path] is in the `lib` folder of this package.
  bool containsInLib(String path) {
    return lib.contains(path);
  }

  /// Return the direct child folder of the root, that contains the [path].
  ///
  /// So, we can know if the [path] is in `lib/`, or `test/`, or `bin/`.
  Folder folderInRootContaining(String path) {
    try {
      var children = root.getChildren();
      for (var folder in children) {
        if (folder is Folder && folder.contains(path)) {
          return folder;
        }
      }
    } on FileSystemException {}
    return null;
  }
}

class _Part {
  final Uri uri;

  _File file;

  _Part(this.uri);
}

/// Normal and dev dependencies specified in a `pubspec.yaml` file.
class _PubspecDependencies {
  final List<String> lib;
  final List<String> dev;

  _PubspecDependencies(this.lib, this.dev);
}

class _ScheduledFile {
  final DeclarationsContext context;
  final String path;

  _ScheduledFile(this.context, this.path);
}

/// Wrapper for a [StreamController] and its unique [Stream] instance.
class _StreamController<T> {
  final StreamController<T> controller = StreamController<T>();
  Stream<T> stream;

  _StreamController() {
    stream = controller.stream;
  }

  void add(T event) {
    controller.add(event);
  }
}