sdk/pkg/analysis_server/lib/src/context_manager.dart

// Copyright (c) 2014, 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 'dart:core';

import 'package:analysis_server/src/plugin/notification_manager.dart';
import 'package:analyzer/file_system/file_system.dart';
import 'package:analyzer/instrumentation/instrumentation.dart';
import 'package:analyzer/src/analysis_options/analysis_options_provider.dart';
import 'package:analyzer/src/context/builder.dart';
import 'package:analyzer/src/context/context_root.dart';
import 'package:analyzer/src/context/packages.dart';
import 'package:analyzer/src/dart/analysis/driver.dart';
import 'package:analyzer/src/file_system/file_system.dart';
import 'package:analyzer/src/generated/engine.dart';
import 'package:analyzer/src/generated/java_engine.dart';
import 'package:analyzer/src/generated/sdk.dart';
import 'package:analyzer/src/generated/source.dart';
import 'package:analyzer/src/generated/source_io.dart';
import 'package:analyzer/src/manifest/manifest_validator.dart';
import 'package:analyzer/src/pubspec/pubspec_validator.dart';
import 'package:analyzer/src/source/package_map_resolver.dart';
import 'package:analyzer/src/source/path_filter.dart';
import 'package:analyzer/src/task/options.dart';
import 'package:analyzer/src/util/glob.dart';
import 'package:analyzer/src/util/yaml.dart';
import 'package:analyzer_plugin/protocol/protocol_common.dart' as protocol;
import 'package:analyzer_plugin/utilities/analyzer_converter.dart';
import 'package:path/path.dart' as pathos;
import 'package:watcher/watcher.dart';
import 'package:yaml/yaml.dart';

/// An indication of which files have been added, changed, removed, or deleted.
///
/// No file should be added to the change set more than once, either with the
/// same or a different kind of change. It does not make sense, for example,
/// for a file to be both added and removed.
class ChangeSet {
  /// A list containing paths of added files.
  final List<String> addedFiles = [];

  /// A list containing paths of changed files.
  final List<String> changedFiles = [];

  /// A list containing paths of removed files.
  final List<String> removedFiles = [];

  /// Return `true` if this change set does not contain any changes.
  bool get isEmpty =>
      addedFiles.isEmpty && changedFiles.isEmpty && removedFiles.isEmpty;

  /// Record that the file with the specified [path] has been added.
  void addedSource(String path) {
    addedFiles.add(path);
  }

  /// Record that the file with the specified [path] has been changed.
  void changedSource(String path) {
    changedFiles.add(path);
  }

  /// Record that the file with the specified [path] has been removed.
  void removedSource(String path) {
    removedFiles.add(path);
  }
}

/// Information tracked by the [ContextManager] for each context.
class ContextInfo {
  /// The [Folder] for which this information object is created.
  final Folder folder;

  /// The [PathFilter] used to filter sources from being analyzed.
  final PathFilter pathFilter;

  /// The enclosed pubspec-based contexts.
  final List<ContextInfo> children = <ContextInfo>[];

  /// The [ContextInfo] that encloses this one, or `null` if this is the virtual
  /// [ContextInfo] object that acts as the ancestor of all other [ContextInfo]
  /// objects.
  ContextInfo parent;

  /// The package description file path for this context.
  String packageDescriptionPath;

  /// The folder disposition for this context.
  final FolderDisposition disposition;

  /// Paths to files which determine the folder disposition and package map.
  ///
  /// TODO(paulberry): if any of these files are outside of [folder], they won't
  /// be watched for changes.  I believe the use case for watching these files
  /// is no longer relevant.
  Set<String> _dependencies = <String>{};

  /// The analysis driver that was created for the [folder].
  AnalysisDriver analysisDriver;

  /// Map from full path to the [Source] object, for each source that has been
  /// added to the context.
  Map<String, Source> sources = HashMap<String, Source>();

  ContextInfo(ContextManagerImpl contextManager, this.parent, Folder folder,
      File packagespecFile, this.disposition)
      : folder = folder,
        pathFilter = PathFilter(
            folder.path, null, contextManager.resourceProvider.pathContext) {
    packageDescriptionPath = packagespecFile.path;
    parent.children.add(this);
  }

  /// Create the virtual [ContextInfo] which acts as an ancestor to all other
  /// [ContextInfo]s.
  ContextInfo._root()
      : folder = null,
        pathFilter = null,
        disposition = null;

  /// Iterate through all [children] and their children, recursively.
  Iterable<ContextInfo> get descendants sync* {
    for (var child in children) {
      yield child;
      yield* child.descendants;
    }
  }

  /// Returns `true` if this is a "top level" context, meaning that the folder
  /// associated with it is not contained within any other folders that have an
  /// associated context.
  bool get isTopLevel => parent.parent == null;

  /// Returns `true` if [path] is excluded, as it is in one of the children.
  bool excludes(String path) {
    return children.any((child) {
      return child.folder.contains(path);
    });
  }

  /// Returns `true` if [resource] is excluded, as it is in one of the children.
  bool excludesResource(Resource resource) => excludes(resource.path);

  /// Return the first [ContextInfo] in [children] whose associated folder is or
  /// contains [path].  If there is no such [ContextInfo], return `null`.
  ContextInfo findChildInfoFor(String path) {
    for (var info in children) {
      if (info.folder.isOrContains(path)) {
        return info;
      }
    }
    return null;
  }

  /// Determine if the given [path] is one of the dependencies most recently
  /// passed to [setDependencies].
  bool hasDependency(String path) => _dependencies.contains(path);

  /// Returns `true` if  [path] should be ignored.
  bool ignored(String path) => pathFilter.ignored(path);

  /// Returns `true` if [path] is the package description file for this context
  /// (pubspec.yaml or .packages).
  bool isPathToPackageDescription(String path) =>
      path == packageDescriptionPath;

  /// Update the set of dependencies for this context.
  void setDependencies(Iterable<String> newDependencies) {
    _dependencies = newDependencies.toSet();
  }

  /// Return `true` if the given [path] is managed by this context or by
  /// any of its children.
  bool _managesOrHasChildThatManages(String path) {
    if (parent == null) {
      for (var child in children) {
        if (child._managesOrHasChildThatManages(path)) {
          return true;
        }
      }
      return false;
    } else {
      if (!folder.isOrContains(path)) {
        return false;
      }
      for (var child in children) {
        if (child._managesOrHasChildThatManages(path)) {
          return true;
        }
      }
      return !pathFilter.ignored(path);
    }
  }
}

/// Class that maintains a mapping from included/excluded paths to a set of
/// folders that should correspond to analysis contexts.
abstract class ContextManager {
  // TODO(brianwilkerson) Support:
  //   setting the default analysis options
  //   setting the default content cache
  //   setting the default SDK
  //   telling server when a context has been added or removed
  //       (see onContextsChanged)
  //   telling server when a context needs to be re-analyzed
  //   notifying the client when results should be flushed
  //   using analyzeFileFunctions to determine which files to analyze
  //
  // TODO(brianwilkerson) Move this class to a public library.

  /// Get the callback interface used to create, destroy, and update contexts.
  ContextManagerCallbacks get callbacks;

  /// Set the callback interface used to create, destroy, and update contexts.
  set callbacks(ContextManagerCallbacks value);

  /// A table mapping [Folder]s to the [AnalysisDriver]s associated with them.
  Map<Folder, AnalysisDriver> get driverMap;

  /// Return the list of excluded paths (folders and files) most recently passed
  /// to [setRoots].
  List<String> get excludedPaths;

  /// Return the list of included paths (folders and files) most recently passed
  /// to [setRoots].
  List<String> get includedPaths;

  /// Like [getDriverFor], but returns the [Folder] which allows plugins to
  /// create & manage their own tree of drivers just like using [getDriverFor].
  ///
  /// This folder should be the root of analysis context, not just the
  /// containing folder of the path (like basename), as this is NOT just a file
  /// API.
  ///
  /// This exists at least temporarily, for plugin support until the new API is
  /// ready.
  Folder getContextFolderFor(String path);

  /// Return the [AnalysisDriver] for the "innermost" context whose associated
  /// folder is or contains the given path.  ("innermost" refers to the nesting
  /// of contexts, so if there is a context for path /foo and a context for
  /// path /foo/bar, then the innermost context containing /foo/bar/baz.dart is
  /// the context for /foo/bar.)
  ///
  /// If no driver contains the given path, `null` is returned.
  AnalysisDriver getDriverFor(String path);

  /// Return a list of all of the analysis drivers reachable from the given
  /// [analysisRoot] (the driver associated with [analysisRoot] and all of its
  /// descendants).
  List<AnalysisDriver> getDriversInAnalysisRoot(Folder analysisRoot);

  /// Determine whether the given [path], when interpreted relative to innermost
  /// context root, contains a folder whose name starts with '.'.
  bool isContainedInDotFolder(String path);

  /// Return `true` if the given [path] is ignored by a [ContextInfo] whose
  /// folder contains it.
  bool isIgnored(String path);

  /// Return `true` if the given absolute [path] is in one of the current
  /// root folders and is not excluded.
  bool isInAnalysisRoot(String path);

  /// Return the number of contexts reachable from the given [analysisRoot] (the
  /// context associated with [analysisRoot] and all of its descendants).
  int numberOfContextsInAnalysisRoot(Folder analysisRoot);

  /// Rebuild the set of contexts from scratch based on the data last sent to
  /// [setRoots]. Only contexts contained in the given list of analysis [roots]
  /// will be rebuilt, unless the list is `null`, in which case every context
  /// will be rebuilt.
  void refresh(List<Resource> roots);

  /// Change the set of paths which should be used as starting points to
  /// determine the context directories.
  void setRoots(List<String> includedPaths, List<String> excludedPaths);
}

/// Callback interface used by [ContextManager] to (a) request that contexts be
/// created, destroyed or updated, (b) inform the client when "pub list"
/// operations are in progress, and (c) determine which files should be
/// analyzed.
///
/// TODO(paulberry): eliminate this interface, and instead have [ContextManager]
/// operations return data structures describing how context state should be
/// modified.
abstract class ContextManagerCallbacks {
  /// Return the notification manager associated with the server.
  AbstractNotificationManager get notificationManager;

  /// Create and return a new analysis driver rooted at the given [folder], with
  /// the given analysis [options].
  AnalysisDriver addAnalysisDriver(
      Folder folder, ContextRoot contextRoot, AnalysisOptions options);

  /// An [event] was processed, so analysis state might be different now.
  void afterWatchEvent(WatchEvent event);

  /// Called when analysis options or URI resolution in the [driver] are
  /// changed.
  void analysisOptionsUpdated(AnalysisDriver driver);

  /// Called when the set of files associated with a context have changed (or
  /// some of those files have been modified).  [changeSet] is the set of
  /// changes that need to be applied to the context.
  void applyChangesToContext(Folder contextFolder, ChangeSet changeSet);

  /// The given [file] was removed from the folder analyzed in the [driver].
  void applyFileRemoved(AnalysisDriver driver, String file);

  /// Sent the given watch [event] to any interested plugins.
  void broadcastWatchEvent(WatchEvent event);

  /// Create and return a context builder that can be used to create a context
  /// for the files in the given [folder] when analyzed using the given
  /// [options].
  ContextBuilder createContextBuilder(Folder folder, AnalysisOptions options);

  /// Remove the context associated with the given [folder].  [flushedFiles] is
  /// a list of the files which will be "orphaned" by removing this context
  /// (they will no longer be analyzed by any context).
  void removeContext(Folder folder, List<String> flushedFiles);
}

/// Class that maintains a mapping from included/excluded paths to a set of
/// folders that should correspond to analysis contexts.
class ContextManagerImpl implements ContextManager {
  /// The name of the `doc` directory.
  static const String DOC_DIR_NAME = 'doc';

  /// The name of the `lib` directory.
  static const String LIB_DIR_NAME = 'lib';

  /// File name of Android manifest files.
  static const String MANIFEST_NAME = 'AndroidManifest.xml';

  /// File name of pubspec files.
  static const String PUBSPEC_NAME = 'pubspec.yaml';

  /// File name of package spec files.
  static const String PACKAGE_SPEC_NAME = '.packages';

  /// The name of the key in an embedder file whose value is the list of
  /// libraries in the SDK.
  /// TODO(brianwilkerson) This is also defined in sdk.dart.
  static const String _EMBEDDED_LIB_MAP_KEY = 'embedded_libs';

  /// The [ResourceProvider] using which paths are converted into [Resource]s.
  final ResourceProvider resourceProvider;

  /// The manager used to access the SDK that should be associated with a
  /// particular context.
  final DartSdkManager sdkManager;

  /// The context used to work with file system paths.
  pathos.Context pathContext;

  /// The list of excluded paths (folders and files) most recently passed to
  /// [setRoots].
  @override
  List<String> excludedPaths = <String>[];

  /// The list of included paths (folders and files) most recently passed to
  /// [setRoots].
  @override
  List<String> includedPaths = <String>[];

  /// A list of the globs used to determine which files should be analyzed.
  final List<Glob> analyzedFilesGlobs;

  /// The default options used to create new analysis contexts.
  final AnalysisOptionsImpl defaultContextOptions;

  /// The instrumentation service used to report instrumentation data.
  final InstrumentationService _instrumentationService;

  @override
  ContextManagerCallbacks callbacks;

  /// Virtual [ContextInfo] which acts as the ancestor of all other
  /// [ContextInfo]s.
  final ContextInfo rootInfo = ContextInfo._root();

  @override
  final Map<Folder, AnalysisDriver> driverMap =
      HashMap<Folder, AnalysisDriver>();

  /// Stream subscription we are using to watch each analysis root directory for
  /// changes.
  final Map<Folder, StreamSubscription<WatchEvent>> changeSubscriptions =
      <Folder, StreamSubscription<WatchEvent>>{};

  ContextManagerImpl(
      this.resourceProvider,
      this.sdkManager,
      this.analyzedFilesGlobs,
      this._instrumentationService,
      this.defaultContextOptions) {
    pathContext = resourceProvider.pathContext;
  }

  /// Check if this map defines embedded libraries.
  bool definesEmbeddedLibs(Map map) => map[_EMBEDDED_LIB_MAP_KEY] != null;

  @override
  Folder getContextFolderFor(String path) {
    return _getInnermostContextInfoFor(path)?.folder;
  }

  /// For testing: get the [ContextInfo] object for the given [folder], if any.
  ContextInfo getContextInfoFor(Folder folder) {
    var info = _getInnermostContextInfoFor(folder.path);
    if (info != null && folder == info.folder) {
      return info;
    }
    return null;
  }

  @override
  AnalysisDriver getDriverFor(String path) {
    return _getInnermostContextInfoFor(path)?.analysisDriver;
  }

  @override
  List<AnalysisDriver> getDriversInAnalysisRoot(Folder analysisRoot) {
    var drivers = <AnalysisDriver>[];
    void addContextAndDescendants(ContextInfo info) {
      drivers.add(info.analysisDriver);
      info.children.forEach(addContextAndDescendants);
    }

    var innermostContainingInfo =
        _getInnermostContextInfoFor(analysisRoot.path);
    if (innermostContainingInfo != null) {
      if (analysisRoot == innermostContainingInfo.folder) {
        addContextAndDescendants(innermostContainingInfo);
      } else {
        for (var info in innermostContainingInfo.children) {
          if (analysisRoot.isOrContains(info.folder.path)) {
            addContextAndDescendants(info);
          }
        }
      }
    }
    return drivers;
  }

  /// Determine whether the given [path], when interpreted relative to innermost
  /// context root, contains a folder whose name starts with '.'.
  @override
  bool isContainedInDotFolder(String path) {
    var info = _getInnermostContextInfoFor(path);
    return info != null && _isContainedInDotFolder(info.folder.path, path);
  }

  @override
  bool isIgnored(String path) {
    var info = rootInfo;
    do {
      info = info.findChildInfoFor(path);
      if (info == null) {
        return false;
      }
      if (info.ignored(path)) {
        return true;
      }
    } while (true);
  }

  @override
  bool isInAnalysisRoot(String path) {
    // check if excluded
    if (_isExcluded(path)) {
      return false;
    }
    // check if in one of the roots
    for (var info in rootInfo.children) {
      if (info.folder.contains(path)) {
        return true;
      }
    }
    // no
    return false;
  }

  @override
  int numberOfContextsInAnalysisRoot(Folder analysisRoot) {
    var count = 0;
    void addContextAndDescendants(ContextInfo info) {
      count++;
      info.children.forEach(addContextAndDescendants);
    }

    var innermostContainingInfo =
        _getInnermostContextInfoFor(analysisRoot.path);
    if (innermostContainingInfo != null) {
      if (analysisRoot == innermostContainingInfo.folder) {
        addContextAndDescendants(innermostContainingInfo);
      } else {
        for (var info in innermostContainingInfo.children) {
          if (analysisRoot.isOrContains(info.folder.path)) {
            addContextAndDescendants(info);
          }
        }
      }
    }
    return count;
  }

  /// Process [options] for the given context [info].
  void processOptionsForDriver(
      ContextInfo info, AnalysisOptionsImpl analysisOptions, YamlMap options) {
    if (options == null) {
      return;
    }

    // Check for embedded options.
    var embeddedOptions = _getEmbeddedOptions(info);
    if (embeddedOptions != null) {
      options = Merger().merge(embeddedOptions, options);
    }

    applyToAnalysisOptions(analysisOptions, options);

    if (analysisOptions.excludePatterns != null) {
      // Set ignore patterns.
      setIgnorePatternsForContext(info, analysisOptions.excludePatterns);
    }
  }

  @override
  void refresh(List<Resource> roots) {
    // Destroy old contexts
    var contextInfos = rootInfo.descendants.toList();
    if (roots == null) {
      contextInfos.forEach(_destroyContext);
    } else {
      roots.forEach((Resource resource) {
        contextInfos.forEach((ContextInfo contextInfo) {
          if (resource is Folder &&
              resource.isOrContains(contextInfo.folder.path)) {
            _destroyContext(contextInfo);
          }
        });
      });
    }

    // Rebuild contexts based on the data last sent to setRoots().
    setRoots(includedPaths, excludedPaths);
  }

  /// Sets the [ignorePatterns] for the context having info [info].
  void setIgnorePatternsForContext(
      ContextInfo info, List<String> ignorePatterns) {
    info.pathFilter.setIgnorePatterns(ignorePatterns);
  }

  @override
  void setRoots(List<String> includedPaths, List<String> excludedPaths) {
    var contextInfos = rootInfo.descendants.toList();
    // included
    var includedFolders = <Folder>[];
    {
      // Sort paths to ensure that outer roots are handled before inner roots,
      // so we can correctly ignore inner roots, which are already managed
      // by outer roots.
      var uniqueIncludedPaths = LinkedHashSet<String>.from(includedPaths);
      var sortedIncludedPaths = uniqueIncludedPaths.toList();
      sortedIncludedPaths.sort((a, b) => a.length - b.length);
      // Convert paths to folders.
      for (var path in sortedIncludedPaths) {
        var resource = resourceProvider.getResource(path);
        if (resource is Folder) {
          includedFolders.add(resource);
        } else if (!resource.exists) {
          // Non-existent resources are ignored.  TODO(paulberry): we should set
          // up a watcher to ensure that if the resource appears later, we will
          // begin analyzing it.
        } else {
          // TODO(scheglov) implemented separate files analysis
          throw UnimplementedError('$path is not a folder. '
              'Only support for folder analysis is implemented currently.');
        }
      }
    }
    this.includedPaths = includedPaths;
    // excluded
    var oldExcludedPaths = this.excludedPaths;
    this.excludedPaths = excludedPaths;
    // destroy old contexts
    for (var contextInfo in contextInfos) {
      var isIncluded = includedFolders.any((folder) {
        return folder.isOrContains(contextInfo.folder.path);
      });
      if (!isIncluded) {
        _destroyContext(contextInfo);
      }
    }
    // create new contexts
    for (var includedFolder in includedFolders) {
      var includedPath = includedFolder.path;
      var isManaged = rootInfo._managesOrHasChildThatManages(includedPath);
      if (!isManaged) {
        var parent = _getParentForNewContext(includedPath);
        changeSubscriptions[includedFolder] = includedFolder.changes
            .listen(_handleWatchEvent, onError: _handleWatchInterruption);
        _createContexts(parent, includedFolder, excludedPaths, false);
      }
    }
    // remove newly excluded sources
    for (var info in rootInfo.descendants) {
      // prepare excluded sources
      Map<String, Source> excludedSources = HashMap<String, Source>();
      info.sources.forEach((String path, Source source) {
        if (_isExcludedBy(excludedPaths, path) &&
            !_isExcludedBy(oldExcludedPaths, path)) {
          excludedSources[path] = source;
        }
      });
      // apply exclusion
      var changeSet = ChangeSet();
      excludedSources.forEach((String path, Source source) {
        info.sources.remove(path);
        changeSet.removedSource(path);
      });
      callbacks.applyChangesToContext(info.folder, changeSet);
    }
    // add previously excluded sources
    for (var info in rootInfo.descendants) {
      var changeSet = ChangeSet();
      _addPreviouslyExcludedSources(
          info, changeSet, info.folder, oldExcludedPaths);
      callbacks.applyChangesToContext(info.folder, changeSet);
    }
  }

  /// Recursively adds all Dart and HTML files to the [changeSet].
  void _addPreviouslyExcludedSources(ContextInfo info, ChangeSet changeSet,
      Folder folder, List<String> oldExcludedPaths) {
    if (info.excludesResource(folder)) {
      return;
    }
    List<Resource> children;
    try {
      children = folder.getChildren();
    } on FileSystemException {
      // The folder no longer exists, or cannot be read, to there's nothing to
      // do.
      return;
    }
    for (var child in children) {
      var path = child.path;
      // Path is being ignored.
      if (info.ignored(path)) {
        continue;
      }
      // add files, recurse into folders
      if (child is File) {
        // ignore if should not be analyzed at all
        if (!_shouldFileBeAnalyzed(child)) {
          continue;
        }
        // ignore if was not excluded
        var wasExcluded = _isExcludedBy(oldExcludedPaths, path) &&
            !_isExcludedBy(excludedPaths, path);
        if (!wasExcluded) {
          continue;
        }
        // do add the file
        var source = createSourceInContext(info.analysisDriver, child);
        changeSet.addedSource(child.path);
        info.sources[path] = source;
      } else if (child is Folder) {
        _addPreviouslyExcludedSources(info, changeSet, child, oldExcludedPaths);
      }
    }
  }

  /// Recursively adds all Dart and HTML files to the [changeSet].
  void _addSourceFiles(ChangeSet changeSet, Folder folder, ContextInfo info) {
    if (info.excludesResource(folder) ||
        folder.shortName.startsWith('.') ||
        _isInTopLevelDocDir(info.folder.path, folder.path)) {
      return;
    }
    List<Resource> children;
    try {
      children = folder.getChildren();
    } on FileSystemException {
      // The directory either doesn't exist or cannot be read. Either way, there
      // are no children that need to be added.
      return;
    }
    for (var child in children) {
      var path = child.path;
      // ignore excluded files or folders
      if (_isExcluded(path) || info.excludes(path) || info.ignored(path)) {
        continue;
      }
      // add files, recurse into folders
      if (child is File) {
        if (_shouldFileBeAnalyzed(child)) {
          var source = createSourceInContext(info.analysisDriver, child);
          changeSet.addedSource(child.path);
          info.sources[path] = source;
        }
      } else if (child is Folder) {
        _addSourceFiles(changeSet, child, info);
      }
    }
  }

  /// Use the given analysis [driver] to analyze the content of the analysis
  /// options file at the given [path].
  void _analyzeAnalysisOptionsFile(AnalysisDriver driver, String path) {
    List<protocol.AnalysisError> convertedErrors;
    try {
      var content = _readFile(path);
      var lineInfo = _computeLineInfo(content);
      var errors = analyzeAnalysisOptions(
          resourceProvider.getFile(path).createSource(),
          content,
          driver.sourceFactory);
      var converter = AnalyzerConverter();
      convertedErrors = converter.convertAnalysisErrors(errors,
          lineInfo: lineInfo, options: driver.analysisOptions);
    } catch (exception) {
      // If the file cannot be analyzed, fall through to clear any previous
      // errors.
    }
    callbacks.notificationManager.recordAnalysisErrors(
        NotificationManager.serverId,
        path,
        convertedErrors ?? <protocol.AnalysisError>[]);
  }

  /// Use the given analysis [driver] to analyze the content of the
  /// AndroidManifest file at the given [path].
  void _analyzeManifestFile(AnalysisDriver driver, String path) {
    List<protocol.AnalysisError> convertedErrors;
    try {
      var content = _readFile(path);
      var validator =
          ManifestValidator(resourceProvider.getFile(path).createSource());
      var lineInfo = _computeLineInfo(content);
      var errors = validator.validate(
          content, driver.analysisOptions.chromeOsManifestChecks);
      var converter = AnalyzerConverter();
      convertedErrors = converter.convertAnalysisErrors(errors,
          lineInfo: lineInfo, options: driver.analysisOptions);
    } catch (exception) {
      // If the file cannot be analyzed, fall through to clear any previous
      // errors.
    }
    callbacks.notificationManager.recordAnalysisErrors(
        NotificationManager.serverId,
        path,
        convertedErrors ?? <protocol.AnalysisError>[]);
  }

  /// Use the given analysis [driver] to analyze the content of the pubspec file
  /// at the given [path].
  void _analyzePubspecFile(AnalysisDriver driver, String path) {
    List<protocol.AnalysisError> convertedErrors;
    try {
      var content = _readFile(path);
      var node = loadYamlNode(content);
      if (node is YamlMap) {
        var validator = PubspecValidator(
            resourceProvider, resourceProvider.getFile(path).createSource());
        var lineInfo = _computeLineInfo(content);
        var errors = validator.validate(node.nodes);
        var converter = AnalyzerConverter();
        convertedErrors = converter.convertAnalysisErrors(errors,
            lineInfo: lineInfo, options: driver.analysisOptions);
      }
    } catch (exception) {
      // If the file cannot be analyzed, fall through to clear any previous
      // errors.
    }
    callbacks.notificationManager.recordAnalysisErrors(
        NotificationManager.serverId,
        path,
        convertedErrors ?? <protocol.AnalysisError>[]);
  }

  void _checkForAnalysisOptionsUpdate(String path, ContextInfo info) {
    if (AnalysisEngine.isAnalysisOptionsFileName(path, pathContext)) {
      var driver = info.analysisDriver;
      if (driver == null) {
        // I suspect that this happens as a result of a race condition: server
        // has determined that the file (at [path]) is in a context, but hasn't
        // yet created a driver for that context.
        return;
      }
      // TODO(brianwilkerson) Set exclusion patterns.
      _analyzeAnalysisOptionsFile(driver, path);
      _updateAnalysisOptions(info);
    }
  }

  void _checkForManifestUpdate(String path, ContextInfo info) {
    if (_isManifest(path)) {
      var driver = info.analysisDriver;
      if (driver == null) {
        // I suspect that this happens as a result of a race condition: server
        // has determined that the file (at [path]) is in a context, but hasn't
        // yet created a driver for that context.
        return;
      }
      _analyzeManifestFile(driver, path);
    }
  }

  void _checkForPackagespecUpdate(String path, ContextInfo info) {
    // Check to see if this is the .packages file for this context and if so,
    // update the context's source factory.
    if (pathContext.basename(path) == PACKAGE_SPEC_NAME) {
      var driver = info.analysisDriver;
      if (driver == null) {
        // I suspect that this happens as a result of a race condition: server
        // has determined that the file (at [path]) is in a context, but hasn't
        // yet created a driver for that context.
        return;
      }

      _updateAnalysisOptions(info);
    }
  }

  void _checkForPubspecUpdate(String path, ContextInfo info) {
    if (_isPubspec(path)) {
      var driver = info.analysisDriver;
      if (driver == null) {
        // I suspect that this happens as a result of a race condition: server
        // has determined that the file (at [path]) is in a context, but hasn't
        // yet created a driver for that context.
        return;
      }
      _analyzePubspecFile(driver, path);
      _updateAnalysisOptions(info);
    }
  }

  /// Compute the set of files that are being flushed, this is defined as
  /// the set of sources in the removed context (context.sources), that are
  /// orphaned by this context being removed (no other context includes this
  /// file.)
  List<String> _computeFlushedFiles(ContextInfo info) {
    var flushedFiles = info.analysisDriver.addedFiles.toSet();
    for (var contextInfo in rootInfo.descendants) {
      var other = contextInfo.analysisDriver;
      if (other != info.analysisDriver) {
        flushedFiles.removeAll(other.addedFiles);
      }
    }
    return flushedFiles.toList(growable: false);
  }

  /// Compute the appropriate [FolderDisposition] for [folder].  Use
  /// [addDependency] to indicate which files needed to be consulted in order to
  /// figure out the [FolderDisposition]; these dependencies will be watched in
  /// order to determine when it is necessary to call this function again.
  ///
  /// TODO(paulberry): use [addDependency] for tracking all folder disposition
  /// dependencies (currently we only use it to track "pub list" dependencies).
  FolderDisposition _computeFolderDisposition(Folder folder,
      void Function(String path) addDependency, File packagespecFile) {
    // Try .packages first.
    if (pathContext.basename(packagespecFile.path) == PACKAGE_SPEC_NAME) {
      var packages = parsePackagesFile(
        resourceProvider,
        packagespecFile,
      );
      return PackagesFileDisposition(packages);
    }

    return NoPackageFolderDisposition();
  }

  /// Compute line information for the given [content].
  LineInfo _computeLineInfo(String content) {
    var lineStarts = StringUtilities.computeLineStarts(content);
    return LineInfo(lineStarts);
  }

  /// Create an object that can be used to find and read the analysis options
  /// file for code being analyzed using the given [packages].
  AnalysisOptionsProvider _createAnalysisOptionsProvider(Packages packages) {
    var packageMap = <String, List<Folder>>{};
    if (packages != null) {
      for (var package in packages.packages) {
        packageMap[package.name] = [package.libFolder];
      }
    }

    var resolvers = <UriResolver>[
      ResourceUriResolver(resourceProvider),
      PackageMapUriResolver(resourceProvider, packageMap),
    ];
    var sourceFactory = SourceFactory(resolvers);
    return AnalysisOptionsProvider(sourceFactory);
  }

  /// Create a new empty context associated with [folder], having parent
  /// [parent] and using [packagesFile] to resolve package URI's.
  ContextInfo _createContext(ContextInfo parent, Folder folder,
      List<String> excludedPaths, File packagesFile) {
    var dependencies = <String>[];
    var disposition =
        _computeFolderDisposition(folder, dependencies.add, packagesFile);
    var info = ContextInfo(this, parent, folder, packagesFile, disposition);

    File optionsFile;
    YamlMap optionMap;
    try {
      var provider = _createAnalysisOptionsProvider(disposition.packages);
      optionsFile = provider.getOptionsFile(info.folder, crawlUp: true);
      if (optionsFile != null) {
        optionMap = provider.getOptionsFromFile(optionsFile);
      }
    } catch (_) {
      // Parse errors are reported elsewhere.
    }
    AnalysisOptions options = AnalysisOptionsImpl.from(defaultContextOptions);
    applyToAnalysisOptions(options, optionMap);

    info.setDependencies(dependencies);
    var includedPath = folder.path;
    var containedExcludedPaths = excludedPaths
        .where((String excludedPath) =>
            pathContext.isWithin(includedPath, excludedPath))
        .toList();
    processOptionsForDriver(info, options, optionMap);
    var contextRoot = ContextRoot(folder.path, containedExcludedPaths,
        pathContext: pathContext);
    if (optionsFile != null) {
      contextRoot.optionsFilePath = optionsFile.path;
    }
    info.analysisDriver =
        callbacks.addAnalysisDriver(folder, contextRoot, options);
    if (optionsFile != null) {
      _analyzeAnalysisOptionsFile(info.analysisDriver, optionsFile.path);
    }
    var pubspecFile = folder.getChildAssumingFile(PUBSPEC_NAME);
    if (pubspecFile.exists) {
      _analyzePubspecFile(info.analysisDriver, pubspecFile.path);
    }

    void checkManifestFilesIn(Folder folder) {
      // Don't traverse into dot directories.
      if (folder.shortName.startsWith('.')) {
        return;
      }

      for (var child in folder.getChildren()) {
        if (child is File) {
          if (child.shortName == MANIFEST_NAME &&
              !excludedPaths.contains(child.path)) {
            _analyzeManifestFile(info.analysisDriver, child.path);
          }
        } else if (child is Folder) {
          if (!excludedPaths.contains(child.path)) {
            checkManifestFilesIn(child);
          }
        }
      }
    }

    checkManifestFilesIn(folder);
    return info;
  }

  /// Potentially create a new context associated with the given [folder].
  ///
  /// If there are subfolders with 'pubspec.yaml' files, separate contexts are
  /// created for them and excluded from the context associated with the
  /// [folder].
  ///
  /// If [withPackageSpecOnly] is `true`, a context will be created only if
  /// there is a 'pubspec.yaml' or '.packages' file in the [folder].
  ///
  /// [parent] should be the parent of any contexts that are created.
  void _createContexts(ContextInfo parent, Folder folder,
      List<String> excludedPaths, bool withPackageSpecOnly) {
    if (_isExcluded(folder.path) || folder.shortName.startsWith('.')) {
      return;
    }
    // Decide whether a context needs to be created for [folder] here, and if
    // so, create it.
    var packageSpec = _findPackageSpecFile(folder);
    var createContext = packageSpec.exists || !withPackageSpecOnly;
    if (withPackageSpecOnly &&
        packageSpec.exists &&
        parent != null &&
        parent.ignored(packageSpec.path)) {
      // Don't create a context if the package spec is required and ignored.
      createContext = false;
    }
    if (createContext) {
      parent = _createContext(parent, folder, excludedPaths, packageSpec);
    }

    // Try to find subfolders with pubspecs or .packages files.
    try {
      for (var child in folder.getChildren()) {
        if (child is Folder) {
          if (!parent.ignored(child.path)) {
            _createContexts(parent, child, excludedPaths, true);
          }
        }
      }
    } on FileSystemException {
      // The directory either doesn't exist or cannot be read. Either way, there
      // are no subfolders that need to be added.
    }

    if (createContext) {
      // Now that the child contexts have been created, add the sources that
      // don't belong to the children.
      var changeSet = ChangeSet();
      _addSourceFiles(changeSet, folder, parent);
      callbacks.applyChangesToContext(folder, changeSet);
    }
  }

  /// Set up a [SourceFactory] that resolves packages as appropriate for the
  /// given [folder].
  SourceFactory _createSourceFactory(AnalysisOptions options, Folder folder) {
    var builder = callbacks.createContextBuilder(folder, options);
    return builder.createSourceFactory(folder.path, options);
  }

  /// Clean up and destroy the context associated with the given folder.
  void _destroyContext(ContextInfo info) {
    changeSubscriptions.remove(info.folder)?.cancel();
    callbacks.removeContext(info.folder, _computeFlushedFiles(info));
    var wasRemoved = info.parent.children.remove(info);
    assert(wasRemoved);
  }

  /// Extract a new [packagespecFile]-based context from [oldInfo].
  void _extractContext(ContextInfo oldInfo, File packagespecFile) {
    var newFolder = packagespecFile.parent;
    var newInfo =
        _createContext(oldInfo, newFolder, excludedPaths, packagespecFile);
    // prepare sources to extract
    Map<String, Source> extractedSources = HashMap<String, Source>();
    oldInfo.sources.forEach((path, source) {
      if (newFolder.contains(path)) {
        extractedSources[path] = source;
      }
    });
    // update new context
    {
      var changeSet = ChangeSet();
      extractedSources.forEach((path, source) {
        newInfo.sources[path] = source;
        changeSet.addedSource(path);
      });
      callbacks.applyChangesToContext(newFolder, changeSet);
    }
    // update old context
    {
      var changeSet = ChangeSet();
      extractedSources.forEach((path, source) {
        oldInfo.sources.remove(path);
        changeSet.removedSource(path);
      });
      callbacks.applyChangesToContext(oldInfo.folder, changeSet);
    }
    // TODO(paulberry): every context that was previously a child of oldInfo is
    // is still a child of oldInfo.  This is wrong--some of them ought to be
    // adopted by newInfo now.
  }

  /// Find the file that should be used to determine whether a context needs to
  /// be created here--this is either the ".packages" file or the "pubspec.yaml"
  /// file.
  File _findPackageSpecFile(Folder folder) {
    // Decide whether a context needs to be created for [folder] here, and if
    // so, create it.
    File packageSpec;

    // Start by looking for .packages.
    packageSpec = folder.getChild(PACKAGE_SPEC_NAME);

    // Fall back to looking for a pubspec.
    if (packageSpec == null || !packageSpec.exists) {
      packageSpec = folder.getChild(PUBSPEC_NAME);
    }
    return packageSpec;
  }

  /// Get analysis options inherited from an `_embedder.yaml` (deprecated)
  /// and/or a package specified configuration.  If more than one
  /// `_embedder.yaml` is associated with the given context, the embedder is
  /// skipped.
  ///
  /// Returns null if there are no embedded/configured options.
  YamlMap _getEmbeddedOptions(ContextInfo info) {
    Map embeddedOptions;
    var locator = info.disposition.getEmbedderLocator(resourceProvider);
    var maps = locator.embedderYamls.values;
    if (maps.length == 1) {
      embeddedOptions = maps.first;
    }
    return embeddedOptions;
  }

  /// Return the [ContextInfo] for the "innermost" context whose associated
  /// folder is or contains the given path.  ("innermost" refers to the nesting
  /// of contexts, so if there is a context for path /foo and a context for
  /// path /foo/bar, then the innermost context containing /foo/bar/baz.dart is
  /// the context for /foo/bar.)
  ///
  /// If no context contains the given path, `null` is returned.
  ContextInfo _getInnermostContextInfoFor(String path) {
    var info = rootInfo.findChildInfoFor(path);
    if (info == null) {
      return null;
    }
    while (true) {
      var childInfo = info.findChildInfoFor(path);
      if (childInfo == null) {
        return info;
      }
      info = childInfo;
    }
  }

  /// Return the parent for a new [ContextInfo] with the given [path] folder.
  ContextInfo _getParentForNewContext(String path) {
    var parent = _getInnermostContextInfoFor(path);
    if (parent != null) {
      return parent;
    }
    return rootInfo;
  }

  void _handleWatchEvent(WatchEvent event) {
    callbacks.broadcastWatchEvent(event);
    _handleWatchEventImpl(event);
    callbacks.afterWatchEvent(event);
  }

  void _handleWatchEventImpl(WatchEvent event) {
    // Figure out which context this event applies to.
    // TODO(brianwilkerson) If a file is explicitly included in one context
    // but implicitly referenced in another context, we will only send a
    // changeSet to the context that explicitly includes the file (because
    // that's the only context that's watching the file).
    var path = event.path;
    var type = event.type;
    var info = _getInnermostContextInfoFor(path);
    if (info == null) {
      // This event doesn't apply to any context.  This could happen due to a
      // race condition (e.g. a context was removed while one of its events was
      // in the event loop).  The event is inapplicable now, so just ignore it.
      return;
    }
    _instrumentationService.logWatchEvent(
        info.folder.path, path, type.toString());
    // First handle changes that affect folderDisposition (since these need to
    // be processed regardless of whether they are part of an excluded/ignored
    // path).
    if (info.hasDependency(path)) {
      _recomputeFolderDisposition(info);
    }
    // maybe excluded globally
    if (_isExcluded(path) ||
        _isContainedInDotFolder(info.folder.path, path) ||
        _isInTopLevelDocDir(info.folder.path, path)) {
      return;
    }
    // maybe excluded from the context, so other context will handle it
    if (info.excludes(path)) {
      return;
    }
    if (info.ignored(path)) {
      return;
    }
    // handle the change
    switch (type) {
      case ChangeType.ADD:
        var resource = resourceProvider.getResource(path);

        var directoryPath = pathContext.dirname(path);

        // Check to see if we need to create a new context.
        if (info.isTopLevel) {
          // Only create a new context if this is not the same directory
          // described by our info object.
          if (info.folder.path != directoryPath) {
            if (_isPubspec(path)) {
              // Check for a sibling .packages file.
              if (!resourceProvider
                  .getFile(pathContext.join(directoryPath, PACKAGE_SPEC_NAME))
                  .exists) {
                _extractContext(info, resource);
                return;
              }
            }
            if (_isPackagespec(path)) {
              // Check for a sibling pubspec.yaml file.
              if (!resourceProvider
                  .getFile(pathContext.join(directoryPath, PUBSPEC_NAME))
                  .exists) {
                _extractContext(info, resource);
                return;
              }
            }
          }
        }

        // If the file went away and was replaced by a folder before we
        // had a chance to process the event, resource might be a Folder. In
        // that case don't add it.
        if (resource is File) {
          if (_shouldFileBeAnalyzed(resource)) {
            info.analysisDriver.addFile(path);
          }
        }
        break;
      case ChangeType.REMOVE:
        // If package spec info is removed, check to see if we can merge
        // contexts. Note that it's important to verify that there is NEITHER a
        // .packages nor a lingering pubspec.yaml before merging.
        if (!info.isTopLevel) {
          var directoryPath = pathContext.dirname(path);

          // Only merge if this is the same directory described by our info
          // object.
          if (info.folder.path == directoryPath) {
            if (_isPubspec(path)) {
              // Check for a sibling .packages file.
              if (!resourceProvider
                  .getFile(pathContext.join(directoryPath, PACKAGE_SPEC_NAME))
                  .exists) {
                _mergeContext(info);
                return;
              }
            }
            if (_isPackagespec(path)) {
              // Check for a sibling pubspec.yaml file.
              if (!resourceProvider
                  .getFile(pathContext.join(directoryPath, PUBSPEC_NAME))
                  .exists) {
                _mergeContext(info);
                return;
              }
            }
          }
        }

        var resource = resourceProvider.getResource(path);
        if (resource is File &&
            _shouldFileBeAnalyzed(resource, mustExist: false)) {
          callbacks.applyFileRemoved(info.analysisDriver, path);
        }
        break;
      case ChangeType.MODIFY:
        var resource = resourceProvider.getResource(path);
        if (resource is File) {
          if (_shouldFileBeAnalyzed(resource)) {
            for (var driver in driverMap.values) {
              driver.changeFile(path);
            }
            break;
          }
        }
    }
    _checkForPackagespecUpdate(path, info);
    _checkForAnalysisOptionsUpdate(path, info);
    _checkForPubspecUpdate(path, info);
    _checkForManifestUpdate(path, info);
  }

  /// On windows, the directory watcher may overflow, and we must recover.
  void _handleWatchInterruption(dynamic error, StackTrace stackTrace) {
    // We've handled the error, so we only have to log it.
    AnalysisEngine.instance.instrumentationService
        .logError('Watcher error; refreshing contexts.\n$error\n$stackTrace');
    // TODO(mfairhurst): Optimize this, or perhaps be less complete.
    refresh(null);
  }

  /// Determine whether the given [path], when interpreted relative to the
  /// context root [root], contains a folder whose name starts with '.'.
  bool _isContainedInDotFolder(String root, String path) {
    var pathDir = pathContext.dirname(path);
    var rootPrefix = root + pathContext.separator;
    if (pathDir.startsWith(rootPrefix)) {
      var suffixPath = pathDir.substring(rootPrefix.length);
      for (var pathComponent in pathContext.split(suffixPath)) {
        if (pathComponent.startsWith('.')) {
          return true;
        }
      }
    }
    return false;
  }

  /// Returns `true` if the given [path] is excluded by [excludedPaths].
  bool _isExcluded(String path) => _isExcludedBy(excludedPaths, path);

  /// Returns `true` if the given [path] is excluded by [excludedPaths].
  bool _isExcludedBy(List<String> excludedPaths, String path) {
    return excludedPaths.any((excludedPath) {
      if (pathContext.isWithin(excludedPath, path)) {
        return true;
      }
      return path == excludedPath;
    });
  }

  /// Determine whether the given [path] is in the direct 'doc' folder of the
  /// context root [root].
  bool _isInTopLevelDocDir(String root, String path) {
    var rootPrefix = root + pathContext.separator;
    if (path.startsWith(rootPrefix)) {
      var suffix = path.substring(rootPrefix.length);
      return suffix == DOC_DIR_NAME ||
          suffix.startsWith(DOC_DIR_NAME + pathContext.separator);
    }
    return false;
  }

  bool _isManifest(String path) => pathContext.basename(path) == MANIFEST_NAME;

  bool _isPackagespec(String path) =>
      pathContext.basename(path) == PACKAGE_SPEC_NAME;

  bool _isPubspec(String path) => pathContext.basename(path) == PUBSPEC_NAME;

  /// Merges [info] context into its parent.
  void _mergeContext(ContextInfo info) {
    // destroy the context
    _destroyContext(info);
    // add files to the parent context
    var parentInfo = info.parent;
    if (parentInfo != null) {
      parentInfo.children.remove(info);
      var changeSet = ChangeSet();
      info.sources.forEach((path, source) {
        parentInfo.sources[path] = source;
        changeSet.addedSource(path);
      });
      callbacks.applyChangesToContext(parentInfo.folder, changeSet);
    }
  }

  /// Read the contents of the file at the given [path], or throw an exception
  /// if the contents cannot be read.
  String _readFile(String path) {
    return resourceProvider.getFile(path).readAsStringSync();
  }

  /// Recompute the [FolderDisposition] for the context described by [info],
  /// and update the client appropriately.
  void _recomputeFolderDisposition(ContextInfo info) {
    // TODO(paulberry): when computePackageMap is changed into an
    // asynchronous API call, we'll want to suspend analysis for this context
    // while we're rerunning "pub list", since any analysis we complete while
    // "pub list" is in progress is just going to get thrown away anyhow.
    var dependencies = <String>[];
    info.setDependencies(dependencies);
    _updateContextPackageUriResolver(info.folder);
  }

  /// Return `true` if the given [file] should be analyzed.
  bool _shouldFileBeAnalyzed(File file, {bool mustExist = true}) {
    for (var glob in analyzedFilesGlobs) {
      if (glob.matches(file.path)) {
        // Emacs creates dummy links to track the fact that a file is open for
        // editing and has unsaved changes (e.g. having unsaved changes to
        // 'foo.dart' causes a link '.#foo.dart' to be created, which points to
        // the non-existent file 'username@hostname.pid'. To avoid these dummy
        // links causing the analyzer to thrash, just ignore links to
        // non-existent files.
        return !mustExist || file.exists;
      }
    }
    return false;
  }

  void _updateAnalysisOptions(ContextInfo info) {
    var driver = info.analysisDriver;
    var contextRoot = info.folder.path;
    var builder =
        callbacks.createContextBuilder(info.folder, defaultContextOptions);
    var options = builder.getAnalysisOptions(contextRoot,
        contextRoot: driver.contextRoot);
    var factory = builder.createSourceFactory(contextRoot, options);
    driver.configure(analysisOptions: options, sourceFactory: factory);
    callbacks.analysisOptionsUpdated(driver);
  }

  void _updateContextPackageUriResolver(Folder contextFolder) {
    var info = getContextInfoFor(contextFolder);
    var driver = info.analysisDriver;
    var sourceFactory =
        _createSourceFactory(driver.analysisOptions, contextFolder);
    driver.configure(sourceFactory: sourceFactory);
  }

  /// Create and return a source representing the given [file] within the given
  /// [driver].
  static Source createSourceInContext(AnalysisDriver driver, File file) {
    // TODO(brianwilkerson) Optimize this, by allowing support for source
    // factories to restore URI's from a file path rather than a source.
    var source = file.createSource();
    if (driver == null) {
      return source;
    }
    var uri = driver.sourceFactory.restoreUri(source);
    return file.createSource(uri);
  }
}

/// An instance of the class [FolderDisposition] represents the information
/// gathered by the [ContextManagerImpl] to determine how to create an analysis
/// driver for a given folder.
///
/// Note: [ContextManagerImpl] may use equality testing and hash codes to
/// determine when two folders should share the same context, so derived classes
/// may need to override operator== and hashCode() if object identity is
/// insufficient.
///
/// TODO(paulberry): consider adding a flag to indicate that it is not necessary
/// to recurse into the given folder looking for additional contexts to create
/// or files to analyze (this could help avoid unnecessarily weighing down the
/// system with file watchers).
abstract class FolderDisposition {
  /// If this [FolderDisposition] was created based on a package root
  /// folder, the absolute path to that folder.  Otherwise `null`.
  String get packageRoot;

  /// If contexts governed by this [FolderDisposition] should resolve packages
  /// using the ".packages" file mechanism (DEP 5), retrieve the [Packages]
  /// object that resulted from parsing the ".packages" file.
  Packages get packages;

  /// Create all the [UriResolver]s which should be used to resolve packages in
  /// contexts governed by this [FolderDisposition].
  ///
  /// [resourceProvider] is provided since it is needed to construct most
  /// [UriResolver]s.
  Iterable<UriResolver> createPackageUriResolvers(
      ResourceProvider resourceProvider);

  /// Return the locator used to locate the _embedder.yaml file used to
  /// configure the SDK. The [resourceProvider] is used to access the file
  /// system in cases where that is necessary.
  EmbedderYamlLocator getEmbedderLocator(ResourceProvider resourceProvider);
}

/// Concrete [FolderDisposition] object indicating that the context for a given
/// folder should not resolve "package:" URIs at all.
class NoPackageFolderDisposition extends FolderDisposition {
  @override
  final String packageRoot;

  NoPackageFolderDisposition({this.packageRoot});

  @override
  Packages get packages => null;

  @override
  Iterable<UriResolver> createPackageUriResolvers(
          ResourceProvider resourceProvider) =>
      const <UriResolver>[];

  @override
  EmbedderYamlLocator getEmbedderLocator(ResourceProvider resourceProvider) =>
      EmbedderYamlLocator(null);
}

/// Concrete [FolderDisposition] object indicating that the context for a given
/// folder should resolve packages using a ".packages" file.
class PackagesFileDisposition extends FolderDisposition {
  @override
  final Packages packages;

  Map<String, List<Folder>> packageMap;

  EmbedderYamlLocator _embedderLocator;

  PackagesFileDisposition(this.packages);

  @override
  String get packageRoot => null;

  Map<String, List<Folder>> buildPackageMap(ResourceProvider resourceProvider) {
    if (packageMap == null) {
      packageMap = <String, List<Folder>>{};
      if (packages != null) {
        for (var package in packages.packages) {
          packageMap[package.name] = [package.libFolder];
        }
      }
    }
    return packageMap;
  }

  @override
  Iterable<UriResolver> createPackageUriResolvers(
      ResourceProvider resourceProvider) {
    if (packages != null) {
      var packageMap = buildPackageMap(resourceProvider);
      return <UriResolver>[
        PackageMapUriResolver(resourceProvider, packageMap),
      ];
    } else {
      return const <UriResolver>[];
    }
  }

  @override
  EmbedderYamlLocator getEmbedderLocator(ResourceProvider resourceProvider) {
    _embedderLocator ??= EmbedderYamlLocator(buildPackageMap(resourceProvider));
    return _embedderLocator;
  }
}