// Copyright 2016 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

import 'dart:async';
import 'package:json_rpc_2/json_rpc_2.dart' as rpc;
import 'package:meta/meta.dart';

import 'asset.dart';
import 'base/common.dart';
import 'base/context.dart';
import 'base/file_system.dart';
import 'base/io.dart';
import 'build_info.dart';
import 'bundle.dart';
import 'compile.dart';
import 'convert.dart' show base64, utf8;
import 'dart/package_map.dart';
import 'globals.dart';
import 'vmservice.dart';

class DevFSConfig {
  /// Should DevFS assume that symlink targets are stable?
  bool cacheSymlinks = false;
  /// Should DevFS assume that there are no symlinks to directories?
  bool noDirectorySymlinks = false;
}

DevFSConfig get devFSConfig => context[DevFSConfig];

/// Common superclass for content copied to the device.
abstract class DevFSContent {
  bool _exists = true;

  /// Return true if this is the first time this method is called
  /// or if the entry has been modified since this method was last called.
  bool get isModified;

  /// Return true if this is the first time this method is called
  /// or if the entry has been modified after the given time
  /// or if the given time is null.
  bool isModifiedAfter(DateTime time);

  int get size;

  Future<List<int>> contentsAsBytes();

  Stream<List<int>> contentsAsStream();

  Stream<List<int>> contentsAsCompressedStream() {
    return contentsAsStream().transform<List<int>>(gzip.encoder);
  }

  /// Return the list of files this content depends on.
  List<String> get fileDependencies => <String>[];
}

// File content to be copied to the device.
class DevFSFileContent extends DevFSContent {
  DevFSFileContent(this.file);

  static DevFSFileContent clone(DevFSFileContent fsFileContent) {
    final DevFSFileContent newFsFileContent = DevFSFileContent(fsFileContent.file);
    newFsFileContent._linkTarget = fsFileContent._linkTarget;
    newFsFileContent._fileStat = fsFileContent._fileStat;
    return newFsFileContent;
  }

  final FileSystemEntity file;
  FileSystemEntity _linkTarget;
  FileStat _fileStat;

  File _getFile() {
    if (_linkTarget != null) {
      return _linkTarget;
    }
    if (file is Link) {
      // The link target.
      return fs.file(file.resolveSymbolicLinksSync());
    }
    return file;
  }

  void _stat() {
    if (_linkTarget != null) {
      // Stat the cached symlink target.
      final FileStat fileStat = _linkTarget.statSync();
      if (fileStat.type == FileSystemEntityType.notFound) {
        _linkTarget = null;
      } else {
        _fileStat = fileStat;
        return;
      }
    }
    final FileStat fileStat = file.statSync();
    _fileStat = fileStat.type == FileSystemEntityType.notFound ? null : fileStat;
    if (_fileStat != null && _fileStat.type == FileSystemEntityType.link) {
      // Resolve, stat, and maybe cache the symlink target.
      final String resolved = file.resolveSymbolicLinksSync();
      final FileSystemEntity linkTarget = fs.file(resolved);
      // Stat the link target.
      final FileStat fileStat = linkTarget.statSync();
      if (fileStat.type == FileSystemEntityType.notFound) {
        _fileStat = null;
        _linkTarget = null;
      } else if (devFSConfig.cacheSymlinks) {
        _linkTarget = linkTarget;
      }
    }
    if (_fileStat == null) {
      printError('Unable to get status of file "${file.path}": file not found.');
    }
  }

  @override
  List<String> get fileDependencies => <String>[_getFile().path];

  @override
  bool get isModified {
    final FileStat _oldFileStat = _fileStat;
    _stat();
    if (_oldFileStat == null && _fileStat == null)
      return false;
    return _oldFileStat == null || _fileStat == null || _fileStat.modified.isAfter(_oldFileStat.modified);
  }

  @override
  bool isModifiedAfter(DateTime time) {
    final FileStat _oldFileStat = _fileStat;
    _stat();
    if (_oldFileStat == null && _fileStat == null)
      return false;
    return time == null
        || _oldFileStat == null
        || _fileStat == null
        || _fileStat.modified.isAfter(time);
  }

  @override
  int get size {
    if (_fileStat == null)
      _stat();
    // Can still be null if the file wasn't found.
    return _fileStat?.size ?? 0;
  }

  @override
  Future<List<int>> contentsAsBytes() => _getFile().readAsBytes();

  @override
  Stream<List<int>> contentsAsStream() => _getFile().openRead();
}

/// Byte content to be copied to the device.
class DevFSByteContent extends DevFSContent {
  DevFSByteContent(this._bytes);

  List<int> _bytes;

  bool _isModified = true;
  DateTime _modificationTime = DateTime.now();

  List<int> get bytes => _bytes;

  set bytes(List<int> value) {
    _bytes = value;
    _isModified = true;
    _modificationTime = DateTime.now();
  }

  /// Return true only once so that the content is written to the device only once.
  @override
  bool get isModified {
    final bool modified = _isModified;
    _isModified = false;
    return modified;
  }

  @override
  bool isModifiedAfter(DateTime time) {
    return time == null || _modificationTime.isAfter(time);
  }

  @override
  int get size => _bytes.length;

  @override
  Future<List<int>> contentsAsBytes() async => _bytes;

  @override
  Stream<List<int>> contentsAsStream() =>
      Stream<List<int>>.fromIterable(<List<int>>[_bytes]);
}

/// String content to be copied to the device.
class DevFSStringContent extends DevFSByteContent {
  DevFSStringContent(String string)
    : _string = string,
      super(utf8.encode(string));

  String _string;

  String get string => _string;

  set string(String value) {
    _string = value;
    super.bytes = utf8.encode(_string);
  }

  @override
  set bytes(List<int> value) {
    string = utf8.decode(value);
  }
}

/// Abstract DevFS operations interface.
abstract class DevFSOperations {
  Future<Uri> create(String fsName);
  Future<dynamic> destroy(String fsName);
  Future<dynamic> writeFile(String fsName, Uri deviceUri, DevFSContent content);
  Future<dynamic> deleteFile(String fsName, Uri deviceUri);
}

/// An implementation of [DevFSOperations] that speaks to the
/// vm service.
class ServiceProtocolDevFSOperations implements DevFSOperations {
  ServiceProtocolDevFSOperations(this.vmService);

  final VMService vmService;

  @override
  Future<Uri> create(String fsName) async {
    final Map<String, dynamic> response = await vmService.vm.createDevFS(fsName);
    return Uri.parse(response['uri']);
  }

  @override
  Future<dynamic> destroy(String fsName) async {
    await vmService.vm.deleteDevFS(fsName);
  }

  @override
  Future<dynamic> writeFile(String fsName, Uri deviceUri, DevFSContent content) async {
    List<int> bytes;
    try {
      bytes = await content.contentsAsBytes();
    } catch (e) {
      return e;
    }
    final String fileContents = base64.encode(bytes);
    try {
      return await vmService.vm.invokeRpcRaw(
        '_writeDevFSFile',
        params: <String, dynamic> {
          'fsName': fsName,
          'uri': deviceUri.toString(),
          'fileContents': fileContents,
        },
      );
    } catch (error) {
      printTrace('DevFS: Failed to write $deviceUri: $error');
    }
  }

  @override
  Future<dynamic> deleteFile(String fsName, Uri deviceUri) async {
    // TODO(johnmccutchan): Add file deletion to the devFS protocol.
  }
}

class DevFSException implements Exception {
  DevFSException(this.message, [this.error, this.stackTrace]);
  final String message;
  final dynamic error;
  final StackTrace stackTrace;
}

class _DevFSHttpWriter {
  _DevFSHttpWriter(this.fsName, VMService serviceProtocol)
    : httpAddress = serviceProtocol.httpAddress;

  final String fsName;
  final Uri httpAddress;

  static const int kMaxInFlight = 6;
  static const int kMaxRetries = 3;

  int _inFlight = 0;
  Map<Uri, DevFSContent> _outstanding;
  Completer<void> _completer;
  HttpClient _client;

  Future<void> write(Map<Uri, DevFSContent> entries) async {
    _client = HttpClient();
    _client.maxConnectionsPerHost = kMaxInFlight;
    _completer = Completer<void>();
    _outstanding = Map<Uri, DevFSContent>.from(entries);
    _scheduleWrites();
    await _completer.future;
    _client.close();
  }

  void _scheduleWrites() {
    while (_inFlight < kMaxInFlight) {
      if (_outstanding.isEmpty) {
        // Finished.
        break;
      }
      final Uri deviceUri = _outstanding.keys.first;
      final DevFSContent content = _outstanding.remove(deviceUri);
      _scheduleWrite(deviceUri, content);
      _inFlight++;
    }
  }

  Future<void> _scheduleWrite(
    Uri deviceUri,
    DevFSContent content, [
    int retry = 0,
  ]) async {
    try {
      final HttpClientRequest request = await _client.putUrl(httpAddress);
      request.headers.removeAll(HttpHeaders.acceptEncodingHeader);
      request.headers.add('dev_fs_name', fsName);
      request.headers.add('dev_fs_uri_b64',
          base64.encode(utf8.encode(deviceUri.toString())));
      final Stream<List<int>> contents = content.contentsAsCompressedStream();
      await request.addStream(contents);
      final HttpClientResponse response = await request.close();
      await response.drain<void>();
    } on SocketException catch (socketException, stackTrace) {
      // We have one completer and can get up to kMaxInFlight errors.
      if (!_completer.isCompleted)
        _completer.completeError(socketException, stackTrace);
      return;
    } catch (e) {
      if (retry < kMaxRetries) {
        printTrace('Retrying writing "$deviceUri" to DevFS due to error: $e');
        // Synchronization is handled by the _completer below.
        unawaited(_scheduleWrite(deviceUri, content, retry + 1));
        return;
      } else {
        printError('Error writing "$deviceUri" to DevFS: $e');
      }
    }
    _inFlight--;
    if ((_outstanding.isEmpty) && (_inFlight == 0)) {
      _completer.complete();
    } else {
      _scheduleWrites();
    }
  }
}

// Basic statistics for DevFS update operation.
class UpdateFSReport {
  UpdateFSReport({bool success = false,
    int invalidatedSourcesCount = 0, int syncedBytes = 0}) {
    _success = success;
    _invalidatedSourcesCount = invalidatedSourcesCount;
    _syncedBytes = syncedBytes;
  }

  bool get success => _success;
  int get invalidatedSourcesCount => _invalidatedSourcesCount;
  int get syncedBytes => _syncedBytes;

  void incorporateResults(UpdateFSReport report) {
    if (!report._success) {
      _success = false;
    }
    _invalidatedSourcesCount += report._invalidatedSourcesCount;
    _syncedBytes += report._syncedBytes;
  }

  bool _success;
  int _invalidatedSourcesCount;
  int _syncedBytes;
}

class DevFS {
  /// Create a [DevFS] named [fsName] for the local files in [rootDirectory].
  DevFS(
    VMService serviceProtocol,
    this.fsName,
    this.rootDirectory, {
    String packagesFilePath,
  }) : _operations = ServiceProtocolDevFSOperations(serviceProtocol),
       _httpWriter = _DevFSHttpWriter(fsName, serviceProtocol),
       _packagesFilePath = packagesFilePath ?? fs.path.join(rootDirectory.path, kPackagesFileName);

  DevFS.operations(
    this._operations,
    this.fsName,
    this.rootDirectory, {
    String packagesFilePath,
  }) : _httpWriter = null,
       _packagesFilePath = packagesFilePath ?? fs.path.join(rootDirectory.path, kPackagesFileName);

  final DevFSOperations _operations;
  final _DevFSHttpWriter _httpWriter;
  final String fsName;
  final Directory rootDirectory;
  String _packagesFilePath;
  final Map<Uri, DevFSContent> _entries = <Uri, DevFSContent>{};
  final Set<String> assetPathsToEvict = <String>{};

  final List<Future<Map<String, dynamic>>> _pendingOperations =
      <Future<Map<String, dynamic>>>[];

  Uri _baseUri;
  Uri get baseUri => _baseUri;

  Uri deviceUriToHostUri(Uri deviceUri) {
    final String deviceUriString = deviceUri.toString();
    final String baseUriString = baseUri.toString();
    if (deviceUriString.startsWith(baseUriString)) {
      final String deviceUriSuffix = deviceUriString.substring(baseUriString.length);
      return rootDirectory.uri.resolve(deviceUriSuffix);
    }
    return deviceUri;
  }

  Future<Uri> create() async {
    printTrace('DevFS: Creating new filesystem on the device ($_baseUri)');
    try {
      _baseUri = await _operations.create(fsName);
    } on rpc.RpcException catch (rpcException) {
      // 1001 is kFileSystemAlreadyExists in //dart/runtime/vm/json_stream.h
      if (rpcException.code != 1001)
        rethrow;
      printTrace('DevFS: Creating failed. Destroying and trying again');
      await destroy();
      _baseUri = await _operations.create(fsName);
    }
    printTrace('DevFS: Created new filesystem on the device ($_baseUri)');
    return _baseUri;
  }

  Future<void> destroy() async {
    printTrace('DevFS: Deleting filesystem on the device ($_baseUri)');
    await _operations.destroy(fsName);
    printTrace('DevFS: Deleted filesystem on the device ($_baseUri)');
  }

  /// Updates files on the device.
  ///
  /// Returns the number of bytes synced.
  Future<UpdateFSReport> update({
    @required String mainPath,
    String target,
    AssetBundle bundle,
    DateTime firstBuildTime,
    bool bundleFirstUpload = false,
    bool bundleDirty = false,
    Set<String> fileFilter,
    @required ResidentCompiler generator,
    String dillOutputPath,
    @required bool trackWidgetCreation,
    bool fullRestart = false,
    String projectRootPath,
    @required String pathToReload,
  }) async {
    assert(trackWidgetCreation != null);
    assert(generator != null);
    // Mark all entries as possibly deleted.
    for (DevFSContent content in _entries.values) {
      content._exists = false;
    }

    // Scan workspace, packages, and assets
    printTrace('DevFS: Starting sync from $rootDirectory');
    logger.printTrace('Scanning project files');
    await _scanDirectory(rootDirectory,
                         recursive: true,
                         fileFilter: fileFilter);
    if (fs.isFileSync(_packagesFilePath)) {
      printTrace('Scanning package files');
      await _scanPackages(fileFilter);
    }
    if (bundle != null) {
      printTrace('Scanning asset files');
      bundle.entries.forEach((String archivePath, DevFSContent content) {
        _scanBundleEntry(archivePath, content);
      });
    }

    // Handle deletions.
    printTrace('Scanning for deleted files');
    final String assetBuildDirPrefix = _asUriPath(getAssetBuildDirectory());
    final List<Uri> toRemove = <Uri>[];
    _entries.forEach((Uri deviceUri, DevFSContent content) {
      if (!content._exists) {
        final Future<Map<String, dynamic>> operation =
            _operations.deleteFile(fsName, deviceUri)
            .then<Map<String, dynamic>>((dynamic v) => v?.cast<String,dynamic>());
        if (operation != null)
          _pendingOperations.add(operation);
        toRemove.add(deviceUri);
        if (deviceUri.path.startsWith(assetBuildDirPrefix)) {
          final String archivePath = deviceUri.path.substring(assetBuildDirPrefix.length);
          assetPathsToEvict.add(archivePath);
        }
      }
    });
    if (toRemove.isNotEmpty) {
      printTrace('Removing deleted files');
      toRemove.forEach(_entries.remove);
      await Future.wait<Map<String, dynamic>>(_pendingOperations);
      _pendingOperations.clear();
    }

    // Update modified files
    int syncedBytes = 0;
    final Map<Uri, DevFSContent> dirtyEntries = <Uri, DevFSContent>{};
    _entries.forEach((Uri deviceUri, DevFSContent content) {
      String archivePath;
      if (deviceUri.path.startsWith(assetBuildDirPrefix))
        archivePath = deviceUri.path.substring(assetBuildDirPrefix.length);
      // When doing full restart, copy content so that isModified does not
      // reset last check timestamp because we want to report all modified
      // files to incremental compiler next time user does hot reload.
      if (content.isModified || ((bundleDirty || bundleFirstUpload) && archivePath != null)) {
        dirtyEntries[deviceUri] = content;
        syncedBytes += content.size;
        if (archivePath != null && (!bundleFirstUpload || content.isModifiedAfter(firstBuildTime)))
          assetPathsToEvict.add(archivePath);
      }
    });
    // We run generator even if [dirtyEntries] was empty because we want to
    // keep logic of accepting/rejecting generator's output simple: we must
    // accept/reject generator's output after every [update] call.  Incremental
    // run with no changes is supposed to be fast (considering that it is
    // initiated by user key press).
    final List<String> invalidatedFiles = <String>[];
    final Set<Uri> filesUris = <Uri>{};
    for (Uri uri in dirtyEntries.keys.toList()) {
      if (!uri.path.startsWith(assetBuildDirPrefix)) {
        final DevFSContent content = dirtyEntries[uri];
        if (content is DevFSFileContent) {
          filesUris.add(uri);
          invalidatedFiles.add(content.file.uri.toString());
          syncedBytes -= content.size;
        }
      }
    }
    // No need to send source files because all compilation is done on the
    // host and result of compilation is single kernel file.
    filesUris.forEach(dirtyEntries.remove);
    printTrace('Compiling dart to kernel with ${invalidatedFiles.length} updated files');
    if (fullRestart) {
      generator.reset();
    }
    final CompilerOutput compilerOutput = await generator.recompile(
      mainPath,
      invalidatedFiles,
      outputPath:  dillOutputPath ?? getDefaultApplicationKernelPath(trackWidgetCreation: trackWidgetCreation),
      packagesFilePath : _packagesFilePath,
    );
    // Don't send full kernel file that would overwrite what VM already
    // started loading from.
    if (!bundleFirstUpload) {
      final String compiledBinary = compilerOutput?.outputFilename;
      if (compiledBinary != null && compiledBinary.isNotEmpty) {
        final Uri entryUri = fs.path.toUri(projectRootPath != null
          ? fs.path.relative(pathToReload, from: projectRootPath)
          : pathToReload,
        );
        if (!dirtyEntries.containsKey(entryUri)) {
          final DevFSFileContent content = DevFSFileContent(fs.file(compiledBinary));
          dirtyEntries[entryUri] = content;
          syncedBytes += content.size;
        }
      }
    }
    if (dirtyEntries.isNotEmpty) {
      printTrace('Updating files');
      if (_httpWriter != null) {
        try {
          await _httpWriter.write(dirtyEntries);
        } on SocketException catch (socketException, stackTrace) {
          printTrace('DevFS sync failed. Lost connection to device: $socketException');
          throw DevFSException('Lost connection to device.', socketException, stackTrace);
        } catch (exception, stackTrace) {
          printError('Could not update files on device: $exception');
          throw DevFSException('Sync failed', exception, stackTrace);
        }
      } else {
        // Make service protocol requests for each.
        dirtyEntries.forEach((Uri deviceUri, DevFSContent content) {
          final Future<Map<String, dynamic>> operation =
              _operations.writeFile(fsName, deviceUri, content)
                  .then<Map<String, dynamic>>((dynamic v) => v?.cast<String, dynamic>());
          if (operation != null)
            _pendingOperations.add(operation);
        });
        await Future.wait<Map<String, dynamic>>(_pendingOperations, eagerError: true);
        _pendingOperations.clear();
      }
    }

    printTrace('DevFS: Sync finished');
    return UpdateFSReport(success: true, syncedBytes: syncedBytes,
        invalidatedSourcesCount: invalidatedFiles.length);
  }

  void _scanFile(Uri deviceUri, FileSystemEntity file) {
    final DevFSContent content = _entries.putIfAbsent(deviceUri, () => DevFSFileContent(file));
    content._exists = true;
  }

  void _scanBundleEntry(String archivePath, DevFSContent content) {
    // We write the assets into the AssetBundle working dir so that they
    // are in the same location in DevFS and the iOS simulator.
    final Uri deviceUri = fs.path.toUri(fs.path.join(getAssetBuildDirectory(), archivePath));

    _entries[deviceUri] = content;
    content._exists = true;
  }

  bool _shouldIgnore(Uri deviceUri) {
    final List<String> ignoredUriPrefixes = <String>['android/',
                                               _asUriPath(getBuildDirectory()),
                                               'ios/',
                                               '.pub/'];
    for (String ignoredUriPrefix in ignoredUriPrefixes) {
      if (deviceUri.path.startsWith(ignoredUriPrefix))
        return true;
    }
    return false;
  }

  bool _shouldSkip(
    FileSystemEntity file,
    String relativePath,
    Uri directoryUriOnDevice, {
    bool ignoreDotFiles = true,
  }) {
    if (file is Directory) {
      // Skip non-files.
      return true;
    }
    assert((file is Link) || (file is File));
    final String basename = fs.path.basename(file.path);
    if (ignoreDotFiles && basename.startsWith('.')) {
      // Skip dot files, but not the '.packages' file (even though in dart1
      // mode devfs['.packages'] will be overwritten with synthesized string content).
      return basename != '.packages';
    }
    return false;
  }

  Uri _directoryUriOnDevice(Uri directoryUriOnDevice, Directory directory) {
    if (directoryUriOnDevice == null) {
      final String relativeRootPath = fs.path.relative(directory.path, from: rootDirectory.path);
      if (relativeRootPath == '.') {
        directoryUriOnDevice = Uri();
      } else {
        directoryUriOnDevice = fs.path.toUri(relativeRootPath);
      }
    }
    return directoryUriOnDevice;
  }

  /// Scan all files from the [fileFilter] that are contained in [directory] and
  /// pass various filters (e.g. ignoreDotFiles).
  Future<bool> _scanFilteredDirectory(
    Set<String> fileFilter,
    Directory directory, {
    Uri directoryUriOnDevice,
    bool ignoreDotFiles = true,
  }) async {
    directoryUriOnDevice =
        _directoryUriOnDevice(directoryUriOnDevice, directory);
    try {
      final String absoluteDirectoryPath = canonicalizePath(directory.path);
      // For each file in the file filter.
      for (String filePath in fileFilter) {
        if (!filePath.startsWith(absoluteDirectoryPath)) {
          // File is not in this directory. Skip.
          continue;
        }
        final String relativePath =
          fs.path.relative(filePath, from: directory.path);
        final FileSystemEntity file = fs.file(filePath);
        if (_shouldSkip(file, relativePath, directoryUriOnDevice, ignoreDotFiles: ignoreDotFiles)) {
          continue;
        }
        final Uri deviceUri = directoryUriOnDevice.resolveUri(fs.path.toUri(relativePath));
        if (!_shouldIgnore(deviceUri))
          _scanFile(deviceUri, file);
      }
    } on FileSystemException catch (e) {
      _printScanDirectoryError(directory.path, e);
      return false;
    }
    return true;
  }

  /// Scan all files in [directory] that pass various filters (e.g. ignoreDotFiles).
  Future<bool> _scanDirectory(
    Directory directory, {
    Uri directoryUriOnDevice,
    bool recursive = false,
    bool ignoreDotFiles = true,
    Set<String> fileFilter,
  }) async {
    directoryUriOnDevice = _directoryUriOnDevice(directoryUriOnDevice, directory);
    if ((fileFilter != null) && fileFilter.isNotEmpty) {
      // When the fileFilter isn't empty, we can skip crawling the directory
      // tree and instead use the fileFilter as the source of potential files.
      return _scanFilteredDirectory(fileFilter,
                                    directory,
                                    directoryUriOnDevice: directoryUriOnDevice,
                                    ignoreDotFiles: ignoreDotFiles);
    }
    try {
      final Stream<FileSystemEntity> files =
          directory.list(recursive: recursive, followLinks: false);
      await for (FileSystemEntity file in files) {
        if (!devFSConfig.noDirectorySymlinks && (file is Link)) {
          // Check if this is a symlink to a directory and skip it.
          try {
            final FileSystemEntityType linkType =
                fs.statSync(file.resolveSymbolicLinksSync()).type;
            if (linkType == FileSystemEntityType.directory)
              continue;
          } on FileSystemException catch (e) {
            _printScanDirectoryError(file.path, e);
            continue;
          }
        }
        final String relativePath =
          fs.path.relative(file.path, from: directory.path);
        if (_shouldSkip(file, relativePath, directoryUriOnDevice, ignoreDotFiles: ignoreDotFiles)) {
          continue;
        }
        final Uri deviceUri = directoryUriOnDevice.resolveUri(fs.path.toUri(relativePath));
        if (!_shouldIgnore(deviceUri))
          _scanFile(deviceUri, file);
      }
    } on FileSystemException catch (e) {
      _printScanDirectoryError(directory.path, e);
      return false;
    }
    return true;
  }

  void _printScanDirectoryError(String path, Exception e) {
    printError(
        'Error while scanning $path.\n'
        'Hot Reload might not work until the following error is resolved:\n'
        '$e\n'
    );
  }

  Future<void> _scanPackages(Set<String> fileFilter) async {
    StringBuffer sb;
    final PackageMap packageMap = PackageMap(_packagesFilePath);

    for (String packageName in packageMap.map.keys) {
      final Uri packageUri = packageMap.map[packageName];
      final String packagePath = fs.path.fromUri(packageUri);
      final Directory packageDirectory = fs.directory(packageUri);
      Uri directoryUriOnDevice = fs.path.toUri(fs.path.join('packages', packageName) + fs.path.separator);
      bool packageExists = packageDirectory.existsSync();

      if (!packageExists) {
        // If the package directory doesn't exist at all, we ignore it.
        continue;
      }

      if (fs.path.isWithin(rootDirectory.path, packagePath)) {
        // We already scanned everything under the root directory.
        directoryUriOnDevice = fs.path.toUri(
            fs.path.relative(packagePath, from: rootDirectory.path) + fs.path.separator
        );
      } else {
        packageExists =
            await _scanDirectory(packageDirectory,
                                 directoryUriOnDevice: directoryUriOnDevice,
                                 recursive: true,
                                 fileFilter: fileFilter);
      }
      if (packageExists) {
        sb ??= StringBuffer();
        sb.writeln('$packageName:$directoryUriOnDevice');
      }
    }
  }
}
/// Converts a platform-specific file path to a platform-independent Uri path.
String _asUriPath(String filePath) => fs.path.toUri(filePath).path + '/';