Refactor fake

pkgs/io_file/lib/io_file.dart

@@ -2,6 +2,7 @@
 // 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.
 
+export 'src/exceptions.dart';
 export 'src/file_system.dart';
 export 'src/vm_file_system_property.dart'
     if (dart.library.html) 'src/web_file_system_property.dart';

pkgs/io_file/lib/src/exceptions.dart

@@ -0,0 +1,66 @@
+// Copyright (c) 2025, 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.
+
+class SystemCallError {
+  final String systemCall;
+  final int errorCode;
+  final String message;
+
+  const SystemCallError(this.systemCall, this.errorCode, this.message);
+}
+
+class IOFileException implements Exception {
+  final String message;
+
+  /// The file system path on which the error occurred.
+  ///
+  /// Can be `null` if the exception does not relate directly
+  /// to a file system path.
+  final String? path;
+
+  /// The underlying OS error.
+  ///
+  /// Can be `null` if the exception is not raised due to an OS error.
+  final SystemCallError? systemCall;
+
+  const IOFileException(this.message, {this.path, this.systemCall});
+
+  String _toStringHelper(String className) {
+    final sb = StringBuffer('$className: $message');
+    if (path != null) {
+      sb.write(', path = "$path"');
+    }
+    if (systemCall != null) {
+      sb.write(
+        ' (${systemCall!.systemCall}: ${systemCall!.message}, '
+        'errno=${systemCall!.errorCode} )',
+      );
+    }
+    return sb.toString();
+  }
+
+  @override
+  String toString() => _toStringHelper('IOFileException');
+}
+
+class PathAccessException extends IOFileException {
+  const PathAccessException(super.message, {super.path, super.systemCall});
+
+  @override
+  String toString() => _toStringHelper('PathAccessException');
+}
+
+class PathExistsException extends IOFileException {
+  const PathExistsException(super.message, {super.path, super.systemCall});
+
+  @override
+  String toString() => _toStringHelper('PathExistsException');
+}
+
+class PathNotFoundException extends IOFileException {
+  const PathNotFoundException(super.message, {super.path, super.systemCall});
+
+  @override
+  String toString() => _toStringHelper('PathNotFoundException');
+}

pkgs/io_file/lib/src/fake_posix_file_system.dart

@@ -0,0 +1,204 @@
+import 'dart:convert';
+
+import 'dart:typed_data';
+
+import 'package:path/path.dart' as p;
+
+import 'exceptions.dart';
+import 'file_system.dart';
+import 'posix_file_system.dart';
+
+sealed class _Entity {}
+
+class _File extends _Entity {
+  _File();
+}
+
+class _Directory extends _Entity {
+  final children = <String, _Entity>{};
+
+  @override
+  String toString() {
+    return '<Directory children=$children>';
+  }
+}
+
+class _FakeMetadata implements Metadata {
+  @override
+  DateTime get access => throw UnimplementedError();
+
+  @override
+  DateTime? get creation => throw UnimplementedError();
+
+  @override
+  bool get isDirectory => this.type == FileSystemType.directory;
+
+  @override
+  bool get isFile => throw UnimplementedError();
+
+  @override
+  bool? get isHidden => throw UnimplementedError();
+
+  @override
+  bool get isLink => throw UnimplementedError();
+
+  @override
+  DateTime get modification => throw UnimplementedError();
+
+  @override
+  int get size => throw UnimplementedError();
+
+  @override
+  final FileSystemType type;
+
+  _FakeMetadata(this.type);
+}
+
+final class FakePosixFileSystem extends PosixFileSystem {
+  final context = p.Context(style: p.Style.posix);
+  final root = _Directory();
+  final tmp = _Directory();
+
+  FakePosixFileSystem() {
+    print('Reset!');
+    root.children['tmp'] = tmp;
+  }
+
+  _Entity? _findComponents(List<String> components) {
+    _Entity e = root;
+    for (var child in components.skip(1)) {
+      print('$child => $e');
+      if (e is _Directory) {
+        if (!e.children.containsKey(child)) return null;
+        e = e.children[child]!;
+      } else {
+        return null;
+      }
+    }
+    return e;
+  }
+
+  _Entity? _findEntity(String path) {
+    path = context.absolute(path);
+    return _findComponents(p.split(path));
+  }
+
+  _Entity? _upToLast(String path) {
+    path = context.absolute(path);
+    return _findComponents(p.split(p.dirname(path)));
+  }
+
+  @override
+  void createDirectory(String path) {
+    print('createDirectory($path)');
+    if (_findEntity(path) != null) {
+      throw PathExistsException(
+        'create directory failed',
+        path: path,
+        systemCall: const SystemCallError('XXX', 17, 'XXX'),
+      );
+    }
+    path = context.absolute(path);
+    final base = context.basename(path);
+
+    final parent = _upToLast(path);
+    print('parent $parent');
+    if (parent is _Directory) {
+      parent.children[base] = _Directory();
+    } else if (parent == null) {
+      throw PathNotFoundException(
+        'create directory failed',
+        path: path,
+        systemCall: const SystemCallError('XXX', 2, 'XXX'),
+      );
+    } else {
+      throw UnsupportedError(path);
+    }
+  }
+
+  @override
+  String createTemporaryDirectory({String? parent, String? prefix}) {
+    final parentDir = parent ?? '/tmp';
+
+    String path = p.join(parentDir, prefix);
+    createDirectory(path);
+    return path;
+  }
+
+  @override
+  Metadata metadata(String path) {
+    final e = _findEntity(path);
+    return _FakeMetadata(switch (e) {
+      _Directory() => FileSystemType.directory,
+      _File() => FileSystemType.file,
+      _ => FileSystemType.unknown,
+    });
+  }
+
+  @override
+  Uint8List readAsBytes(String path) {
+    // TODO: implement readAsBytes
+    throw UnimplementedError();
+  }
+
+  @override
+  void removeDirectory(String path) {
+    // TODO: implement removeDirectory
+  }
+
+  @override
+  void removeDirectoryTree(String path) {
+    final parent = _upToLast(path);
+    final base = context.basename(path);
+
+    if (parent is _Directory) {
+      if (parent.children.containsKey(base)) {
+        // Check that it is a directory.
+        parent.children.remove(base);
+      } else {
+        throw UnsupportedError('XXX');
+      }
+    } else {
+      throw UnsupportedError('XXX');
+    }
+  }
+
+  @override
+  void rename(String oldPath, String newPath) {
+    // TODO: implement rename
+  }
+
+  @override
+  bool same(String path1, String path2) {
+    // TODO: implement same
+    throw UnimplementedError();
+  }
+
+  @override
+  void writeAsBytes(
+    String path,
+    Uint8List data, [
+    WriteMode mode = WriteMode.failExisting,
+  ]) {
+    // TODO: implement writeAsBytes
+  }
+
+  @override
+  void writeAsString(
+    String path,
+    String contents, [
+    WriteMode mode = WriteMode.failExisting,
+    Encoding encoding = utf8,
+    String? lineTerminator,
+  ]) {
+    final parent = _upToLast(path);
+    final base = context.basename(path);
+
+    if (parent is _Directory) {
+      // Do something with the file contents.
+      parent.children[base] = _File();
+    } else {
+      throw UnsupportedError('XXX');
+    }
+  }
+}

pkgs/io_file/lib/src/file_system.dart

@@ -132,7 +132,7 @@ class WriteMode {
 ///
 /// TODO(brianquinlan): Far now, this class is not meant to be implemented,
 /// extended outside of this package. Clarify somewhere that people implementing
-/// this class should reach out to be.
+/// this class should reach out to me.
 @sealed
 abstract class FileSystem {
   /// Create a directory at the given path.

pkgs/io_file/lib/src/posix_file_system.dart

@@ -0,0 +1,3 @@
+import '../io_file.dart';
+
+abstract class PosixFileSystem extends FileSystem {}

pkgs/io_file/lib/src/vm_file_system_property.dart

@@ -10,4 +10,4 @@ import 'vm_windows_file_system.dart';
 
 /// Return the default [FileSystem] for the current platform.
 FileSystem get fileSystem =>
-    Platform.isWindows ? WindowsFileSystem() : PosixFileSystem();
+    Platform.isWindows ? WindowsFileSystem() : NativePosixFileSystem();