Add shared_preferences (#15)

packages/shared_preferences/lib/shared_preferences_elinux.dart

@@ -0,0 +1,108 @@
+// Copyright 2021 Sony Group Corporation. All rights reserved.
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'dart:async';
+import 'dart:convert' show json;
+
+import 'package:file/file.dart';
+import 'package:file/local.dart';
+import 'package:meta/meta.dart';
+import 'package:path/path.dart' as path;
+import 'package:path_provider_elinux/path_provider_elinux.dart';
+import 'package:shared_preferences_platform_interface/shared_preferences_platform_interface.dart';
+
+/// The Linux implementation of [SharedPreferencesStorePlatform].
+///
+/// This class implements the `package:shared_preferences` functionality for Linux.
+class SharedPreferencesELinux extends SharedPreferencesStorePlatform {
+  /// The default instance of [SharedPreferencesELinux] to use.
+  static SharedPreferencesELinux instance = SharedPreferencesELinux();
+
+  /// Registers the eLinux implementation.
+  static void registerWith() {
+    SharedPreferencesStorePlatform.instance = instance;
+  }
+
+  /// Local copy of preferences
+  Map<String, Object>? _cachedPreferences;
+
+  /// File system used to store to disk. Exposed for testing only.
+  @visibleForTesting
+  FileSystem fs = LocalFileSystem();
+
+  /// Gets the file where the preferences are stored.
+  Future<File?> _getLocalDataFile() async {
+    final pathProvider = PathProviderELinux();
+    final directory = await pathProvider.getApplicationSupportPath();
+    if (directory == null) return null;
+    return fs.file(path.join(directory, 'shared_preferences.json'));
+  }
+
+  /// Gets the preferences from the stored file. Once read, the preferences are
+  /// maintained in memory.
+  Future<Map<String, Object>> _readPreferences() async {
+    if (_cachedPreferences != null) {
+      return _cachedPreferences!;
+    }
+
+    Map<String, Object> preferences = {};
+    final File? localDataFile = await _getLocalDataFile();
+    if (localDataFile != null && localDataFile.existsSync()) {
+      String stringMap = localDataFile.readAsStringSync();
+      if (stringMap.isNotEmpty) {
+        preferences = json.decode(stringMap).cast<String, Object>();
+      }
+    }
+    _cachedPreferences = preferences;
+    return preferences;
+  }
+
+  /// Writes the cached preferences to disk. Returns [true] if the operation
+  /// succeeded.
+  Future<bool> _writePreferences(Map<String, Object> preferences) async {
+    try {
+      var localDataFile = await _getLocalDataFile();
+      if (localDataFile == null) {
+        print("Unable to determine where to write preferences.");
+        return false;
+      }
+      if (!localDataFile.existsSync()) {
+        localDataFile.createSync(recursive: true);
+      }
+      var stringMap = json.encode(preferences);
+      localDataFile.writeAsStringSync(stringMap);
+    } catch (e) {
+      print("Error saving preferences to disk: $e");
+      return false;
+    }
+    return true;
+  }
+
+  @override
+  Future<bool> clear() async {
+    var preferences = await _readPreferences();
+    preferences.clear();
+    return _writePreferences(preferences);
+  }
+
+  @override
+  Future<Map<String, Object>> getAll() async {
+    return _readPreferences();
+  }
+
+  @override
+  Future<bool> remove(String key) async {
+    var preferences = await _readPreferences();
+    preferences.remove(key);
+    return _writePreferences(preferences);
+  }
+
+  @override
+  Future<bool> setValue(String valueType, String key, Object value) async {
+    var preferences = await _readPreferences();
+    preferences[key] = value;
+    return _writePreferences(preferences);
+  }
+}