feat: add local backup export import core

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

lib/infrastructure/local/local_media_storage.dart

@@ -1,3 +1,4 @@
+import 'dart:convert';
 import 'dart:io';
 import 'dart:typed_data';
 
@@ -7,7 +8,8 @@ import 'package:path_provider/path_provider.dart';
 import '../../application/application.dart';
 import '../../domain/domain.dart';
 
-final class PathProviderLocalMediaStorage implements LocalMediaStorage {
+final class PathProviderLocalMediaStorage
+    implements LocalMediaStorage, LocalBackupMediaStore {
   const PathProviderLocalMediaStorage();
 
   static const _mediaDirectoryName = 'gametime_media';
@@ -77,6 +79,64 @@ final class PathProviderLocalMediaStorage implements LocalMediaStorage {
     }
   }
 
+  @override
+  Future<List<EmbeddedBackupMediaFile>> readEmbeddableFiles(
+    List<LocalBackupResource> mediaAssets,
+  ) async {
+    final files = <EmbeddedBackupMediaFile>[];
+    for (final resource in mediaAssets) {
+      final localUri = resource.payload['localUri'];
+      if (localUri is! String || localUri.isEmpty) {
+        continue;
+      }
+      final file = _fileFromLocalUri(localUri);
+      if (!await file.exists()) {
+        continue;
+      }
+      final bytes = await file.readAsBytes();
+      files.add(
+        EmbeddedBackupMediaFile(
+          mediaAssetId: resource.id,
+          role: 'original',
+          fileName: p.basename(file.path),
+          mimeType: resource.payload['mimeType'] as String?,
+          sizeBytes: bytes.length,
+          base64: base64Encode(bytes),
+        ),
+      );
+    }
+    return files;
+  }
+
+  @override
+  Future<Map<String, RestoredMediaFile>> restoreEmbeddedFiles(
+    List<EmbeddedBackupMediaFile> files,
+  ) async {
+    final restored = <String, RestoredMediaFile>{};
+    final directory = await _restoredBackupDirectory();
+    await directory.create(recursive: true);
+    for (final file in files) {
+      final bytes = switch (_decodeBase64OrNull(file.base64)) {
+        final decoded? => decoded,
+        null => null,
+      };
+      if (bytes == null) {
+        continue;
+      }
+      final extension = p.extension(file.fileName).toLowerCase();
+      final target = File(
+        p.join(directory.path, '${file.mediaAssetId}$extension'),
+      );
+      await target.writeAsBytes(bytes, flush: true);
+      restored[file.mediaAssetId] = RestoredMediaFile(
+        mediaAssetId: file.mediaAssetId,
+        localUri: target.uri.toString(),
+        sizeBytes: bytes.length,
+      );
+    }
+    return restored;
+  }
+
   Future<Directory> _kindDirectory(MediaKind kind) async {
     final root = await _rootDirectory();
     final child = switch (kind) {
@@ -90,6 +150,27 @@ final class PathProviderLocalMediaStorage implements LocalMediaStorage {
     final documents = await getApplicationDocumentsDirectory();
     return Directory(p.join(documents.path, _mediaDirectoryName));
   }
+
+  Future<Directory> _restoredBackupDirectory() async {
+    final root = await _rootDirectory();
+    return Directory(p.join(root.path, 'restored'));
+  }
+}
+
+File _fileFromLocalUri(String localUri) {
+  final uri = Uri.tryParse(localUri);
+  if (uri != null && uri.scheme == 'file') {
+    return File.fromUri(uri);
+  }
+  return File(localUri);
+}
+
+Uint8List? _decodeBase64OrNull(String value) {
+  try {
+    return base64Decode(value);
+  } on FormatException {
+    return null;
+  }
 }
 
 final class _ImageDimensions {