feat: New account data wallpaper feature

lib/utils/account_config.dart

@@ -0,0 +1,65 @@
+import 'package:matrix/matrix.dart';
+
+extension ApplicationAccountConfigExtension on Client {
+  static const String accountDataKey = 'im.fluffychat.account_config';
+
+  ApplicationAccountConfig get applicationAccountConfig =>
+      ApplicationAccountConfig.fromJson(
+        accountData[accountDataKey]?.content ?? {},
+      );
+
+  Future<void> setApplicationAccountConfig(
+    ApplicationAccountConfig config,
+  ) =>
+      setAccountData(
+        userID!,
+        accountDataKey,
+        config.toJson(),
+      );
+
+  /// Only updates the specified values in ApplicationAccountConfig
+  Future<void> updateApplicationAccountConfig(
+    ApplicationAccountConfig config,
+  ) {
+    final currentConfig = applicationAccountConfig;
+    return setAccountData(
+      userID!,
+      accountDataKey,
+      ApplicationAccountConfig(
+        wallpaperUrl: config.wallpaperUrl ?? currentConfig.wallpaperUrl,
+        wallpaperOpacity:
+            config.wallpaperOpacity ?? currentConfig.wallpaperOpacity,
+      ).toJson(),
+    );
+  }
+}
+
+class ApplicationAccountConfig {
+  final Uri? wallpaperUrl;
+  final double? wallpaperOpacity;
+
+  const ApplicationAccountConfig({
+    this.wallpaperUrl,
+    this.wallpaperOpacity,
+  });
+
+  static double _sanitizedOpacity(double? opacity) {
+    if (opacity == null) return 1;
+    if (opacity > 1 || opacity < 0) return 1;
+    return opacity;
+  }
+
+  factory ApplicationAccountConfig.fromJson(Map<String, dynamic> json) =>
+      ApplicationAccountConfig(
+        wallpaperUrl: json['wallpaper_url'] is String
+            ? Uri.tryParse(json['wallpaper_url'])
+            : null,
+        wallpaperOpacity:
+            _sanitizedOpacity(json.tryGet<double>('wallpaper_opacity')),
+      );
+
+  Map<String, dynamic> toJson() => {
+        'wallpaper_url': wallpaperUrl?.toString(),
+        'wallpaper_opacity': wallpaperOpacity,
+      };
+}