neon: allow apps to define custom themes

packages/neon/neon/lib/src/app.dart

@@ -2,6 +2,7 @@ import 'dart:async';
 import 'dart:convert';
 import 'dart:io';
 
+import 'package:collection/collection.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter_native_splash/flutter_native_splash.dart';
 import 'package:neon/l10n/localizations.dart';
@@ -285,7 +286,13 @@ class _NeonAppState extends State<NeonApp> with WidgetsBindingObserver, tray.Tra
                       ? _accountsBloc.getCapabilitiesBlocFor(activeAccountSnapshot.data!).capabilities
                       : null,
                   builder: (final context, final capabilitiesSnapshot) {
-                    final nextcloudTheme = capabilitiesSnapshot.data?.capabilities.theming;
+                    final appTheme = AppTheme(
+                      capabilitiesSnapshot.data?.capabilities.theming,
+                      keepOriginalAccentColor: themeKeepOriginalAccentColor,
+                      oledAsDark: themeOLEDAsDark,
+                      appThemes: _appImplementations.map((final a) => a.theme).whereNotNull(),
+                    );
+
                     return MaterialApp.router(
                       localizationsDelegates: [
                         ..._appImplementations.map((final app) => app.localizationsDelegate),
@@ -298,17 +305,8 @@ class _NeonAppState extends State<NeonApp> with WidgetsBindingObserver, tray.Tra
                         ...AppLocalizations.supportedLocales,
                       },
                       themeMode: themeMode,
-                      theme: getThemeFromNextcloudTheme(
-                        nextcloudTheme,
-                        Brightness.light,
-                        keepOriginalAccentColor: nextcloudTheme == null || themeKeepOriginalAccentColor,
-                      ),
-                      darkTheme: getThemeFromNextcloudTheme(
-                        nextcloudTheme,
-                        Brightness.dark,
-                        keepOriginalAccentColor: nextcloudTheme == null || themeKeepOriginalAccentColor,
-                        oledAsDark: themeOLEDAsDark,
-                      ),
+                      theme: appTheme.lightTheme,
+                      darkTheme: appTheme.darkTheme,
                       routerConfig: _routerDelegate,
                     );
                   },

packages/neon/neon/lib/src/models/app_implementation.dart

@@ -86,6 +86,11 @@ abstract class AppImplementation<T extends Bloc, R extends NextcloudAppOptions>
   void dispose() {
     options.dispose();
   }
+
+  /// A custom theme that will be injected into the widget tree.
+  ///
+  /// You can later acess it through `Theme.of(context).extension<ThemeName>()`.
+  ThemeExtension? theme;
 }
 
 extension AppImplementationFind on Iterable<AppImplementation> {

packages/neon/neon/lib/src/utils/theme.dart

@@ -7,40 +7,79 @@ import 'package:nextcloud/nextcloud.dart';
 const themePrimaryColor = Color(0xFFF37736);
 
 @internal
-ThemeData getThemeFromNextcloudTheme(
-  final CoreServerCapabilities_Ocs_Data_Capabilities_Theming? nextcloudTheme,
-  final Brightness brightness, {
-  required final bool keepOriginalAccentColor,
-  final bool oledAsDark = false,
-}) {
-  if (oledAsDark) {
-    assert(brightness == Brightness.dark, 'Brightness.dark is required for oledAsDark.');
-  }
+@immutable
+class AppTheme {
+  AppTheme(
+    this.nextcloudTheme, {
+    final bool keepOriginalAccentColor = false,
+    this.oledAsDark = false,
+    this.appThemes,
+  }) : keepOriginalAccentColor = nextcloudTheme == null || keepOriginalAccentColor;
+
+  final CoreServerCapabilities_Ocs_Data_Capabilities_Theming? nextcloudTheme;
+  final bool keepOriginalAccentColor;
+  final bool oledAsDark;
+  final Iterable<ThemeExtension>? appThemes;
+
+  late final _primaryColor = nextcloudTheme?.color != null ? HexColor(nextcloudTheme!.color!) : themePrimaryColor;
+  late final _keepOriginalAccentColorOverride = keepOriginalAccentColor ? _primaryColor : null;
 
-  final primaryColor = nextcloudTheme?.color != null ? HexColor(nextcloudTheme!.color!) : themePrimaryColor;
+  ColorScheme _buildColorScheme(final Brightness brightness) {
+    final oledBackgroundOverride = oledAsDark && brightness == Brightness.dark ? Colors.black : null;
 
-  final oledBackgroundOverride = oledAsDark ? Colors.black : null;
-  final keepOriginalAccentColorOverride = keepOriginalAccentColor ? primaryColor : null;
-  final colorScheme = ColorScheme.fromSeed(
-    seedColor: primaryColor,
+    return ColorScheme.fromSeed(
+      seedColor: _primaryColor,
       brightness: brightness,
     ).copyWith(
       background: oledBackgroundOverride,
-    primary: keepOriginalAccentColorOverride,
-    secondary: keepOriginalAccentColorOverride,
+      primary: _keepOriginalAccentColorOverride,
+      secondary: _keepOriginalAccentColorOverride,
     );
+  }
+
+  ThemeData _getTheme(final Brightness brightness) {
+    final colorScheme = _buildColorScheme(brightness);
 
     return ThemeData(
       useMaterial3: true,
       colorScheme: colorScheme,
       scaffoldBackgroundColor: colorScheme.background,
       cardColor: colorScheme.background, // For LicensePage
-    snackBarTheme: const SnackBarThemeData(
+      snackBarTheme: _snackBarTheme,
+      dividerTheme: _dividerTheme,
+      extensions: [
+        const NeonTheme(),
+        ...?appThemes,
+      ],
+    );
+  }
+
+  ThemeData get lightTheme => _getTheme(Brightness.light);
+  ThemeData get darkTheme => _getTheme(Brightness.dark);
+
+  static const _snackBarTheme = SnackBarThemeData(
     behavior: SnackBarBehavior.floating,
-    ),
-    dividerTheme: const DividerThemeData(
+  );
+
+  static const _dividerTheme = DividerThemeData(
     thickness: 1.5,
     space: 30,
-    ),
   );
 }
+
+@internal
+@immutable
+class NeonTheme extends ThemeExtension<NeonTheme> {
+  const NeonTheme();
+
+  @override
+  NeonTheme copyWith() => const NeonTheme();
+
+  @override
+  NeonTheme lerp(final NeonTheme? other, final double t) {
+    if (other is! NeonTheme) {
+      return this;
+    }
+    return const NeonTheme();
+  }
+}