feat(theme): load theme by ThemeDefinition (#108)

lib/core/theme/theme_registry_service.dart

@@ -5,8 +5,13 @@ import 'package:flutter/foundation.dart';
 import 'package:path/path.dart' as p;
 
 import 'parser/jsonc_preprocessor.dart';
+import 'parser/querya_theme_from_manifest.dart';
+import 'parser/querya_theme_from_vscode.dart';
 import 'parser/querya_theme_manifest.dart';
+import 'parser/vscode_theme_manifest.dart';
+import 'querya_theme.dart';
 import 'theme_definition.dart';
+import 'theme_load_result.dart';
 import 'theme_paths.dart';
 
 /// Scans theme directories and exposes lightweight [ThemeDefinition] metadata.
@@ -42,6 +47,73 @@ class ThemeRegistryService {
     return List.unmodifiable(definitions);
   }
 
+  /// Parses a scanned [definition] into a runtime [QueryaTheme].
+  Future<ThemeLoadResult> loadTheme(ThemeDefinition definition) async {
+    final path = definition.path;
+    if (path == null || path.isEmpty) {
+      return ThemeLoadFailure(
+        definition: definition,
+        message: 'Theme file path is missing.',
+      );
+    }
+
+    final file = File(path);
+    if (!await file.exists()) {
+      return ThemeLoadFailure(
+        definition: definition,
+        message: 'Theme file not found.',
+      );
+    }
+
+    try {
+      final raw = await file.readAsString();
+      final theme = switch (definition.format) {
+        ThemeFormat.queryaCustom => _loadCustomTheme(raw),
+        ThemeFormat.vscode => _loadVsCodeTheme(raw),
+      };
+      return ThemeLoadSuccess(definition: definition, theme: theme);
+    } on QueryaThemeManifestParseException catch (e) {
+      return ThemeLoadFailure(
+        definition: definition,
+        message: e.message,
+        error: e,
+      );
+    } on VsCodeThemeParseException catch (e) {
+      return ThemeLoadFailure(
+        definition: definition,
+        message: e.message,
+        error: e,
+      );
+    } on IOException catch (e) {
+      return ThemeLoadFailure(
+        definition: definition,
+        message: 'Failed to read theme file.',
+        error: e,
+      );
+    } on Object catch (e) {
+      return ThemeLoadFailure(
+        definition: definition,
+        message: 'Failed to load theme.',
+        error: e,
+      );
+    }
+  }
+
+  QueryaTheme _loadCustomTheme(String raw) {
+    final manifest = QueryaThemeManifest.fromJsonString(raw);
+    return queryaThemeFromManifest(manifest);
+  }
+
+  QueryaTheme _loadVsCodeTheme(String raw) {
+    final manifest = VsCodeThemeManifest.fromJsonString(raw);
+    if (manifest.colors.isEmpty) {
+      throw VsCodeThemeParseException(
+        'Theme file has no "colors" section to import.',
+      );
+    }
+    return buildQueryaThemeFromVsCodeManifest(manifest);
+  }
+
   Future<void> _scanDirectory(
     Directory directory,
     ThemeSource source,

test/core/theme/theme_registry_service_test.dart

@@ -1,9 +1,12 @@
 import 'dart:io';
 
+import 'package:flutter/material.dart';
 import 'package:flutter_test/flutter_test.dart';
 import 'package:path/path.dart' as p;
 import 'package:path_provider_platform_interface/path_provider_platform_interface.dart';
+import 'package:querya_desktop/core/theme/parser/color_parser.dart';
 import 'package:querya_desktop/core/theme/theme_definition.dart';
+import 'package:querya_desktop/core/theme/theme_load_result.dart';
 import 'package:querya_desktop/core/theme/theme_registry_service.dart';
 
 class _FakePathProvider extends PathProviderPlatform {
@@ -155,4 +158,70 @@ void main() {
       expect(definitions, hasLength(1));
     });
   });
+
+  group('ThemeRegistryService.loadTheme', () {
+    test('loads custom theme successfully', () async {
+      await _copyFixture(
+        'querya_custom_dark.json',
+        File(p.join(themesDir.path, 'querya_custom_dark.json')),
+      );
+
+      final definition = (await registry.loadThemeDefinitions()).single;
+      final result = await registry.loadTheme(definition);
+
+      expect(result, isA<ThemeLoadSuccess>());
+      final success = result as ThemeLoadSuccess;
+      expect(success.definition, definition);
+      expect(success.theme.brightness, Brightness.dark);
+      expect(success.theme.colorScheme.primary, parseQueryaThemeColor('#38BDF8'));
+    });
+
+    test('loads VS Code theme successfully', () async {
+      await _copyFixture(
+        'dark_subset.json',
+        File(p.join(themesDir.path, 'dark_subset.json')),
+      );
+
+      final definition = (await registry.loadThemeDefinitions()).single;
+      final result = await registry.loadTheme(definition);
+
+      expect(result, isA<ThemeLoadSuccess>());
+      final success = result as ThemeLoadSuccess;
+      expect(success.theme.editor.background, parseQueryaThemeColor('#1e1e1e'));
+    });
+
+    test('returns failure for deleted file', () async {
+      const definition = ThemeDefinition(
+        id: 'missing-theme',
+        name: 'Missing Theme',
+        source: ThemeSource.filesystem,
+        format: ThemeFormat.queryaCustom,
+        isDark: true,
+        path: '/no/such/theme.json',
+      );
+
+      final result = await registry.loadTheme(definition);
+
+      expect(result, isA<ThemeLoadFailure>());
+      expect((result as ThemeLoadFailure).message, 'Theme file not found.');
+    });
+
+    test('returns failure for invalid custom file', () async {
+      final file = File(p.join(themesDir.path, 'broken.json'));
+      await _copyFixture('querya_custom_invalid_missing_id.json', file);
+      final definition = ThemeDefinition(
+        id: 'broken',
+        name: 'Broken',
+        source: ThemeSource.filesystem,
+        format: ThemeFormat.queryaCustom,
+        isDark: true,
+        path: file.path,
+      );
+
+      final result = await registry.loadTheme(definition);
+
+      expect(result, isA<ThemeLoadFailure>());
+      expect((result as ThemeLoadFailure).message, contains('id'));
+    });
+  });
 }