add onLoadFailed to imageLoadingConfig

lib/network/images.dart

@@ -1,5 +1,6 @@
 import 'dart:typed_data';
 
+import 'package:flutter_qjs/flutter_qjs.dart';
 import 'package:venera/foundation/cache_manager.dart';
 import 'package:venera/foundation/comic_source/comic_source.dart';
 import 'package:venera/foundation/consts.dart';
@@ -83,16 +84,33 @@ class ImageDownloader {
       );
     }
 
+    Future<Map<String, dynamic>?> Function()? onLoadFailed;
+
     var configs = <String, dynamic>{};
     if (sourceKey != null) {
       var comicSource = ComicSource.find(sourceKey);
       configs = (await comicSource!.getImageLoadingConfig
-              ?.call(imageKey, cid, eid)) ?? {};
+              ?.call(imageKey, cid, eid)) ??
+          {};
     }
+    var retryLimit = 5;
+    while (true) {
+      try {
         configs['headers'] ??= {
           'user-agent': webUA,
         };
 
+        if (configs['onLoadFailed'] is JSInvokable) {
+          onLoadFailed = () async {
+            dynamic result = configs['onLoadFailed']();
+            if (result is Future) {
+              result = await result;
+            }
+            if (result is! Map<String, dynamic>) return null;
+            return result;
+          };
+        }
+
         var dio = AppDio(BaseOptions(
           headers: configs['headers'],
           method: configs['method'] ?? 'GET',
@@ -138,6 +156,20 @@ class ImageDownloader {
           totalBytes: data.length,
           imageBytes: data,
         );
+        return;
+      } catch (e) {
+        if(retryLimit < 0 || onLoadFailed == null) {
+          rethrow;
+        }
+        var newConfig = await onLoadFailed();
+        onLoadFailed = null;
+        if(newConfig == null) {
+          rethrow;
+        }
+        configs = newConfig;
+        retryLimit--;
+      }
+    }
   }
 }