Use a separate cache for unencrypted thumbnails

lib/core/cache/thumbnail_cache_manager.dart

@@ -0,0 +1,22 @@
+import 'package:flutter_cache_manager/flutter_cache_manager.dart';
+import 'package:path_provider/path_provider.dart';
+import 'package:path/path.dart' as p;
+
+class ThumbnailCacheManager extends BaseCacheManager {
+  static const key = 'cached-thumbnail-data';
+
+  static ThumbnailCacheManager _instance;
+
+  factory ThumbnailCacheManager() {
+    _instance ??= ThumbnailCacheManager._();
+    return _instance;
+  }
+
+  ThumbnailCacheManager._() : super(key, maxNrOfCacheObjects: 20000);
+
+  @override
+  Future<String> getFilePath() async {
+    var directory = await getTemporaryDirectory();
+    return p.join(directory.path, key);
+  }
+}

lib/ui/thumbnail_widget.dart

@@ -1,9 +1,11 @@
 import 'package:cached_network_image/cached_network_image.dart';
 import 'package:dio/dio.dart';
 import 'package:flutter/material.dart';
+import 'package:flutter_cache_manager/flutter_cache_manager.dart';
 import 'package:photos/core/cache/image_cache.dart';
 import 'dart:io' as io;
 import 'package:photos/core/cache/thumbnail_cache.dart';
+import 'package:photos/core/cache/thumbnail_cache_manager.dart';
 import 'package:photos/core/configuration.dart';
 import 'package:photos/file_repository.dart';
 import 'package:photos/models/file.dart';
@@ -123,6 +125,7 @@ class _ThumbnailWidgetState extends State<ThumbnailWidget> {
         placeholder: (context, url) => loadWidget,
         errorWidget: (context, url, error) => Icon(Icons.error),
         fit: BoxFit.cover,
+        cacheManager: ThumbnailCacheManager(),
       );
     } else {
       if (ThumbnailFileLruCache.get(widget.file) != null) {

lib/ui/zoomable_image.dart

@@ -5,6 +5,7 @@ import 'package:flutter/widgets.dart';
 import 'package:logging/logging.dart';
 import 'package:photos/core/cache/image_cache.dart';
 import 'package:photos/core/cache/thumbnail_cache.dart';
+import 'package:photos/core/cache/thumbnail_cache_manager.dart';
 import 'package:photos/models/file.dart';
 import 'package:photos/ui/loading_widget.dart';
 import 'package:photo_view/photo_view.dart';
@@ -96,7 +97,10 @@ class _ZoomableImageState extends State<ZoomableImage>
 
   void _loadUnencryptedThumbnail() {
     if (!_loadedSmallThumbnail && !_loadedFinalImage) {
-      _imageProvider = CachedNetworkImageProvider(_photo.getThumbnailUrl());
+      _imageProvider = CachedNetworkImageProvider(
+        _photo.getThumbnailUrl(),
+        cacheManager: ThumbnailCacheManager(),
+      );
       _loadedSmallThumbnail = true;
     }
   }