perf: cache signed storage URLs

lib/services/storage_service.dart

@@ -15,6 +15,9 @@ class StorageService {
   static const int _maxImageBytes = 500 * 1024;
   static const int _maxWidth = 1080;
   static const int _signedUrlExpirySeconds = 3600;
+  static const _signedUrlRefreshBuffer = Duration(minutes: 3);
+  static const _maxSignedUrlCacheEntries = 500;
+  static final Map<String, _SignedUrlCacheEntry> _signedUrlCache = {};
 
   /// Upload a car image for a specific hotwheels entry.
   /// Returns the storage path on success (e.g. `uid/123.jpg`).
@@ -40,16 +43,32 @@ class StorageService {
           ),
         );
 
+    _signedUrlCache.remove(path);
+
     return path;
   }
 
   /// Generates a temporary signed URL for a private image path.
   static Future<String?> createSignedUrl(String? path) async {
     if (path == null || path.isEmpty) return null;
+
+    final now = DateTime.now();
+    final cached = _signedUrlCache[path];
+    if (cached != null &&
+        now.isBefore(cached.expiresAt.subtract(_signedUrlRefreshBuffer))) {
+      return cached.url;
+    }
+
     try {
-      return await supabase.storage
+      final signed = await supabase.storage
           .from(_bucket)
           .createSignedUrl(path, _signedUrlExpirySeconds);
+      _signedUrlCache[path] = _SignedUrlCacheEntry(
+        url: signed,
+        expiresAt: now.add(const Duration(seconds: _signedUrlExpirySeconds)),
+      );
+      _pruneSignedUrlCache(now);
+      return signed;
     } catch (e) {
       debugPrint('StorageService.createSignedUrl error: $e');
       return null;
@@ -59,6 +78,7 @@ class StorageService {
   /// Deletes an image using its storage path.
   static Future<void> deleteCarImage(String? path) async {
     if (path == null || path.isEmpty) return;
+    _signedUrlCache.remove(path);
     try {
       await supabase.storage.from(_bucket).remove([path]);
     } catch (e) {
@@ -66,6 +86,22 @@ class StorageService {
     }
   }
 
+  static void invalidateSignedUrl(String? path) {
+    if (path == null || path.isEmpty) return;
+    _signedUrlCache.remove(path);
+  }
+
+  static void _pruneSignedUrlCache(DateTime now) {
+    _signedUrlCache.removeWhere((_, entry) => now.isAfter(entry.expiresAt));
+
+    if (_signedUrlCache.length <= _maxSignedUrlCacheEntries) return;
+    final overflow = _signedUrlCache.length - _maxSignedUrlCacheEntries;
+    final keys = _signedUrlCache.keys.take(overflow).toList();
+    for (final key in keys) {
+      _signedUrlCache.remove(key);
+    }
+  }
+
   static Future<Uint8List> _compressImage(File source) async {
     final bytes = await source.readAsBytes();
     final decoded = img.decodeImage(bytes);
@@ -102,3 +138,10 @@ class StorageService {
     return out;
   }
 }
+
+class _SignedUrlCacheEntry {
+  final String url;
+  final DateTime expiresAt;
+
+  const _SignedUrlCacheEntry({required this.url, required this.expiresAt});
+}