feat(mobile): image caching & viewer improvements (#4095)

mobile/lib/shared/cache/original_image_provider.dart

@@ -0,0 +1,73 @@
+import 'dart:async';
+import 'dart:io';
+import 'dart:ui' as ui;
+
+import 'package:flutter/foundation.dart';
+import 'package:flutter/widgets.dart';
+import 'package:immich_mobile/shared/models/asset.dart';
+
+/// Loads the original image for local assets
+@immutable
+final class OriginalImageProvider extends ImageProvider<OriginalImageProvider> {
+  final Asset asset;
+
+  const OriginalImageProvider(this.asset);
+
+  @override
+  Future<OriginalImageProvider> obtainKey(ImageConfiguration configuration) =>
+      SynchronousFuture<OriginalImageProvider>(this);
+
+  @override
+  ImageStreamCompleter loadImage(
+    OriginalImageProvider key,
+    ImageDecoderCallback decode,
+  ) =>
+      MultiFrameImageStreamCompleter(
+        codec: _loadAsync(key, decode),
+        scale: 1.0,
+        informationCollector: () sync* {
+          yield ErrorDescription(asset.fileName);
+        },
+      );
+
+  Future<ui.Codec> _loadAsync(
+    OriginalImageProvider key,
+    ImageDecoderCallback decode,
+  ) async {
+    final ui.ImmutableBuffer buffer;
+    if (asset.isImage) {
+      final File? file = await asset.local?.originFile;
+      if (file == null) {
+        throw StateError("Opening file for asset ${asset.fileName} failed");
+      }
+      try {
+        buffer = await ui.ImmutableBuffer.fromFilePath(file.path);
+      } catch (error) {
+        throw StateError("Loading asset ${asset.fileName} failed");
+      }
+    } else {
+      final thumbBytes = await asset.local?.thumbnailData;
+      if (thumbBytes == null) {
+        throw StateError("Loading thumb for video ${asset.fileName} failed");
+      }
+      buffer = await ui.ImmutableBuffer.fromUint8List(thumbBytes);
+    }
+    try {
+      final codec = await decode(buffer);
+      debugPrint("Decoded image ${asset.fileName}");
+      return codec;
+    } catch (error) {
+      throw StateError("Decoding asset ${asset.fileName} failed");
+    }
+  }
+
+  @override
+  bool operator ==(Object other) {
+    if (other is! OriginalImageProvider) return false;
+    if (identical(this, other)) return true;
+    return asset == other.asset;
+  }
+
+  @override
+  int get hashCode => asset.hashCode;
+}