immich/mobile-v2/lib/presentation/components/image/cache/image_loader.dart

import 'dart:async';
import 'dart:ui' as ui;

import 'package:flutter/material.dart';
import 'package:flutter_cache_manager/flutter_cache_manager.dart';
import 'package:immich_mobile/service_locator.dart';
import 'package:immich_mobile/utils/immich_api_client.dart';

/// An exception for the [ImageLoader] and the Immich image providers
class ImageLoadingException implements Exception {
  final String message;
  const ImageLoadingException(this.message);

  @override
  String toString() => 'ImageLoadingException: $message';
}

/// Loads the codec from the URI and sends the events to the [chunkEvents] stream
///
/// Credit to [flutter_cached_network_image](https://github.com/Baseflow/flutter_cached_network_image/blob/develop/cached_network_image/lib/src/image_provider/_image_loader.dart)
/// for this wonderful implementation of their image loader
abstract final class ImageLoader {
  static Future<ui.Codec> loadImageFromCache(
    String uri, {
    required CacheManager cache,
    required ImageDecoderCallback decode,
    StreamController<ImageChunkEvent>? chunkEvents,
  }) async {
    final stream = cache.getFileStream(
      uri,
      headers: di<ImApiClient>().headers,
      withProgress: chunkEvents != null,
    );

    await for (final result in stream) {
      if (result is DownloadProgress) {
        // We are downloading the file, so update the [chunkEvents]
        chunkEvents?.add(
          ImageChunkEvent(
            cumulativeBytesLoaded: result.downloaded,
            expectedTotalBytes: result.totalSize,
          ),
        );
      } else if (result is FileInfo) {
        // We have the file
        final buffer = await ui.ImmutableBuffer.fromFilePath(result.file.path);
        return await decode(buffer);
      }
    }

    // If we get here, the image failed to load from the cache stream
    throw const ImageLoadingException('Could not load image from stream');
  }
}