venera/lib/foundation/image_provider/base_image_provider.dart

import 'dart:async' show Future, StreamController, scheduleMicrotask;
import 'dart:collection';
import 'dart:convert';
import 'dart:ui' as ui show Codec;
import 'dart:ui';
import 'package:flutter/foundation.dart';
import 'package:flutter/material.dart';
import 'package:venera/foundation/cache_manager.dart';

abstract class BaseImageProvider<T extends BaseImageProvider<T>>
    extends ImageProvider<T> {
  const BaseImageProvider();

  @override
  ImageStreamCompleter loadImage(T key, ImageDecoderCallback decode) {
    final chunkEvents = StreamController<ImageChunkEvent>();
    return MultiFrameImageStreamCompleter(
      codec: _loadBufferAsync(key, chunkEvents, decode),
      chunkEvents: chunkEvents.stream,
      scale: 1.0,
      informationCollector: () sync* {
        yield DiagnosticsProperty<ImageProvider>(
          'Image provider: $this \n Image key: $key',
          this,
          style: DiagnosticsTreeStyle.errorProperty,
        );
      },
    );
  }

  Future<ui.Codec> _loadBufferAsync(
    T key,
    StreamController<ImageChunkEvent> chunkEvents,
    ImageDecoderCallback decode,
  ) async {
    try {
      int retryTime = 1;

      bool stop = false;

      chunkEvents.onCancel = () {
        stop = true;
      };

      Uint8List? data;

      while (data == null && !stop) {
        try {
          if(_cache.containsKey(key.key)){
            data = _cache[key.key];
          } else {
            data = await load(chunkEvents);
            _checkCacheSize();
            _cache[key.key] = data;
            _cacheSize += data.length;
          }
        } catch (e) {
          if(e.toString().contains("Invalid Status Code: 404")) {
            rethrow;
          }
          if(e.toString().contains("Invalid Status Code: 403")) {
            rethrow;
          }
          if (e.toString().contains("handshake")) {
            if (retryTime < 5) {
              retryTime = 5;
            }
          }
          retryTime <<= 1;
          if (retryTime > (1 << 3) || stop) {
            rethrow;
          }
          await Future.delayed(Duration(seconds: retryTime));
        }
      }

      if(stop) {
        throw Exception("Image loading is stopped");
      }

      if(data!.isEmpty) {
        throw Exception("Empty image data");
      }

      try {
        final buffer = await ImmutableBuffer.fromUint8List(data);
        return await decode(buffer);
      } catch (e) {
        await CacheManager().delete(this.key);
        if (data.length < 2 * 1024) {
          // data is too short, it's likely that the data is text, not image
          try {
            var text = const Utf8Codec(allowMalformed: false).decoder.convert(data);
            throw Exception("Expected image data, but got text: $text");
          } catch (e) {
            // ignore
          }
        }
        rethrow;
      }
    } catch (e) {
      scheduleMicrotask(() {
        PaintingBinding.instance.imageCache.evict(key);
      });
      rethrow;
    } finally {
      chunkEvents.close();
    }
  }

  static final _cache = LinkedHashMap<String, Uint8List>();

  static var _cacheSize = 0;

  static var _cacheSizeLimit = 50 * 1024 * 1024;

  static void _checkCacheSize(){
    while (_cacheSize > _cacheSizeLimit){
      var firstKey = _cache.keys.first;
      _cacheSize -= _cache[firstKey]!.length;
      _cache.remove(firstKey);
    }
  }

  static void clearCache(){
    _cache.clear();
    _cacheSize = 0;
  }

  static void setCacheSizeLimit(int size){
    _cacheSizeLimit = size;
    _checkCacheSize();
  }

  Future<Uint8List> load(StreamController<ImageChunkEvent> chunkEvents);

  String get key;

  @override
  bool operator ==(Object other) {
    return other is BaseImageProvider<T> && key == other.key;
  }

  @override
  int get hashCode => key.hashCode;

  @override
  String toString() {
    return "$runtimeType($key)";
  }
}

typedef FileDecoderCallback = Future<ui.Codec> Function(Uint8List);