interned_bytes.dart

interned_bytes.dart

import 'dart:convert';
import 'dart:typed_data';

import 'package:collection/collection.dart';
import 'package:json_annotation/json_annotation.dart';
import 'package:meta/meta.dart';

@immutable
class InternedBytes {
  static final _internedInstances = <WeakReference<InternedBytes>>[];

  factory InternedBytes(Uint8List bytes) {
    InternedBytes? result;
    final newInstance = InternedBytes._(bytes);
    final deadReferences = <WeakReference<InternedBytes>>[];

    for (final reference in _internedInstances) {
      final existingInstance = reference.target;

      if (existingInstance == null) {
        deadReferences.add(reference);
      } else if (newInstance._equals(existingInstance)) {
        result = existingInstance;
        break;
      }
    }

    deadReferences.forEach(_internedInstances.remove);

    if (result == null) {
      result = newInstance;
      _internedInstances.add(WeakReference(newInstance));
    }

    return result;
  }

  InternedBytes._(this.bytes) : hashCode = const DeepCollectionEquality().hash(bytes);

  final Uint8List bytes;

  bool _equals(InternedBytes other) =>
      hashCode == other.hashCode && const DeepCollectionEquality().equals(bytes, other.bytes);

  @override
  bool operator ==(Object other) => identical(this, other);

  @override
  final int hashCode;
}

class InternedBytesBase64Converter implements JsonConverter<InternedBytes, String> {
  const InternedBytesBase64Converter();

  @override
  InternedBytes fromJson(String json) => InternedBytes(base64Decode(json));

  @override
  String toJson(InternedBytes object) => base64Encode(object.bytes);
}