Time Aware Least Recently Used Cache - by Simon Lightfoot http://en.wikipedia.org/wiki/Cache_algorithms#LRU

lru_cache.dart

// MIT License
//
// Copyright (c) 2019 Simon Lightfoot
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in all
// copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
// SOFTWARE.
//
import 'package:meta/meta.dart';
import 'package:quiver/collection.dart' show LruMap;

/// Time Aware Least Recently Used Cache - by Simon Lightfoot
/// http://en.wikipedia.org/wiki/Cache_algorithms#LRU
class LruCache<T> {
  LruCache(
    this.maximumSize, {
    this.ttl = const Duration(minutes: 10),
  }) : _cacheMap = LruMap(maximumSize: maximumSize);

  final int maximumSize;
  final Duration ttl;

  final LruMap<String, Expirable<T>> _cacheMap;

  T operator [](String key) {
    final item = _cacheMap[key];
    if (item?.expired ?? false) {
      invalid(key);
      return null;
    }
    return item?.value;
  }

  void operator []=(String key, T value) {
    _cacheMap[key] = Expirable.fromNow(ttl, value);
  }

  bool invalid(String key) {
    return _cacheMap.remove(key) != null;
  }

  void clear() {
    _cacheMap.clear();
  }
}

@immutable
class Expirable<T> {
  const Expirable(this.expiry, this.value);

  factory Expirable.fromNow(Duration ttl, T value) {
    return Expirable(DateTime.now().add(ttl), value);
  }

  final DateTime expiry;
  final T value;

  bool get expired => DateTime.now().compareTo(expiry) >= 0;

  @override
  bool operator ==(Object other) =>
      identical(this, other) || other is Expirable && runtimeType == other.runtimeType && value == other.value;

  @override
  int get hashCode => value.hashCode;

  @override
  String toString() {
    return 'Expirable { value: $value, expiry: $expiry }';
  }
}