/* * Copyright (C) 2020-2022 Yomichan Authors * * This program is free software: you can redistribute it and/or modify * it under the terms of the GNU General Public License as published by * the Free Software Foundation, either version 3 of the License, or * (at your option) any later version. * * This program is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the * GNU General Public License for more details. * * You should have received a copy of the GNU General Public License * along with this program. If not, see <https://www.gnu.org/licenses/>. */ /** * Class which caches a map of values, keeping the most recently accessed values. */ class CacheMap { /** * Creates a new CacheMap. * @param {number} maxSize The maximum number of entries able to be stored in the cache. */ constructor(maxSize) { if (!( typeof maxSize === 'number' && Number.isFinite(maxSize) && maxSize >= 0 && Math.floor(maxSize) === maxSize )) { throw new Error('Invalid maxCount'); } this._maxSize = maxSize; this._map = new Map(); this._listFirst = this._createNode(null, null); this._listLast = this._createNode(null, null); this._resetEndNodes(); } /** * Returns the number of items in the cache. * @type {number} */ get size() { return this._map.size; } /** * Returns the maximum number of items that can be added to the cache. * @type {number} */ get maxSize() { return this._maxSize; } /** * Returns whether or not an element exists at the given key. * @param {*} key The key of the element. * @returns {boolean} `true` if an element with the specified key exists, `false` otherwise. */ has(key) { return this._map.has(key); } /** * Gets an element at the given key, if it exists. Otherwise, returns undefined. * @param {*} key The key of the element. * @returns {*} The existing value at the key, if any; `undefined` otherwise. */ get(key) { const node = this._map.get(key); if (typeof node === 'undefined') { return void 0; } this._updateRecency(node); return node.value; } /** * Sets a value at a given key. * @param {*} key The key of the element. * @param {*} value The value to store in the cache. */ set(key, value) { let node = this._map.get(key); if (typeof node !== 'undefined') { this._updateRecency(node); node.value = value; } else { if (this._maxSize <= 0) { return; } node = this._createNode(key, value); this._addNode(node, this._listFirst); this._map.set(key, node); // Remove for (let removeCount = this._map.size - this._maxSize; removeCount > 0; --removeCount) { node = this._listLast.previous; this._removeNode(node); this._map.delete(node.key); } } } /** * Clears the cache. */ clear() { this._map.clear(); this._resetEndNodes(); } // Private _updateRecency(node) { this._removeNode(node); this._addNode(node, this._listFirst); } _createNode(key, value) { return {key, value, previous: null, next: null}; } _addNode(node, previous) { const next = previous.next; node.next = next; node.previous = previous; previous.next = node; next.previous = node; } _removeNode(node) { node.next.previous = node.previous; node.previous.next = node.next; } _resetEndNodes() { this._listFirst.next = this._listLast; this._listLast.previous = this._listFirst; } }