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/*
* Copyright (C) 2023 Yomitan Authors
* 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;
}
}
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