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/*
* Copyright (C) 2020 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 using an arbitrary length path,
* keeping the most recently accessed values.
*/
class CacheMap {
/**
* Creates a new CacheMap.
* @param maxCount The maximum number of entries able to be stored in the cache.
* @param create A function to create a value for the corresponding path.
* The signature is: create(path)
*/
constructor(maxCount, create) {
if (!(
typeof maxCount === 'number' &&
Number.isFinite(maxCount) &&
maxCount >= 0 &&
Math.floor(maxCount) === maxCount
)) {
throw new Error('Invalid maxCount');
}
this._maxCount = maxCount;
this._create = create;
this._count = 0;
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.
*/
get count() {
return this._count;
}
/**
* Returns the maximum number of items that can be added to the cache.
*/
get maxCount() {
return this._maxCount;
}
/**
* Returns whether or not an item exists at the given path.
* @param path Array corresponding to the key of the cache.
* @returns A boolean indicating whether ot not the item exists.
*/
has(path) {
const node = this._accessNode(false, false, null, false, path);
return (node !== null);
}
/**
* Gets an item at the given path, if it exists. Otherwise, returns undefined.
* @param path Array corresponding to the key of the cache.
* @returns The existing value at the path, if any; otherwise, undefined.
*/
get(path) {
const node = this._accessNode(false, false, null, true, path);
return (node !== null ? node.value : void 0);
}
/**
* Gets an item at the given path, if it exists. Otherwise, creates a new item
* and adds it to the cache. If the count exceeds the maximum count, items will be removed.
* @param path Array corresponding to the key of the cache.
* @returns The existing value at the path, if any; otherwise, a newly created value.
*/
getOrCreate(path) {
return this._accessNode(true, false, null, true, path).value;
}
/**
* Sets a value at a given path.
* @param path Array corresponding to the key of the cache.
* @param value The value to store in the cache.
*/
set(path, value) {
this._accessNode(false, true, value, true, path);
}
/**
* Clears the cache.
*/
clear() {
this._map.clear();
this._count = 0;
this._resetEndNodes();
}
// Private
_accessNode(create, set, value, updateRecency, path) {
let ii = path.length;
if (ii === 0) { throw new Error('Invalid path'); }
let map = this._map;
let i = 0;
for (; i < ii; ++i) {
const map2 = map.get(path[i]);
if (typeof map2 === 'undefined') { break; }
map = map2;
}
if (i === ii) {
// Found (map should now be a node)
if (updateRecency) { this._updateRecency(map); }
if (set) { map.value = value; }
return map;
}
// Create new
if (create) {
value = this._create(path);
} else if (!set) {
return null;
}
// Create mapping
--ii;
for (; i < ii; ++i) {
const map2 = new Map();
map.set(path[i], map2);
map = map2;
}
// Assign
const node = this._createNode(value, path);
this._addNode(node, this._listFirst);
map.set(path[ii], node);
++this._count;
this._updateCount();
return node;
}
_updateRecency(node) {
this._removeNode(node);
this._addNode(node, this._listFirst);
}
_updateCount() {
for (let removeCount = this._count - this._maxCount; removeCount > 0; --removeCount) {
const node = this._listLast.previous;
this._removeNode(node);
this._removeMapping(node.path);
--this._count;
}
}
_createNode(value, path) {
return {value, path, 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;
}
_removeMapping(path) {
const ii = path.length - 1;
let i = 0;
const maps = [];
let map = this._map;
for (; i < ii; ++i) {
const map2 = map.get(path[i]);
if (typeof map2 === 'undefined') { return; }
maps.push([map, map2]);
map = map2;
}
// Delete node
map.delete(path[ii]);
// Clear empty paths
for (i = ii - 1; i >= 0; --i) {
let map2;
[map, map2] = maps[i];
if (map2.size > 0) { return; }
map.delete(path[i]);
}
}
_resetEndNodes() {
this._listFirst.next = this._listLast;
this._listLast.previous = this._listFirst;
}
}
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