'use strict';
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const mimicFn = require("mimic-fn");
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const mapAgeCleaner = require("map-age-cleaner");
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const decoratorInstanceMap = new WeakMap();
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const cacheStore = new WeakMap();
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/**
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[Memoize](https://en.wikipedia.org/wiki/Memoization) functions - An optimization used to speed up consecutive function calls by caching the result of calls with identical input.
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@param fn - Function to be memoized.
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@example
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```
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import mem = require('mem');
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let i = 0;
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const counter = () => ++i;
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const memoized = mem(counter);
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memoized('foo');
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//=> 1
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// Cached as it's the same arguments
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memoized('foo');
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//=> 1
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// Not cached anymore as the arguments changed
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memoized('bar');
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//=> 2
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memoized('bar');
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//=> 2
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```
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*/
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const mem = (fn, { cacheKey, cache = new Map(), maxAge } = {}) => {
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if (typeof maxAge === 'number') {
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// TODO: Drop after https://github.com/SamVerschueren/map-age-cleaner/issues/5
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// @ts-expect-error
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mapAgeCleaner(cache);
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}
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const memoized = function (...arguments_) {
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const key = cacheKey ? cacheKey(arguments_) : arguments_[0];
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const cacheItem = cache.get(key);
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if (cacheItem) {
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return cacheItem.data;
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}
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const result = fn.apply(this, arguments_);
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cache.set(key, {
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data: result,
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maxAge: maxAge ? Date.now() + maxAge : Number.POSITIVE_INFINITY
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});
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return result;
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};
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mimicFn(memoized, fn, {
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ignoreNonConfigurable: true
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});
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cacheStore.set(memoized, cache);
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return memoized;
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};
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/**
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@returns A [decorator](https://github.com/tc39/proposal-decorators) to memoize class methods or static class methods.
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@example
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```
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import mem = require('mem');
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class Example {
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index = 0
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@mem.decorator()
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counter() {
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return ++this.index;
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}
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}
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class ExampleWithOptions {
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index = 0
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@mem.decorator({maxAge: 1000})
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counter() {
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return ++this.index;
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}
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}
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```
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*/
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mem.decorator = (options = {}) => (target, propertyKey, descriptor) => {
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const input = target[propertyKey];
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if (typeof input !== 'function') {
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throw new TypeError('The decorated value must be a function');
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}
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delete descriptor.value;
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delete descriptor.writable;
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descriptor.get = function () {
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if (!decoratorInstanceMap.has(this)) {
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const value = mem(input, options);
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decoratorInstanceMap.set(this, value);
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return value;
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}
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return decoratorInstanceMap.get(this);
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};
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};
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/**
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Clear all cached data of a memoized function.
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@param fn - Memoized function.
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*/
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mem.clear = (fn) => {
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const cache = cacheStore.get(fn);
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if (!cache) {
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throw new TypeError('Can\'t clear a function that was not memoized!');
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}
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if (typeof cache.clear !== 'function') {
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throw new TypeError('The cache Map can\'t be cleared!');
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}
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cache.clear();
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};
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module.exports = mem;
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