@sap/xssec/src/cache/LRUCache.js

XS Advanced Container Security API for node.js

/**
 * Implements a Least Recently Used (LRU) cache using a Map.
 * Due to the nature of Map, the order of insertion is preserved in keys() which allows for an implementation with average O(1) complexity for get and put.
 * @param {number} capacity
 */
class LRUCache {
    /**
     * Creates an instance of LRUCache.
     * @param {number} size - The maximum number of items the cache can hold.
     */
    constructor(size) {
        this.size = size;
        this.map = new Map();
    }

    /**
     * Retrieve a value from the cache.
     * @param {string} key - The key of the item to retrieve.
     * @returns {*} The value associated with the key, or null if the key does not exist.
     */
    get(key) {
        if (!this.map.has(key)) return null;

        const value = this.map.get(key);

        // accessed key must be re-inserted at end of queue for LRU strategy
        this.map.delete(key);
        this.map.set(key, value);

        return value;
    }

    /**
     * Insert or update a value in the cache.
     * @param {string} key - The key of the item to insert or update.
     * @param {*} value - The value to associate with the key.
     */
    set(key, value) {
        if (this.map.has(key)) {
            // existing key must be re-inserted at end of queue for LRU strategy
            this.map.delete(key);
        } else if (this.map.size >= this.size) {
            // Map.keys() is in insertion order
            const oldestKey = this.map.keys().next().value;
            this.map.delete(oldestKey);
        }

        this.map.set(key, value);
    }
}

module.exports = LRUCache;