The DatabaseCache class

databaseCache.js

const DatabaseService = require('./databaseService');

/**
 * Database options.
 * @typedef {Object.<string, boolean|number|string>} DatabaseOptions
 */

/**
 * A cache entry.
 * @typedef {Object} CacheEntry
 * @property {!number} expiration The expiration as an epoch timestamp.
 * @property {DatabaseService} service The DatabaseService.
 */

/**
 * @class DatabaseCache
 */
class DatabaseCache {
    /**
     * Creates a cache.
     *
     * @constructor
     * @param [number] cacheTtl The time-to-live in seconds. Currently defaults to one hour.
     */
    constructor(cacheTtl = 3600) {
        /**
         * The cache.
         * @type {Object.<string, CacheEntry>}
         * @public
         */
        this.cache = {};

        /**
         * Cache time-to-live in milliseconds.
         * @type {!number}
         * @public
         */
        this.cacheTtl = cacheTtl * 1000;
    }

    /**
     * Determine if an unexpired cached database service exists.
     *
     * @param {string} cacheId The cache identifier.
     * @returns {boolean} True if the cached database exists.
     */
    cacheExists(cacheId) {
        if (this.isCacheExpired(cacheId)) return false;
        return this.cache[cacheId] ? true : false;
    }

    /**
     * Get a cached DatabaseService or create a new one if it does not exist yet or it is expired.
     *
     * @param {string} cacheId The cache identifier.
     * @param {DatabaseOptions} dbArgs Database settings to be passed to DatabaseService when creating new connections.
     * @returns {DatabaseService} the cached DatabaseService object.
     */
    getCache(cacheId, dbArgs) {
        // This will return true if the cache does not exist.
        if (this.isCacheExpired(cacheId)) {
            // Remove the cache if it does exist as we know it is expired.
            if (this.cache[cacheId]) {
                this.removeCache(cacheId);
            }
            const service = new DatabaseService(dbArgs);
            /** @constant {CacheEntry} */
            const obj = {
                expiration: Date.now() + this.cacheTtl,
                service: service,
            };
            this.cache[cacheId] = obj;
        }
        return this.cache[cacheId].service;
    }

    /**
     * Get the keys of the cache.
     *
     * @returns {Array<string>} An Array consisting of all the cache keys.
     */
    getCacheKeys() {
        return Object.keys(this.cache);
    }

    /**
     * Get the size of the cache.
     *
     * @returns {number} The number of cache entries.
     */
    getCacheSize() {
        return Object.keys(this.cache).length;
    }

    /**
     * Get the cached database service.
     *
     * @param {string} cacheId The cache identifier.
     * @param {DatabaseOptions} dbArgs Database settings to be passed to DatabaseService when creating new connections.
     * @returns {DatabaseService} the cached DatabaseService object.
     */
    getService(cacheId, dbArgs) {
        const cache = this.getCache(cacheId, dbArgs);
        return cache;
    }

    /**
     * Determines if the cache entry has expired.
     *
     * @param {string} cacheId The cache identifier.
     * @return {boolean} True if expired.
     */
    isCacheExpired(cacheId) {
        if (!this.cache[cacheId] || !this.cache[cacheId].service) return true;
        return this.cache[cacheId] && this.cache[cacheId].service && this.cache[cacheId].expiration < Date.now();
    }

    /**
     * Removes a cache entry.
     *
     * @param {string} cacheId The cache identifier.
     */
    removeCache(cacheId) {
        delete this.cache[cacheId];
    }
}

module.exports = DatabaseCache;