const crypto = require('crypto');
const { Component } = require('inferno');
const { createElement } = require('inferno-create-element');

const cache = {};

function computeHash(props) {
    return crypto.createHash('md5').update(JSON.stringify(props)).digest("hex");
}

module.exports = {
    /**
     * Create cached component from a given component class.
     * The cache ID is caculated from the input props.
     * 
     * @param {Component}   type        JSX component class
     * @param {string}      prefix      Cache ID prefix
     * @param {Function}    transform   Transform the input props to target props and 
     *                                  its result is used to compute cache ID 
     * @returns Cached JSX element if cache ID is found. 
     *          Otherwise, create a new element and cache it if the transform function is provided.
     */
    cacheComponent(type, prefix, transform) {
        if (typeof transform !== 'function') {
            return props => createElement(type, props);
        } else {
            return props => {
                const targetProps = transform(props);
                const cacheId = prefix + '-' + computeHash(targetProps);
                if (!cacheId) {
                    return createElement(type, targetProps);
                }
                if (!cache[cacheId]) {
                    cache[cacheId] = createElement(type, targetProps);
                }
                return cache[cacheId];
            };
        }
    }
};