@oat-sa/tao-core-sdk/src/core/delegator.js

Core libraries of TAO

/**
 * 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; under version 2
 * of the License (non-upgradable).
 *
 * 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, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
 *
 * Copyright (c) 2016-2019 (original work) Open Assessment Technologies SA ;
 */
/**
 * @author Jean-Sébastien Conan <jean-sebastien.conan@vesperiagroup.com>
 */
import _ from 'lodash';

const defaults = {
    name: 'provided',
    eventifier: true
};

/**
 * Creates a function that delegates api calls to an provider
 * @param {Object} api - The api providing the calls
 * @param {Object} provider - The provider on which delegate the calls
 * @param {Object} [config] - An optional configuration set
 * @param {String} [config.name] - The name of the provider
 * @param {Boolean} [config.eventifier] - Enable the eventifier support (default: true)
 * @param {Boolean} [config.forward] - Forward the calls to the provider instead of delegate (default: false)
 * @param {Function} [config.defaultProvider] - An optional default delegated function called if the provider do not have the requested target.
 * @param {Function} [config.wrapper] - An optional function that will wrap the response
 * @param {Boolean} [config.required] - Throws exception if a delegated method is missing (default: false)
 * @returns {delegate} - The delegate function
 */
function delegator(api, provider, config) {
    const extendedConfig = _.defaults(config || {}, defaults);
    const eventifier = !!(extendedConfig.eventifier && api && api.trigger);
    const context = extendedConfig.forward ? provider : api;
    let defaultProvider = _.isFunction(extendedConfig.defaultProvider) ? extendedConfig.defaultProvider : _.noop;
    const wrapper = _.isFunction(extendedConfig.wrapper) ? extendedConfig.wrapper : null;
    const name = extendedConfig.name;

    if (extendedConfig.required) {
        defaultProvider = null;
    }

    /**
     * Delegates a function call from the api to the provider.
     * If the api supports eventifier, fires the related event
     *
     * @param {String} fnName - The name of the delegated method to call
     * @param {...*} [args] - Following parameters will be forwarded as is
     * @returns {Object} - The delegated method must return a response
     * @private
     * @throws Error
     */
    function delegate(fnName, ...args) {
        let response;

        if (provider) {
            if (_.isFunction(provider[fnName]) || defaultProvider) {
                // delegate the call to the provider
                response = (provider[fnName] || defaultProvider).apply(context, args);

                if (wrapper) {
                    response = wrapper(response);
                }

                // if supported fires the method related event
                if (eventifier) {
                    // the response has to be provided as first argument in all events
                    api.trigger(fnName, response, ...args);
                }
            } else {
                throw new Error(`There is no method called ${fnName} in the ${name} provider!`);
            }
        } else {
            throw new Error(`There is no ${name} provider!`);
        }

        return response;
    }

    return delegate;
}

export default delegator;