@sap/odata-v4/lib/utils/Visitor.js

OData V4.0 server library

'use strict';

const EventEmitter = require('events').EventEmitter;

/**
* The `listener` function which will be called on event.
*
* @callback Listener
* @param {*} nextProperty The first context property which is the next context property for the next recursive call
* @param {Array} nextStack The current stack
* @param {*} nextContext The second context property which is the next context property for the next recursive call
* @param {Next} next The callback to be called
*/

/**
* The `next` function which has to be called on event for recursion.
*
* @callback Next
* @param {*} nextProperty The first context property which is the next context property for the next recursive call
* @param {Array} nextStack The current stack
* @param {*} nextContext The second context property which is the next context property for the next recursive call
* @param {string} [eventName] The name of the event to fire. This is optional
*/


/**
 * The Visitor visits each property of the provided object
 *
 * @extends EventEmitter
 */
class Visitor extends EventEmitter {

    /**
     * Creates an instance of Visitor.
     */
    constructor() {
        super();
    }

    /**
     * Registers an event listener on the visitor.
     *
     * @param {string} name The name of the event listener.
     * @param {Listener} listener The listener to call on the registered event name
     * @returns {EventEmitter} this instance
     */
    on(name, listener) {
        return super.on(name, listener.bind(this));
    }

    /**
     * This method visits the target and can do recursive calls up on calling the next function.
     *
     * @param {*} target The root context to visit
     * @param {?*} currentContext The current context to have as a second context
     * @param {*|Array} stack The current stack filled by the application
     */
    visit(target, currentContext = null, stack = []) {

        const next = (nextProperty, nextContext, nextStack, eventName) => {
            if (eventName) {
                this.emit(eventName, nextProperty, nextStack, nextContext, next);
            }
            this.visit(nextProperty, nextContext, nextStack);
        };

        this.emit('visit', target, stack, currentContext, next);
    }
}

module.exports = Visitor;