// See LICENSE for usage information

// The following lines allow the ping function to be loaded via commonjs, AMD,
// and script tags, directly into window globals.
// Thanks to https://github.com/umdjs/umd/blob/master/templates/returnExports.js
(function (root, factory) { if (typeof define === 'function' && define.amd) { define([], factory); } else if (typeof module === 'object' && module.exports) { module.exports = factory(); } else { root.ping = factory(); }
}(this, function () {

    /**
     * Creates and loads an image element by url.
     * @param  {String} url
     * @return {Promise} promise that resolves to an image element or
     *                   fails to an Error.
     */
    function request_image(url) {
        return new Promise(function(resolve, reject) {
            var img = new Image();
            img.onload = function() { resolve(img); };
            img.onerror = function() { reject(url); };
            img.src = url + '?random-no-cache=' + Math.floor((1 + Math.random()) * 0x10000).toString(16);
        });
    }

    /**
     * Pings a url.
     * @param  {String} url
     * @param  {Number} multiplier - optional, factor to adjust the ping by.  0.3 works well for HTTP servers.
     * @return {Promise} promise that resolves to a ping (ms, float).
     */
    function ping(url, multiplier) {
        return new Promise(function(resolve, reject) {
            var start = (new Date()).getTime();
            var response = function() { 
                var delta = ((new Date()).getTime() - start);
                delta *= (multiplier || 1);
                resolve(delta); 
            };
            request_image(url).then(response).catch(response);
            
            // Set a timeout for max-pings, 5s.
            setTimeout(function() { reject(Error('Timeout')); }, 5000);
        });
    }
    
    return ping;
}));