/**
 * A plugin which enables rendering of math equations inside
 * of reveal.js slides. Essentially a thin wrapper for MathJax.
 *
 * @author Hakim El Hattab
 */
var RevealMath = window.RevealMath || (function () {

    var options = Reveal.getConfig().math || {};
    var mathjax = options.mathjax || 'https://cdnjs.cloudflare.com/ajax/libs/mathjax/2.7.0/MathJax.js';
    var config = options.config || 'TeX-AMS_HTML-full';
    var url = mathjax + '?config=' + config;

    var defaultOptions = {
        messageStyle: 'none',
        tex2jax: {
            inlineMath: [['$', '$'], ['\\(', '\\)']],
            skipTags: ['script', 'noscript', 'style', 'textarea', 'pre']
        },
        skipStartupTypeset: true
    };

    function defaults(options, defaultOptions) {

        for (var i in defaultOptions) {
            if (!options.hasOwnProperty(i)) {
                options[i] = defaultOptions[i];
            }
        }

    }

    function loadScript(url, callback) {

        var head = document.querySelector('head');
        var script = document.createElement('script');
        script.type = 'text/javascript';
        script.src = url;

        // Wrapper for callback to make sure it only fires once
        var finish = function () {
            if (typeof callback === 'function') {
                callback.call();
                callback = null;
            }
        };

        script.onload = finish;

        // IE
        script.onreadystatechange = function () {
            if (this.readyState === 'loaded') {
                finish();
            }
        };

        // Normal browsers
        head.appendChild(script);

    }

    return {
        init: function () {

            defaults(options, defaultOptions);
            defaults(options.tex2jax, defaultOptions.tex2jax);
            options.mathjax = options.config = null;

            loadScript(url, function () {

                MathJax.Hub.Config(options);

                // Typeset followed by an immediate reveal.js layout since
                // the typesetting process could affect slide height
                MathJax.Hub.Queue(['Typeset', MathJax.Hub]);
                MathJax.Hub.Queue(Reveal.layout);

                // Reprocess equations in slides when they turn visible
                Reveal.addEventListener('slidechanged', function (event) {

                    MathJax.Hub.Queue(['Typeset', MathJax.Hub, event.currentSlide]);

                });

            });

        }
    }

})();

Reveal.registerPlugin('math', RevealMath);