(function() {
    var defaults = {
        offsetBottom: 100,
        showTime: 1100,
        queueInterval: 200
    };

    var observer;

    function init(setting) {
        defaults = Object.assign({}, defaults, setting || {});

        if (observer) {
            observer.disconnect();
            observer = null;
        }

        if (!window.IntersectionObserver) {
            loadAllImages();
            return;
        }

        observer = new IntersectionObserver(function(entries, self) {
            entries.forEach(function(entry) {
                if (!entry.isIntersecting) return;

                var img = entry.target;
                loadImage(img);
                self.unobserve(img);
            });
        }, {
            rootMargin: "0px 0px " + defaults.offsetBottom + "px 0px",
            threshold: 0.01
        });

        observeImages();
    }

    function getPendingImages() {
        return document.querySelectorAll('img.lazyload[data-lazy-src], .post-content img[data-lazy-src]:not(.lazy-loaded)');
    }

    function observeImages() {
        var images = getPendingImages();

        images.forEach(function(img) {
            observer.observe(img);
        });
    }

    function markLoaded(img, callback) {
        img.classList.add('lazy-loaded');
        img.removeAttribute('data-lazy-src');
        if (callback) callback();
    }

    function loadImage(img, callback) {
        var src = img.getAttribute('data-lazy-src');
        if (!src) {
            if (callback) callback();
            return;
        }

        img.decoding = 'async';

        var temp = new Image();
        temp.decoding = 'async';

        temp.onload = function() {
            img.src = src;
            requestAnimationFrame(function() {
                markLoaded(img, callback);
            });
        };

        temp.onerror = function() {
            img.src = src;
            markLoaded(img, callback);
        };

        temp.src = src;
    }

    function loadAllImages() {
        var images = getPendingImages();
        images.forEach(function(img) {
            loadImage(img);
        });
    }

    window.lazyLoadInit = init;
    window.lazyLoadRefresh = observeImages;
})();