class Layzr {

    constructor(config){
        this._lastScroll = 0;
        this._ticking = false;
        config = config || {};
        this._optionsContainer = document.querySelector(config.container) || window;
        this._optionsSelector = config.selector || '[data-layzr]';
        this._optionsAttr = config.attr || 'data-lazyr';
        this._optionsAttrRetina = config.retinaAttr || 'data-layzr-retina';
        this._optionsAttrBg = config.bgAttr || 'data-layzr-bg';
        this._optionsAttrHidden = config.hiddenAttr || 'data-layzr-hidden';
        this._optionsThreshold = config.threshold || 0;
        this._optionsCallback = config.callback || null;
        this._retina = window.devicePixelRatio > 1;
        this._srcAttr = this._retina ? this._optionsAttrRetina : this._optionsAttr;
        this._nodes = document.querySelectorAll(this._optionsSelector);
        this._create();
    }

    _requestScroll(){
        if ( this._optionsContainer === window ) {
            this._lastScroll = window.scrollY || window.pageYOffset;
        } else {
            this._lastScroll = this._optionsContainer.scrollTop + this._getOffset(this._optionsContainer);
        }
        this._requestTick();
    }

    _requestTick() {
        this._ticking || (requestAnimationFrame(this.update.bind(this)), this._ticking = !0);
    }

    _getOffset(a) {
        var b = 0;
        do isNaN(a.offsetTop) || (b += a.offsetTop);
        while (a = a.offsetParent);
        return b
    }

    _getContainerHeight() {
        return this._optionsContainer.innerHeight || this._optionsContainer.offsetHeight;
    }

    _create() {
        this._requestScroll();
        this._optionsContainer.addEventListener("scroll", this._requestScroll.bind(this), !1);
        this._optionsContainer.addEventListener("resize", this._requestScroll.bind(this), !1);
    }

    _destroy() {
        this._optionsContainer.removeEventListener("scroll", this._requestScroll.bind(this), !1);
        this._optionsContainer.removeEventListener("resize", this._requestScroll.bind(this), !1);
    }

    _inViewport(a) {
        var b = this._lastScroll,
            c = b + this._getContainerHeight(),
            d = this._getOffset(a),
            e = d + this._getContainerHeight(),
            f = this._optionsThreshold / 100 * window.innerHeight;
        return e >= b - f && c + f >= d && !a.hasAttribute(this._optionsAttrHidden);
    }

    _reveal(a) {
        var b = a.getAttribute(this._srcAttr) || a.getAttribute(this._optionsAttr);
        a.hasAttribute(this._optionsAttrBg) ? a.style.backgroundImage = "url(" + b + ")" : a.setAttribute("src", b), "function" == typeof this._optionsCallback && this._optionsCallback.call(a), a.removeAttribute(this._optionsAttr), a.removeAttribute(this._optionsAttrRetina), a.removeAttribute(this._optionsAttrBg), a.removeAttribute(this._optionsAttrHidden);
    }

    updateSelector() {
        this._nodes = document.querySelectorAll(this._optionsSelector);
    }

    update() {
        for (var a = this._nodes.length, b = 0; a > b; b++) {
            var c = this._nodes[b];
            c.hasAttribute(this._optionsAttr) && this._inViewport(c) && this._reveal(c)
        }
        this._ticking = !1;
    }
}