var GLASS_TARGETS = [
    {
        selector: ".btn-primary",
        options: {
            distortionScale: -300,
            displace: 0,
            backgroundOpacity: 0.1
        }
    },
    {
        selector: ".btn-secondary",
        options: {
            distortionScale: -300,
            displace: 0,
            backgroundOpacity: 0.1
        }
    },
    {
        selector: ".hero-greeting",
        options: {
            distortionScale: -200,
            displace: 0,
            backgroundOpacity: 0.08
        }
    },
    {
        selector: ".feature-box",
        options: {
            distortionScale: -220,
            displace: 0,
            backgroundOpacity: 0.12,
            saturation: 1.3,
            cornerRadius: 30
        }
    }
];

function initGlassSurface(el, opts) {
    if (!el || el.getAttribute("data-glass")) return;
    el.setAttribute("data-glass", "true");
    opts = opts || {};
    var distortionScale = opts.distortionScale !== undefined ? opts.distortionScale : -180;
    var displace = opts.displace !== undefined ? opts.displace : 0;
    var backgroundOpacity = opts.backgroundOpacity !== undefined ? opts.backgroundOpacity : 0;
    var saturation = opts.saturation !== undefined ? opts.saturation : 1;
    var redOffset = opts.redOffset !== undefined ? opts.redOffset : 0;
    var greenOffset = opts.greenOffset !== undefined ? opts.greenOffset : 10;
    var blueOffset = opts.blueOffset !== undefined ? opts.blueOffset : 20;
    var borderWidth = opts.borderWidth !== undefined ? opts.borderWidth : 0.07;
    var brightness = opts.brightness !== undefined ? opts.brightness : 50;
    var opacity = opts.opacity !== undefined ? opts.opacity : 0.93;
    var blur = opts.blur !== undefined ? opts.blur : 11;
    var mixBlendMode = opts.mixBlendMode || "difference";

    var uid = Math.random().toString(36).slice(2, 9);
    var filterId = "glass-filter-" + uid;
    var redGradId = "red-grad-" + uid;
    var blueGradId = "blue-grad-" + uid;
    var softId = "soft-" + uid;

    var isWebkit = /Safari/.test(navigator.userAgent) && !/Chrome/.test(navigator.userAgent);
    var isFirefox = /Firefox/.test(navigator.userAgent);
    var div = document.createElement("div");
    div.style.backdropFilter = "url(#" + filterId + ")";
    var svgSupported = !isWebkit && !isFirefox && div.style.backdropFilter !== "";

    var rect = el.getBoundingClientRect();
    var w = Math.round(rect.width) || 160;
    var h = Math.round(rect.height) || 40;
    var r = opts.cornerRadius !== undefined ? opts.cornerRadius : Math.round(h / 2);
    var edge = Math.min(w, h) * (borderWidth * 0.5);

    var mapSvg = '<svg width="' + w + '" height="' + h + '" viewBox="0 0 ' + w + ' ' + h + '" xmlns="http://www.w3.org/2000/svg">' +
        '<defs>' +
        '<linearGradient id="' + redGradId + '" x1="100%" y1="0%" x2="0%" y2="0%"><stop offset="0%" stop-color="#0000"/><stop offset="100%" stop-color="red"/></linearGradient>' +
        '<linearGradient id="' + blueGradId + '" x1="0%" y1="0%" x2="0%" y2="100%"><stop offset="0%" stop-color="#0000"/><stop offset="100%" stop-color="blue"/></linearGradient>' +
        '<filter id="' + softId + '" filterUnits="userSpaceOnUse" x="0" y="0" width="' + w + '" height="' + h + '" color-interpolation-filters="sRGB"><feGaussianBlur stdDeviation="' + blur + '"/></filter>' +
        '</defs>' +
        '<rect x="0" y="0" width="' + w + '" height="' + h + '" fill="black"/>' +
        '<rect x="0" y="0" width="' + w + '" height="' + h + '" rx="' + r + '" fill="url(#' + redGradId + ')"/>' +
        '<rect x="0" y="0" width="' + w + '" height="' + h + '" rx="' + r + '" fill="url(#' + blueGradId + ')" style="mix-blend-mode:' + mixBlendMode + '"/>' +
        '<rect x="' + edge + '" y="' + edge + '" width="' + (w - edge * 2) + '" height="' + (h - edge * 2) + '" rx="' + r + '" fill="hsl(0 0% ' + brightness + '% / ' + opacity + ')" filter="url(#' + softId + ')"/>' +
        '</svg>';
    var mapUrl = "data:image/svg+xml," + encodeURIComponent(mapSvg);

    el.style.setProperty("--glass-frost", backgroundOpacity);
    el.style.setProperty("--glass-saturation", saturation);
    el.style.setProperty("--filter-id", "url(#" + filterId + ")");
    el.classList.add(svgSupported ? "glass-surface--svg" : "glass-surface--fallback");

    var filterSvg = document.createElementNS("http://www.w3.org/2000/svg", "svg");
    filterSvg.setAttribute("class", "glass-surface__filter");
    filterSvg.innerHTML = '<defs>' +
        '<filter id="' + filterId + '" color-interpolation-filters="sRGB" x="0%" y="0%" width="100%" height="100%">' +
        '<feImage href="' + mapUrl + '" x="0" y="0" width="100%" height="100%" preserveAspectRatio="none" result="map"/>' +
        '<feDisplacementMap in="SourceGraphic" in2="map" scale="' + (distortionScale + redOffset) + '" xChannelSelector="R" yChannelSelector="G" result="dispRed"/>' +
        '<feColorMatrix in="dispRed" type="matrix" values="1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0" result="red"/>' +
        '<feDisplacementMap in="SourceGraphic" in2="map" scale="' + (distortionScale + greenOffset) + '" xChannelSelector="R" yChannelSelector="G" result="dispGreen"/>' +
        '<feColorMatrix in="dispGreen" type="matrix" values="0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 1 0" result="green"/>' +
        '<feDisplacementMap in="SourceGraphic" in2="map" scale="' + (distortionScale + blueOffset) + '" xChannelSelector="R" yChannelSelector="G" result="dispBlue"/>' +
        '<feColorMatrix in="dispBlue" type="matrix" values="0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 1 0" result="blue"/>' +
        '<feBlend in="red" in2="green" mode="screen" result="rg"/>' +
        '<feBlend in="rg" in2="blue" mode="screen" result="output"/>' +
        '<feGaussianBlur in="output" stdDeviation="' + (displace || 0.7) + '"/>' +
        '</filter></defs>';

    var childNodes = Array.prototype.slice.call(el.childNodes);
    var wrap = document.createElement("div");
    wrap.className = "glass-surface__content";
    childNodes.forEach(function (n) { wrap.appendChild(n); });

    el.appendChild(filterSvg);
    if (!svgSupported) {
        var sheen = document.createElement("span");
        sheen.className = "glass-surface__sheen";
        sheen.setAttribute("aria-hidden", "true");
        var rim = document.createElement("span");
        rim.className = "glass-surface__rim";
        rim.setAttribute("aria-hidden", "true");
        el.appendChild(sheen);
        el.appendChild(rim);
    }
    el.appendChild(wrap);
}

function applyGlassSurfaces(root) {
    var base = root || document;
    GLASS_TARGETS.forEach(function (target) {
        base.querySelectorAll(target.selector).forEach(function (el) {
            initGlassSurface(el, target.options);
        });
    });
}