/* Social-post export engine — generalization of the pipeline proven in
   fotografia.andmore.pt/views/sessions/open_spots_ig.php.

   Responsibilities: render a live-preview element to a high-resolution JPG
   via html2canvas, pre-baking CSS blur (html2canvas can't render
   `filter: blur()`), waiting for webfonts, and bundling multi-slide exports
   into a ZIP (JSZip). Pure mechanism — all template/DOM knowledge lives in
   the page that uses it. */

window.SocialEngine = (function () {
    'use strict';

    function chunk(arr, size) {
        size = Math.max(1, size | 0);
        var out = [];
        for (var i = 0; i < arr.length; i += size) out.push(arr.slice(i, i + size));
        return out;
    }

    /* html2canvas does not render CSS `filter: blur(...)`. Pre-bake the blur
       into the photo with Canvas 2D, swap the bg-image to that bitmap, drop
       the inline filter/transform, and return a restore() callback. The blur
       radius is multiplied by the export scale so the upscaled bitmap matches
       what's on screen. Resolves null when there is nothing to bake. */
    function bakeBlur(bgEl, photoUrl, blurAmount, scale) {
        return new Promise(function (resolve) {
            if (!bgEl || !photoUrl || !(blurAmount > 0)) return resolve(null);

            var rect   = bgEl.getBoundingClientRect();
            var W      = Math.max(1, Math.round(rect.width  * scale));
            var H      = Math.max(1, Math.round(rect.height * scale));
            var blurPx = blurAmount * scale;

            var img = new Image();
            // Photos go through the same-origin media proxy (or are local hub
            // uploads), so no crossOrigin attribute is needed and the canvas
            // stays untainted.
            img.onload = function () {
                try {
                    var canvas = document.createElement('canvas');
                    canvas.width  = W;
                    canvas.height = H;
                    var ctx = canvas.getContext('2d');
                    ctx.filter = 'blur(' + blurPx + 'px) brightness(0.85)';

                    // Draw slightly larger than the canvas so the soft edges
                    // don't reveal blank pixels — same trick as the CSS scale().
                    var overscan = 1.1 + (blurAmount / 200);
                    var ratio = Math.max(W / img.width, H / img.height) * overscan;
                    var dw = img.width  * ratio;
                    var dh = img.height * ratio;
                    ctx.drawImage(img, (W - dw) / 2, (H - dh) / 2, dw, dh);

                    var dataUrl  = canvas.toDataURL('image/jpeg', 0.9);
                    var original = {
                        backgroundImage: bgEl.style.backgroundImage,
                        filter:          bgEl.style.filter,
                        transform:       bgEl.style.transform,
                    };
                    bgEl.style.backgroundImage = "url('" + dataUrl + "')";
                    bgEl.style.filter          = 'none';
                    bgEl.style.transform       = 'none';

                    resolve(function () {
                        bgEl.style.backgroundImage = original.backgroundImage;
                        bgEl.style.filter          = original.filter;
                        bgEl.style.transform       = original.transform;
                    });
                } catch (e) {
                    console.warn('Blur bake failed; exporting without baked blur.', e);
                    resolve(null);
                }
            };
            img.onerror = function () {
                console.warn('Failed to load photo for blur bake; exporting without baked blur.');
                resolve(null);
            };
            img.src = photoUrl;
        });
    }

    /* Render `el` (the live preview, at its on-screen size — its CSS uses
       viewport-relative clamp()s, so rendering at another width would re-flow)
       and let html2canvas upscale the pixel buffer to `targetW` via `scale`.
       opts.blur = { bgEl, photoUrl, amount } enables the bake step.
       Returns a JPEG Blob. */
    async function renderBlob(el, targetW, opts) {
        opts = opts || {};
        if (typeof html2canvas !== 'function') {
            throw new Error('A biblioteca de exportação ainda está a carregar. Tenta novamente em segundos.');
        }
        var rect    = el.getBoundingClientRect();
        var actualW = rect.width  || el.offsetWidth  || targetW;
        var actualH = rect.height || el.offsetHeight || targetW;
        var scale   = actualW > 0 ? (targetW / actualW) : 1;

        if (document.fonts && document.fonts.ready) {
            await document.fonts.ready;
        }
        var restore = null;
        if (opts.blur) {
            restore = await bakeBlur(opts.blur.bgEl, opts.blur.photoUrl, opts.blur.amount, scale);
        }
        try {
            var canvas = await html2canvas(el, {
                backgroundColor: '#000',
                scale: scale,
                useCORS: true,
                logging: false,
                width:  actualW,
                height: actualH,
                windowWidth:  document.documentElement.clientWidth,
                windowHeight: document.documentElement.clientHeight,
            });
            return await new Promise(function (resolve, reject) {
                canvas.toBlob(function (blob) {
                    if (!blob) { reject(new Error('Falha ao gerar a imagem.')); return; }
                    resolve(blob);
                }, 'image/jpeg', 0.95);
            });
        } finally {
            if (restore) restore();
        }
    }

    function saveBlob(blob, fileName) {
        var url  = URL.createObjectURL(blob);
        var link = document.createElement('a');
        link.href     = url;
        link.download = fileName;
        document.body.appendChild(link);
        link.click();
        document.body.removeChild(link);
        setTimeout(function () { URL.revokeObjectURL(url); }, 1500);
    }

    /* files: [{ blob, name }]. One file downloads directly; several are
       bundled into a single ZIP. */
    async function saveAll(files, zipName) {
        if (!files.length) return;
        if (files.length === 1) { saveBlob(files[0].blob, files[0].name); return; }
        if (typeof JSZip !== 'function') {
            // ZIP library missing — degrade to sequential downloads.
            files.forEach(function (f) { saveBlob(f.blob, f.name); });
            return;
        }
        var zip = new JSZip();
        files.forEach(function (f) { zip.file(f.name, f.blob); });
        var blob = await zip.generateAsync({ type: 'blob' });
        saveBlob(blob, zipName);
    }

    return {
        chunk:      chunk,
        renderBlob: renderBlob,
        saveBlob:   saveBlob,
        saveAll:    saveAll,
    };
})();