export function downscaleRgbaToDataUrl(pixels, srcW, srcH, dstSize) {
    const dst = new Uint8ClampedArray(dstSize * dstSize * 4);
    for (let y = 0; y < dstSize; y++) {
        const y0 = Math.floor((y * srcH) / dstSize);
        const y1 = Math.max(y0 + 1, Math.floor(((y + 1) * srcH) / dstSize));
        for (let x = 0; x < dstSize; x++) {
            const x0 = Math.floor((x * srcW) / dstSize);
            const x1 = Math.max(x0 + 1, Math.floor(((x + 1) * srcW) / dstSize));
            let r = 0, g = 0, b = 0, c = 0;
            for (let sy = y0; sy < y1; sy++)
                for (let sx = x0; sx < x1; sx++) {
                    const i = (sy * srcW + sx) * 4;
                    r += pixels[i]; g += pixels[i + 1]; b += pixels[i + 2]; c++;
                }
            const o = (y * dstSize + x) * 4;
            dst[o] = c ? Math.round(r / c) : 0;
            dst[o + 1] = c ? Math.round(g / c) : 0;
            dst[o + 2] = c ? Math.round(b / c) : 0;
            dst[o + 3] = 255;
        }
    }
    if (typeof document !== 'undefined' && document.createElement) {
        try {
            const canvas = document.createElement('canvas');
            canvas.width = dstSize; canvas.height = dstSize;
            const ctx = canvas.getContext('2d');
            if (ctx) { ctx.putImageData(new ImageData(dst, dstSize, dstSize), 0, 0); return canvas.toDataURL('image/jpeg', 0.6); }
        } catch { /* fallback */ }
    }
    return 'data:image/jpeg;base64,';
}

function uniformFrames(count, frameCount) {
    const seen = new Set(); const out = [];
    for (let i = 0; i < count; i++) {
        const f = Math.max(0, Math.min(frameCount - 1, Math.round(((i + 0.5) / count) * frameCount)));
        if (!seen.has(f)) { seen.add(f); out.push(f); }
    }
    return out;
}

function pickFrames(show, count, frameCount, fps) {
    const sections = show.track && show.track.sections;
    if (sections && sections.length) {
        const mids = []; const seen = new Set();
        for (const s of sections) {
            let mid;
            if (Number.isFinite(s.startFrame) && Number.isFinite(s.endFrame)) mid = Math.round((s.startFrame + s.endFrame) / 2);
            else if (Number.isFinite(s.start) && Number.isFinite(s.end)) mid = Math.round(((s.start + s.end) / 2) * fps);
            else continue;
            mid = Math.max(0, Math.min(frameCount - 1, mid));
            if (!seen.has(mid)) { seen.add(mid); mids.push(mid); }
        }
        if (!mids.length) return uniformFrames(count, frameCount);
        if (mids.length >= count) {
            if (mids.length === count) return mids;
            mids.sort((a, b) => a - b);
            const out = [];
            for (let i = 0; i < count; i++) {
                const idx = Math.min(mids.length - 1, Math.floor(((i + 0.5) / count) * mids.length));
                const v = mids[idx]; if (!out.includes(v)) out.push(v);
            }
            return out;
        }
        const need = count - mids.length;
        for (const f of uniformFrames(need, frameCount)) if (!seen.has(f)) { seen.add(f); mids.push(f); }
        if (mids.length < count) for (const f of uniformFrames(count, frameCount)) if (!seen.has(f) && mids.length < count) { seen.add(f); mids.push(f); }
        const sorted = [...seen].sort((a, b) => a - b);
        if (sorted.length <= count) return sorted;
        const out = [];
        for (let i = 0; i < count; i++) {
            const idx = Math.min(sorted.length - 1, Math.floor(((i + 0.5) / count) * sorted.length));
            const v = sorted[idx]; if (!out.includes(v)) out.push(v);
        }
        return out;
    }
    return uniformFrames(count, frameCount);
}

export async function captureThumbnails(show, { count = 8, size = 32 } = {}) {
    if (!show || !show.ready || !show.track || !show.engine) return [];
    const fps = show.fps || 60;
    const frameCount = show.frameCount || (show.track && show.track.frameCount) || Math.round((show.track.duration || 0) * fps) || 0;
    if (!frameCount) return [];
    const originalFrame = show.timeline ? show.timeline.frame : 0;
    const origW = show.engine.width, origH = show.engine.height;
    const frames = pickFrames(show, count, frameCount, fps).sort((a, b) => a - b);
    const out = [];
    try {
        for (const frame of frames) {
            try {
                if (typeof show.warmUp === 'function') {
                    const wf = typeof show.warmupFrames === 'function' ? show.warmupFrames() : 120;
                    show.warmUp(frame, Math.min(120, wf));
                } else if (show.engine.compositor) {
                    if (typeof show.engine.warmUp === 'function') show.engine.warmUp(frame, 120);
                    else show.engine.compositor.reset();
                }
            } catch { /* ignore */ }
            let target; try { target = show.renderFrame(frame); } catch { continue; }
            let pixels; try { pixels = show.readPixels(target); } catch { continue; }
            if (!pixels || !pixels.length) continue;
            let dataUrl = ''; try { dataUrl = downscaleRgbaToDataUrl(pixels, origW, origH, size); } catch { dataUrl = 'data:image/jpeg;base64,'; }
            let kind = '';
            try {
                const sec = show.track.sectionAt ? show.track.sectionAt(frame) : null;
                if (sec && sec.kind) kind = sec.kind;
                else if (show.track.sections) for (const s of show.track.sections) if (Number.isFinite(s.startFrame) && frame >= s.startFrame && frame < s.endFrame) { kind = s.kind || ''; break; }
            } catch { /* ignore */ }
            out.push({ kind: kind || '', time: frame / fps, frame, dataUrl });
        }
    } finally {
        try {
            if (typeof show.seek === 'function') show.seek(originalFrame);
            else if (show.timeline && typeof show.timeline.seek === 'function') {
                show.timeline.seek(originalFrame);
                try { const t = show.renderFrame(originalFrame); if (typeof show.present === 'function') show.present(t); } catch { /* ignore */ }
            }
        } catch { /* ignore */ }
        try {
            if (show.engine && (show.engine.width !== origW || show.engine.height !== origH)) {
                if (typeof show.engine.setSize === 'function') show.engine.setSize(origW, origH);
                else if (typeof show.setSize === 'function') show.setSize(origW, origH);
            }
        } catch { /* ignore */ }
    }
    return out;
}