document.addEventListener('DOMContentLoaded', () => {
    // --- 1. DOM REFERENCES ---
    const qrContainer = document.getElementById('qr-container');
    const downloadBtn = document.getElementById('btn-download');
    const stickyWrapper = document.querySelector('.sticky-wrapper');

    // Gauge Elements
    const capMeter = document.getElementById('capacity-meter');
    const capBar = document.getElementById('capacity-bar');
    const capText = document.getElementById('capacity-text');
    const capLabel = document.getElementById('capacity-label');

    // Inputs
    const modeSelector = document.getElementById('mode-selector');
    const optEcc = document.getElementById('opt-ecc');
    const optSize = document.getElementById('opt-size');
    const optFg = document.getElementById('opt-fg');
    const optBg = document.getElementById('opt-bg');
    const hexFg = document.getElementById('hex-fg');
    const hexBg = document.getElementById('hex-bg');

    const fmtRadios = document.getElementsByName('opt-fmt');

    let debounceTimer;

    // --- 2. STATE GETTERS (Pure Functions) ---

    function getFormat() {
        for (const r of fmtRadios) {
            if (r.checked) return r.value;
        }
        return 'png';
    }

    function getDataString() {
        const mode = modeSelector.value;
        if (mode === 'text') {
            return document.getElementById('inp-text').value;
        } else if (mode === 'wifi') {
            const ssid = document.getElementById('inp-wifi-ssid').value;
            const pass = document.getElementById('inp-wifi-pass').value;
            const type = document.getElementById('inp-wifi-type').value;
            // Note: Even if empty, we return the structure so the logic can decide
            if (!ssid) return '';
            const cleanSSID = ssid.replace(/([\\;,:])/g, '\\$1');
            const cleanPass = pass.replace(/([\\;,:])/g, '\\$1');
            return `WIFI:S:${cleanSSID};T:${type};P:${cleanPass};;`;
        } else if (mode === 'email') {
            const to = document.getElementById('inp-email-to').value;
            const sub = document.getElementById('inp-email-sub').value;
            const body = document.getElementById('inp-email-body').value;
            if (!to) return '';
            return `mailto:${to}?subject=${encodeURIComponent(sub)}&body=${encodeURIComponent(body)}`;
        }
        return '';
    }

    // --- 3. RENDER HELPERS ---

    function generateSVGString(modules, size, fg, bg) {
        const count = modules.length;
        const modSize = size / count;

        let pathData = '';
        for (let r = 0; r < count; r++) {
            for (let c = 0; c < count; c++) {
                if (modules[r][c]) {
                    const x = c * modSize;
                    const y = r * modSize;
                    pathData += `M${x},${y}h${modSize}v${modSize}h-${modSize}z`;
                }
            }
        }

        return `
        <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 ${size} ${size}" width="${size}" height="${size}">
            <rect width="100%" height="100%" fill="${bg}"/>
            <path d="${pathData}" fill="${fg}" shape-rendering="crispEdges"/>
        </svg>
        `;
    }

    function renderError(title, subtitle) {
        qrContainer.innerHTML = `
            <div class="qr-error-msg">
                ERROR: ${title}<br>
                <span style="font-size:0.7em; opacity:0.8; display:block; margin-top:0.5rem;">
                    ${subtitle}
                </span>
            </div>
        `;
        downloadBtn.disabled = true;
        downloadBtn.textContent = "GENERATION FAILED";
        stickyWrapper.classList.add('has-error');
    }

    // --- 4. CORE LOGIC ---

    // A. Capacity Gauge (Fast / Instant)
    function updateCapacityUI(textData) {
        if (!textData) {
            capMeter.style.display = 'none';
            return;
        }

        const blob = new Blob([textData]);
        const bytes = blob.size;

        // Limits based on Version 40 (Byte Mode)
        const maxCapacityMap = { 'L': 2950, 'M': 2328, 'Q': 1660, 'H': 1270 };
        const maxBytes = maxCapacityMap[optEcc.value] || 1270;

        const raw_usage = Math.round((bytes / maxBytes) * 100);
        const usage = Math.min(100, raw_usage);

        if (usage > 50) {
            capMeter.style.display = 'block';
            capBar.style.width = `${usage}%`;

            capText.textContent = `${usage}% (${bytes} / ${maxBytes} B)`;

            if (raw_usage <= 100) {
                capLabel.textContent = 'CAPACITY';
            } else {
                capLabel.textContent = 'OVER CAPACITY';
            }

            if (usage > 90) {
                capBar.style.backgroundColor = 'red';
                capText.style.color = 'red';
                capLabel.style.color = 'red';
            } else {
                capBar.style.backgroundColor = '#000';
                capText.style.color = '#000';
                capLabel.style.color = '#000';
            }
        } else {
            capMeter.style.display = 'none';
        }
    }

// B. The Main Renderer (Stateless: Flush and Rebuild)
    function renderQR() {
        // 1. Gather State
        const textData = getDataString();
        const format = getFormat();
        const ecc = QRCode.CorrectLevel[optEcc.value];
        const colorDark = optFg.value;
        const colorLight = optBg.value;

        hexFg.textContent = colorDark;
        hexBg.textContent = colorLight;

        // 2. Reset DOM
        qrContainer.innerHTML = '';
        stickyWrapper.classList.remove('has-error');

        // 3. Handle Empty State
        if (!textData || textData.trim() === '') {
            downloadBtn.disabled = true;
            downloadBtn.textContent = `DOWNLOAD ${format.toUpperCase()}`;
            return;
        }

        downloadBtn.textContent = `DOWNLOAD ${format.toUpperCase()}`;

        // 4. Validate Size
        let size = parseInt(optSize.value) || 256;
        if (size < 64) size = 64;
        if (size > 4000) size = 4000;

        // 5. Generate
        try {
            const instance = new QRCode(qrContainer, {
                text: textData,
                width: size,
                height: size,
                colorDark : colorDark,
                colorLight : colorLight,
                correctLevel : ecc
            });

            // 6. Post-Process
            if (format === 'svg') {
                const modules = instance._oQRCode.modules;
                const nodes = qrContainer.childNodes;
                for(let i=0; i<nodes.length; i++) {
                    if(nodes[i].style) nodes[i].style.display = 'none';
                }
                const svgString = generateSVGString(modules, size, colorDark, colorLight);
                qrContainer.insertAdjacentHTML('beforeend', svgString);
            }
            else {
                const img = qrContainer.querySelector('img');
                if(img) img.style.display = 'block';
            }

            downloadBtn.disabled = false;

        } catch (e) {
            // 7. Smart Error Handling

            // Calculate usage to guess the error type
            const blob = new Blob([textData]);
            const bytes = blob.size;
            const maxCapacityMap = { 'L': 2953, 'M': 2331, 'Q': 1663, 'H': 1273 };
            const maxBytes = maxCapacityMap[optEcc.value] || 1273;

            // If we are over (or extremely close to) the limit, it's definitely a capacity issue.
            // (We use >= because sometimes overhead pushes it over even if bytes == maxBytes)
            if (bytes >= maxBytes) {
                renderError(
                    "CAPACITY EXCEEDED",
                    "REDUCE TEXT OR LOWER ECC LEVEL"
                );
            }
            else {
                // If usage is low but it crashed, it's a real bug (e.g. invalid char code).
                // Show the specific error for debugging.
                console.error(e); // Keep looking at console for devs
                renderError(
                    "UNKNOWN ERROR",
                    `CODE: ${e.name || 'Except'} // ${e.message || 'Check Console'}`
                );
            }
        }
    }

    // --- 5. EVENT ORCHESTRATION ---

    function handleUpdate(immediate = false) {
        const text = getDataString();

        // Always update gauge immediately
        updateCapacityUI(text);

        // Debounce the heavy rendering
        clearTimeout(debounceTimer);
        if (immediate) {
            renderQR();
        } else {
            debounceTimer = setTimeout(renderQR, 300);
        }
    }

    // --- 6. LISTENERS ---

    // Configuration Inputs (Colors, ECC, Size) -> Trigger Rebuild
    [optEcc, optSize, optFg, optBg].forEach(el => {
        el.addEventListener('input', () => handleUpdate(false));
    });

    // Format Change -> Trigger Rebuild (Instant)
    fmtRadios.forEach(r => r.addEventListener('change', () => handleUpdate(true)));

    // Mode Switch -> Change Form & Rebuild
    modeSelector.addEventListener('change', (e) => {
        const newMode = e.target.value;
        document.querySelectorAll('.input-form').forEach(f => f.classList.remove('active'));
        document.getElementById(`form-${newMode}`).classList.add('active');
        handleUpdate(true);
    });

    // Data Entry -> Debounced Rebuild
    document.querySelectorAll('.input-form').forEach(form => {
        form.addEventListener('input', () => handleUpdate(false));
    });

    // Download Handler
    downloadBtn.addEventListener('click', () => {
        const format = getFormat();

        if (format === 'png') {
            const img = qrContainer.querySelector('img');
            if (img && img.src) {
                const link = document.createElement('a');
                link.href = img.src;
                link.download = `qr-manifesto-${Date.now()}.png`;
                document.body.appendChild(link);
                link.click();
                link.remove();
            }
        } else {
            const svgEl = qrContainer.querySelector('svg');
            if (svgEl) {
                const serializer = new XMLSerializer();
                const svgString = serializer.serializeToString(svgEl);
                const blob = new Blob([svgString], {type: 'image/svg+xml;charset=utf-8'});
                const url = URL.createObjectURL(blob);
                const link = document.createElement('a');
                link.href = url;
                link.download = `qr-manifesto-${Date.now()}.svg`;
                document.body.appendChild(link);
                link.click();
                link.remove();
            }
        }
    });

    // Initial Render
    handleUpdate(true);
});