script.js

document.getElementById('generateBtn').addEventListener('click', generateQR);
document.getElementById('copyBtn').addEventListener('click', copyToClipboard);

// Set default timestamp to current time
const now = new Date();
now.setMinutes(now.getMinutes() - now.getTimezoneOffset());
document.getElementById('timestamp').value = now.toISOString().slice(0, 19);

function generateQR() {
    const sellerName = document.getElementById('sellerName').value.trim();
    const vatNumber = document.getElementById('vatNumber').value.trim();
    let timestamp = document.getElementById('timestamp').value;
    const invoiceTotal = document.getElementById('invoiceTotal').value.trim();
    const vatTotal = document.getElementById('vatTotal').value.trim();

    if (!sellerName || !vatNumber || !timestamp || !invoiceTotal || !vatTotal) {
        alert('Please fill in all fields');
        return;
    }

    // Format timestamp to YYYY-MM-DDTHH:MM:SSZ if needed, or keep as is.
    // datetime-local gives YYYY-MM-DDTHH:MM:SS
    // ZATCA often expects 'Z' at the end if it's UTC, or just the string. 
    // Let's ensure it has seconds and append 'Z' to match the previous default format for consistency,
    // assuming the user wants to treat the picked time as the invoice time.
    // A simple approach is to just ensure it looks like an ISO string.
    if (timestamp.length === 16) {
        timestamp += ':00'; // Add seconds if missing
    }
    if (!timestamp.endsWith('Z')) {
        timestamp += 'Z'; // Append Z to indicate ISO format (UTC)
    }

    // 1. Seller Name
    const tag1 = getTLV(1, sellerName);
    // 2. VAT Registration Number
    const tag2 = getTLV(2, vatNumber);
    // 3. Time Stamp
    const tag3 = getTLV(3, timestamp);
    // 4. Invoice Total
    const tag4 = getTLV(4, invoiceTotal);
    // 5. VAT Total
    const tag5 = getTLV(5, vatTotal);

    // Concatenate all TLV buffers
    const allTags = concatenateBuffers([tag1, tag2, tag3, tag4, tag5]);

    // Base64 Encode
    const base64 = arrayBufferToBase64(allTags);

    // Display
    const outputSection = document.getElementById('outputSection');
    const textarea = document.getElementById('qrOutput');
    outputSection.classList.remove('hidden');
    textarea.value = base64;
}

function getTLV(tag, value) {
    const encoder = new TextEncoder();
    const valBytes = encoder.encode(value);
    const length = valBytes.length;
    
    // Tag is 1 byte
    const tagByte = new Uint8Array([tag]);
    
    // Length is 1 byte (assuming < 256 for this simple app)
    const lenByte = new Uint8Array([length]);
    
    return concatenateBuffers([tagByte, lenByte, valBytes]);
}

function concatenateBuffers(arrays) {
    let totalLength = 0;
    for (const arr of arrays) {
        totalLength += arr.length;
    }
    const result = new Uint8Array(totalLength);
    let offset = 0;
    for (const arr of arrays) {
        result.set(arr, offset);
        offset += arr.length;
    }
    return result;
}

function arrayBufferToBase64(buffer) {
    let binary = '';
    const bytes = new Uint8Array(buffer);
    const len = bytes.byteLength;
    for (let i = 0; i < len; i++) {
        binary += String.fromCharCode(bytes[i]);
    }
    return window.btoa(binary);
}

function copyToClipboard() {
    const textarea = document.getElementById('qrOutput');
    textarea.select();
    document.execCommand('copy'); // Fallback for older browsers or non-secure contexts
    
    // Modern API
    if (navigator.clipboard) {
        navigator.clipboard.writeText(textarea.value).then(() => {
            const btn = document.getElementById('copyBtn');
            const originalText = btn.innerText;
            btn.innerText = 'Copied!';
            setTimeout(() => {
                btn.innerText = originalText;
            }, 2000);
        });
    }
}