// Version: v5
document.addEventListener('DOMContentLoaded', () => {
    const printBtn = document.getElementById('printBtn');
    const clearBtn = document.getElementById('clearBtn');

    // Set default date to current date
    const today = new Date().toISOString().split('T')[0];
    invoiceDateInput.value = today;

    // Set default invoice number
    invoiceNumberInput.value = "001";

    // Event Listeners for input changes
    invoiceDateInput.addEventListener('change', updateInvoice);
    invoiceNumberInput.addEventListener('change', updateInvoice);
    courseTopicSelect.addEventListener('change', updateInvoice); // Listen to new dropdown

    // Print button functionality with validation
    printBtn.addEventListener('click', () => {
        if (!invoiceDateInput.value || !invoiceNumberInput.value || !courseTopicSelect.value) {
            alert('Please fill in all required fields: Date, Invoice Number, and Topic.');
            return;
        }

        // Generate file name in the format: GST_Invoice_INV-MM-DD-YYYY.pdf
        const dt = new Date(invoiceDateInput.value);
        const MM = String(dt.getMonth() + 1).padStart(2, '0');
        const DD = String(dt.getDate()).padStart(2, '0');
        const YYYY = dt.getFullYear();
        const invoiceNum = invoiceNumberInput.value; // Assuming this holds the invoice number
        const generatedFileName = `GST_Invoice_${invoiceNum}-${MM}-${DD}-${YYYY}.pdf`;
        console.log('Generated file name:', generatedFileName);

        // Set document title to the filename (without .pdf) for dynamic PDF save name
        document.title = `GST_Invoice_${invoiceNum}-${MM}-${DD}-${YYYY}`;

        // First, ensure the invoice content is fully updated
        updateInvoice();
        // Then, trigger the print dialog
        window.print();
    });

    // Clear button functionality
    clearBtn.addEventListener('click', () => {
        // Clear all input fields and reset the invoice display
        invoiceDateInput.value = today;
        invoiceNumberInput.value = "001";
        courseTopicSelect.value = '';
        // Call updateInvoice to reset displayed values to their defaults
        updateInvoice();
    });

    // Initial population of the dropdown when the page loads
    populateTopicsDropdown();
    // Initial invoice update to show default values
    updateInvoice();
});