/**
 * Auto-calculates invoice Due Date from Invoice Date + Payment Terms.
 * Parses common terms formats: "Net 30", "N/15", "Due on Receipt", "COD", "2% 10 Net 30".
 * Only fires when Terms or Invoice Date changes; user can always override the Due Date field.
 */
(function () {
    /// <summary>
    /// Extracts the net payment days from a free-text terms string.
    /// Returns null when the string can't be parsed (due date is left unchanged).
    /// </summary>
    function parseDays(terms) {
        if (!terms || !terms.trim()) return null;
        const t = terms.trim().toLowerCase();
        if (/\b(receipt|due\s*now|cod|immediate)\b/.test(t)) return 0;
        // "Net N" or "N/N" (e.g., "2% 10 Net 30" or "N/30")
        let m = t.match(/\bnet\s+(\d+)/) || t.match(/\bn\/(\d+)/);
        if (m) return parseInt(m[1], 10);
        // Plain number (e.g., "30 days", "30")
        m = t.match(/\b(\d+)\b/);
        if (m) return parseInt(m[1], 10);
        return null;
    }

    function recalcDueDate() {
        const termsEl = document.getElementById('Terms');
        const invoiceDateEl = document.getElementById('InvoiceDate');
        const dueDateEl = document.getElementById('DueDate');
        if (!termsEl || !invoiceDateEl || !dueDateEl) return;

        const days = parseDays(termsEl.value);
        if (days === null) return;

        const rawDate = invoiceDateEl.value;
        if (!rawDate) return;

        // Parse as local date to avoid UTC-offset shifting the day
        const [y, mo, d] = rawDate.split('-').map(Number);
        const due = new Date(y, mo - 1, d + days);
        const yyyy = due.getFullYear();
        const mm = String(due.getMonth() + 1).padStart(2, '0');
        const dd = String(due.getDate()).padStart(2, '0');
        dueDateEl.value = `${yyyy}-${mm}-${dd}`;
    }

    document.addEventListener('DOMContentLoaded', function () {
        const termsEl = document.getElementById('Terms');
        const invoiceDateEl = document.getElementById('InvoiceDate');
        if (termsEl) {
            termsEl.addEventListener('change', recalcDueDate);
            termsEl.addEventListener('blur', recalcDueDate);
        }
        if (invoiceDateEl) {
            invoiceDateEl.addEventListener('change', recalcDueDate);
        }
    });
})();