fix: correct rounding drift, XSS hazard, nookPct coupling, confirm guard, BE filename

- Rounding drift: last installment computed as remainder (contract - cumSoFar) so column sums match exactly
- XSS: input values set via .value property assignment instead of attribute interpolation in innerHTML
- nookPct: getInputs() now derives nookPct as 100 - ngpmPct (single source of truth)
- Confirm guard: onCountChange only prompts when n differs from current installments.length
- Export filename: uses Buddhist Era year (getFullYear() + 543) consistent with all date displays

construction-installment-calculator/index.html

@@ -281,11 +281,12 @@ function toThaiDate(date) {
 }
 
 function getInputs() {
+  const ngpmPct = parseFloat(document.getElementById('ngpmPct').value) || 0;
   return {
     contract: parseAmount(document.getElementById('contractAmount').value),
     startDate: document.getElementById('startDate').value,
-    ngpmPct: parseFloat(document.getElementById('ngpmPct').value) || 0,
-    nookPct: parseFloat(document.getElementById('nookPct').value) || 0,
+    ngpmPct,
+    nookPct: 100 - ngpmPct,
   };
 }
 
@@ -299,12 +300,18 @@ function recalcAll() {
   installments.forEach((inst, i) => {
     const days = parseFloat(inst.days) || 0;
     const pct  = parseFloat(inst.percent) || 0;
+    const isLast = i === installments.length - 1;
     cumDays += days;
     sumPct  += pct;
 
-    const total = contract > 0 ? Math.round(contract * pct / 100) : 0;
-    const ngpm  = Math.round(total * ngpmPct / 100);
-    const nook  = total - ngpm;
+    let total, ngpm, nook;
+    if (contract > 0) {
+      total = isLast ? (contract - cumTotal) : Math.round(contract * pct / 100);
+      ngpm  = isLast ? (Math.round(contract * ngpmPct / 100) - cumNgpm) : Math.round(total * ngpmPct / 100);
+      nook  = total - ngpm;
+    } else {
+      total = 0; ngpm = 0; nook = 0;
+    }
     cumTotal += total; cumNgpm += ngpm; cumNook += nook;
 
     const deliveryDate = hasStart ? toThaiDate(addDays(startDate, cumDays)) : '—';
@@ -360,12 +367,12 @@ function renderTable() {
     tr.innerHTML = `
       <td class="center">${i + 1}</td>
       <td class="editable-cell">
-        <input type="number" value="${inst.days}" min="0"
+        <input type="number" class="inp-days" min="0"
           onchange="installments[${i}].days=this.value; recalcAll()"
           oninput="installments[${i}].days=this.value; recalcAll()">
       </td>
       <td class="editable-cell">
-        <input type="number" value="${inst.percent}" min="0" max="100" step="0.01"
+        <input type="number" class="inp-pct" min="0" max="100" step="0.01"
           onchange="installments[${i}].percent=this.value; recalcAll()"
           oninput="installments[${i}].percent=this.value; recalcAll()">
       </td>
@@ -380,6 +387,9 @@ function renderTable() {
         <button class="btn-del" onclick="deleteRow(${i})" title="ลบงวดนี้">✕</button>
       </td>
     `;
+    // Set values safely via property assignment (not attribute interpolation)
+    tr.querySelector('.inp-days').value = inst.days;
+    tr.querySelector('.inp-pct').value = inst.percent;
     tbody.appendChild(tr);
   });
 
@@ -416,7 +426,7 @@ function deleteRow(i) {
 function onCountChange(n) {
   n = parseInt(n) || 1;
   if (n < 1) n = 1;
-  if (installments.length > 0) {
+  if (n !== installments.length && installments.length > 0) {
     if (!confirm(`การเปลี่ยนจำนวนงวดเป็น ${n} งวด จะล้างข้อมูลเดิม ต้องการดำเนินการต่อไหม?`)) {
       document.getElementById('installmentCount').value = installments.length;
       return;
@@ -472,7 +482,7 @@ function exportExcel() {
   XLSX.utils.book_append_sheet(wb, ws, 'งวดงาน');
 
   const today = new Date();
-  const fname = `งวดงาน_${today.getFullYear()}${String(today.getMonth()+1).padStart(2,'0')}${String(today.getDate()).padStart(2,'0')}.xlsx`;
+  const fname = `งวดงาน_${today.getFullYear()+543}${String(today.getMonth()+1).padStart(2,'0')}${String(today.getDate()).padStart(2,'0')}.xlsx`;
   XLSX.writeFile(wb, fname);
 }