Merge pull request 'feat(po): TCS & Discount below GST (#133)' (#149) from claude/issue-133-tcs-discount into master

Reviewed-on: #149

App/CLAUDE.md

@@ -267,7 +267,17 @@ A crew-management module built incrementally per the **wiki `Crewing-Implementat
 
 ### GST Calculation
 
-`totalAmount = sum(quantity × unitPrice × (1 + gstRate))` for each line item. The `gstRate` is stored as a decimal on `POLineItem` (e.g., `0.18` = 18%). This applies in Server Actions when computing `totalPrice` per line and the PO `totalAmount`.
+Per line item: `lineInclGst = quantity × unitPrice × (1 + gstRate)`. The `gstRate` is stored as a decimal on `POLineItem` (e.g., `0.18` = 18%).
+
+**TCS & Discount (issue #133):** two **PO-level** charges shown below GST, stored as **absolute** rupee amounts on `PurchaseOrder.tcsAmount` / `discountAmount` (`Decimal?`, default 0; null/0 on historical & imported POs). The PO forms offer a percentage control bidirectionally linked to the rupee value (a convenience — only the absolute amount is persisted); discount is applied **post-GST**.
+
+`totalAmount` **folds the charges in** — it is the net payable:
+
+```
+totalAmount = Σ(quantity × unitPrice × (1 + gstRate)) + tcsAmount − discountAmount
+```
+
+So payments, reports, and the advance-payment slider all operate on the true amount due. The single source of truth for this math is **`lib/po-money.ts`** (`computePoMoney` / `poNetPayable`), used by `createPo`, `updatePo`, import, both manager-edit actions (which **preserve** the PO's existing TCS/Discount when recomputing), the PO detail/forms, and the PDF/XLSX export.
 
 ### Environment Variables
 

App/app/(portal)/approvals/[id]/manager-line-edit-actions.ts

@@ -3,6 +3,7 @@
 import { auth } from "@/auth";
 import { db } from "@/lib/db";
 import { hasPermission } from "@/lib/permissions";
+import { poNetPayable } from "@/lib/po-money";
 import { revalidatePath } from "next/cache";
 import { z } from "zod";
 
@@ -49,9 +50,12 @@ export async function managerEditLineItems({
     unitPrice: Number(li.unitPrice),
   }));
 
-  const newTotal = parsed.data.reduce(
+  // Recompute the total from the edited line items, preserving the PO-level
-    (sum, item) => sum + item.quantity * item.unitPrice * (1 + item.gstRate),
+  // TCS / Discount charges (#133) so a manager line edit doesn't drop them.
-    0
+  const newTotal = poNetPayable(
+    parsed.data,
+    Number(po.tcsAmount ?? 0),
+    Number(po.discountAmount ?? 0)
   );
 
   await db.purchaseOrder.update({

App/app/(portal)/approvals/[id]/manager-po-edit-actions.ts

@@ -4,6 +4,7 @@ import { auth } from "@/auth";
 import { db } from "@/lib/db";
 import { hasPermission } from "@/lib/permissions";
 import { createPoSchema } from "@/lib/validations/po";
+import { poNetPayable } from "@/lib/po-money";
 import { parsePoTerms } from "@/lib/terms";
 import { revalidatePath } from "next/cache";
 
@@ -73,9 +74,11 @@ export async function managerEditPo(
   try { termsRaw = JSON.parse((formData.get("termsJson") as string) || "[]"); } catch { /* ignore */ }
   const terms = parsePoTerms(termsRaw);
 
-  const newTotal = data.lineItems.reduce(
+  // Preserve PO-level TCS / Discount charges (#133) when recomputing the total.
-    (sum, item) => sum + item.quantity * item.unitPrice * (1 + item.gstRate),
+  const newTotal = poNetPayable(
-    0
+    data.lineItems,
+    Number(po.tcsAmount ?? 0),
+    Number(po.discountAmount ?? 0)
   );
 
   // Snapshot all original values for the audit trail

App/app/(portal)/po/[id]/edit/actions.ts

@@ -3,6 +3,7 @@
 import { auth } from "@/auth";
 import { db } from "@/lib/db";
 import { createPoSchema } from "@/lib/validations/po";
+import { poNetPayable } from "@/lib/po-money";
 import { parsePoTerms } from "@/lib/terms";
 import { notify } from "@/lib/notifier";
 import { revalidatePath } from "next/cache";
@@ -64,6 +65,8 @@ export async function updatePo(
     tcTransitInsurance: formData.get("tcTransitInsurance") || undefined,
     tcPaymentTerms: formData.get("tcPaymentTerms") || undefined,
     tcOthers: formData.get("tcOthers") || undefined,
+    tcsAmount: formData.get("tcsAmount") || undefined,
+    discountAmount: formData.get("discountAmount") || undefined,
     lineItems: parseLineItems(formData),
   });
 
@@ -77,10 +80,8 @@ export async function updatePo(
   try { termsRaw = JSON.parse((formData.get("termsJson") as string) || "[]"); } catch { /* ignore */ }
   const terms = parsePoTerms(termsRaw);
 
-  const total = data.lineItems.reduce(
+  // totalAmount = subtotal + GST + TCS − Discount (#133)
-    (sum, item) => sum + item.quantity * item.unitPrice * (1 + item.gstRate),
+  const total = poNetPayable(data.lineItems, data.tcsAmount, data.discountAmount);
-    0
-  );
 
   const isSubmit   = intent === "submit"   && po.status === "DRAFT";
   const isResubmit = intent === "resubmit" && po.status === "EDITS_REQUESTED";
@@ -164,6 +165,8 @@ export async function updatePo(
       tcOthers: data.tcOthers ?? null,
       terms,
       totalAmount: total,
+      tcsAmount: data.tcsAmount,
+      discountAmount: data.discountAmount,
       status: shouldSubmit ? "MGR_REVIEW" : "DRAFT",
       submittedAt: shouldSubmit ? new Date() : po.submittedAt,
       lineItems: {

App/app/(portal)/po/[id]/edit/edit-po-form.tsx

@@ -11,7 +11,9 @@ import { VendorSelect } from "@/components/ui/vendor-select";
 import { DeliveryLocationField } from "@/components/po/delivery-location-field";
 import { ProjectCodeField } from "@/components/po/project-code-field";
 import { PoTermsEditor } from "@/components/po/po-terms-editor";
+import { TcsDiscountFields } from "@/components/po/tcs-discount-fields";
 import { UnsavedChangesGuard } from "@/components/po/unsaved-changes-guard";
+import { computePoMoney } from "@/lib/po-money";
 import type { CatalogueCategory, PoTerm } from "@/lib/terms";
 import type { LineItemInput } from "@/lib/validations/po";
 
@@ -34,8 +36,10 @@ type SerializedLineItem = {
   accountId: string | null;
 };
 
-type PoWithItems = Omit<PurchaseOrder, "totalAmount"> & {
+type PoWithItems = Omit<PurchaseOrder, "totalAmount" | "tcsAmount" | "discountAmount"> & {
   totalAmount: number;
+  tcsAmount: number;
+  discountAmount: number;
   lineItems: SerializedLineItem[];
 };
 
@@ -72,6 +76,8 @@ export function EditPoForm({ po, vessels, accounts, vendors, companies, delivery
   const [multiAccount, setMultiAccount] = useState(hasPerLineAccounts);
   const [defaultAccountId, setDefaultAccountId] = useState(po.accountId ?? "");
   const [terms, setTerms] = useState<PoTerm[]>(initialTerms);
+  const [tcs, setTcs] = useState(po.tcsAmount ?? 0);
+  const [discount, setDiscount] = useState(po.discountAmount ?? 0);
   const [dirty, setDirty] = useState(false);
   const markDirty = () => setDirty(true);
 
@@ -85,6 +91,8 @@ export function EditPoForm({ po, vessels, accounts, vendors, companies, delivery
     const data = new FormData(form);
     data.set("intent", intent);
     data.set("termsJson", JSON.stringify(terms));
+    data.set("tcsAmount", String(tcs));
+    data.set("discountAmount", String(discount));
     lineItems.forEach((item, i) => {
       data.set(`lineItems[${i}].name`, item.name);
       data.set(`lineItems[${i}].description`, item.description ?? "");
@@ -259,6 +267,20 @@ export function EditPoForm({ po, vessels, accounts, vendors, companies, delivery
         />
       </section>
 
+      {/* Charges (TCS & Discount, below GST) */}
+      <section className="rounded-lg border border-neutral-200 bg-white p-6">
+        <h2 className="text-base font-semibold text-neutral-900 mb-4">Charges</h2>
+        <TcsDiscountFields
+          base={computePoMoney(lineItems).inclGst}
+          currency={po.currency}
+          tcs={tcs}
+          discount={discount}
+          onTcsChange={(v) => { setTcs(v); markDirty(); }}
+          onDiscountChange={(v) => { setDiscount(v); markDirty(); }}
+          disabled={!!submitting}
+        />
+      </section>
+
       {/* Vendor */}
       <section className="rounded-lg border border-neutral-200 bg-white p-6">
         <h2 className="text-base font-semibold text-neutral-900 mb-4">Vendor</h2>

App/app/(portal)/po/[id]/edit/page.tsx

@@ -62,6 +62,8 @@ export default async function EditPoPage({ params }: Props) {
   const serializedPo = {
     ...po,
     totalAmount: po.totalAmount.toNumber(),
+    tcsAmount: po.tcsAmount ? po.tcsAmount.toNumber() : 0,
+    discountAmount: po.discountAmount ? po.discountAmount.toNumber() : 0,
     lineItems: po.lineItems.map((li) => ({
       ...li,
       quantity: li.quantity.toNumber(),

App/app/(portal)/po/new/actions.ts

@@ -6,6 +6,7 @@ import { requirePermission } from "@/lib/permissions";
 import { createPoSchema } from "@/lib/validations/po";
 import { parsePoTerms } from "@/lib/terms";
 import { generatePoNumber } from "@/lib/po-number";
+import { poNetPayable } from "@/lib/po-money";
 import { notify } from "@/lib/notifier";
 import { revalidatePath } from "next/cache";
 
@@ -70,6 +71,8 @@ export async function createPo(
     tcTransitInsurance: formData.get("tcTransitInsurance") || undefined,
     tcPaymentTerms: formData.get("tcPaymentTerms") || undefined,
     tcOthers: formData.get("tcOthers") || undefined,
+    tcsAmount: formData.get("tcsAmount") || undefined,
+    discountAmount: formData.get("discountAmount") || undefined,
     lineItems,
   });
 
@@ -83,11 +86,8 @@ export async function createPo(
   try { termsRaw = JSON.parse((formData.get("termsJson") as string) || "[]"); } catch { /* ignore */ }
   const terms = parsePoTerms(termsRaw);
 
-  // totalAmount = grand total including GST
+  // totalAmount = subtotal + GST + TCS − Discount (PO-level charges below GST, #133)
-  const total = data.lineItems.reduce(
+  const total = poNetPayable(data.lineItems, data.tcsAmount, data.discountAmount);
-    (sum, item) => sum + item.quantity * item.unitPrice * (1 + item.gstRate),
-    0
-  );
 
   const po = await db.purchaseOrder.create({
     data: {
@@ -95,6 +95,8 @@ export async function createPo(
       title: data.title,
       status: intent === "submit" ? "SUBMITTED" : "DRAFT",
       totalAmount: total,
+      tcsAmount: data.tcsAmount,
+      discountAmount: data.discountAmount,
       currency: data.currency,
       vesselId: data.vesselId,
       accountId: data.accountId,

App/app/(portal)/po/new/new-po-form.tsx

@@ -11,6 +11,8 @@ import { VendorSelect } from "@/components/ui/vendor-select";
 import { DeliveryLocationField } from "@/components/po/delivery-location-field";
 import { ProjectCodeField } from "@/components/po/project-code-field";
 import { PoTermsEditor } from "@/components/po/po-terms-editor";
+import { TcsDiscountFields } from "@/components/po/tcs-discount-fields";
+import { computePoMoney } from "@/lib/po-money";
 import { UnsavedChangesGuard } from "@/components/po/unsaved-changes-guard";
 import type { CatalogueCategory, PoTerm } from "@/lib/terms";
 import { uploadPoDocuments } from "@/app/actions/upload-po-documents";
@@ -58,6 +60,8 @@ export function NewPoForm({ vessels, accounts, vendors, companies, deliveryOptio
     initialLineItems && initialLineItems.length > 0 ? initialLineItems : [EMPTY_LINE]
   );
   const [files, setFiles] = useState<File[]>([]);
+  const [tcs, setTcs] = useState(0);
+  const [discount, setDiscount] = useState(0);
   const [submitting, setSubmitting] = useState<"draft" | "submit" | null>(null);
   const [error, setError] = useState("");
   const [multiAccount, setMultiAccount] = useState(initialMultiAccount ?? false);
@@ -75,6 +79,8 @@ export function NewPoForm({ vessels, accounts, vendors, companies, deliveryOptio
     const data = new FormData(form);
     data.set("intent", intent);
     data.set("termsJson", JSON.stringify(terms));
+    data.set("tcsAmount", String(tcs));
+    data.set("discountAmount", String(discount));
     lineItems.forEach((item, i) => {
       data.set(`lineItems[${i}].name`, item.name);
       data.set(`lineItems[${i}].description`, item.description ?? "");
@@ -247,6 +253,20 @@ export function NewPoForm({ vessels, accounts, vendors, companies, deliveryOptio
         />
       </section>
 
+      {/* Charges (TCS & Discount, below GST) */}
+      <section className="rounded-lg border border-neutral-200 bg-white p-6">
+        <h2 className="text-base font-semibold text-neutral-900 mb-4">Charges</h2>
+        <TcsDiscountFields
+          base={computePoMoney(lineItems).inclGst}
+          currency="INR"
+          tcs={tcs}
+          discount={discount}
+          onTcsChange={(v) => { setTcs(v); markDirty(); }}
+          onDiscountChange={(v) => { setDiscount(v); markDirty(); }}
+          disabled={!!submitting}
+        />
+      </section>
+
       {/* Vendor */}
       <section className="rounded-lg border border-neutral-200 bg-white p-6">
         <h2 className="text-base font-semibold text-neutral-900 mb-4">Vendor</h2>

App/app/api/po/[id]/export/route.ts

@@ -136,7 +136,11 @@ export async function GET(request: NextRequest, { params }: Props) {
 
   const totalTaxable = items.reduce((s, i) => s + i.taxable, 0);
   const totalGst     = items.reduce((s, i) => s + i.gstAmt, 0);
-  const grandTotal   = totalTaxable + totalGst;
+  const inclGst      = totalTaxable + totalGst;
+  // PO-level charges shown below GST (#133). Net payable = incl-GST + TCS − Discount.
+  const tcsAmount      = Number(po.tcsAmount ?? 0);
+  const discountAmount = Number(po.discountAmount ?? 0);
+  const grandTotal     = inclGst + tcsAmount - discountAmount;
 
   const approvalAction = [...po.actions].reverse()
     .find(a => a.actionType === "APPROVED" || a.actionType === "APPROVED_WITH_NOTE");
@@ -436,31 +440,30 @@ export async function GET(request: NextRequest, { params }: Props) {
     }
 
     // ══ Totals ════════════════════════════════════════════════════════════
+    // Rows: taxable, GST, optional TCS / Discount (#133), then GRAND TOTAL.
     const TOT_ROW = HDR_ROW + 1 + BODY_ROWS + 1;
-    ws.getRow(TOT_ROW).height     = 14;
+    const totalRows: Array<{ label: string; value: number; grand?: boolean }> = [
-    ws.getRow(TOT_ROW + 1).height = 14;
+      { label: "Total taxable value", value: totalTaxable },
-    ws.getRow(TOT_ROW + 2).height = 16;
+      { label: gstLabel, value: totalGst },
+    ];
+    if (tcsAmount > 0) totalRows.push({ label: "TCS", value: tcsAmount });
+    if (discountAmount > 0) totalRows.push({ label: "Discount", value: -discountAmount });
+    totalRows.push({ label: "GRAND TOTAL", value: grandTotal, grand: true });
 
-    // "Total taxable value"
+    totalRows.forEach((row, i) => {
-    sc(TOT_ROW, 6, "Total taxable value", { font: fBold, fill: fillTot, border: bordAll, align: alignR });
+      const r = TOT_ROW + i;
-    ws.mergeCells(`F${TOT_ROW}:G${TOT_ROW}`);
+      ws.getRow(r).height = row.grand ? 16 : 14;
-    sc(TOT_ROW, 8, totalTaxable, { font: fBold, fill: fillTot, border: bordAll, align: alignR, numFmt: NUM_FMT });
+      const font = row.grand ? { ...fBold, size: 10 } : fBold;
-    ws.mergeCells(`H${TOT_ROW}:I${TOT_ROW}`);
+      const fill = row.grand ? fillGT : fillTot;
-
+      sc(r, 6, row.label, { font, fill, border: bordAll, align: alignR });
-    // "GST"
+      ws.mergeCells(`F${r}:G${r}`);
-    sc(TOT_ROW + 1, 6, gstLabel, { font: fBold, fill: fillTot, border: bordAll, align: alignR });
+      sc(r, 8, row.value, { font, fill, border: bordAll, align: alignR, numFmt: NUM_FMT });
-    ws.mergeCells(`F${TOT_ROW + 1}:G${TOT_ROW + 1}`);
+      ws.mergeCells(`H${r}:I${r}`);
-    sc(TOT_ROW + 1, 8, totalGst, { font: fBold, fill: fillTot, border: bordAll, align: alignR, numFmt: NUM_FMT });
+    });
-    ws.mergeCells(`H${TOT_ROW + 1}:I${TOT_ROW + 1}`);
+    const GT_ROW = TOT_ROW + totalRows.length - 1;
-
-    // "GRAND TOTAL"
-    sc(TOT_ROW + 2, 6, "GRAND TOTAL", { font: { ...fBold, size: 10 }, fill: fillGT, border: bordAll, align: alignR });
-    ws.mergeCells(`F${TOT_ROW + 2}:G${TOT_ROW + 2}`);
-    sc(TOT_ROW + 2, 8, grandTotal, { font: { ...fBold, size: 10 }, fill: fillGT, border: bordAll, align: alignR, numFmt: NUM_FMT });
-    ws.mergeCells(`H${TOT_ROW + 2}:I${TOT_ROW + 2}`);
 
     // ══ Instructions ═════════════════════════════════════════════════════
-    const INST_ROW = TOT_ROW + 4;
+    const INST_ROW = GT_ROW + 2;
     ws.getRow(INST_ROW).height = 16;
     sc(INST_ROW, 1, "INSTRUCTIONS TO VENDORS", { font: { ...fBold, size: 10 }, fill: fillInst, border: bordAll, align: alignC });
     ws.mergeCells(`A${INST_ROW}:I${INST_ROW}`);
@@ -868,6 +871,14 @@ ${cleanPdf ? "" : `<div class="no-print" style="margin-bottom:8px">
     <td class="tot-lbl">${gstLabel}</td>
     <td class="tot-val">${fmtNum(totalGst)}</td>
   </tr>
+  ${tcsAmount > 0 ? `<tr>
+    <td class="tot-lbl">TCS</td>
+    <td class="tot-val">${fmtNum(tcsAmount)}</td>
+  </tr>` : ""}
+  ${discountAmount > 0 ? `<tr>
+    <td class="tot-lbl">Discount</td>
+    <td class="tot-val">-${fmtNum(discountAmount)}</td>
+  </tr>` : ""}
   <tr>
     <td class="gt-lbl">GRAND TOTAL</td>
     <td class="gt-val">${fmtNum(grandTotal)}</td>

App/components/po/po-detail.tsx

@@ -22,6 +22,8 @@ type PoWithRelations = {
   title: string;
   status: import("@prisma/client").POStatus;
   totalAmount: import("@prisma/client").Prisma.Decimal;
+  tcsAmount?: import("@prisma/client").Prisma.Decimal | null;
+  discountAmount?: import("@prisma/client").Prisma.Decimal | null;
   currency: string;
   poDate: Date | null;
   projectCode: string | null;
@@ -154,6 +156,15 @@ export async function PoDetail({ po, currentUserId, currentRole, readOnly = fals
   );
   const attachmentGroups = groupAttachments(docsWithUrls);
 
+  // PO-level charges shown below GST (#133). totalAmount already folds these in.
+  const tcsAmount = Number(po.tcsAmount ?? 0);
+  const discountAmount = Number(po.discountAmount ?? 0);
+  const hasCharges = tcsAmount > 0 || discountAmount > 0;
+  const itemsInclGst = po.lineItems.reduce(
+    (s, li) => s + Number(li.quantity) * Number(li.unitPrice) * (1 + Number(li.gstRate ?? 0.18)),
+    0
+  );
+
   // Feature-flagged: the PO's submitter (or Accounts / Manager / SuperUser) may add
   // attachments after the fact, in any state except rejected/cancelled. Never in
   // readOnly. The server action re-checks this permission.
@@ -459,6 +470,30 @@ export async function PoDetail({ po, currentUserId, currentRole, readOnly = fals
           originalItems={originalLineItems}
           originalItemsLabel={lineItemsDiffLabel}
         />
+        {hasCharges && (
+          <dl className="mt-4 ml-auto w-full max-w-xs space-y-1 text-sm">
+            <div className="flex justify-between">
+              <dt className="text-neutral-500">Total (incl. GST)</dt>
+              <dd className="text-neutral-700">{formatCurrency(itemsInclGst, po.currency)}</dd>
+            </div>
+            {tcsAmount > 0 && (
+              <div className="flex justify-between">
+                <dt className="text-neutral-500">TCS</dt>
+                <dd className="text-neutral-700">+ {formatCurrency(tcsAmount, po.currency)}</dd>
+              </div>
+            )}
+            {discountAmount > 0 && (
+              <div className="flex justify-between">
+                <dt className="text-neutral-500">Discount</dt>
+                <dd className="text-neutral-700">− {formatCurrency(discountAmount, po.currency)}</dd>
+              </div>
+            )}
+            <div className="flex justify-between border-t border-neutral-100 pt-1 font-semibold text-neutral-900">
+              <dt>Net payable</dt>
+              <dd>{formatCurrency(Number(po.totalAmount), po.currency)}</dd>
+            </div>
+          </dl>
+        )}
       </div>
 
       {/* Terms & Conditions (issue #11): dynamic snapshot when present, else legacy tc* + fixed line. */}

App/components/po/tcs-discount-fields.tsx

@@ -0,0 +1,123 @@
+"use client";
+
+import { formatCurrency } from "@/lib/utils";
+import { amountToPercent, percentToAmount } from "@/lib/po-money";
+
+/**
+ * PO-level TCS and Discount charges, shown below GST (issue #133).
+ *
+ * Each charge is entered as an absolute rupee amount **or** as a percentage of the
+ * GST-inclusive line-items total (`base`) — the two are bidirectionally linked.
+ * Only the absolute amount is stored (the parent persists `tcs` / `discount`); the
+ * percentage is a convenience. Discount is applied post-GST.
+ */
+interface Props {
+  base: number; // GST-inclusive line-items total — the % base
+  currency: string;
+  tcs: number;
+  discount: number;
+  onTcsChange: (amount: number) => void;
+  onDiscountChange: (amount: number) => void;
+  disabled?: boolean;
+}
+
+const INPUT =
+  "w-full rounded-lg border border-neutral-300 px-3 py-2 text-sm focus:border-primary-500 focus:outline-none focus:ring-2 focus:ring-primary-500/20";
+
+function round2(n: number): number {
+  return Math.round((n + Number.EPSILON) * 100) / 100;
+}
+
+function ChargeRow({
+  label,
+  hint,
+  base,
+  value,
+  onChange,
+  disabled,
+}: {
+  label: string;
+  hint: string;
+  base: number;
+  value: number;
+  onChange: (amount: number) => void;
+  disabled?: boolean;
+}) {
+  const percent = round2(amountToPercent(value, base));
+
+  return (
+    <div className="grid grid-cols-1 gap-3 sm:grid-cols-[1fr_auto_auto] sm:items-end">
+      <div>
+        <label className="block text-sm font-medium text-neutral-700 mb-1.5">{label}</label>
+        <p className="text-xs text-neutral-400">{hint}</p>
+      </div>
+      <div className="sm:w-40">
+        <label className="block text-xs text-neutral-500 mb-1">Amount (₹)</label>
+        <input
+          type="number"
+          min={0}
+          step="0.01"
+          value={value === 0 ? "" : value}
+          placeholder="0.00"
+          disabled={disabled}
+          onChange={(e) => onChange(Math.max(0, Number(e.target.value) || 0))}
+          className={INPUT}
+        />
+      </div>
+      <div className="sm:w-32">
+        <label className="block text-xs text-neutral-500 mb-1">% of total</label>
+        <input
+          type="number"
+          min={0}
+          step="0.01"
+          value={percent === 0 ? "" : percent}
+          placeholder="0"
+          disabled={disabled || base === 0}
+          onChange={(e) => onChange(round2(percentToAmount(Number(e.target.value) || 0, base)))}
+          className={INPUT}
+        />
+      </div>
+    </div>
+  );
+}
+
+export function TcsDiscountFields({
+  base,
+  currency,
+  tcs,
+  discount,
+  onTcsChange,
+  onDiscountChange,
+  disabled,
+}: Props) {
+  const netPayable = base + (tcs || 0) - (discount || 0);
+
+  return (
+    <div className="space-y-5">
+      <p className="text-xs text-neutral-400">
+        Optional charges applied after GST. Enter a rupee amount or a percentage of the
+        GST-inclusive total — they stay in sync. Stored as an absolute amount.
+      </p>
+      <ChargeRow
+        label="TCS"
+        hint="Tax Collected at Source, added to the total."
+        base={base}
+        value={tcs}
+        onChange={onTcsChange}
+        disabled={disabled}
+      />
+      <ChargeRow
+        label="Discount"
+        hint="Applied post-GST, subtracted from the total."
+        base={base}
+        value={discount}
+        onChange={onDiscountChange}
+        disabled={disabled}
+      />
+      <div className="flex items-center justify-between border-t border-neutral-100 pt-3 text-sm">
+        <span className="font-medium text-neutral-600">Net payable</span>
+        <span className="font-semibold text-neutral-900">{formatCurrency(netPayable, currency)}</span>
+      </div>
+    </div>
+  );
+}

App/lib/po-money.ts

@@ -0,0 +1,67 @@
+/**
+ * Single source of truth for PO money math (issue #133).
+ *
+ * A PO's value is built up as:
+ *
+ *     taxable   = Σ qty · unitPrice                 (ex-GST)
+ *     gst       = Σ qty · unitPrice · gstRate
+ *     inclGst   = taxable + gst                      (the line-items total)
+ *     netPayable = inclGst + tcs − discount          (PO-level charges, below GST)
+ *
+ * `netPayable` is what is stored in `PurchaseOrder.totalAmount`, so payments,
+ * reports, and the advance-payment slider all operate on the true amount due.
+ *
+ * TCS and Discount are **absolute** rupee amounts (the UI's % control is only a
+ * convenience that writes back the rupee value). Discount is applied **post-GST**.
+ * The percentage shown for either is taken against `inclGst` (the GST-inclusive
+ * line-items total) — see `amountToPercent` / `percentToAmount`.
+ */
+
+export interface MoneyItem {
+  quantity: number;
+  unitPrice: number;
+  gstRate?: number | null;
+}
+
+export const DEFAULT_GST_RATE = 0.18;
+
+export interface PoMoney {
+  taxable: number;
+  gst: number;
+  inclGst: number;
+  tcs: number;
+  discount: number;
+  netPayable: number;
+}
+
+export function computePoMoney(
+  items: MoneyItem[],
+  tcs = 0,
+  discount = 0
+): PoMoney {
+  const taxable = items.reduce((s, i) => s + i.quantity * i.unitPrice, 0);
+  const gst = items.reduce(
+    (s, i) => s + i.quantity * i.unitPrice * (i.gstRate ?? DEFAULT_GST_RATE),
+    0
+  );
+  const inclGst = taxable + gst;
+  const t = tcs || 0;
+  const d = discount || 0;
+  return { taxable, gst, inclGst, tcs: t, discount: d, netPayable: inclGst + t - d };
+}
+
+/** Net payable (PO totalAmount) for a set of line items plus PO-level charges. */
+export function poNetPayable(items: MoneyItem[], tcs = 0, discount = 0): number {
+  return computePoMoney(items, tcs, discount).netPayable;
+}
+
+/** Convert an absolute charge to its percentage of a base (0 when base is 0). */
+export function amountToPercent(amount: number, base: number): number {
+  if (!base) return 0;
+  return (amount / base) * 100;
+}
+
+/** Convert a percentage of a base back to an absolute charge. */
+export function percentToAmount(percent: number, base: number): number {
+  return (percent / 100) * base;
+}

App/lib/validations/po.ts

@@ -48,6 +48,9 @@ export const createPoSchema = z.object({
   tcTransitInsurance: z.string().optional(),
   tcPaymentTerms: z.string().optional(),
   tcOthers: z.string().optional(),
+  // PO-level charges, stored absolute (issue #133). Discount is applied post-GST.
+  tcsAmount: z.coerce.number().nonnegative("TCS cannot be negative").default(0),
+  discountAmount: z.coerce.number().nonnegative("Discount cannot be negative").default(0),
   lineItems: z.array(lineItemSchema).min(1, "At least one line item is required"),
 });
 

App/prisma/migrations/20260629120000_po_tcs_discount/migration.sql

@@ -0,0 +1,5 @@
+-- Issue #133: PO-level TCS and Discount, shown below GST.
+-- Absolute rupee amounts (nullable, default 0 so historical/imported POs read as 0).
+-- totalAmount already includes these: subtotal + GST + tcsAmount - discountAmount.
+ALTER TABLE "PurchaseOrder" ADD COLUMN "tcsAmount" DECIMAL(12,2) DEFAULT 0;
+ALTER TABLE "PurchaseOrder" ADD COLUMN "discountAmount" DECIMAL(12,2) DEFAULT 0;

App/prisma/schema.prisma

@@ -569,6 +569,13 @@ model PurchaseOrder {
   status             POStatus  @default(DRAFT)
   totalAmount        Decimal   @db.Decimal(12, 2)
   currency           String    @default("INR")
+  // PO-level charges shown below GST (issue #133). Stored as ABSOLUTE rupee
+  // amounts — the UI offers a % control bidirectionally linked to the rupee value
+  // for convenience, but only the absolute amount is persisted. Discount is applied
+  // post-GST. Nullable + default 0 so historical/imported POs read as 0.
+  // NOTE: totalAmount already folds these in: subtotal + GST + tcsAmount − discountAmount.
+  tcsAmount          Decimal?  @default(0) @db.Decimal(12, 2)
+  discountAmount     Decimal?  @default(0) @db.Decimal(12, 2)
   dateRequired       DateTime?
   projectCode        String?
   managerNote        String?

App/tests/integration/po-tcs-discount.test.ts

@@ -0,0 +1,115 @@
+/**
+ * Integration test for PO-level TCS & Discount (issue #133).
+ * Verifies totalAmount folds in the charges (subtotal + GST + TCS − Discount),
+ * the absolute amounts are persisted, edits update them, and a manager line edit
+ * preserves them.
+ */
+import { vi, describe, it, expect, beforeAll, afterEach } from "vitest";
+
+vi.mock("@/auth", () => ({ auth: vi.fn() }));
+vi.mock("next/cache", () => ({ revalidatePath: vi.fn() }));
+vi.mock("@/lib/notifier", () => ({ notify: vi.fn() }));
+
+import { auth } from "@/auth";
+import { db } from "@/lib/db";
+import type { Role } from "@prisma/client";
+import { createPo } from "@/app/(portal)/po/new/actions";
+import { updatePo } from "@/app/(portal)/po/[id]/edit/actions";
+import { managerEditLineItems } from "@/app/(portal)/approvals/[id]/manager-line-edit-actions";
+import { makeSession, getSeedUser, getSeedVessel, getSeedAccount, makePoForm, deletePosByTitle } from "./helpers";
+
+const PREFIX = "INTTEST_TCSDISC_";
+let techId: string;
+let managerId: string;
+let vesselId: string;
+let accountId: string;
+
+beforeAll(async () => {
+  const [tech, manager, vessel, account] = await Promise.all([
+    getSeedUser("tech@pelagia.local"),
+    getSeedUser("manager@pelagia.local"),
+    getSeedVessel("MV Pelagia Star"),
+    getSeedAccount("700201"),
+  ]);
+  techId = tech.id;
+  managerId = manager.id;
+  vesselId = vessel.id;
+  accountId = account.id;
+});
+
+afterEach(async () => {
+  await deletePosByTitle(PREFIX);
+  vi.clearAllMocks();
+});
+
+function as(userId: string, role: Role) {
+  vi.mocked(auth as unknown as () => Promise<unknown>).mockResolvedValue(makeSession(userId, role));
+}
+
+// One line item: 10 × ₹100 @ 18% GST ⇒ taxable 1000, GST 180, incl-GST 1180.
+function form(title: string, intent: string, tcs: number, discount: number) {
+  const f = makePoForm({
+    title, vesselId, accountId, intent: "draft",
+    lineItems: [{ description: "Item", quantity: 10, unit: "pc", unitPrice: 100, gstRate: 0.18 }],
+  });
+  f.set("intent", intent); // create: draft/submit · edit: save
+  f.set("tcsAmount", String(tcs));
+  f.set("discountAmount", String(discount));
+  return f;
+}
+
+describe("PO TCS & Discount", () => {
+  it("folds TCS and Discount into totalAmount and stores the absolute amounts", async () => {
+    as(techId, "TECHNICAL");
+    const result = await createPo(form(`${PREFIX}Create`, "draft", 118, 100));
+    expect(result).not.toHaveProperty("error");
+
+    const po = await db.purchaseOrder.findUniqueOrThrow({ where: { id: (result as { id: string }).id } });
+    expect(Number(po.tcsAmount)).toBeCloseTo(118, 2);
+    expect(Number(po.discountAmount)).toBeCloseTo(100, 2);
+    expect(Number(po.totalAmount)).toBeCloseTo(1180 + 118 - 100, 2); // 1198
+  });
+
+  it("defaults to zero charges ⇒ totalAmount is just incl-GST", async () => {
+    as(techId, "TECHNICAL");
+    const result = await createPo(form(`${PREFIX}Zero`, "draft", 0, 0));
+    const po = await db.purchaseOrder.findUniqueOrThrow({ where: { id: (result as { id: string }).id } });
+    expect(Number(po.totalAmount)).toBeCloseTo(1180, 2);
+    expect(Number(po.tcsAmount)).toBe(0);
+    expect(Number(po.discountAmount)).toBe(0);
+  });
+
+  it("edit updates the charges and recomputes the total", async () => {
+    as(techId, "TECHNICAL");
+    const created = await createPo(form(`${PREFIX}Edit`, "draft", 0, 0));
+    const poId = (created as { id: string }).id;
+
+    as(techId, "TECHNICAL");
+    const edited = await updatePo(poId, form(`${PREFIX}Edit`, "save", 50, 30));
+    expect(edited).not.toHaveProperty("error");
+
+    const po = await db.purchaseOrder.findUniqueOrThrow({ where: { id: poId } });
+    expect(Number(po.tcsAmount)).toBeCloseTo(50, 2);
+    expect(Number(po.discountAmount)).toBeCloseTo(30, 2);
+    expect(Number(po.totalAmount)).toBeCloseTo(1180 + 50 - 30, 2); // 1200
+  });
+
+  it("a manager line edit preserves the PO's TCS & Discount", async () => {
+    as(techId, "TECHNICAL");
+    const created = await createPo(form(`${PREFIX}MgrEdit`, "submit", 118, 100)); // ⇒ MGR_REVIEW
+    const poId = (created as { id: string }).id;
+
+    as(managerId, "MANAGER");
+    const res = await managerEditLineItems({
+      poId,
+      // Double the quantity: incl-GST becomes 20 × 100 × 1.18 = 2360.
+      lineItems: [{ name: "Item", quantity: 20, unit: "pc", unitPrice: 100 }],
+    });
+    expect(res).not.toHaveProperty("error");
+
+    const po = await db.purchaseOrder.findUniqueOrThrow({ where: { id: poId } });
+    expect(Number(po.tcsAmount)).toBeCloseTo(118, 2);
+    expect(Number(po.discountAmount)).toBeCloseTo(100, 2);
+    expect(Number(po.totalAmount)).toBeCloseTo(2360 + 118 - 100, 2); // 2378
+  });
+});

App/tests/unit/po-money.test.ts

@@ -0,0 +1,56 @@
+import { describe, expect, it } from "vitest";
+import {
+  computePoMoney,
+  poNetPayable,
+  amountToPercent,
+  percentToAmount,
+} from "@/lib/po-money";
+
+const items = [
+  { quantity: 10, unitPrice: 100, gstRate: 0.18 }, // taxable 1000, gst 180
+  { quantity: 2, unitPrice: 50, gstRate: 0.05 },   // taxable 100,  gst 5
+];
+
+describe("computePoMoney", () => {
+  it("breaks down taxable, GST and incl-GST", () => {
+    const m = computePoMoney(items);
+    expect(m.taxable).toBe(1100);
+    expect(m.gst).toBeCloseTo(185, 5);
+    expect(m.inclGst).toBeCloseTo(1285, 5);
+    expect(m.netPayable).toBeCloseTo(1285, 5); // no charges ⇒ equals inclGst
+  });
+
+  it("adds TCS and subtracts Discount post-GST", () => {
+    const m = computePoMoney(items, 50, 85);
+    expect(m.tcs).toBe(50);
+    expect(m.discount).toBe(85);
+    expect(m.netPayable).toBeCloseTo(1285 + 50 - 85, 5);
+  });
+
+  it("defaults a missing gstRate to 18%", () => {
+    expect(computePoMoney([{ quantity: 1, unitPrice: 100 }]).gst).toBeCloseTo(18, 5);
+  });
+
+  it("treats nullish charges as zero", () => {
+    const m = computePoMoney(items, undefined, undefined);
+    expect(m.netPayable).toBeCloseTo(1285, 5);
+  });
+});
+
+describe("poNetPayable", () => {
+  it("is incl-GST + TCS − Discount", () => {
+    expect(poNetPayable(items, 100, 200)).toBeCloseTo(1285 + 100 - 200, 5);
+  });
+});
+
+describe("percent ↔ amount conversion", () => {
+  it("round-trips against a base", () => {
+    expect(amountToPercent(128.5, 1285)).toBeCloseTo(10, 5);
+    expect(percentToAmount(10, 1285)).toBeCloseTo(128.5, 5);
+  });
+
+  it("is zero-safe when the base is zero", () => {
+    expect(amountToPercent(50, 0)).toBe(0);
+    expect(percentToAmount(10, 0)).toBe(0);
+  });
+});