Add issue/cancel lifecycle, GST derivation and integer-paise totals

issue_invoice allocates the number, freezes vendor and bank details and
stores server-computed totals in one transaction. Issued invoices are
cancelled, not deleted. Tax heads derive from supplier state and place of
supply (a disagreeing choice is rejected); unregistered suppliers issue a
plain Invoice. Adds GSTIN checksum validation, canonical India Compliance
state list, server-side drafts, series validation, relative and
magic-byte-checked asset paths, and GST settings. PDF re-exports use the
frozen vendor snapshot.

src/lib/api.ts

@@ -2,6 +2,7 @@ import { invoke } from "@tauri-apps/api/core";
 import type {
   BankAccount,
   Client,
+  DraftSummary,
   Invoice,
   InvoiceInput,
   InvoiceSeries,
@@ -27,10 +28,18 @@ export const api = {
   deleteClient: (id: number) => invoke<void>("delete_client", { id }),
 
   peekNextInvoiceNumber: () => invoke<string>("peek_next_invoice_number"),
-  createInvoice: (input: InvoiceInput) => invoke<Invoice>("create_invoice", { input }),
+  issueInvoice: (input: InvoiceInput, renderPrefs: Record<string, unknown>) =>
+    invoke<Invoice>("issue_invoice", { input, renderPrefs }),
+  cancelInvoice: (id: number, reason: string) =>
+    invoke<Invoice>("cancel_invoice", { id, reason }),
   listInvoices: () => invoke<InvoiceSummary[]>("list_invoices"),
   getInvoice: (id: number) => invoke<Invoice>("get_invoice", { id }),
-  deleteInvoice: (id: number) => invoke<void>("delete_invoice", { id }),
+
+  saveDraft: (id: number | null, payload: unknown) =>
+    invoke<number>("save_draft", { id, payload }),
+  listDrafts: () => invoke<DraftSummary[]>("list_drafts"),
+  getDraft: (id: number) => invoke<unknown>("get_draft", { id }),
+  deleteDraft: (id: number) => invoke<void>("delete_draft", { id }),
 
   importAsset: (sourcePath: string, kind: string) =>
     invoke<string>("import_asset", { sourcePath, kind }),

src/lib/invoice.test.ts

@@ -0,0 +1,58 @@
+import { describe, expect, it } from "vitest";
+import { computeLineAmount, computeTotals } from "./invoice";
+import { EMPTY_ITEM, type InvoiceItem } from "./types";
+
+// These cases mirror the unit tests in src-tauri/src/gst.rs, so the on-screen preview
+// and the stored totals stay identical.
+
+const fixed = (amount: number): InvoiceItem => ({ ...EMPTY_ITEM, mode: "fixed", amount });
+const rate = (r: number, quantity: number): InvoiceItem => ({
+  ...EMPTY_ITEM,
+  mode: "rate",
+  rate: r,
+  quantity,
+  unit: "hour",
+});
+
+describe("computeTotals", () => {
+  it("splits 18% on 7310.00 into 657.90 CGST and SGST", () => {
+    const t = computeTotals([fixed(7310)], 0, "cgst_sgst", 18);
+    expect(t.subtotal).toBe(7310);
+    expect(t.cgst).toBe(657.9);
+    expect(t.sgst).toBe(657.9);
+    expect(t.igst).toBe(0);
+    expect(t.total).toBe(8625.8);
+  });
+
+  it("rounds odd paise half up for IGST and per head for CGST/SGST", () => {
+    const igst = computeTotals([fixed(33.33)], 0, "igst", 5);
+    expect(igst.igst).toBe(1.67);
+    expect(igst.total).toBe(35);
+    const split = computeTotals([fixed(33.33)], 0, "cgst_sgst", 5);
+    expect([split.cgst, split.sgst]).toEqual([0.83, 0.83]);
+    expect(split.total).toBe(34.99);
+  });
+
+  it("handles fractional quantities", () => {
+    const t = computeTotals([rate(1200, 1.5)], 0, "none", 0);
+    expect(t.subtotal).toBe(1800);
+    expect(t.total).toBe(1800);
+    expect(computeLineAmount(rate(99.99, 2.5))).toBe(249.98);
+  });
+
+  it("clamps the discount to the subtotal", () => {
+    const items = [fixed(100), fixed(50.5)];
+    const over = computeTotals(items, 999.99, "igst", 18);
+    expect(over.discount).toBe(150.5);
+    expect(over.taxable).toBe(0);
+    expect(over.total).toBe(0);
+    expect(computeTotals(items, -5, "none", 0).discount).toBe(0);
+    expect(computeTotals(items, 50.5, "none", 0).taxable).toBe(100);
+  });
+
+  it("ignores the rate when no tax applies", () => {
+    const t = computeTotals([fixed(1000)], 0, "none", 18);
+    expect(t.taxTotal).toBe(0);
+    expect(t.total).toBe(1000);
+  });
+});

src/lib/invoice.ts

@@ -1,12 +1,23 @@
-import { round2 } from "./format";
 import type { InvoiceItem, TaxType } from "./types";
 
+// The preview must show exactly what Rust stores (src-tauri/src/gst.rs), so money is
+// computed in integer paise with round-half-up, the same way.
+
+const toPaise = (rupees: number) => Math.round((Number.isFinite(rupees) ? rupees : 0) * 100);
+
+function linePaise(item: InvoiceItem): number {
+  if (item.mode === "rate") {
+    return Math.round(toPaise(item.rate || 0) * (item.quantity || 0));
+  }
+  return toPaise(item.amount || 0);
+}
+
+/** Round-half-up division for non-negative integers. */
+const divRound = (num: number, den: number) => Math.floor((num + den / 2) / den);
+
 /** Amount for a single line: a fixed total, or rate × quantity. */
 export function computeLineAmount(item: InvoiceItem): number {
-  if (item.mode === "rate") {
-    return round2((item.rate || 0) * (item.quantity || 0));
-  }
-  return round2(item.amount || 0);
+  return linePaise(item) / 100;
 }
 
 export interface Totals {
@@ -26,29 +37,30 @@ export function computeTotals(
   taxType: TaxType,
   taxRate: number,
 ): Totals {
-  const subtotal = round2(items.reduce((sum, item) => sum + computeLineAmount(item), 0));
-  const discountValue = round2(Math.min(Math.max(discount || 0, 0), subtotal));
-  const taxable = round2(subtotal - discountValue);
+  const subtotal = items.reduce((sum, item) => sum + linePaise(item), 0);
+  const discountPaise = Math.min(Math.max(toPaise(discount), 0), Math.max(subtotal, 0));
+  const taxable = subtotal - discountPaise;
+  const rateBp = Math.round((Number.isFinite(taxRate) ? taxRate : 0) * 100);
 
   let cgst = 0;
   let sgst = 0;
   let igst = 0;
   if (taxType === "cgst_sgst") {
-    cgst = round2((taxable * (taxRate / 2)) / 100);
-    sgst = round2((taxable * (taxRate / 2)) / 100);
+    cgst = divRound(taxable * rateBp, 20_000);
+    sgst = cgst;
   } else if (taxType === "igst") {
-    igst = round2((taxable * taxRate) / 100);
+    igst = divRound(taxable * rateBp, 10_000);
   }
-  const taxTotal = round2(cgst + sgst + igst);
+  const taxTotal = cgst + sgst + igst;
 
   return {
-    subtotal,
-    discount: discountValue,
-    taxable,
-    cgst,
-    sgst,
-    igst,
-    taxTotal,
-    total: round2(taxable + taxTotal),
+    subtotal: subtotal / 100,
+    discount: discountPaise / 100,
+    taxable: taxable / 100,
+    cgst: cgst / 100,
+    sgst: sgst / 100,
+    igst: igst / 100,
+    taxTotal: taxTotal / 100,
+    total: (taxable + taxTotal) / 100,
   };
 }

src/lib/pdf.tsx

@@ -17,12 +17,24 @@ function blobToBase64(blob: Blob): Promise<string> {
   });
 }
 
+function vendorFromSnapshot(snapshot: string | undefined, live: Settings): Settings {
+  if (!snapshot) return live;
+  try {
+    return { ...live, ...(JSON.parse(snapshot) as Partial<Settings>) };
+  } catch {
+    return live;
+  }
+}
+
 export async function buildPdfProps(
   invoice: Invoice,
   settings: Settings,
   bank: BankAccount | null,
 ): Promise<InvoicePdfProps> {
-  const logoDataUri = settings.logoPath ? await api.readAssetDataUri(settings.logoPath) : null;
+  // Re-exports use the vendor details frozen at issue; live settings are only a fallback for
+  // legacy rows without a snapshot.
+  const vendor = vendorFromSnapshot(invoice.vendorSnapshot, settings);
+  const logoDataUri = vendor.logoPath ? await api.readAssetDataUri(vendor.logoPath) : null;
   const signatureDataUri = invoice.signaturePath
     ? await api.readAssetDataUri(invoice.signaturePath)
     : null;
@@ -37,7 +49,7 @@ export async function buildPdfProps(
   }
 
   return {
-    vendor: settings,
+    vendor,
     bank: resolvedBank,
     logoDataUri,
     signatureDataUri,

src/lib/types.ts

@@ -19,7 +19,7 @@ export interface Settings {
   currency: string;
   onboarded: boolean;
   theme: string;
-  gstRegistration: string;
+  gstRegistration: GstRegistration;
   defaultHsnSac: string;
   signatoryName: string;
   signatoryDesignation: string;
@@ -65,9 +65,41 @@ export interface InvoiceItem {
   quantity: number;
   amount: number;
   sortOrder: number;
+  /** Optional so older callers that build items by hand keep compiling; stored as "" when absent. */
+  hsnSac?: string;
 }
 
+export type GstRegistration = "unregistered" | "regular";
+
+/** What the webview sends to issue an invoice; totals, tax and words are derived in Rust. */
 export interface InvoiceInput {
+  invoiceDate: string;
+  dueDate: string;
+  clientId: number | null;
+  clientName: string;
+  clientAddress: string;
+  clientGstin: string;
+  poNumber: string;
+  placeOfSupplyStateCode: string;
+  discount: number;
+  taxType: TaxType;
+  taxRate: number;
+  reverseCharge: boolean;
+  bankAccountId: number | null;
+  signaturePath: string | null;
+  notes: string;
+  saveClient: boolean;
+  draftId: number | null;
+  items: InvoiceItem[];
+}
+
+export type InvoiceStatus = "draft" | "issued" | "cancelled";
+
+/** An invoice as stored: all amounts are derived on the Rust side. */
+export interface Invoice {
+  id: number;
+  number: string;
+  seriesId: number | null;
   invoiceDate: string;
   dueDate: string;
   clientId: number | null;
@@ -89,18 +121,25 @@ export interface InvoiceInput {
   bankSnapshot: string;
   signaturePath: string | null;
   notes: string;
-  saveClient: boolean;
+  status: InvoiceStatus;
+  createdAt: string;
+  updatedAt: string;
+  docType: "invoice" | "tax_invoice";
+  reverseCharge: boolean;
+  /** JSON of the supplier details at issue time; empty when unknown. */
+  vendorSnapshot: string;
+  snapshotOrigin: string;
+  cancelledAt: string | null;
+  cancelReason: string;
+  archivedPdfSha256: string | null;
   items: InvoiceItem[];
 }
 
-export interface Invoice extends Omit<InvoiceInput, "saveClient"> {
+export interface DraftSummary {
   id: number;
-  number: string;
-  seriesId: number | null;
-  status: string;
-  createdAt: string;
   updatedAt: string;
-  items: InvoiceItem[];
+  clientName: string | null;
+  total: number | null;
 }
 
 export interface InvoiceSummary {
@@ -110,7 +149,7 @@ export interface InvoiceSummary {
   dueDate: string;
   clientName: string;
   total: number;
-  status: string;
+  status: InvoiceStatus;
   createdAt: string;
 }
 
@@ -122,10 +161,12 @@ export const EMPTY_ITEM: InvoiceItem = {
   quantity: 1,
   amount: 0,
   sortOrder: 0,
+  hsnSac: "",
 };
 
+/** GST state codes, same list as STATES in src-tauri/src/gst.rs (from India Compliance). */
 export const INDIAN_STATES: { code: string; name: string }[] = [
-  { code: "01", name: "Jammu & Kashmir" },
+  { code: "01", name: "Jammu and Kashmir" },
   { code: "02", name: "Himachal Pradesh" },
   { code: "03", name: "Punjab" },
   { code: "04", name: "Chandigarh" },
@@ -149,18 +190,20 @@ export const INDIAN_STATES: { code: string; name: string }[] = [
   { code: "22", name: "Chhattisgarh" },
   { code: "23", name: "Madhya Pradesh" },
   { code: "24", name: "Gujarat" },
-  { code: "26", name: "Dadra & Nagar Haveli and Daman & Diu" },
+  { code: "26", name: "Dadra and Nagar Haveli and Daman and Diu" },
   { code: "27", name: "Maharashtra" },
   { code: "29", name: "Karnataka" },
   { code: "30", name: "Goa" },
-  { code: "31", name: "Lakshadweep" },
+  { code: "31", name: "Lakshadweep Islands" },
   { code: "32", name: "Kerala" },
   { code: "33", name: "Tamil Nadu" },
   { code: "34", name: "Puducherry" },
-  { code: "35", name: "Andaman & Nicobar Islands" },
+  { code: "35", name: "Andaman and Nicobar Islands" },
   { code: "36", name: "Telangana" },
   { code: "37", name: "Andhra Pradesh" },
   { code: "38", name: "Ladakh" },
+  { code: "96", name: "Other Countries" },
+  { code: "97", name: "Other Territory" },
 ];
 
 export const UNIT_LABELS: Record<LineUnit, string> = {

src/lib/validators.test.ts

@@ -0,0 +1,27 @@
+import { describe, expect, it } from "vitest";
+import { gstinChecksumError, gstinFullError, vendorGstinError } from "./validators";
+
+// Same GSTINs as the Rust tests in src-tauri/src/gst.rs.
+describe("GSTIN checksum", () => {
+  it("accepts valid GSTINs", () => {
+    expect(gstinChecksumError("27AAPFU0939F1ZV")).toBeUndefined();
+    expect(gstinChecksumError("07AAGFF2194N1Z1")).toBeUndefined();
+    expect(gstinChecksumError("29ABCDE1234F1ZW")).toBeUndefined();
+  });
+
+  it("rejects a wrong check digit and bad shapes", () => {
+    expect(gstinChecksumError("29ABCDE1234F1Z5")).toMatch(/expected W/);
+    expect(gstinChecksumError("27AAPFU0939F1ZX")).toMatch(/check digit/);
+    expect(gstinChecksumError("27AAPFU0939F1Z")).toMatch(/15-character/);
+  });
+
+  it("cross-checks the PAN and the state", () => {
+    expect(gstinFullError("27AAPFU0939F1ZV", "AAPFU0939F")).toBeUndefined();
+    expect(gstinFullError("27AAPFU0939F1ZV", "AAPFU0939G")).toMatch(/PAN/);
+    expect(gstinFullError("")).toBeUndefined();
+    expect(vendorGstinError("unregistered", "", "", "29")).toBeUndefined();
+    expect(vendorGstinError("regular", "", "", "27")).toMatch(/needs a GSTIN/);
+    expect(vendorGstinError("regular", "27AAPFU0939F1ZV", "AAPFU0939F", "29")).toMatch(/state code/);
+    expect(vendorGstinError("regular", "27AAPFU0939F1ZV", "AAPFU0939F", "27")).toBeUndefined();
+  });
+});

src/lib/validators.ts

@@ -22,6 +22,50 @@ export function gstinError(value: string): string | undefined {
   return GSTIN_RE.test(v) ? undefined : "Enter a valid 15-character GSTIN";
 }
 
+const GSTIN_CHARS = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";
+
+/** Standard GSTIN mod-36 check digit. Returns an error message, or undefined when valid. */
+export function gstinChecksumError(value: string): string | undefined {
+  const v = norm(value);
+  if (!GSTIN_RE.test(v)) return "Enter a valid 15-character GSTIN";
+  let sum = 0;
+  for (let i = 0; i < 14; i++) {
+    const product = GSTIN_CHARS.indexOf(v[i]) * (i % 2 === 0 ? 1 : 2);
+    sum += Math.floor(product / 36) + (product % 36);
+  }
+  const expected = GSTIN_CHARS[(36 - (sum % 36)) % 36];
+  return v[14] === expected ? undefined : `GSTIN check digit looks wrong (expected ${expected})`;
+}
+
+/**
+ * Full GSTIN check: shape, check digit and, when a PAN is given, that the GSTIN
+ * contains that PAN. Empty (or "NA") is valid; the field is optional.
+ */
+export function gstinFullError(value: string, pan = ""): string | undefined {
+  const v = norm(value);
+  if (!v || v === "NA") return undefined;
+  const base = gstinError(v) ?? gstinChecksumError(v);
+  if (base) return base;
+  if (pan.trim() && v.slice(2, 12) !== norm(pan)) return "GSTIN does not contain the PAN";
+  return undefined;
+}
+
+/** Supplier GSTIN rules for a registered business; an unregistered one needs none. */
+export function vendorGstinError(
+  registration: string,
+  gstin: string,
+  pan: string,
+  stateCode: string,
+): string | undefined {
+  if (registration === "unregistered") return undefined;
+  const g = norm(gstin);
+  if (!g) return "A registered business needs a GSTIN";
+  const base = gstinFullError(g, pan);
+  if (base) return base;
+  if (g.slice(0, 2) !== stateCode) return `GSTIN starts with ${g.slice(0, 2)}, but your state code is ${stateCode}`;
+  return undefined;
+}
+
 export function emailError(value: string): string | undefined {
   if (!value.trim()) return undefined;
   return EMAIL_RE.test(value.trim()) ? undefined : "Enter a valid email address";

src/views/AppSettings.tsx

@@ -23,8 +23,14 @@ import {
 import { Add, Save, TrashCan } from "@carbon/icons-react";
 import { confirm } from "@tauri-apps/plugin-dialog";
 import { api } from "../lib/api";
-import { INDIAN_STATES, type BankAccount, type Settings, type TaxType } from "../lib/types";
-import { emailError, ifscError, panError, phoneError } from "../lib/validators";
+import {
+  INDIAN_STATES,
+  type BankAccount,
+  type GstRegistration,
+  type Settings,
+  type TaxType,
+} from "../lib/types";
+import { emailError, ifscError, panError, phoneError, vendorGstinError } from "../lib/validators";
 import { ImagePicker } from "../components/ImagePicker";
 
 const blankBank = (): BankAccount => ({
@@ -70,7 +76,19 @@ export default function AppSettings({
   const setBank = <K extends keyof BankAccount>(key: K, value: BankAccount[K]) =>
     setEditing((prev) => (prev ? { ...prev, [key]: value } : prev));
 
+  const registered = form.gstRegistration !== "unregistered";
+  const gstinProblem = vendorGstinError(
+    form.gstRegistration,
+    form.vendorGstin,
+    form.vendorPan,
+    form.vendorStateCode,
+  );
+
   const saveAll = async () => {
+    if (gstinProblem) {
+      setError(gstinProblem);
+      return;
+    }
     setBusy(true);
     setError(null);
     setNotice(null);
@@ -140,6 +158,22 @@ export default function AppSettings({
       <section className="voiced-stack" style={{ marginBottom: "2.5rem" }}>
         <h3>Vendor details</h3>
         <Grid narrow>
+          <Column sm={4} md={8} lg={12}>
+            <RadioButtonGroup
+              legendText="GST registration"
+              name="s-gstReg"
+              orientation="horizontal"
+              valueSelected={form.gstRegistration}
+              onChange={(value) => {
+                set("gstRegistration", value as GstRegistration);
+                if (value === "unregistered") set("defaultTaxType", "none");
+                else if (form.defaultTaxType === "none") set("defaultTaxType", "cgst_sgst");
+              }}
+            >
+              <RadioButton id="s-gr-un" labelText="Unregistered" value="unregistered" />
+              <RadioButton id="s-gr-reg" labelText="Regular" value="regular" />
+            </RadioButtonGroup>
+          </Column>
           <Column sm={4} md={8} lg={12}>
             <TextInput
               id="s-vendorName"
@@ -187,14 +221,18 @@ export default function AppSettings({
               invalidText={panError(form.vendorPan)}
             />
           </Column>
-          <Column sm={4} md={4} lg={6}>
-            <TextInput
-              id="s-vendorGstin"
-              labelText="GSTIN (blank if unregistered)"
-              value={form.vendorGstin}
-              onChange={(e) => set("vendorGstin", e.target.value.toUpperCase())}
-            />
-          </Column>
+          {registered ? (
+            <Column sm={4} md={4} lg={6}>
+              <TextInput
+                id="s-vendorGstin"
+                labelText="GSTIN"
+                value={form.vendorGstin}
+                onChange={(e) => set("vendorGstin", e.target.value.toUpperCase())}
+                invalid={Boolean(gstinProblem)}
+                invalidText={gstinProblem}
+              />
+            </Column>
+          ) : null}
           <Column sm={4} md={8} lg={12}>
             <Select
               id="s-vendorState"
@@ -207,6 +245,22 @@ export default function AppSettings({
               ))}
             </Select>
           </Column>
+          <Column sm={4} md={4} lg={6}>
+            <TextInput
+              id="s-signatoryName"
+              labelText="Authorised signatory name"
+              value={form.signatoryName}
+              onChange={(e) => set("signatoryName", e.target.value)}
+            />
+          </Column>
+          <Column sm={4} md={4} lg={6}>
+            <TextInput
+              id="s-signatoryDesignation"
+              labelText="Signatory designation"
+              value={form.signatoryDesignation}
+              onChange={(e) => set("signatoryDesignation", e.target.value)}
+            />
+          </Column>
           <Column sm={4} md={8} lg={8}>
             <ImagePicker
               kind="logo"
@@ -229,17 +283,29 @@ export default function AppSettings({
       <section className="voiced-stack" style={{ marginBottom: "2.5rem" }}>
         <h3>Defaults</h3>
         <Grid narrow>
-          <Column sm={4} md={4} lg={5}>
-            <NumberInput
-              id="s-taxRate"
-              label="Default tax rate (%)"
-              min={0}
-              max={100}
-              step={0.5}
-              value={form.defaultTaxRate}
-              onChange={(_e, { value }) => set("defaultTaxRate", Number(value) || 0)}
-            />
-          </Column>
+          {registered ? (
+            <>
+            <Column sm={4} md={4} lg={5}>
+              <NumberInput
+                id="s-taxRate"
+                label="Default tax rate (%)"
+                min={0}
+                max={100}
+                step={0.5}
+                value={form.defaultTaxRate}
+                onChange={(_e, { value }) => set("defaultTaxRate", Number(value) || 0)}
+              />
+            </Column>
+  <Column sm={4} md={4} lg={5}>
+                <TextInput
+                  id="s-hsn"
+                  labelText="Default HSN/SAC"
+                  value={form.defaultHsnSac}
+                  onChange={(e) => set("defaultHsnSac", e.target.value)}
+                />
+              </Column>
+            </>
+          ) : null}
           <Column sm={4} md={4} lg={5}>
             <NumberInput
               id="s-terms"
@@ -261,18 +327,20 @@ export default function AppSettings({
               <SelectItem value="g100" text="Carbon dark (g100)" />
             </Select>
           </Column>
-          <Column sm={4} md={8} lg={16}>
-            <RadioButtonGroup
-              legendText="Default tax treatment"
-              name="s-taxType"
-              valueSelected={form.defaultTaxType}
-              onChange={(value) => set("defaultTaxType", value as TaxType)}
-            >
-              <RadioButton id="s-tt-cgst" labelText="CGST + SGST (within state)" value="cgst_sgst" />
-              <RadioButton id="s-tt-igst" labelText="IGST (inter-state)" value="igst" />
-              <RadioButton id="s-tt-none" labelText="No tax" value="none" />
-            </RadioButtonGroup>
-          </Column>
+          {registered ? (
+            <Column sm={4} md={8} lg={16}>
+              <RadioButtonGroup
+                legendText="Default tax treatment"
+                name="s-taxType"
+                valueSelected={form.defaultTaxType}
+                onChange={(value) => set("defaultTaxType", value as TaxType)}
+              >
+                <RadioButton id="s-tt-cgst" labelText="CGST + SGST (within state)" value="cgst_sgst" />
+                <RadioButton id="s-tt-igst" labelText="IGST (inter-state)" value="igst" />
+                <RadioButton id="s-tt-none" labelText="No tax" value="none" />
+              </RadioButtonGroup>
+            </Column>
+          ) : null}
         </Grid>
       </section>
 

src/views/InvoiceHistory.tsx

@@ -3,6 +3,7 @@ import {
   Button,
   InlineLoading,
   InlineNotification,
+  Modal,
   Table,
   TableBody,
   TableCell,
@@ -10,9 +11,10 @@ import {
   TableHead,
   TableHeader,
   TableRow,
+  Tag,
+  TextInput,
 } from "@carbon/react";
-import { Download, TrashCan } from "@carbon/icons-react";
-import { confirm } from "@tauri-apps/plugin-dialog";
+import { Download, Close } from "@carbon/icons-react";
 import { api } from "../lib/api";
 import { formatAmount, formatDate } from "../lib/format";
 import { exportInvoicePdf } from "../lib/pdf";
@@ -23,6 +25,8 @@ export default function InvoiceHistory({ settings }: { settings: Settings }) {
   const [loading, setLoading] = useState(true);
   const [error, setError] = useState<string | null>(null);
   const [busyId, setBusyId] = useState<number | null>(null);
+  const [cancelTarget, setCancelTarget] = useState<InvoiceSummary | null>(null);
+  const [reason, setReason] = useState("");
 
   const load = async () => {
     try {
@@ -52,16 +56,15 @@ export default function InvoiceHistory({ settings }: { settings: Settings }) {
     }
   };
 
-  const onDelete = async (row: InvoiceSummary) => {
-    const ok = await confirm(`Delete invoice ${row.number}? This cannot be undone.`, {
-      title: "Delete invoice",
-      kind: "warning",
-    });
-    if (!ok) return;
+  const onCancel = async () => {
+    if (!cancelTarget) return;
     try {
-      await api.deleteInvoice(row.id);
+      await api.cancelInvoice(cancelTarget.id, reason);
+      setCancelTarget(null);
+      setReason("");
       await load();
     } catch (e) {
+      setCancelTarget(null);
       setError(String(e));
     }
   };
@@ -99,7 +102,15 @@ export default function InvoiceHistory({ settings }: { settings: Settings }) {
                   <TableCell>{formatDate(row.invoiceDate)}</TableCell>
                   <TableCell>{row.clientName || "—"}</TableCell>
                   <TableCell>₹{formatAmount(row.total)}</TableCell>
-                  <TableCell>{row.status}</TableCell>
+                  <TableCell>
+                    {row.status === "cancelled" ? (
+                      <Tag type="red" size="sm">
+                        Cancelled
+                      </Tag>
+                    ) : (
+                      row.status
+                    )}
+                  </TableCell>
                   <TableCell>
                     <div className="voiced-header-action">
                       <Button
@@ -111,14 +122,19 @@ export default function InvoiceHistory({ settings }: { settings: Settings }) {
                       >
                         {busyId === row.id ? "Exporting…" : "PDF"}
                       </Button>
-                      <Button
-                        kind="ghost"
-                        size="sm"
-                        renderIcon={TrashCan}
-                        onClick={() => onDelete(row)}
-                      >
-                        Delete
-                      </Button>
+                      {row.status === "issued" ? (
+                        <Button
+                          kind="ghost"
+                          size="sm"
+                          renderIcon={Close}
+                          onClick={() => {
+                            setReason("");
+                            setCancelTarget(row);
+                          }}
+                        >
+                          Cancel
+                        </Button>
+                      ) : null}
                     </div>
                   </TableCell>
                 </TableRow>
@@ -127,6 +143,26 @@ export default function InvoiceHistory({ settings }: { settings: Settings }) {
           </Table>
         </TableContainer>
       )}
+
+      <Modal
+        open={cancelTarget !== null}
+        danger
+        modalHeading={`Cancel invoice ${cancelTarget?.number ?? ""}?`}
+        primaryButtonText="Cancel invoice"
+        secondaryButtonText="Keep invoice"
+        onRequestClose={() => setCancelTarget(null)}
+        onRequestSubmit={onCancel}
+      >
+        <p style={{ marginBottom: "1rem" }}>
+          The invoice stays in the list as cancelled and its number is not reused.
+        </p>
+        <TextInput
+          id="cancelReason"
+          labelText="Reason (optional)"
+          value={reason}
+          onChange={(e) => setReason(e.target.value)}
+        />
+      </Modal>
     </div>
   );
 }

src/views/NewInvoice.tsx

@@ -6,8 +6,6 @@ import {
   Grid,
   InlineNotification,
   NumberInput,
-  RadioButton,
-  RadioButtonGroup,
   Select,
   SelectItem,
   TextArea,
@@ -29,6 +27,7 @@ import type {
 } from "../lib/types";
 import { computeLineAmount, computeTotals } from "../lib/invoice";
 import { amountInWords } from "../lib/numberToWords";
+import { gstinFullError } from "../lib/validators";
 import { addDays, formatAmount, todayIso } from "../lib/format";
 import { buildPdfProps, exportPdfFromProps } from "../lib/pdf";
 import { InvoicePreview } from "../components/InvoicePreview";
@@ -41,6 +40,7 @@ interface NewInvoiceProps {
 }
 
 export default function NewInvoice({ settings }: NewInvoiceProps) {
+  const newItem = (): InvoiceItem => ({ ...EMPTY_ITEM, hsnSac: settings.defaultHsnSac });
   const today = todayIso();
   const [invoiceDate, setInvoiceDate] = useState(today);
   const [dueDate, setDueDate] = useState(addDays(today, settings.paymentTermsDays));
@@ -55,13 +55,11 @@ export default function NewInvoice({ settings }: NewInvoiceProps) {
   const [placeOfSupply, setPlaceOfSupply] = useState(settings.vendorStateCode);
   const [saveClient, setSaveClient] = useState(false);
 
-  const [items, setItems] = useState<InvoiceItem[]>([{ ...EMPTY_ITEM }]);
+  const [items, setItems] = useState<InvoiceItem[]>([newItem()]);
   const [discount, setDiscount] = useState(0);
 
-  const [taxesApplicable, setTaxesApplicable] = useState(settings.defaultTaxType !== "none");
-  const [taxType, setTaxType] = useState<TaxType>(
-    settings.defaultTaxType === "none" ? "cgst_sgst" : settings.defaultTaxType,
-  );
+  const registered = settings.gstRegistration !== "unregistered";
+  const [reverseCharge, setReverseCharge] = useState(false);
   const [taxRate, setTaxRate] = useState(settings.defaultTaxRate);
 
   const [banks, setBanks] = useState<BankAccount[]>([]);
@@ -122,7 +120,14 @@ export default function NewInvoice({ settings }: NewInvoiceProps) {
     };
   }, [signaturePath]);
 
-  const effectiveTaxType: TaxType = taxesApplicable ? taxType : "none";
+  // Rust derives the tax type from the supplier state and the place of supply; this
+  // mirrors that rule so the preview and the value sent for the cross-check agree.
+  const effectiveTaxType: TaxType = !registered
+    ? "none"
+    : !placeOfSupply || placeOfSupply === settings.vendorStateCode
+      ? "cgst_sgst"
+      : "igst";
+  const clientGstinError = gstinFullError(clientGstin);
   const totals = useMemo(
     () => computeTotals(items, discount, effectiveTaxType, taxRate),
     [items, discount, effectiveTaxType, taxRate],
@@ -159,7 +164,7 @@ export default function NewInvoice({ settings }: NewInvoiceProps) {
   const updateItem = (index: number, patch: Partial<InvoiceItem>) =>
     setItems((prev) => prev.map((item, i) => (i === index ? { ...item, ...patch } : item)));
 
-  const addItem = () => setItems((prev) => [...prev, { ...EMPTY_ITEM }]);
+  const addItem = () => setItems((prev) => [...prev, newItem()]);
   const removeItem = (index: number) =>
     setItems((prev) => (prev.length === 1 ? prev : prev.filter((_, i) => i !== index)));
 
@@ -179,7 +184,7 @@ export default function NewInvoice({ settings }: NewInvoiceProps) {
     setClientGstin("");
     setPoNumber("");
     setSaveClient(false);
-    setItems([{ ...EMPTY_ITEM }]);
+    setItems([newItem()]);
     setDiscount(0);
     setNotes("");
     setInvoiceDate(todayIso());
@@ -193,6 +198,10 @@ export default function NewInvoice({ settings }: NewInvoiceProps) {
   };
 
   const onSave = async () => {
+    if (clientGstinError) {
+      setError(`Client GSTIN: ${clientGstinError}`);
+      return;
+    }
     setSaving(true);
     setError(null);
     setSaved(null);
@@ -206,27 +215,18 @@ export default function NewInvoice({ settings }: NewInvoiceProps) {
         clientGstin,
         poNumber,
         placeOfSupplyStateCode: placeOfSupply,
-        subtotal: totals.subtotal,
-        discount: totals.discount,
+        discount,
         taxType: effectiveTaxType,
         taxRate,
-        cgstAmount: totals.cgst,
-        sgstAmount: totals.sgst,
-        igstAmount: totals.igst,
-        total: totals.total,
-        amountInWords: words,
+        reverseCharge: registered && reverseCharge,
         bankAccountId: bankId,
-        bankSnapshot: bank ? JSON.stringify(bank) : "",
         signaturePath,
         notes,
         saveClient,
-        items: items.map((item, index) => ({
-          ...item,
-          sortOrder: index,
-          amount: computeLineAmount(item),
-        })),
+        draftId: null,
+        items: items.map((item, index) => ({ ...item, sortOrder: index })),
       };
-      const invoice = await api.createInvoice(input);
+      const invoice = await api.issueInvoice(input, {});
       const props = await buildPdfProps(invoice, settings, bank);
       const path = await exportPdfFromProps(props, invoice.number);
       if (path) setSaved(path);
@@ -336,6 +336,8 @@ export default function NewInvoice({ settings }: NewInvoiceProps) {
                 labelText="Client GSTIN (optional)"
                 value={clientGstin}
                 onChange={(e) => setClientGstin(e.target.value.toUpperCase())}
+                invalid={Boolean(clientGstinError)}
+                invalidText={clientGstinError}
               />
             </Column>
             <Column sm={4} md={4} lg={5}>
@@ -391,6 +393,16 @@ export default function NewInvoice({ settings }: NewInvoiceProps) {
                     onChange={(e) => updateItem(index, { description: e.target.value })}
                   />
                 </div>
+                {registered ? (
+                  <div style={{ flex: "0 1 120px" }}>
+                    <TextInput
+                      id={`hsn-${index}`}
+                      labelText="HSN/SAC"
+                      value={item.hsnSac ?? ""}
+                      onChange={(e) => updateItem(index, { hsnSac: e.target.value })}
+                    />
+                  </div>
+                ) : null}
                 <div style={{ flex: "0 1 150px" }}>
                   <Select
                     id={`mode-${index}`}
@@ -479,26 +491,14 @@ export default function NewInvoice({ settings }: NewInvoiceProps) {
                 onChange={(_e, { value }) => setDiscount(Number(value) || 0)}
               />
             </Column>
-            <Column sm={4} md={8} lg={16}>
-              <Toggle
-                id="taxes"
-                labelText="Taxes applicable"
-                toggled={taxesApplicable}
-                onToggle={setTaxesApplicable}
-              />
-            </Column>
-            {taxesApplicable ? (
+            {registered ? (
               <>
                 <Column sm={4} md={8} lg={16}>
-                  <RadioButtonGroup
-                    legendText="Tax treatment"
-                    name="taxType"
-                    valueSelected={taxType}
-                    onChange={(value) => setTaxType(value as TaxType)}
-                  >
-                    <RadioButton id="t-cgst" labelText="CGST + SGST (within state)" value="cgst_sgst" />
-                    <RadioButton id="t-igst" labelText="IGST (inter-state)" value="igst" />
-                  </RadioButtonGroup>
+                  <p className="voiced-page__subtitle" style={{ marginBottom: 0 }}>
+                    {effectiveTaxType === "igst"
+                      ? "IGST (inter-state supply)"
+                      : "CGST + SGST (supply within the supplier's state)"}
+                  </p>
                 </Column>
                 <Column sm={4} md={4} lg={8}>
                   <NumberInput
@@ -511,6 +511,14 @@ export default function NewInvoice({ settings }: NewInvoiceProps) {
                     onChange={(_e, { value }) => setTaxRate(Number(value) || 0)}
                   />
                 </Column>
+                <Column sm={4} md={8} lg={16}>
+                  <Toggle
+                    id="reverseCharge"
+                    labelText="Tax payable on reverse charge"
+                    toggled={reverseCharge}
+                    onToggle={setReverseCharge}
+                  />
+                </Column>
               </>
             ) : null}
           </Grid>

src/views/Onboarding.tsx

@@ -15,9 +15,9 @@ import {
   TextInput,
 } from "@carbon/react";
 import { api } from "../lib/api";
-import type { BankAccount, Settings, TaxType } from "../lib/types";
+import type { BankAccount, GstRegistration, Settings, TaxType } from "../lib/types";
 import { INDIAN_STATES } from "../lib/types";
-import { emailError, ifscError, panError, phoneError } from "../lib/validators";
+import { emailError, ifscError, panError, phoneError, vendorGstinError } from "../lib/validators";
 import { ImagePicker } from "../components/ImagePicker";
 
 interface OnboardingProps {
@@ -73,9 +73,22 @@ export default function Onboarding({ initial, onDone }: OnboardingProps) {
   const bankSet = <K extends keyof BankAccount>(key: K, value: BankAccount[K]) =>
     setBank((prev) => ({ ...prev, [key]: value }));
 
+  const registered = form.gstRegistration !== "unregistered";
+  const gstinProblem = vendorGstinError(
+    form.gstRegistration,
+    form.vendorGstin,
+    form.vendorPan,
+    form.vendorStateCode,
+  );
   const businessInvalid = useMemo(
-    () => Boolean(panError(form.vendorPan) || emailError(form.vendorEmail) || phoneError(form.vendorPhone)),
-    [form.vendorPan, form.vendorEmail, form.vendorPhone],
+    () =>
+      Boolean(
+        panError(form.vendorPan) ||
+          emailError(form.vendorEmail) ||
+          phoneError(form.vendorPhone) ||
+          gstinProblem,
+      ),
+    [form.vendorPan, form.vendorEmail, form.vendorPhone, gstinProblem],
   );
 
   const finish = async () => {
@@ -110,6 +123,22 @@ export default function Onboarding({ initial, onDone }: OnboardingProps) {
               adjust anything that has changed.
             </p>
           </Column>
+          <Column sm={4} md={8} lg={12}>
+            <RadioButtonGroup
+              legendText="GST registration"
+              name="ob-gstReg"
+              orientation="horizontal"
+              valueSelected={form.gstRegistration}
+              onChange={(value) => {
+                set("gstRegistration", value as GstRegistration);
+                if (value === "unregistered") set("defaultTaxType", "none");
+                else if (form.defaultTaxType === "none") set("defaultTaxType", "cgst_sgst");
+              }}
+            >
+              <RadioButton id="ob-gr-un" labelText="Unregistered" value="unregistered" />
+              <RadioButton id="ob-gr-reg" labelText="Regular" value="regular" />
+            </RadioButtonGroup>
+          </Column>
           <Column sm={4} md={8} lg={12}>
             <TextInput
               id="vendorName"
@@ -158,14 +187,18 @@ export default function Onboarding({ initial, onDone }: OnboardingProps) {
               invalidText={panError(form.vendorPan)}
             />
           </Column>
-          <Column sm={4} md={4} lg={6}>
-            <TextInput
-              id="vendorGstin"
-              labelText="GSTIN (leave blank if not registered)"
-              value={form.vendorGstin}
-              onChange={(e) => set("vendorGstin", e.target.value.toUpperCase())}
-            />
-          </Column>
+          {registered ? (
+            <Column sm={4} md={4} lg={6}>
+              <TextInput
+                id="vendorGstin"
+                labelText="GSTIN"
+                value={form.vendorGstin}
+                onChange={(e) => set("vendorGstin", e.target.value.toUpperCase())}
+                invalid={Boolean(gstinProblem)}
+                invalidText={gstinProblem}
+              />
+            </Column>
+          ) : null}
           <Column sm={4} md={8} lg={12}>
             <Select
               id="vendorState"
@@ -287,16 +320,18 @@ export default function Onboarding({ initial, onDone }: OnboardingProps) {
               onChange={(_e, { value }) => setPadding(Number(value) || 3)}
             />
           </Column>
-          <Column sm={4} md={4} lg={6}>
-            <NumberInput
-              id="taxRate"
-              label="Default tax rate (%)"
-              min={0}
-              max={100}
-              value={form.defaultTaxRate}
-              onChange={(_e, { value }) => set("defaultTaxRate", Number(value) || 0)}
-            />
-          </Column>
+          {registered ? (
+            <Column sm={4} md={4} lg={6}>
+              <NumberInput
+                id="taxRate"
+                label="Default tax rate (%)"
+                min={0}
+                max={100}
+                value={form.defaultTaxRate}
+                onChange={(_e, { value }) => set("defaultTaxRate", Number(value) || 0)}
+              />
+            </Column>
+          ) : null}
           <Column sm={4} md={4} lg={6}>
             <NumberInput
               id="terms"
@@ -307,18 +342,20 @@ export default function Onboarding({ initial, onDone }: OnboardingProps) {
               onChange={(_e, { value }) => set("paymentTermsDays", Number(value) || 0)}
             />
           </Column>
-          <Column sm={4} md={8} lg={12}>
-            <RadioButtonGroup
-              legendText="Default tax treatment"
-              name="taxType"
-              valueSelected={form.defaultTaxType}
-              onChange={(value) => set("defaultTaxType", value as TaxType)}
-            >
-              <RadioButton id="tt-cgst" labelText="CGST + SGST (within state)" value="cgst_sgst" />
-              <RadioButton id="tt-igst" labelText="IGST (inter-state)" value="igst" />
-              <RadioButton id="tt-none" labelText="No tax" value="none" />
-            </RadioButtonGroup>
-          </Column>
+          {registered ? (
+            <Column sm={4} md={8} lg={12}>
+              <RadioButtonGroup
+                legendText="Default tax treatment"
+                name="taxType"
+                valueSelected={form.defaultTaxType}
+                onChange={(value) => set("defaultTaxType", value as TaxType)}
+              >
+                <RadioButton id="tt-cgst" labelText="CGST + SGST (within state)" value="cgst_sgst" />
+                <RadioButton id="tt-igst" labelText="IGST (inter-state)" value="igst" />
+                <RadioButton id="tt-none" labelText="No tax" value="none" />
+              </RadioButtonGroup>
+            </Column>
+          ) : null}
         </Grid>
       ),
     },