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/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>