Feat/voucher docs (#664)

* feat: implement inbox document picker and linking functionality

* feat: implement self-billing invoice functionality

- Added support for registering self-billed invoices received from customers.
- Updated the invoice schema to include fields for self-billing metadata such as `is_self_billed`, `external_invoice_number`, `self_billing_agreement_ref`, and `received_date`.
- Created API route for handling self-billed invoice submissions, including validation and error handling.
- Implemented database migrations to add necessary columns and constraints for self-billing invoices.
- Developed tests to ensure correct behavior of self-billing invoice creation and validation rules.
- Updated Swedish localization files to include new terms related to self-billing.

* feat: enforce SIE import requirement for non-Fortnox providers in migration process

* feat: streamline invoice processing and enhance error logging across APIs

lib/invoices/__tests__/ensure-invoice-number.test.ts

@@ -86,4 +86,34 @@ describe('ensureInvoiceNumber', () => {
       ensureInvoiceNumber(supabase as never, 'company-1', invoice)
     ).rejects.toThrow('no value returned')
   })
+
+  it('returns the external number for a self-billed invoice without touching the RPC', async () => {
+    // A received self-billing invoice carries the counterparty's number; we must
+    // never consume our own löpnummerserie (BFL 5 kap 6§).
+    const invoice = {
+      id: 'inv-1',
+      invoice_number: null,
+      is_self_billed: true,
+      external_invoice_number: 'KUND-55012',
+    }
+
+    const result = await ensureInvoiceNumber(supabase as never, 'company-1', invoice)
+
+    expect(result).toBe('KUND-55012')
+    expect(supabase.rpc).not.toHaveBeenCalled()
+  })
+
+  it('throws when a self-billed invoice is missing the external number', async () => {
+    const invoice = {
+      id: 'inv-1',
+      invoice_number: null,
+      is_self_billed: true,
+      external_invoice_number: null,
+    }
+
+    await expect(
+      ensureInvoiceNumber(supabase as never, 'company-1', invoice)
+    ).rejects.toThrow('missing external_invoice_number')
+    expect(supabase.rpc).not.toHaveBeenCalled()
+  })
 })

lib/invoices/display.ts

@@ -3,3 +3,16 @@ export const INVOICE_NUMBER_DRAFT_LABEL = '(Utkast)'
 export function invoiceNumberDisplay(value: string | null | undefined): string {
   return value ?? INVOICE_NUMBER_DRAFT_LABEL
 }
+
+/**
+ * The number to show for an invoice. Self-billing invoices we received carry
+ * the counterparty's number in `external_invoice_number` (our own
+ * `invoice_number` is null by design), so fall back to it before the draft
+ * label.
+ */
+export function invoiceDisplayNumber(invoice: {
+  invoice_number?: string | null
+  external_invoice_number?: string | null
+}): string {
+  return invoice.invoice_number ?? invoice.external_invoice_number ?? INVOICE_NUMBER_DRAFT_LABEL
+}

lib/invoices/ensure-invoice-number.ts

@@ -4,6 +4,8 @@ import type { Invoice, InvoiceDocumentType } from '@/types'
 type InvoiceShape = Pick<Invoice, 'id' | 'invoice_number'> & {
   invoice_number: string | null
   document_type?: InvoiceDocumentType | null
+  is_self_billed?: boolean | null
+  external_invoice_number?: string | null
 }
 
 /**
@@ -24,6 +26,17 @@ export async function ensureInvoiceNumber(
     return invoice.invoice_number
   }
 
+  // Self-billing invoices we received carry the COUNTERPARTY's number; we must
+  // never consume our own löpnummerserie for them (BFL 5 kap 6§). The DB
+  // constraint invoices_self_billed_numbering guarantees the external number is
+  // present, but guard here so a future caller can't silently mint an F-number.
+  if (invoice.is_self_billed) {
+    if (!invoice.external_invoice_number) {
+      throw new Error('Self-billed invoice is missing external_invoice_number')
+    }
+    return invoice.external_invoice_number
+  }
+
   const { data: assigned, error: rpcError } = await supabase.rpc('generate_invoice_number', {
     p_company_id: companyId,
     p_invoice_id: invoice.id,