fix(SEPA Payment Order): keep stored BIC and sync bank name (backport #459)

banking/docs/en/banking/sepa-payment-order.md

@@ -24,9 +24,9 @@ SEPA Payment Orders enable users to:
 - Ensures compliance with IBAN standards before submission
 
 ### 2. Automatic BIC and Bank Name Resolution
-- EUR payments from an EEA IBAN to an EEA IBAN do not need a BIC. The system removes the BIC from these payments.
+- EUR payments from an EEA IBAN to an EEA IBAN do not need a BIC. The system leaves out the BIC from the XML file for these payments.
 - All other payments (e.g. from or to Switzerland) keep the BIC. If the BIC does not belong to the IBAN, submit fails and the error shows the row.
-- For German IBANs (starting with "DE"), the system populates the bank name.
+- The system sets the bank name from the IBAN (German, Austrian and Swiss IBANs) or else from the BIC. When neither is known, the bank name is empty.
 - A **Bank Account** with a German IBAN can only link to a **Bank** whose _SWIFT Number_ belongs to that IBAN.
 
 ### 3. Currency Validation

banking/ebics/doctype/sepa_payment_order/sepa_payment_order.py

@@ -76,18 +76,9 @@ class SEPAPaymentOrder(Document):
 
 	def before_validate(self):
 		register_fintech()
-		from fintech import iban
-
-		debtor_in_eea = (self.iban or "")[:2].upper() in EEA_COUNTRIES
 		for payment in self.payments:
-			country = (payment.iban or "")[:2].upper()
-			if debtor_in_eea and country in EEA_COUNTRIES and payment.currency == "EUR":
-				# SEPA payments within the EEA are IBAN-only. A BIC copied from the Bank can
-				# belong to another branch, which makes the payment fail.
-				payment.swift_number = None
-			if country == "DE" and not payment.bank_name:
-				with contextlib.suppress(Exception):
-					payment.bank_name = iban.get_bankname(payment.iban)
+			# Read-only, so always derive it from the current IBAN or BIC. Else it goes stale.
+			payment.bank_name = get_bank_name(payment.iban, payment.swift_number)
 
 	def validate(self):
 		self.validate_ibans()
@@ -255,19 +246,27 @@ def to_sepa_credit_transfer(self) -> "SEPACreditTransfer":
 			batch=self.batch_booking == "Process as batch",
 			scheme=self.scheme,
 		)
+		debtor_in_eea = self.iban[:2].upper() in EEA_COUNTRIES
 		invalid_rows = []
 		for payment in self.payments:
 			iban = payment.iban.replace(" ", "")
+			bic = payment.swift_number
+			if debtor_in_eea and iban[:2].upper() in EEA_COUNTRIES and payment.currency == "EUR":
+				# SEPA payments within the EEA are IBAN-only. A BIC copied from the Bank can
+				# belong to another branch, which makes the payment fail. Keep the stored BIC,
+				# in case debtor, IBAN or currency change later.
+				bic = None
+
 			try:
 				account = Account(
-					iban=(iban, payment.swift_number) if payment.swift_number else iban,
+					iban=(iban, bic) if bic else iban,
 					name=payment.recipient,
 				)
 			except ValueError:
-				if payment.swift_number:
+				if bic:
 					message = _(
 						"Row {0}: BIC {1} does not belong to IBAN {2}. Please correct or remove the BIC."
-					).format(payment.idx, payment.swift_number, iban)
+					).format(payment.idx, bic, iban)
 				else:
 					message = _("Row {0}: IBAN {1} is invalid.").format(payment.idx, iban)
 				invalid_rows.append(message)
@@ -358,6 +357,23 @@ def get_payable_expense_claims(company: str, currency: str, date: str, posted_fr
 	)
 
 
+def get_bank_name(iban: str | None, bic: str | None) -> str | None:
+	"""Return the bank name for a DE, AT or CH IBAN, or for a European BIC.
+
+	NOTE: call register_fintech() before calling this function.
+	"""
+	from fintech import iban as fintech_iban
+
+	for iban_or_bic in (iban, bic):
+		if not iban_or_bic:
+			continue
+		# Unsupported country or unknown BIC
+		with contextlib.suppress(ValueError, NotImplementedError):
+			return fintech_iban.get_bankname(iban_or_bic)
+
+	return None
+
+
 @frappe.whitelist()
 def get_recipient_details(doctype: str, name: str):
 	"""Return recipient and IBAN for Supplier or Employee."""

banking/ebics/doctype/sepa_payment_order/test_sepa_payment_order.py

@@ -205,9 +205,26 @@ def test_eea_payment_has_no_bic(self):
 
 		order.run_method("before_validate")
 
-		self.assertFalse(order.payments[0].swift_number)
+		# Stored BIC is kept, in case the payment later needs it
+		self.assertEqual(order.payments[0].swift_number, "DEUTDEFF")
 		order.verify_xml_render()
 
+	def test_bank_name_follows_iban(self):
+		order = self.new_payment_order(execution_date=today())
+		self.add_payment(order, SUPPLIER_IBAN, swift_number=None)
+		order.run_method("before_validate")
+		self.assertEqual(order.payments[0].bank_name, "BSK 1818 AG")
+
+		# Unsupported country without BIC: stale name is cleared
+		order.payments[0].iban = "FR1420041010050500013M02606"
+		order.run_method("before_validate")
+		self.assertIsNone(order.payments[0].bank_name)
+
+		# Falls back to the BIC
+		order.payments[0].swift_number = "BNPAFRPP"
+		order.run_method("before_validate")
+		self.assertEqual(order.payments[0].bank_name, "BNP PARIBAS SA")
+
 	def test_bic_mismatch_names_row(self):
 		order = self.new_payment_order(execution_date=today())
 		self.add_payment(order, SUPPLIER_IBAN, swift_number=None)