fix: multi-tax detection and net_amount calculation

eu_einvoice/european_e_invoice/custom/sales_invoice.py

@@ -19,7 +19,7 @@
 from frappe.core.utils import html2text
 from frappe.model.naming import parse_naming_series
 from frappe.utils import cstr
-from frappe.utils.data import date_diff, flt, getdate, to_markdown
+from frappe.utils.data import cint, date_diff, flt, getdate, to_markdown
 
 from eu_einvoice.common_codes import CommonCodeRetriever
 from eu_einvoice.schematron import get_validation_errors
@@ -502,6 +502,23 @@ def _add_line_item(self, item: SalesInvoiceItem):
 		li.settlement.monetary_summation.total_amount = flt(item.net_amount, item.precision("net_amount"))
 		self.doc.trade.items.add(li)
 
+	def _sum_item_net_matching_on_net_total_rate(self, tax) -> float | None:
+		"""Sum ``net_amount`` for items whose resolved VAT % matches this tax row (multi-rate invoices)."""
+		tax_row_vat_percent = flt(
+			tax.rate or frappe.db.get_value("Account", tax.account_head, "tax_rate") or 0.0
+		)
+		if not tax_row_vat_percent:
+			return 0.0
+		sum_net_amount = 0
+		for line_item in self.invoice.items:
+			item_rate = get_item_rate(line_item.item_tax_template, self.invoice.taxes)
+			if item_rate is None:
+				return None
+			if flt(item_rate) == tax_row_vat_percent:
+				sum_net_amount += line_item.net_amount
+
+		return flt(sum_net_amount, self.invoice.precision("net_total"))
+
 	def _add_taxes_and_charges(self):
 		tax_added = False
 		for i, tax in enumerate(self.invoice.taxes):
@@ -528,6 +545,14 @@ def _add_taxes_and_charges(self):
 
 				self.doc.trade.settlement.service_charge.add(service_charge)
 			elif tax.charge_type == "On Net Total":
+				tax_rate = tax.rate or frappe.db.get_value("Account", tax.account_head, "tax_rate") or 0
+				# Skip rows with 0% tax rate and non-zero tax amount: Assumption here is that if a tax_rate
+				# is not 0% and the tax amount is 0, then the tax is not applicable, as no item with
+				# this tax rate exists and hence it would throw validation errors.
+				# Possible 0% tax rates and their codes can be applied as 0% VAT, does not
+				# create a tax_amount.
+				if tax.tax_amount == 0 and tax_rate != 0:
+					continue
 				trade_tax = ApplicableTradeTax()
 				trade_tax.calculated_amount = tax.tax_amount
 				trade_tax.type_code = "VAT"
@@ -538,7 +563,7 @@ def _add_taxes_and_charges(self):
 						("Sales Taxes and Charges Template", self.invoice.taxes_and_charges),
 					]
 				)
-				tax_rate = tax.rate or frappe.db.get_value("Account", tax.account_head, "tax_rate") or 0
+
 				trade_tax.rate_applicable_percent = tax_rate
 
 				if len(self.invoice.taxes) == 1:
@@ -548,15 +573,15 @@ def _add_taxes_and_charges(self):
 						# We only have one tax rate on the line items, but it was not specified on the tax row
 						# so we use the tax rate from the line items.
 						trade_tax.rate_applicable_percent = self.item_tax_rates.pop()
-				elif hasattr(tax, "net_amount"):
-					trade_tax.basis_amount = tax.net_amount
-				elif hasattr(tax, "custom_net_amount"):
-					trade_tax.basis_amount = tax.custom_net_amount
-				elif tax.tax_amount and tax_rate:
-					# We don't know the basis amount for this tax, so we try to calculate it
-					trade_tax.basis_amount = round(tax.tax_amount / tax_rate * 100, 2)
 				else:
-					trade_tax.basis_amount = 0
+					basis = (
+						self._sum_item_net_matching_on_net_total_rate(tax)
+						or (hasattr(tax, "net_amount") and flt(tax.net_amount))
+						or (hasattr(tax, "custom_net_amount") and flt(tax.custom_net_amount))
+						or (tax.tax_amount and tax_rate and round(tax.tax_amount / tax_rate * 100, 2))
+						or 0
+					)
+					trade_tax.basis_amount = basis
 
 				self.doc.trade.settlement.trade_tax.add(trade_tax)
 				tax_added = True
@@ -947,19 +972,36 @@ def _attach_xml_file(doc: SalesInvoice, xml_content: bytes, field_name: str | No
 		doc.db_set(field_name, file_doc.file_url)
 
 
-def get_item_rate(item_tax_template: str | None, taxes: list[dict]) -> float | None:
-	"""Get the tax rate for an item from the item tax template and the taxes table."""
+def get_item_rate(item_tax_template: str | None, taxes: list) -> float | None:
+	"""Resolve the VAT % for this line from the Item Tax Template and the invoice tax rows.
+
+	1) Return the ``tax_rate`` of the first template row (in template order) whose ``tax_type``
+	   matches one of the invoice's ``account_head`` values. On ERPNext v15 and earlier, only
+	   non-zero rates are considered. From v16 (``not_applicable`` on **Item Tax Template Detail**),
+	   zero rates are included and rows with ``not_applicable`` set are excluded.
+	2) If the template did not match: if there is exactly one *On Net Total* row, use its ``rate``.
+	"""
 	if item_tax_template:
-		# match the accounts from the taxes table with the rate from the item tax template
-		tax_template = frappe.get_doc("Item Tax Template", item_tax_template)
+		tax_template = frappe.get_cached_doc("Item Tax Template", item_tax_template)
 		applicable_accounts = [tax.account_head for tax in taxes if tax.account_head]
+		has_not_applicable = bool(frappe.get_meta("Item Tax Template Detail").get_field("not_applicable"))
+
+		def _template_row_matches(item_tax) -> bool:
+			if item_tax.tax_type not in applicable_accounts:
+				return False
+			if has_not_applicable:
+				return not cint(getattr(item_tax, "not_applicable", 0))
+			return bool(item_tax.tax_rate)
 
 		for item_tax in tax_template.taxes:
-			if item_tax.tax_type in applicable_accounts:
+			if _template_row_matches(item_tax):
 				return item_tax.tax_rate
 
-	# if only one tax is on net total, return its rate
-	tax_rates = [invoice_tax.rate for invoice_tax in taxes if invoice_tax.charge_type == "On Net Total"]
+	tax_rates = [
+		invoice_tax.rate
+		for invoice_tax in taxes
+		if invoice_tax.charge_type == "On Net Total" and invoice_tax.rate is not None
+	]
 	return tax_rates[0] if len(tax_rates) == 1 else None