feat: add support for OSS/IOSS

Author: samupl

src/ksef/models/invoice_rows.py

@@ -1,6 +1,7 @@
 """Models for individual invoice rows/positions."""
 
-from typing import Literal, Sequence
+from decimal import Decimal
+from typing import Literal, Optional, Sequence
 
 from pydantic import BaseModel
 
@@ -37,12 +38,16 @@
     "np II",
 ]
 
+# Set of valid P_12 integer rates for quick lookup
+VALID_P12_RATES = {23, 22, 8, 7, 5, 4, 3}
+
 
 class InvoiceRow(BaseModel):
     """Single individual invoice position."""
 
     name: str  # P_7, nazwa (rodzaj) towaru lub usługi
-    tax: TaxRate  # P_12, tax rate
+    tax: Optional[TaxRate] = None  # P_12, standard tax rate
+    tax_oss: Optional[Decimal] = None  # P_12_XII, OSS/IOSS procedure tax rate (arbitrary %)
 
 
 class InvoiceRows(BaseModel):

src/ksef/xml_converters.py

@@ -195,11 +195,16 @@ def _build_invoice_data(root: ElementTree.Element, invoice: Invoice) -> None:
         invoice_data_row = ElementTree.SubElement(invoice_data, "FaWiersz")
         invoice_data_row_number = ElementTree.SubElement(invoice_data_row, "NrWierszaFa")
         invoice_data_row_name = ElementTree.SubElement(invoice_data_row, "P_7")
-        invoice_data_row_tax_rate = ElementTree.SubElement(invoice_data_row, "P_12")
 
         invoice_data_row_number.text = str(index)
         invoice_data_row_name.text = row.name
-        invoice_data_row_tax_rate.text = str(row.tax)
+
+        if row.tax_oss is not None:
+            invoice_data_row_tax_oss = ElementTree.SubElement(invoice_data_row, "P_12_XII")
+            invoice_data_row_tax_oss.text = str(row.tax_oss)
+        elif row.tax is not None:
+            invoice_data_row_tax_rate = ElementTree.SubElement(invoice_data_row, "P_12")
+            invoice_data_row_tax_rate.text = str(row.tax)
 
 
 def convert_invoice_to_xml(invoice: Invoice, invoicing_software_name: str = "python-ksef") -> bytes: