feat: add document-level discount (BT-21) and Skonto payment terms (BT-20)

invoice_logic.py

@@ -89,6 +89,31 @@ def berechne_faelligkeit(invoice_date_str, term_days):
     return (base_date + timedelta(days=days)).strftime("%Y-%m-%d")
 
 
+def format_skonto_text(skonto_percent, skonto_days, invoice_date_str):
+    """Baut den Freitext fuer eine Skonto-Vereinbarung. EN16931 kennt kein eigenes strukturiertes
+    Skonto-Feld - der Text wird daher als cbc:Note (UBL) bzw. ram:Description (CII) neben dem
+    regulaeren Faelligkeitsdatum in den Zahlungsbedingungen (BT-20) abgelegt. Gibt "" zurueck,
+    wenn kein gueltiges Skonto vereinbart ist (KEIN Rateraten bei fehlenden Angaben)."""
+    try:
+        percent = float(skonto_percent)
+    except (TypeError, ValueError):
+        return ""
+    if percent <= 0:
+        return ""
+    try:
+        days = int(skonto_days)
+    except (TypeError, ValueError):
+        return ""
+    if days <= 0:
+        return ""
+
+    percent_str = f"{percent:.2f}".rstrip("0").rstrip(".")
+    skonto_date = berechne_faelligkeit(invoice_date_str, days)
+    if skonto_date:
+        return f"Bei Zahlung bis {skonto_date} gewähren wir {percent_str}% Skonto."
+    return f"Bei Zahlung innerhalb von {days} Tagen gewähren wir {percent_str}% Skonto."
+
+
 def kaufmaennisches_runden(betrag, nachkommastellen=2):
     if not betrag:
         return 0.0
@@ -384,6 +409,33 @@ def generate_compliant_xrechnung(data):
     payee_acc = ET.SubElement(payment_means, f"{{{CAC}}}PayeeFinancialAccount")
     ET.SubElement(payee_acc, f"{{{CBC}}}ID").text = str(data["iban"]).replace(" ", "")
 
+    # BT-20 Skonto-Vereinbarung als Freitext in cac:PaymentTerms/cbc:Note - EN16931 kennt kein
+    # eigenes strukturiertes Skonto-Feld. Muss laut UBL-Schema NACH PaymentMeans und VOR
+    # AllowanceCharge/TaxTotal stehen.
+    _skonto_text = format_skonto_text(data.get("skonto_percent"), data.get("skonto_days"), data["invoice_date"])
+    if _skonto_text:
+        payment_terms = ET.SubElement(root, f"{{{CAC}}}PaymentTerms")
+        ET.SubElement(payment_terms, f"{{{CBC}}}Note").text = _skonto_text
+
+    # BT-21 Dokumentenweiter Rabatt (BG-20). Muss laut UBL-Schema NACH PaymentTerms und VOR
+    # TaxTotal stehen. Voll EN16931-konform: bei gemischten Steuersaetzen wird JE Steuersatz ein
+    # eigener AllowanceCharge-Block mit dem anteilig zugeordneten Rabattbetrag erzeugt, damit jede
+    # Steuergruppe (BG-23) ihren eigenen Rabattanteil fuehrt (BR-CO-10/BR-DEC).
+    if data.get("allowance_amount", 0.0) > 0:
+        for bucket in data.get("tax_buckets") or []:
+            bucket_allowance = bucket.get("allowance_amount", 0.0)
+            if bucket_allowance <= 0:
+                continue
+            allowance_charge = ET.SubElement(root, f"{{{CAC}}}AllowanceCharge")
+            ET.SubElement(allowance_charge, f"{{{CBC}}}ChargeIndicator").text = "false"
+            ET.SubElement(allowance_charge, f"{{{CBC}}}AllowanceChargeReason").text = str(data.get("allowance_reason") or "Rabatt")
+            ET.SubElement(allowance_charge, f"{{{CBC}}}Amount", {"currencyID": "EUR"}).text = f"{bucket_allowance:.2f}"
+            ac_tax_cat = ET.SubElement(allowance_charge, f"{{{CAC}}}TaxCategory")
+            ET.SubElement(ac_tax_cat, f"{{{CBC}}}ID").text = bucket["category"]
+            ET.SubElement(ac_tax_cat, f"{{{CBC}}}Percent").text = f"{bucket['rate']:.2f}"
+            ac_tax_scheme = ET.SubElement(ac_tax_cat, f"{{{CAC}}}TaxScheme")
+            ET.SubElement(ac_tax_scheme, f"{{{CBC}}}ID").text = "VAT"
+
     # --- STEUERN (Gezielt erzwungener CBC Namespace für Beträge) ---
     tax_total = ET.SubElement(root, f"{{{CAC}}}TaxTotal")
     ET.SubElement(tax_total, f"{{{CBC}}}TaxAmount", {"currencyID": "EUR"}).text = f"{data['total_vat_amount']:.2f}"
@@ -644,15 +696,38 @@ def generate_compliant_zugferd_cii(data):
         end_pt = ET.SubElement(period, f"{{{RAM}}}EndDateTime")
         ET.SubElement(end_pt, f"{{{UDT}}}DateTimeString", {"format": "102"}).text = format_cii_date(data["service_end_date"])
 
-    # BT-9 Fälligkeitsdatum, abgeleitet aus dem tatsächlichen Zahlungsziel der Rechnung. Erfüllt
+    # BT-21 Dokumentenweiter Rabatt (BG-20). Muss laut CII-Schema NACH BillingSpecifiedPeriod und
-    # allein BR-CO-25 (Fälligkeitsdatum ODER Zahlungsbedingungen - wir nutzen nur das Datum).
+    # VOR SpecifiedTradePaymentTerms stehen. Voll EN16931-konform: bei gemischten Steuersaetzen wird
-    # Kein fester Fallback: ohne gültiges Zahlungsziel wird der Block weggelassen (die UI blockiert
+    # JE Steuersatz ein eigener SpecifiedTradeAllowanceCharge-Block mit dem anteilig zugeordneten
-    # dann den Export).
+    # Rabattbetrag erzeugt (jede Steuergruppe fuehrt ihren eigenen Rabattanteil).
+    if data.get("allowance_amount", 0.0) > 0:
+        for bucket in data.get("tax_buckets") or []:
+            bucket_allowance = bucket.get("allowance_amount", 0.0)
+            if bucket_allowance <= 0:
+                continue
+            allowance_charge = ET.SubElement(header_settle, f"{{{RAM}}}SpecifiedTradeAllowanceCharge")
+            indicator = ET.SubElement(allowance_charge, f"{{{RAM}}}ChargeIndicator")
+            ET.SubElement(indicator, f"{{{UDT}}}Indicator").text = "false"
+            ET.SubElement(allowance_charge, f"{{{RAM}}}ActualAmount").text = f"{bucket_allowance:.2f}"
+            ET.SubElement(allowance_charge, f"{{{RAM}}}Reason").text = str(data.get("allowance_reason") or "Rabatt")
+            ac_tax = ET.SubElement(allowance_charge, f"{{{RAM}}}CategoryTradeTax")
+            ET.SubElement(ac_tax, f"{{{RAM}}}TypeCode").text = "VAT"
+            ET.SubElement(ac_tax, f"{{{RAM}}}CategoryCode").text = bucket["category"]
+            ET.SubElement(ac_tax, f"{{{RAM}}}RateApplicablePercent").text = f"{bucket['rate']:.2f}"
+
+    # BT-9 Fälligkeitsdatum, abgeleitet aus dem tatsächlichen Zahlungsziel der Rechnung, sowie
+    # optional die BT-20 Skonto-Freitextbeschreibung. ram:Description muss laut Schema VOR
+    # ram:DueDateDateTime stehen. Kein fester Fallback: ohne gültiges Zahlungsziel UND ohne
+    # Skonto wird der Block weggelassen (die UI blockiert dann den Export bzgl. Zahlungsziel).
     _cii_due = berechne_faelligkeit(data["invoice_date"], data.get("payment_term_days"))
-    if _cii_due:
+    _skonto_text = format_skonto_text(data.get("skonto_percent"), data.get("skonto_days"), data["invoice_date"])
+    if _cii_due or _skonto_text:
         payment_terms = ET.SubElement(header_settle, f"{{{RAM}}}SpecifiedTradePaymentTerms")
-        due_date_elem = ET.SubElement(payment_terms, f"{{{RAM}}}DueDateDateTime")
+        if _skonto_text:
-        ET.SubElement(due_date_elem, f"{{{UDT}}}DateTimeString", {"format": "102"}).text = _cii_due.replace("-", "")
+            ET.SubElement(payment_terms, f"{{{RAM}}}Description").text = _skonto_text
+        if _cii_due:
+            due_date_elem = ET.SubElement(payment_terms, f"{{{RAM}}}DueDateDateTime")
+            ET.SubElement(due_date_elem, f"{{{UDT}}}DateTimeString", {"format": "102"}).text = _cii_due.replace("-", "")
 
     header_sum = ET.SubElement(header_settle, f"{{{RAM}}}SpecifiedTradeSettlementHeaderMonetarySummation")
     ET.SubElement(header_sum, f"{{{RAM}}}LineTotalAmount").text = f"{data.get('line_net_total', data['total_net_amount']):.2f}"

main.py

@@ -330,7 +330,17 @@ with col2:
         # pro Position mit dem jeweils eingetragenen Steuersatz (Multi-Tax-Support).
         vat_rate = st.number_input("Standard-Steuersatz für neue Positionen (%)", value=float(data.get("vat_rate_percent") or 19.0))
 
-        totals = compute_invoice_totals(edited_items)
+        c_disc1, c_disc2, c_disc3, c_disc4 = st.columns(4)
+        with c_disc1:
+            discount_percent = st.number_input("Rabatt (BT-21, %)", value=0.0, min_value=0.0, max_value=100.0, step=0.5)
+        with c_disc2:
+            discount_reason = st.text_input("Rabattgrund", value="")
+        with c_disc3:
+            skonto_percent = st.number_input("Skonto (BT-20, %)", value=0.0, min_value=0.0, max_value=100.0, step=0.5)
+        with c_disc4:
+            skonto_days = st.text_input("Skonto-Frist (Tage)", value="")
+
+        totals = compute_invoice_totals(edited_items, discount_percent=discount_percent)
         computed_net_amount = totals["tax_basis_total"]
         computed_vat_amount = totals["total_vat_amount"]
         computed_gross_amount = totals["total_gross_amount"]
@@ -360,6 +370,9 @@ with col2:
             "tax_buckets": totals["tax_buckets"],
             "line_net_total": totals["line_net_total"],
             "allowance_amount": totals["allowance_amount"],
+            "allowance_reason": discount_reason,
+            "skonto_percent": skonto_percent,
+            "skonto_days": skonto_days,
             "delivery_note_id": dn_id,
             "order_id": o_id,
             "contract_id": c_id,

tests/test_invoice_logic.py

@@ -14,6 +14,7 @@ from invoice_logic import (
     PAYMENT_MEANS_CODES,
     aggregate_tax_subtotals,
     compute_invoice_totals,
+    format_skonto_text,
 )
 
 
@@ -215,3 +216,91 @@ def test_generate_compliant_zugferd_cii_mixed_rates_two_header_taxes():
     header_taxes = root.findall(
         ".//ram:ApplicableHeaderTradeSettlement/ram:ApplicableTradeTax", ns)
     assert len(header_taxes) == 2
+
+
+def test_format_skonto_text_with_valid_percent_and_days():
+    text = format_skonto_text(2.0, 10, "2026-01-15")
+    assert "2026-01-25" in text
+    assert "2%" in text
+
+
+def test_format_skonto_text_returns_empty_when_no_percent():
+    assert format_skonto_text(0, 10, "2026-01-15") == ""
+    assert format_skonto_text(None, 10, "2026-01-15") == ""
+
+
+def test_format_skonto_text_returns_empty_when_no_days():
+    assert format_skonto_text(2.0, "", "2026-01-15") == ""
+    assert format_skonto_text(2.0, None, "2026-01-15") == ""
+
+
+def _discounted_invoice():
+    data = _single_rate_invoice()
+    items = [{"total_amount": 200.0, "vat_rate_percent": 19.0, "name": "Beratung",
+              "description": "", "quantity": 2.0, "unit": "Std.", "unit_price": 100.0}]
+    totals = compute_invoice_totals(items, discount_percent=10.0)
+    data["items"] = items
+    data["tax_buckets"] = totals["tax_buckets"]
+    data["line_net_total"] = totals["line_net_total"]
+    data["allowance_amount"] = totals["allowance_amount"]
+    data["allowance_reason"] = "Treuerabatt"
+    data["total_net_amount"] = totals["tax_basis_total"]
+    data["total_vat_amount"] = totals["total_vat_amount"]
+    data["total_gross_amount"] = totals["total_gross_amount"]
+    data["skonto_percent"] = 2.0
+    data["skonto_days"] = "10"
+    return data
+
+
+def test_generate_compliant_xrechnung_includes_allowance_charge_and_payment_terms():
+    xml_str = generate_compliant_xrechnung(_discounted_invoice())
+    root = ET.fromstring(xml_str.encode("utf-8"))
+    ns = {"cbc": "urn:oasis:names:specification:ubl:schema:xsd:CommonBasicComponents-2",
+          "cac": "urn:oasis:names:specification:ubl:schema:xsd:CommonAggregateComponents-2"}
+    allowance = root.find(".//cac:AllowanceCharge", ns)
+    assert allowance.find("cbc:AllowanceChargeReason", ns).text == "Treuerabatt"
+    assert allowance.find("cbc:Amount", ns).text == "20.00"
+    payment_terms_note = root.find(".//cac:PaymentTerms/cbc:Note", ns).text
+    assert "Skonto" in payment_terms_note
+
+
+def test_generate_compliant_zugferd_cii_includes_allowance_charge_and_payment_terms_description():
+    xml_str = generate_compliant_zugferd_cii(_discounted_invoice())
+    root = ET.fromstring(xml_str.encode("utf-8"))
+    ns = {"ram": "urn:un:unece:uncefact:data:standard:ReusableAggregateBusinessInformationEntity:100"}
+    allowance = root.find(".//ram:SpecifiedTradeAllowanceCharge", ns)
+    assert allowance.find("ram:ActualAmount", ns).text == "20.00"
+    assert allowance.find("ram:Reason", ns).text == "Treuerabatt"
+    description = root.find(".//ram:SpecifiedTradePaymentTerms/ram:Description", ns).text
+    assert "Skonto" in description
+
+
+def test_generate_compliant_xrechnung_mixed_rate_discount_emits_allowance_per_rate():
+    """Voll EN16931-konform: ein Rabatt auf eine Rechnung mit 19%- UND 7%-Positionen erzeugt
+    JE Steuersatz einen eigenen AllowanceCharge-Block mit anteiligem Rabattbetrag."""
+    items = [
+        {"total_amount": 100.0, "vat_rate_percent": 19.0, "name": "A", "description": "",
+         "quantity": 1.0, "unit": "Stk.", "unit_price": 100.0},
+        {"total_amount": 100.0, "vat_rate_percent": 7.0, "name": "B", "description": "",
+         "quantity": 1.0, "unit": "Stk.", "unit_price": 100.0},
+    ]
+    totals = compute_invoice_totals(items, discount_percent=10.0)
+    data = _single_rate_invoice()
+    data["items"] = items
+    data["tax_buckets"] = totals["tax_buckets"]
+    data["line_net_total"] = totals["line_net_total"]
+    data["allowance_amount"] = totals["allowance_amount"]
+    data["allowance_reason"] = "Aktionsrabatt"
+    data["total_net_amount"] = totals["tax_basis_total"]
+    data["total_vat_amount"] = totals["total_vat_amount"]
+    data["total_gross_amount"] = totals["total_gross_amount"]
+    xml_str = generate_compliant_xrechnung(data)
+    root = ET.fromstring(xml_str.encode("utf-8"))
+    ns = {"cbc": "urn:oasis:names:specification:ubl:schema:xsd:CommonBasicComponents-2",
+          "cac": "urn:oasis:names:specification:ubl:schema:xsd:CommonAggregateComponents-2"}
+    allowances = root.findall(".//cac:AllowanceCharge", ns)
+    assert len(allowances) == 2
+    percents = sorted(a.find("cac:TaxCategory/cbc:Percent", ns).text for a in allowances)
+    assert percents == ["19.00", "7.00"] or percents == ["7.00", "19.00"]
+    total_alloc = sum(float(a.find("cbc:Amount", ns).text) for a in allowances)
+    assert abs(total_alloc - 20.0) < 0.001