feat: create validated ZUGFeRD invoices in one console command

jr_einvoice/calc.py

@@ -1,24 +1,28 @@
-from __future__ import annotations
 from dataclasses import dataclass
-from typing import Dict
+from decimal import Decimal, ROUND_HALF_UP
 from .models import Invoice
 
+CENT = Decimal('0.01')
+
+def rounded(value: Decimal) -> Decimal:
+    return value.quantize(CENT, rounding=ROUND_HALF_UP)
+
+def line_net(item) -> Decimal:
+    return rounded(item.quantity * item.unit_price_net)
+
 @dataclass(frozen=True)
 class Totals:
-    net_total: float
-    tax_total: float
-    gross_total: float
-    tax_by_rate: Dict[float, float]
+    net_total: Decimal
+    tax_total: Decimal
+    gross_total: Decimal
+    tax_by_rate: dict[Decimal, Decimal]
+    basis_by_rate: dict[Decimal, Decimal]
 
 def compute_totals(inv: Invoice) -> Totals:
-    net = 0.0
-    tax_total = 0.0
-    tax_by_rate: Dict[float, float] = {}
-    for it in inv.items:
-        line_net = float(it.quantity) * float(it.unit_price_net)
-        net += line_net
-        tax = line_net * float(it.tax_rate) / 100.0
-        tax_total += tax
-        tax_by_rate[it.tax_rate] = tax_by_rate.get(it.tax_rate, 0.0) + tax
-    gross = net + tax_total
-    return Totals(net_total=net, tax_total=tax_total, gross_total=gross, tax_by_rate=tax_by_rate)
+    bases = {}
+    for item in inv.items:
+        bases[item.tax_rate] = bases.get(item.tax_rate, Decimal(0)) + line_net(item)
+    taxes = {rate: rounded(base * rate / 100) for rate, base in bases.items()}
+    net = sum(bases.values(), Decimal(0))
+    tax = sum(taxes.values(), Decimal(0))
+    return Totals(net, tax, net + tax, taxes, bases)