first commit

app/domain/costs.py

@@ -0,0 +1,14 @@
+from decimal import Decimal, ROUND_HALF_UP
+
+
+def money(value):
+    return Decimal(str(value)).quantize(Decimal("0.01"), rounding=ROUND_HALF_UP)
+
+
+def calculate_costs(gross, vat_rate=23, vat_deduction_percent=50):
+    gross = Decimal(str(gross)); rate = Decimal(str(vat_rate))
+    deduction = Decimal(str(vat_deduction_percent)) / Decimal("100")
+    net = gross / (Decimal("1") + rate / Decimal("100")); vat = gross - net
+    deductible_vat = vat * deduction
+    return {"gross": money(gross), "net": money(net), "vat": money(vat),
+            "deductible_vat": money(deductible_vat), "final_cost": money(gross - deductible_vat)}