Add bill line charge rate and quantity

CHANGELOG.md

@@ -8,14 +8,16 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/) and this p
 
 ### Added
 
-- `bill`: Line discount and charge `base` property, to use instead of the line sum in order to comply with EN16931.
+- `bill`: line discount and charge `base` property, to use instead of the line sum in order to comply with EN16931.
+- `bill`: line Charge support for Quantity and Rate special cases for charges like tariffs that result in a fixed amount base on a rate, like, 1 cent for every 100g of sugar.
 
 ### Changed
 
 - `bill`: line totals will be rounded to currency precision for presentation only
 - `bill`: document Discount and Charge base and amounts always rounded to currency's precision
 - `bill`: line Discount and Charge base and amounts always rounded to currency's precision
-- `bill`: `round-then-sum` rounding rule _now_ implies that line totals will not be calculated with additional precision, this brings closer aliance with EN16931 requirements.
+- `tax`: renamed rounding rules `sum-then-round` to `precise`, and `round-then-sum` to `currency`, to more accurately reflect their objectives.
+- `bill`: `currency` rounding rule implies that line totals will be calculated with the currency's precisions, bringing closer alliance with EN16931 requirements.
 
 ## [v0.211.0] - 2025-02-28
 

bill/bill.go

@@ -12,6 +12,7 @@ func init() {
 		Order{},
 		Payment{},
 		CorrectionOptions{},
+		Line{},
 	)
 }
 

bill/calculator.go

@@ -192,6 +192,9 @@ func calculate(doc billable) error {
 		pd.Terms.CalculateDues(zero, t.Payable)
 	}
 
+	roundLines(doc.getLines(), cur)
+	roundDiscounts(doc.getDiscounts(), cur)
+	roundCharges(doc.getCharges(), cur)
 	t.round(zero)
 	doc.setTotals(t)
 

bill/calculator_test.go

@@ -43,11 +43,11 @@ func TestCalculate(t *testing.T) {
 			},
 		})
 		inv.Tax.PricesInclude = ""
-		inv.Tax.Rounding = tax.RoundingRuleRoundThenSum
+		inv.Tax.Rounding = tax.RoundingRuleCurrency
 		require.NoError(t, inv.Calculate())
 		assert.Equal(t, "3.48", inv.Totals.Tax.String())
 
-		inv.Tax.Rounding = tax.RoundingRuleSumThenRound
+		inv.Tax.Rounding = tax.RoundingRulePrecise
 		require.NoError(t, inv.Calculate())
 		assert.Equal(t, "3.49", inv.Totals.Tax.String())
 	})

bill/charges.go

@@ -103,9 +103,6 @@ type Charge struct {
 	Ext tax.Extensions `json:"ext,omitempty" jsonschema:"title=Extensions"`
 	// Additional semi-structured information.
 	Meta cbc.Meta `json:"meta,omitempty" jsonschema:"title=Meta"`
-
-	// internal amount for calculations
-	amount num.Amount
 }
 
 // Normalize performs normalization on the line and embedded objects using the
@@ -175,14 +172,12 @@ func calculateCharges(lines []*Charge, cur currency.Code, sum num.Amount, rr cbc
 		if l.Percent != nil && !l.Percent.IsZero() {
 			base := sum
 			if l.Base != nil {
-				base = l.Base.RescaleUp(zero.Exp())
+				base = l.Base.RescaleUp(zero.Exp() + linePrecisionExtra)
+				base = tax.ApplyRoundingRule(rr, cur, base)
 			}
-			l.amount = l.Percent.Of(base)
-			l.amount = tax.ApplyRoundingRule(rr, cur, l.amount)
-		} else {
-			l.amount = l.Amount.Rescale(zero.Exp())
+			l.Amount = l.Percent.Of(base)
 		}
-		l.Amount = l.amount.Rescale(zero.Exp())
+		l.Amount = tax.ApplyRoundingRule(rr, cur, l.Amount)
 	}
 }
 
@@ -192,12 +187,23 @@ func calculateChargeSum(charges []*Charge, cur currency.Code) *num.Amount {
 	}
 	total := cur.Def().Zero()
 	for _, l := range charges {
-		total = total.MatchPrecision(l.amount)
-		total = total.Add(l.amount)
+		total = total.MatchPrecision(l.Amount)
+		total = total.Add(l.Amount)
 	}
 	return &total
 }
 
+func (m *Charge) round(cur currency.Code) {
+	cd := cur.Def()
+	m.Amount = cd.Rescale(m.Amount)
+}
+
+func roundCharges(lines []*Charge, cur currency.Code) {
+	for _, l := range lines {
+		l.round(cur)
+	}
+}
+
 func extendJSONSchemaWithChargeKey(schema *jsonschema.Schema) {
 	prop, ok := schema.Properties.Get("key")
 	if !ok {

bill/charges_test.go

@@ -48,22 +48,24 @@ func TestChargeTotals(t *testing.T) {
 			},
 		}
 		base := num.MakeAmount(30000, 2)
-		calculateCharges(ls, currency.EUR, base, tax.RoundingRuleSumThenRound)
+		calculateCharges(ls, currency.EUR, base, tax.RoundingRulePrecise)
 		sum := calculateChargeSum(ls, currency.EUR)
 		require.NotNil(t, sum)
 		assert.Equal(t, 1, ls[0].Index)
 		assert.Nil(t, ls[0].Base)
 		assert.Equal(t, 2, ls[1].Index)
-		assert.Equal(t, "200.00", sum.String())
+		assert.Equal(t, "200.0000", sum.String())
 		assert.Equal(t, "100.00", ls[0].Amount.String())
 		assert.Nil(t, ls[1].Base)
 		assert.Equal(t, "20%", ls[1].Percent.String())
 		assert.Equal(t, "60.00", ls[1].Amount.String())
 		assert.Equal(t, "200.00", ls[2].Base.String())
+		assert.Equal(t, "40.0000", ls[2].Amount.String())
+		roundCharges(ls, currency.EUR)
 		assert.Equal(t, "40.00", ls[2].Amount.String())
 
 		ls = []*Charge{}
-		calculateCharges(ls, currency.EUR, base, tax.RoundingRuleSumThenRound)
+		calculateCharges(ls, currency.EUR, base, tax.RoundingRulePrecise)
 		sum = calculateChargeSum(ls, currency.EUR)
 		assert.Nil(t, sum)
 	})
@@ -80,13 +82,14 @@ func TestChargeTotals(t *testing.T) {
 			},
 		}
 		base := num.MakeAmount(30844212, 6)
-		calculateCharges(ls, currency.EUR, base, tax.RoundingRuleSumThenRound)
+		calculateCharges(ls, currency.EUR, base, tax.RoundingRulePrecise)
 		sum := calculateChargeSum(ls, currency.EUR)
 		require.NotNil(t, sum)
 		assert.Equal(t, "50.00", ls[0].Amount.String())
-		assert.Equal(t, "6.17", ls[1].Amount.String())
-		assert.Equal(t, "6.168842", ls[1].amount.String())
+		assert.Equal(t, "6.168842", ls[1].Amount.String())
 		assert.Equal(t, "56.168842", sum.String())
+		roundCharges(ls, currency.EUR)
+		assert.Equal(t, "6.17", ls[1].Amount.String())
 	})
 
 	t.Run("with precision, round-then-sum", func(t *testing.T) {
@@ -101,14 +104,14 @@ func TestChargeTotals(t *testing.T) {
 			},
 		}
 		base := num.MakeAmount(30844212, 6)
-		calculateCharges(ls, currency.EUR, base, tax.RoundingRuleRoundThenSum)
+		calculateCharges(ls, currency.EUR, base, tax.RoundingRuleCurrency)
 		sum := calculateChargeSum(ls, currency.EUR)
 		require.NotNil(t, sum)
-		assert.Equal(t, "50.00", ls[0].amount.String())
 		assert.Equal(t, "50.00", ls[0].Amount.String())
 		assert.Equal(t, "6.17", ls[1].Amount.String())
-		assert.Equal(t, "6.17", ls[1].amount.String())
 		assert.Equal(t, "56.17", sum.String())
+		roundCharges(ls, currency.EUR)
+		assert.Equal(t, "6.17", ls[1].Amount.String()) // no change
 	})
 
 	t.Run("with fixed base", func(t *testing.T) {
@@ -120,11 +123,13 @@ func TestChargeTotals(t *testing.T) {
 			},
 		}
 		base := num.MakeAmount(30844212, 6)
-		calculateCharges(ls, currency.EUR, base, tax.RoundingRuleSumThenRound)
+		calculateCharges(ls, currency.EUR, base, tax.RoundingRulePrecise)
 		sum := calculateChargeSum(ls, currency.EUR)
 		require.NotNil(t, sum)
+		assert.Equal(t, "10.0240", ls[0].Amount.String())
+		assert.Equal(t, "10.0240", sum.String())
+		roundCharges(ls, currency.EUR)
 		assert.Equal(t, "10.02", ls[0].Amount.String())
-		assert.Equal(t, "10.02", sum.String())
 	})
 
 	t.Run("with fixed amount", func(t *testing.T) {
@@ -135,12 +140,13 @@ func TestChargeTotals(t *testing.T) {
 			},
 		}
 		base := num.MakeAmount(30844212, 6)
-		calculateCharges(ls, currency.EUR, base, tax.RoundingRuleSumThenRound)
+		calculateCharges(ls, currency.EUR, base, tax.RoundingRulePrecise)
 		sum := calculateChargeSum(ls, currency.EUR)
 		require.NotNil(t, sum)
-		assert.Equal(t, "50.18", ls[0].amount.String())
+		assert.Equal(t, "50.1762", ls[0].Amount.String())
+		assert.Equal(t, "50.1762", sum.String())
+		roundCharges(ls, currency.EUR)
 		assert.Equal(t, "50.18", ls[0].Amount.String())
-		assert.Equal(t, "50.18", sum.String())
 	})
 
 	t.Run("with fixed base high precision", func(t *testing.T) {
@@ -152,12 +158,14 @@ func TestChargeTotals(t *testing.T) {
 			},
 		}
 		base := num.MakeAmount(30844212, 6)
-		calculateCharges(ls, currency.EUR, base, tax.RoundingRuleSumThenRound)
+		calculateCharges(ls, currency.EUR, base, tax.RoundingRulePrecise)
 		sum := calculateChargeSum(ls, currency.EUR)
 		require.NotNil(t, sum)
-		assert.Equal(t, "10.0247", ls[0].amount.String())
-		assert.Equal(t, "10.02", ls[0].Amount.String())
+		assert.Equal(t, "50.1234", ls[0].Base.String())
+		assert.Equal(t, "10.0247", ls[0].Amount.String())
 		assert.Equal(t, "10.0247", sum.String())
+		roundCharges(ls, currency.EUR)
+		assert.Equal(t, "10.02", ls[0].Amount.String())
 	})
 
 	t.Run("with fixed base high precision, round-then-sum", func(t *testing.T) {
@@ -169,12 +177,14 @@ func TestChargeTotals(t *testing.T) {
 			},
 		}
 		base := num.MakeAmount(30844212, 6)
-		calculateCharges(ls, currency.EUR, base, tax.RoundingRuleRoundThenSum)
+		calculateCharges(ls, currency.EUR, base, tax.RoundingRuleCurrency)
 		sum := calculateChargeSum(ls, currency.EUR)
 		require.NotNil(t, sum)
 		assert.Equal(t, "50.1234", ls[0].Base.String())
-		assert.Equal(t, "10.02", ls[0].amount.String())
 		assert.Equal(t, "10.02", ls[0].Amount.String())
 		assert.Equal(t, "10.02", sum.String())
+		roundCharges(ls, currency.EUR)
+		assert.Equal(t, "50.1234", ls[0].Base.String(), "should maintain original precision")
+		assert.Equal(t, "10.02", ls[0].Amount.String())
 	})
 }

bill/discounts.go

@@ -119,9 +119,6 @@ type Discount struct {
 	Ext tax.Extensions `json:"ext,omitempty" jsonschema:"title=Extensions"`
 	// Additional semi-structured information.
 	Meta cbc.Meta `json:"meta,omitempty" jsonschema:"title=Meta"`
-
-	// internal amount for calculations
-	amount num.Amount
 }
 
 // Normalize performs normalization on the line and embedded objects using the
@@ -190,14 +187,12 @@ func calculateDiscounts(lines []*Discount, cur currency.Code, sum num.Amount, rr
 		if l.Percent != nil && !l.Percent.IsZero() {
 			base := sum
 			if l.Base != nil {
-				base = l.Base.RescaleUp(zero.Exp())
+				base = l.Base.RescaleUp(zero.Exp() + linePrecisionExtra)
+				base = tax.ApplyRoundingRule(rr, cur, base)
 			}
-			l.amount = l.Percent.Of(base)
-			l.amount = tax.ApplyRoundingRule(rr, cur, l.amount)
-		} else {
-			l.amount = l.Amount.Rescale(zero.Exp())
+			l.Amount = l.Percent.Of(base)
 		}
-		l.Amount = l.amount.Rescale(zero.Exp())
+		l.Amount = tax.ApplyRoundingRule(rr, cur, l.Amount)
 	}
 }
 
@@ -207,12 +202,23 @@ func calculateDiscountSum(discounts []*Discount, cur currency.Code) *num.Amount
 	}
 	total := cur.Def().Zero()
 	for _, l := range discounts {
-		total = total.MatchPrecision(l.amount)
-		total = total.Add(l.amount)
+		total = total.MatchPrecision(l.Amount)
+		total = total.Add(l.Amount)
 	}
 	return &total
 }
 
+func (m *Discount) round(cur currency.Code) {
+	cd := cur.Def()
+	m.Amount = cd.Rescale(m.Amount)
+}
+
+func roundDiscounts(lines []*Discount, cur currency.Code) {
+	for _, l := range lines {
+		l.round(cur)
+	}
+}
+
 func extendJSONSchemaWithDiscountKey(schema *jsonschema.Schema) {
 	prop, ok := schema.Properties.Get("key")
 	if !ok {