Special way to add decimals

alasco-tech · Jun 27, 2024 · d952a23 · d952a23
1 parent ae7e545
commit d952a23
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Showing 4 changed files with 67 additions and 18 deletions.
diff --git a/pytests/test_money.py b/pytests/test_money.py
@@ -129,12 +129,45 @@ def test_minus_zero(decimal):
         Money("-0"),
         -Money("0"),
         -1 * Money("0"),
+        Money("0") * -1,
     ],
 )
 def test_advanced_negation(decimal):
     assert str(Money(decimal).amount) == "-0"
 
 
+@pytest.mark.parametrize("left", ["0", "-0"])
+@pytest.mark.parametrize("right", ["0", "-0"])
+def test_add_with_negative_zeros(left, right):
+    expected = Decimal(left) + Decimal(right)
+
+    money_left = Money(left)
+    money_right = Money(right)
+
+    assert str(money_left.amount) == str(left)
+    assert str(money_right.amount) == str(right)
+
+    assert str((money_left + Decimal(right)).amount) == str(expected)
+    assert str((Decimal(left) + money_right).amount) == str(expected)
+    assert str((money_left + money_right).amount) == str(expected)
+
+
+@pytest.mark.parametrize("left", ["0", "-0"])
+@pytest.mark.parametrize("right", ["0", "-0"])
+def test_sub_with_negative_zeros(left, right):
+    expected = Decimal(left) - Decimal(right)
+
+    money_left = Money(left)
+    money_right = Money(right)
+
+    assert str(money_left.amount) == str(left)
+    assert str(money_right.amount) == str(right)
+
+    assert str((money_left - Decimal(right)).amount) == str(expected)
+    assert str((Decimal(left) - money_right).amount) == str(expected)
+    assert str((money_left - money_right).amount) == str(expected)
+
+
 def test_equality_to_other_types():
     x = Money(0)
     assert x != None  # noqa: E711

diff --git a/src/money.rs b/src/money.rs
@@ -93,11 +93,11 @@ impl Money {
     fn __add__(&self, other: Bound<PyAny>) -> PyResult<Self> {
         if let Ok(other_money) = other.extract::<Self>() {
             Ok(Self {
-                amount: self.amount + other_money.amount,
+                amount: decimal_add(self.amount, other_money.amount),
             })
         } else if let Ok(other_decimal) = get_decimal(other) {
             Ok(Self {
-                amount: self.amount + other_decimal,
+                amount: decimal_add(self.amount, other_decimal),
             })
         } else {
             Err(pyo3::exceptions::PyTypeError::new_err(
@@ -113,11 +113,11 @@ impl Money {
     fn __sub__(&self, other: Bound<PyAny>) -> PyResult<Self> {
         if let Ok(other_money) = other.extract::<Self>() {
             Ok(Self {
-                amount: self.amount - other_money.amount,
+                amount: decimal_add(self.amount, -other_money.amount),
             })
         } else if let Ok(other_decimal) = get_decimal(other) {
             Ok(Self {
-                amount: self.amount - other_decimal,
+                amount: decimal_add(self.amount, -other_decimal),
             })
         } else {
             Err(pyo3::exceptions::PyTypeError::new_err(
@@ -320,6 +320,22 @@ pub fn sum_(elems: Bound<PyAny>) -> PyResult<Money> {
     Ok(Money { amount })
 }
 
+// Adds decimals the way of Python
+pub fn decimal_add(left: Decimal, right: Decimal) -> Decimal {
+    let zero = Decimal::new(0, 0);
+
+    if left.abs() == zero && right.abs() == zero {
+        if left.is_sign_negative() && right.is_sign_negative() {
+            -zero
+        } else {
+            zero
+        }
+    } else {
+        left + right
+    }
+}
+
+// Rounds decimals the way of Python
 fn round_with_negative_scale(value: Decimal, scale: i32, round_up: bool) -> Decimal {
     let strategy = if round_up {
         RoundingStrategy::MidpointAwayFromZero

diff --git a/src/money_vat.rs b/src/money_vat.rs
@@ -7,9 +7,9 @@ use std::collections::hash_map::DefaultHasher;
 use std::hash::{Hash, Hasher};
 use std::str::FromStr;
 
-use crate::money::get_decimal;
 use crate::money::Money;
 use crate::money::MONEY_PRECISION;
+use crate::money::{decimal_add, get_decimal};
 use crate::money_vat_ratio::MoneyWithVATRatio;
 
 const GERMAN_VAT_RATES: [i16; 5] = [0, 5, 7, 16, 19];
@@ -169,16 +169,16 @@ impl MoneyWithVAT {
         if let Ok(other_money_with_vat) = other.extract::<Self>() {
             Ok(Self {
                 net: Money {
-                    amount: self.net.amount + other_money_with_vat.net.amount,
+                    amount: decimal_add(self.net.amount, other_money_with_vat.net.amount),
                 },
                 tax: Money {
-                    amount: self.tax.amount + other_money_with_vat.tax.amount,
+                    amount: decimal_add(self.tax.amount, other_money_with_vat.tax.amount),
                 },
             })
         } else if let Ok(other_decimal) = get_decimal(other) {
             Ok(Self {
                 net: Money {
-                    amount: self.net.amount + other_decimal,
+                    amount: decimal_add(self.net.amount, other_decimal),
                 },
                 tax: self.tax.clone(),
             })
@@ -197,16 +197,16 @@ impl MoneyWithVAT {
         if let Ok(other_money_with_vat) = other.extract::<Self>() {
             Ok(Self {
                 net: Money {
-                    amount: self.net.amount - other_money_with_vat.net.amount,
+                    amount: decimal_add(self.net.amount, -other_money_with_vat.net.amount),
                 },
                 tax: Money {
-                    amount: self.tax.amount - other_money_with_vat.tax.amount,
+                    amount: decimal_add(self.tax.amount, -other_money_with_vat.tax.amount),
                 },
             })
         } else if let Ok(other_decimal) = get_decimal(other) {
             Ok(Self {
                 net: Money {
-                    amount: self.net.amount - other_decimal,
+                    amount: decimal_add(self.net.amount, -other_decimal),
                 },
                 tax: self.tax.clone(),
             })

diff --git a/src/money_vat_ratio.rs b/src/money_vat_ratio.rs
@@ -4,7 +4,7 @@ use pyo3::types::{PyCFunction, PyDict, PyTuple};
 use rust_decimal::prelude::FromPrimitive;
 use rust_decimal::Decimal;
 
-use crate::money::get_decimal;
+use crate::money::{decimal_add, get_decimal};
 
 #[pyclass]
 #[derive(Debug, Clone)]
@@ -58,22 +58,22 @@ impl MoneyWithVATRatio {
 
     fn __neg__(&self) -> Self {
         Self {
-            net_ratio: Decimal::new(0, 0) - self.net_ratio,
-            gross_ratio: Decimal::new(0, 0) - self.gross_ratio,
+            net_ratio: -self.net_ratio,
+            gross_ratio: -self.gross_ratio,
         }
     }
 
     fn __add__(&self, other: Self) -> Self {
         Self {
-            net_ratio: self.net_ratio + other.net_ratio,
-            gross_ratio: self.gross_ratio + other.gross_ratio,
+            net_ratio: decimal_add(self.net_ratio, other.net_ratio),
+            gross_ratio: decimal_add(self.gross_ratio, other.gross_ratio),
         }
     }
 
     fn __sub__(&self, other: Self) -> Self {
         Self {
-            net_ratio: self.net_ratio - other.net_ratio,
-            gross_ratio: self.gross_ratio - other.gross_ratio,
+            net_ratio: decimal_add(self.net_ratio, -other.net_ratio),
+            gross_ratio: decimal_add(self.gross_ratio, -other.gross_ratio),
         }
     }