reports: Balance classes support addition.

conservancy_beancount/reports/core.py

@@ -49,6 +49,7 @@ from ..beancount_types import (
 )
 
 DecimalCompat = data.DecimalCompat
+BalanceType = TypeVar('BalanceType', bound='Balance')
 RelatedType = TypeVar('RelatedType', bound='RelatedPostings')
 
 class Balance(Mapping[str, data.Amount]):
@@ -69,6 +70,25 @@ class Balance(Mapping[str, data.Amount]):
             currency: amount.number for currency, amount in source
         }
 
+    def _add_amount(self,
+                    currency_map: MutableMapping[str, Decimal],
+                    amount: data.Amount,
+    ) -> None:
+        try:
+            currency_map[amount.currency] += amount.number
+        except KeyError:
+            currency_map[amount.currency] = amount.number
+
+    def _add_other(self,
+                   currency_map: MutableMapping[str, Decimal],
+                   other: Union[data.Amount, 'Balance'],
+    ) -> None:
+        if isinstance(other, Balance):
+            for amount in other.values():
+                self._add_amount(currency_map, amount)
+        else:
+            self._add_amount(currency_map, other)
+
     def __repr__(self) -> str:
         return f"{type(self).__name__}({self._currency_map!r})"
 
@@ -80,6 +100,12 @@ class Balance(Mapping[str, data.Amount]):
             (key, bc_amount.abs(amt)) for key, amt in self.items()
         )
 
+    def __add__(self: BalanceType, other: Union[data.Amount, 'Balance']) -> BalanceType:
+        retval_map = self._currency_map.copy()
+        self._add_other(retval_map, other)
+        return type(self)((code, data.Amount(number, code))
+                          for code, number in retval_map.items())
+
     def __eq__(self, other: Any) -> bool:
         if (self.is_zero()
             and isinstance(other, Balance)
@@ -149,11 +175,9 @@ class Balance(Mapping[str, data.Amount]):
 class MutableBalance(Balance):
     __slots__ = ()
 
-    def add_amount(self, amount: data.Amount) -> None:
-        try:
-            self._currency_map[amount.currency] += amount.number
-        except KeyError:
-            self._currency_map[amount.currency] = amount.number
+    def __iadd__(self: BalanceType, other: Union[data.Amount, Balance]) -> BalanceType:
+        self._add_other(self._currency_map, other)
+        return self
 
 
 class RelatedPostings(Sequence[data.Posting]):
@@ -234,7 +258,7 @@ class RelatedPostings(Sequence[data.Posting]):
     def iter_with_balance(self) -> Iterator[Tuple[data.Posting, Balance]]:
         balance = MutableBalance()
         for post in self:
-            balance.add_amount(post.units)
+            balance += post.units
             yield post, balance
 
     def balance(self) -> Balance:
@@ -249,10 +273,10 @@ class RelatedPostings(Sequence[data.Posting]):
         balance = MutableBalance()
         for post in self:
             if post.cost is None:
-                balance.add_amount(post.units)
+                balance += post.units
             else:
                 number = post.units.number * post.cost.number
-                balance.add_amount(data.Amount(number, post.cost.currency))
+                balance += data.Amount(number, post.cost.currency)
         return balance
 
     def meta_values(self,

tests/test_reports_balance.py

@@ -179,6 +179,84 @@ def test_eq(kwargs1, kwargs2, expected):
     actual = bal1 == bal2
     assert actual == expected
 
+@pytest.mark.parametrize('number,currency', {
+    (50, 'USD'),
+    (-50, 'USD'),
+    (50000, 'BRL'),
+    (-4000, 'BRL'),
+})
+def test_add_amount(number, currency):
+    start_amounts = testutil.balance_map(USD=500)
+    start_bal = core.Balance(start_amounts)
+    add_amount = testutil.Amount(number, currency)
+    actual = start_bal + add_amount
+    if currency == 'USD':
+        assert len(actual) == 1
+        assert actual['USD'] == testutil.Amount(500 + number)
+    else:
+        assert len(actual) == 2
+        assert actual['USD'] == testutil.Amount(500)
+        assert actual[currency] == add_amount
+    assert start_bal == start_amounts
+
+@pytest.mark.parametrize('number,currency', {
+    (50, 'USD'),
+    (-50, 'USD'),
+    (50000, 'BRL'),
+    (-4000, 'BRL'),
+})
+def test_iadd_amount(number, currency):
+    start_amounts = testutil.balance_map(USD=500)
+    balance = core.MutableBalance(start_amounts)
+    add_amount = testutil.Amount(number, currency)
+    balance += add_amount
+    if currency == 'USD':
+        assert len(balance) == 1
+        assert balance['USD'] == testutil.Amount(500 + number)
+    else:
+        assert len(balance) == 2
+        assert balance['USD'] == testutil.Amount(500)
+        assert balance[currency] == add_amount
+
+@pytest.mark.parametrize('balance_map_kwargs', [
+    {},
+    {'USD': 0},
+    {'EUR': 10},
+    {'JPY': 20, 'BRL': 30},
+    {'EUR': -15},
+    {'JPY': -25, 'BRL': -35},
+    {'JPY': 40, 'USD': 0, 'EUR': -50},
+])
+def test_add_balance(balance_map_kwargs):
+    start_numbers = {'USD': 500, 'BRL': 40000}
+    start_bal = core.Balance(testutil.balance_map(**start_numbers))
+    expect_numbers = start_numbers.copy()
+    for code, number in balance_map_kwargs.items():
+        expect_numbers[code] = expect_numbers.get(code, 0) + number
+    add_bal = core.Balance(testutil.balance_map(**balance_map_kwargs))
+    actual = start_bal + add_bal
+    expected = core.Balance(testutil.balance_map(**expect_numbers))
+    assert actual == expected
+
+@pytest.mark.parametrize('balance_map_kwargs', [
+    {},
+    {'USD': 0},
+    {'EUR': 10},
+    {'JPY': 20, 'BRL': 30},
+    {'EUR': -15},
+    {'JPY': -25, 'BRL': -35},
+    {'JPY': 40, 'USD': 0, 'EUR': -50},
+])
+def test_iadd_balance(balance_map_kwargs):
+    start_numbers = {'USD': 500, 'BRL': 40000}
+    balance = core.MutableBalance(testutil.balance_map(**start_numbers))
+    expect_numbers = start_numbers.copy()
+    for code, number in balance_map_kwargs.items():
+        expect_numbers[code] = expect_numbers.get(code, 0) + number
+    balance += core.Balance(testutil.balance_map(**balance_map_kwargs))
+    expected = core.Balance(testutil.balance_map(**expect_numbers))
+    assert balance == expected
+
 @pytest.mark.parametrize('balance_map_kwargs,expected', DEFAULT_STRINGS)
 def test_str(balance_map_kwargs, expected):
     amounts = testutil.balance_map(**balance_map_kwargs)