more methods and tests

tests/tests_unit/test_exchange_rates.py

@@ -4,7 +4,12 @@ from decimal import Decimal
 from money.currency import Currency
 from money.money import Money
 
-from xexe.exchange_rates import ExchangeRate, ExchangeRates, add_equal_rates
+from xexe.exchange_rates import (
+    ExchangeRate,
+    ExchangeRates,
+    add_equal_rates,
+    add_inverse_rates,
+)
 
 
 def test_exchange_rate_creation_works():
@@ -124,6 +129,26 @@ def test_present_dates_works_fine():
     }
 
 
+def test_exchange_rates_is_rate_present_method_works_fine():
+    a_rate = ExchangeRate(
+        from_currency=Currency.USD,
+        to_currency=Currency.EUR,
+        rate=Decimal("1.2"),
+        rate_date=datetime.date(2020, 3, 10),
+    )
+    another_rate = ExchangeRate(
+        from_currency=Currency.GBP,
+        to_currency=Currency.JPY,
+        rate=Decimal("10"),
+        rate_date=datetime.date(2019, 10, 3),
+    )
+
+    rates = ExchangeRates({a_rate})
+
+    assert rates.is_rate_present(a_rate)
+    assert not rates.is_rate_present(another_rate)
+
+
 def test_add_equal_rates_returns_expected_values():
     a_rate = ExchangeRate(
         from_currency=Currency.USD,
@@ -170,3 +195,73 @@ def test_add_equal_rates_runs_on_empty_rates():
     empty_rates = add_equal_rates(empty_rates)
 
     assert True
+
+
+def test_add_equal_rates_overwrites():
+    a_rate = ExchangeRate(
+        from_currency=Currency.USD,
+        to_currency=Currency.USD,
+        rate=Decimal("1.2"),
+        rate_date=datetime.date(2020, 3, 10),
+    )
+
+    rates = ExchangeRates([a_rate])
+
+    assert len(rates) == 1
+
+    rates = add_equal_rates(rates, overwrite=True)
+
+    assert len(rates) == 1
+    assert list(rates)[0].amount == 1
+
+
+def test_add_equal_rates_does_not_overwrite():
+    a_rate = ExchangeRate(
+        from_currency=Currency.USD,
+        to_currency=Currency.USD,
+        rate=Decimal("1.2"),
+        rate_date=datetime.date(2020, 3, 10),
+    )
+
+    rates = ExchangeRates([a_rate])
+
+    assert len(rates) == 1
+
+    rates = add_equal_rates(rates, overwrite=False)
+
+    assert len(rates) == 1
+    assert list(rates)[0].amount == Decimal("1.2")
+
+
+def test_add_inverse_rates_returns_expected():
+    a_rate = ExchangeRate(
+        from_currency=Currency.EUR,
+        to_currency=Currency.USD,
+        rate=Decimal("1.25"),
+        rate_date=datetime.date(2020, 3, 10),
+    )
+    inverse_rate = ExchangeRate(
+        from_currency=Currency.USD,
+        to_currency=Currency.EUR,
+        rate=Decimal("0.8"),
+        rate_date=datetime.date(2020, 3, 10),
+    )
+
+    rates = ExchangeRates([a_rate])
+
+    assert len(rates) == 1
+
+    rates = add_inverse_rates(rates)
+
+    assert len(rates) == 2
+
+    assert rates.is_rate_present(inverse_rate)
+    assert rates[inverse_rate.descriptor].amount == Decimal("0.8")
+
+
+def test_add_inverse_rates_runs_on_empty_rates():
+    empty_rates = ExchangeRates()
+
+    empty_rates = add_inverse_rates(empty_rates)
+
+    assert True

xexe/exchange_rates.py

@@ -3,7 +3,7 @@ from decimal import Decimal
 from numbers import Number
 from typing import Iterable, Set, Union
 
-from money.currency import Currency
+from money.currency import Currency, CurrencyHelper
 from money.money import Money
 
 
@@ -13,7 +13,7 @@ class ExchangeRate:
         self,
         from_currency: Currency,
         to_currency: Currency,
-        rate: Union[Money, Number],
+        rate: Union[Money, Number, str],
         rate_date: datetime.date,
     ) -> None:
         self.from_currency = from_currency
@@ -66,26 +66,64 @@ class ExchangeRates:
         self._rate_index[new_rate.descriptor] = new_rate
 
     def __iter__(self):
-        return iter(self._rate_index.values())
+        return iter(list(self._rate_index.values()))
 
     def __len__(self):
         return len(self._rate_index)
 
+    def __contains__(self, rate) -> bool:
+        if not isinstance(rate, ExchangeRate):
+            raise TypeError("ExchangeRates can only hold Rates.")
 
-def add_equal_rates(rates: ExchangeRates) -> ExchangeRates:
+        if rate.descriptor in self._rate_index:
+            return True
+
+        return False
+
+    def is_rate_present(self, rate: ExchangeRate) -> bool:
+        if rate.descriptor in self._rate_index:
+            return True
+
+        return False
+
+    def __getitem__(self, rate_descriptor) -> ExchangeRate:
+        return self._rate_index[rate_descriptor]
+
+
+def add_equal_rates(rates: ExchangeRates, overwrite: bool = False) -> ExchangeRates:
 
     present_currencies = rates.present_currencies
     present_dates = rates.present_dates
 
     for date in present_dates:
         for currency in present_currencies:
-            rates.add_rate(
-                ExchangeRate(
+            new_rate = ExchangeRate(
                 from_currency=currency,
                 to_currency=currency,
                 rate=Money(1, currency),
                 rate_date=date,
             )
-            )
+            if new_rate in rates and not overwrite:
+                continue
+            rates.add_rate(new_rate)
+
+    return rates
+
+
+def add_inverse_rates(rates: ExchangeRates) -> ExchangeRates:
+
+    # Hey, I haven't thought properly what happens here if the inverse rate is
+    # *already* present in the rates set. It's probably going to be fucky. I
+    # would advise only running this against sets where you don't have inverse
+    # rates already present.
+
+    for rate in rates:
+        inverse_rate = ExchangeRate(
+            from_currency=rate.to_currency,
+            to_currency=rate.from_currency,
+            rate_date=rate.rate_date,
+            rate=f"{1 / rate.amount:.{CurrencyHelper.decimal_precision_for_currency(rate.from_currency)}f}",
+        )
+        rates.add_rate(inverse_rate)
 
     return rates