tests and small refactors for exchange rates

xexe/exchange_rates.py

@@ -1,5 +1,7 @@
 import datetime
-from typing import Iterable, Union
+from decimal import Decimal
+from numbers import Number
+from typing import Iterable, Set, Union
 
 from money.currency import Currency
 from money.money import Money
@@ -11,11 +13,13 @@ class ExchangeRate:
         self,
         from_currency: Currency,
         to_currency: Currency,
-        rate: Money,
+        rate: Union[Money, Number],
         rate_date: datetime.date,
     ) -> None:
         self.from_currency = from_currency
         self.to_currency = to_currency
+        if not isinstance(rate, Money):
+            rate = Money(rate, to_currency)
         self.rate = rate
         self.rate_date = rate_date
 
@@ -27,6 +31,10 @@ class ExchangeRate:
             + str(self.rate_date.strftime("%Y-%m-%d"))
         )
 
+    @property
+    def amount(self) -> Decimal:
+        return self.rate.amount
+
 
 class ExchangeRates:
 
@@ -40,8 +48,44 @@ class ExchangeRates:
                     raise TypeError("ExchangeRates can only hold Rates.")
                 self._rate_index[rate.descriptor] = rate
 
+    @property
+    def present_currencies(self) -> Set[Currency]:
+        present_currencies = set()
+
+        for rate in self:
+            present_currencies.add(rate.from_currency)
+            present_currencies.add(rate.to_currency)
+
+        return present_currencies
+
+    @property
+    def present_dates(self) -> Set[datetime.date]:
+        return {rate.rate_date for rate in self}
+
     def add_rate(self, new_rate: ExchangeRate) -> None:
         self._rate_index[new_rate.descriptor] = new_rate
 
     def __iter__(self):
         return iter(self._rate_index.values())
+
+    def __len__(self):
+        return len(self._rate_index)
+
+
+def add_equal_rates(rates: ExchangeRates) -> 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(
+                    from_currency=currency,
+                    to_currency=currency,
+                    rate=Money(1, currency),
+                    rate_date=date,
+                )
+            )
+
+    return rates