implement rate fetching logics

xexe/rate_fetching.py

@@ -0,0 +1,72 @@
+import datetime
+import os
+from abc import ABC, abstractmethod
+
+from money.currency import Currency
+from money.money import Money
+from xecd_rates_client import XecdClient
+
+
+class ExchangeRate:
+
+    def __init__(
+        self,
+        from_currency: Currency,
+        to_currency: Currency,
+        rate: Money,
+        rate_date: datetime.date = None,
+    ) -> None:
+        self.from_currency
+        self.to_currency
+        self.rate
+        self.rate_date
+
+
+class RateFetcher(ABC):
+    @abstractmethod
+    def fetch_rate(
+        self, from_currency: Currency, to_currency: Currency, rate_date: datetime.date
+    ) -> ExchangeRate:
+        pass
+
+
+class MockRateFetcher(RateFetcher):
+
+    def __init__(self) -> None:
+        super().__init__()
+
+    def fetch_rate(
+        self, from_currency: Currency, to_currency: Currency, rate_date: datetime.date
+    ) -> ExchangeRate:
+
+        return ExchangeRate(
+            from_currency=from_currency,
+            to_currency=to_currency,
+            rate=Money("42.0", to_currency),
+            rate_date=rate_date,
+        )
+
+
+class XERateFetcher(RateFetcher):
+
+    def __init__(self) -> None:
+        super().__init__()
+        self.xe_client = XecdClient(
+            account_id=os.environ["XE_ACCOUNT_ID"],
+            api_key=os.environ["XE_API_KEY"],
+        )
+
+    def fetch_rate(
+        self, from_currency: Currency, to_currency: Currency, rate_date: datetime.date
+    ) -> ExchangeRate:
+        response = self.xe_client.historic_rate(
+            rate_date.strftime("%Y-%m-%d"),
+            "12:00",
+            from_currency.value,  # .value will access the ISO 4217 str code of the currency
+            to_currency.value,
+            1,
+            # always 1, because the rate we want is how much of to_curr does
+            # 1 unit of from_curr get us.
+        )
+
+        # handle response into proper object