fetching and writing rates

xexe/exchange_rates.py

@@ -0,0 +1,47 @@
+import datetime
+from typing import Iterable, Union
+
+from money.currency import Currency
+from money.money import Money
+
+
+class ExchangeRate:
+
+    def __init__(
+        self,
+        from_currency: Currency,
+        to_currency: Currency,
+        rate: Money,
+        rate_date: datetime.date,
+    ) -> None:
+        self.from_currency = from_currency
+        self.to_currency = to_currency
+        self.rate = rate
+        self.rate_date = rate_date
+
+    @property
+    def descriptor(self) -> str:
+        return (
+            str(self.from_currency.value)
+            + str(self.to_currency.value)
+            + str(self.rate_date.strformat("%Y-%m-%d"))
+        )
+
+
+class ExchangeRates:
+
+    def __init__(self, rates: Union[Iterable[ExchangeRate], None] = None):
+
+        self._rate_index = {}
+
+        if rates is not None:
+            for rate in rates:
+                if not isinstance(rate, ExchangeRate):
+                    raise TypeError("ExchangeRates can only hold Rates.")
+                self._rate_index[rate.descriptor] = rate
+
+    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())

xexe/processes.py

@@ -6,7 +6,10 @@ from typing import List
 from money.currency import Currency
 from xecd_rates_client import XecdClient
 
-from xexe.utils import DateRange
+from xexe.exchange_rates import ExchangeRates
+from xexe.rate_fetching import MockRateFetcher, RateFetcher, XERateFetcher
+from xexe.rate_writing import CSVRateWriter, RateWriter
+from xexe.utils import DateRange, generate_currency_and_dates_combinations
 
 logger = logging.getLogger()
 
@@ -57,43 +60,70 @@ def run_get_rates(
 ) -> None:
     logger.info("Getting rates")
 
-    process_state = GetRatesProcessState(output=output)
+    process_state = GetRatesProcessState(output=output, dry_run=dry_run)
 
-    rates_fetcher = get_rates_fetcher(process_state.fetcher_type)
+    rates = obtain_rates_from_source(
+        process_state, date_range=date_range, currencies=currencies
+    )
+    write_rates_to_output(process_state, rates)
 
-    try:
-        rates = rates_fetcher.fetch()
-    except Exception as e:
-        process_state.record_rate_fetching_error(e)
-        raise ConnectionError(f"Could not fetch rates. See logs.")
 
-    rates_writer = get_rates_writer(process_state.output_type)
+def obtain_rates_from_source(
+    process_state, date_range: DateRange, currencies: List[Currency]
+) -> ExchangeRates:
+    rates_fetcher = process_state.get_fetcher()
 
-    try:
-        rates_writer.write(rates)
-    except Exception as e:
-        process_state.record_rate_writing_error(e)
-        raise Exception(f"Could not write rates. See logs.")
+    currency_and_date_combinations = generate_currency_and_dates_combinations(
+        date_range=date_range, currencies=currencies
+    )
+
+    rates = ExchangeRates()
+    for combination in currency_and_date_combinations:
+        try:
+            rate = rates_fetcher.fetch_rate(
+                from_currency=combination["from_currency"],
+                to_currency=combination["to_currency"],
+                rate_date=combination["date"],
+            )
+        except Exception as e:
+            logger.error(f"Error while fetching rates.")
+            logger.error(e, exc_info=True)
+            raise ConnectionError(f"Could not fetch rates. See logs.")
+
+        rates.add_rate(rate)
+
+    return rates
+
+
+def write_rates_to_output(process_state, rates):
+    rates_writer = process_state.get_writer()
+    rates_writer.write_rates(rates)
 
 
 class GetRatesProcessState:
     def __init__(self, output: str, dry_run: bool) -> None:
-        self.writer_type = self._infer_writer_type(output)
-        self.fetcher_type = self._infer_fetcher_type(dry_run)
+        self.writer = self._select_writer(output)
+        self.fetcher = self._select_fetcher(dry_run)
 
     @staticmethod
-    def _infer_writer_type(output: str) -> str:
+    def _select_writer(output: str) -> CSVRateWriter:
         output_is_csv_file_path = bool(pathlib.Path(output).suffix == ".csv")
 
         if output_is_csv_file_path:
-            return "csv_file"
+            return CSVRateWriter(output_file_path=output)
 
         raise ValueError(f"Don't know how to handle passed output: {output}")
 
     @staticmethod
-    def _infer_fetcher_type(dry_run: bool) -> str:
+    def _select_fetcher(dry_run: bool) -> str:
         if dry_run:
-            return MockFetcher
+            return MockRateFetcher
 
         if not dry_run:
-            return XEFetcher
+            return XERateFetcher
+
+    def get_fetcher(self) -> RateFetcher:
+        return self.fetcher
+
+    def get_writer(self) -> RateWriter:
+        return self.writer

xexe/rate_fetching.py

@@ -6,20 +6,7 @@ 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
+from xexe.exchange_rates import ExchangeRate
 
 
 class RateFetcher(ABC):
@@ -42,7 +29,7 @@ class MockRateFetcher(RateFetcher):
         return ExchangeRate(
             from_currency=from_currency,
             to_currency=to_currency,
-            rate=Money("42.0", to_currency),
+            rate=Money(42, to_currency),
             rate_date=rate_date,
         )
 

xexe/rate_writing.py

@@ -0,0 +1,34 @@
+import csv
+import pathlib
+from abc import ABC, abstractmethod
+
+from xexe.exchange_rates import ExchangeRates
+
+
+class RateWriter(ABC):
+    @abstractmethod
+    def write_rates(self, rates: ExchangeRates) -> None:
+        pass
+
+
+class CSVRateWriter(RateWriter):
+
+    def __init__(self, output_file_path: pathlib.Path) -> None:
+        super().__init__()
+        self.output_file_path = output_file_path
+
+    def write_rates(self, rates: ExchangeRates) -> None:
+        with open(self.output_file_path, mode="w", newline="") as csvfile:
+            csv_writer = csv.writer(csvfile)
+            csv_writer.writerow(["from_currency", "to_currency", "rate", "rate_date"])
+
+            # Write the exchange rate data
+            for rate in rates._rate_index.values():
+                csv_writer.writerow(
+                    [
+                        rate.from_currency.value,
+                        rate.to_currency.value,
+                        rate.rate.amount,
+                        rate.rate_date.strftime("%Y-%m-%d"),
+                    ]
+                )

xexe/utils.py

@@ -1,6 +1,6 @@
 import datetime
 from itertools import combinations
-from typing import Set
+from typing import Set, Tuple
 
 from money.currency import Currency
 
@@ -69,13 +69,13 @@ class DateRange:
 
 def generate_currency_and_dates_combinations(
     date_range: DateRange, currencies: Set[Currency]
-):
+) -> Tuple[dict]:
     currency_pairs = list(combinations(currencies, 2))
 
-    combinations = []
+    currency_date_combinations = []
     for date in date_range:
         for from_currency, to_currency in currency_pairs:
-            combinations.append(
+            currency_date_combinations.append(
                 {
                     "from_currency": from_currency,
                     "to_currency": to_currency,
@@ -83,7 +83,6 @@ def generate_currency_and_dates_combinations(
                 }
             )
 
-    combinations = tuple(combinations)
+    currency_date_combinations = tuple(currency_date_combinations)
 
-    # Convert the result to a tuple
-    return combinations
+    return currency_date_combinations