feat: internal code for automatic exchange rate fetching

app/apps/currencies/exchange_rates/fetcher.py

@@ -0,0 +1,162 @@
+import logging
+from datetime import timedelta
+
+from django.db.models import QuerySet
+from django.utils import timezone
+
+from apps.currencies.exchange_rates.providers import (
+    SynthFinanceProvider,
+    CoinGeckoProvider,
+)
+from apps.currencies.models import ExchangeRateService, ExchangeRate, Currency
+
+logger = logging.getLogger(__name__)
+
+
+# Map service types to provider classes
+PROVIDER_MAPPING = {
+    "synth_finance": SynthFinanceProvider,
+    "coingecko": CoinGeckoProvider,
+}
+
+
+class ExchangeRateFetcher:
+    @staticmethod
+    def fetch_due_rates(force: bool = False) -> None:
+        """
+        Fetch rates for all services that are due for update.
+
+        Args:
+            force (bool): If True, fetches all active services regardless of their last fetch time.
+                         If False, only fetches services that are due according to their interval.
+        """
+        services = ExchangeRateService.objects.filter(is_active=True)
+        current_time = timezone.now()
+
+        for service in services:
+            try:
+                if force:
+                    logger.info(f"Force fetching rates for {service.name}")
+                    ExchangeRateFetcher._fetch_service_rates(service)
+                    continue
+
+                # Regular schedule-based fetching
+                if service.last_fetch is None:
+                    logger.info(f"First fetch for service: {service.name}")
+                    ExchangeRateFetcher._fetch_service_rates(service)
+                    continue
+
+                # Calculate when the next fetch should occur
+                next_fetch_due = service.last_fetch + timedelta(
+                    hours=service.fetch_interval_hours
+                )
+
+                # Check if it's time for the next fetch
+                if current_time >= next_fetch_due:
+                    logger.info(
+                        f"Fetching rates for {service.name}. "
+                        f"Last fetch: {service.last_fetch}, "
+                        f"Interval: {service.fetch_interval_hours}h"
+                    )
+                    ExchangeRateFetcher._fetch_service_rates(service)
+                else:
+                    logger.debug(
+                        f"Skipping {service.name}. "
+                        f"Next fetch due at: {next_fetch_due}"
+                    )
+
+            except Exception as e:
+                logger.error(f"Error checking fetch schedule for {service.name}: {e}")
+
+    @staticmethod
+    def _get_unique_currency_pairs(
+        service: ExchangeRateService,
+    ) -> tuple[QuerySet, set]:
+        """
+        Get unique currency pairs from both target_currencies and target_accounts
+        Returns a tuple of (target_currencies QuerySet, exchange_currencies set)
+        """
+        # Get currencies from target_currencies
+        target_currencies = set(service.target_currencies.all())
+
+        # Add currencies from target_accounts
+        for account in service.target_accounts.all():
+            if account.currency and account.exchange_currency:
+                target_currencies.add(account.currency)
+
+        # Convert back to QuerySet for compatibility with existing code
+        target_currencies_qs = Currency.objects.filter(
+            id__in=[curr.id for curr in target_currencies]
+        )
+
+        # Get unique exchange currencies
+        exchange_currencies = set()
+
+        # From target_currencies
+        for currency in target_currencies:
+            if currency.exchange_currency:
+                exchange_currencies.add(currency.exchange_currency)
+
+        # From target_accounts
+        for account in service.target_accounts.all():
+            if account.exchange_currency:
+                exchange_currencies.add(account.exchange_currency)
+
+        return target_currencies_qs, exchange_currencies
+
+    @staticmethod
+    def _fetch_service_rates(service: ExchangeRateService) -> None:
+        """Fetch rates for a specific service"""
+        try:
+            provider = service.get_provider()
+
+            # Check if API key is required but missing
+            if provider.requires_api_key() and not service.api_key:
+                logger.error(f"API key required but not provided for {service.name}")
+                return
+
+            # Get unique currency pairs from both sources
+            target_currencies, exchange_currencies = (
+                ExchangeRateFetcher._get_unique_currency_pairs(service)
+            )
+
+            # Skip if no currencies to process
+            if not target_currencies or not exchange_currencies:
+                logger.info(f"No currency pairs to process for service {service.name}")
+                return
+
+            rates = provider.get_rates(target_currencies, exchange_currencies)
+
+            # Track processed currency pairs to avoid duplicates
+            processed_pairs = set()
+
+            for from_currency, to_currency, rate in rates:
+                # Create a unique identifier for this currency pair
+                pair_key = (from_currency.id, to_currency.id)
+                if pair_key in processed_pairs:
+                    continue
+
+                if provider.rates_inverted:
+                    # If rates are inverted, we need to swap currencies
+                    ExchangeRate.objects.create(
+                        from_currency=to_currency,
+                        to_currency=from_currency,
+                        rate=rate,
+                        date=timezone.now(),
+                    )
+                    processed_pairs.add((to_currency.id, from_currency.id))
+                else:
+                    # If rates are not inverted, we can use them as is
+                    ExchangeRate.objects.create(
+                        from_currency=from_currency,
+                        to_currency=to_currency,
+                        rate=rate,
+                        date=timezone.now(),
+                    )
+                    processed_pairs.add((from_currency.id, to_currency.id))
+
+            service.last_fetch = timezone.now()
+            service.save()
+
+        except Exception as e:
+            logger.error(f"Error fetching rates for {service.name}: {e}")