changes

app/apps/currencies/utils/convert.py

@@ -0,0 +1,42 @@
+from django.db.models import Func, F, Value, DurationField, Case, When, DecimalField, Q
+from django.db.models.functions import Abs, Extract
+from django.utils import timezone
+from django.core.exceptions import ValidationError
+from django.utils.translation import gettext_lazy as _
+
+from apps.currencies.models import ExchangeRate
+
+
+def convert(amount, from_currency, to_currency, date=None):
+    if from_currency == to_currency:
+        return amount
+
+    if date is None:
+        date = timezone.localtime(timezone.now())
+
+    try:
+        exchange_rate = (
+            ExchangeRate.objects.filter(
+                Q(from_currency=from_currency, to_currency=to_currency)
+                | Q(from_currency=to_currency, to_currency=from_currency)
+            )
+            .annotate(
+                date_diff=Func(
+                    Extract(F("date") - Value(date), "epoch"), function="ABS"
+                ),
+                effective_rate=Case(
+                    When(from_currency=from_currency, then=F("rate")),
+                    default=1 / F("rate"),
+                    output_field=DecimalField(),
+                ),
+            )
+            .order_by("date_diff")
+            .first()
+        )
+
+        if exchange_rate is None:
+            return None
+
+        return amount * exchange_rate.effective_rate
+    except ExchangeRate.DoesNotExist:
+        return None