Add FuelPurchase model, List, Create views and templates

main/models.py

@@ -1,3 +1,45 @@
 from django.db import models
+from django.db.models import F, Q
 
-# Create your models here.
+
+class FuelPurchase(models.Model):
+    purchase_date = models.DateField(null=False, blank=False, verbose_name="Purchase Date")
+    total_cost = models.DecimalField(null=False, blank=False, max_digits=10, decimal_places=2, verbose_name="Total Cost (€)")
+    price_per_litre = models.DecimalField(null=False, blank=False, max_digits=6, decimal_places=3, verbose_name="Price per Litre (€)")
+    amount_litres = models.DecimalField(null=False, blank=False, max_digits=7, decimal_places=2, verbose_name="Amount (litres)")
+
+    class Meta:
+        constraints = [
+            models.UniqueConstraint(
+                fields=[
+                    'purchase_date',
+                    'total_cost',
+                    'price_per_litre',
+                    'amount_litres',
+                ],
+                name='unique_fuel_purchase'
+            ),
+            models.CheckConstraint(
+                check=Q(total_cost__gt=0) & Q(total_cost__lt=100),
+                name="total_cost_range"
+            ),
+            models.CheckConstraint(
+                check=Q(price_per_litre__gt=0) & Q(price_per_litre__lt=5),
+                name="price_per_litre_range"
+            ),
+            models.CheckConstraint(
+                check=Q(amount_litres__gt=0) & Q(amount_litres__lt=100),
+                name="amount_litres_range"
+            ),
+        ]
+        verbose_name = "Fuel Purchase"
+        verbose_name_plural = "Fuel Purchases"
+
+    def save(self, *args, **kwargs):
+        if not self.amount_litres and self.price_per_litre:
+            self.amount_litres = self.total_cost / self.price_per_litre
+        super().save(*args, **kwargs)
+
+    def __str__(self):
+        date_str = self.purchase_date.strftime("%d.%m.%Y")
+        return f"{date_str} : {self.total_cost} € - {self.price_per_litre} €/L"