correct discount model

hub/services/models/pricing.py

@@ -131,54 +131,98 @@ class ProgressiveDiscountModel(models.Model):
         """Calculate price using progressive percentage discounts."""
         final_price = 0
         remaining_units = units
-        processed_units = 0
 
-        # Get all tiers sorted by threshold
-        discount_tiers = self.tiers.all().order_by("threshold")
+        discount_tiers = self.tiers.all().order_by("min_units")
 
-        for i, tier in enumerate(discount_tiers):
-            # Calculate how many units fall into this tier
-            if i < discount_tiers.count() - 1:
-                next_threshold = discount_tiers[i + 1].threshold
-                tier_units = min(remaining_units, next_threshold - processed_units)
-            else:
-                # Last tier handles all remaining units
-                tier_units = remaining_units
-
-            # Calculate discounted rate for this tier
-            discounted_rate = base_rate * (1 - tier.discount_percent / 100)
-
-            # Add the price for units in this tier
-            final_price += discounted_rate * tier_units
-
-            # Update tracking variables
-            remaining_units -= tier_units
-            processed_units += tier_units
-
-            # Exit if all units have been processed
+        for tier in discount_tiers:
             if remaining_units <= 0:
                 break
 
+            # Determine how many units fall into this tier
+            tier_min = tier.min_units
+            tier_max = tier.max_units if tier.max_units else float("inf")
+
+            # Skip if we haven't reached this tier yet
+            if units < tier_min:
+                continue
+
+            # Calculate units in this tier
+            units_start = max(0, units - remaining_units)
+            units_end = min(units, tier_max if tier.max_units else units)
+            tier_units = max(0, units_end - max(units_start, tier_min - 1))
+
+            if tier_units > 0:
+                discounted_rate = base_rate * (1 - tier.discount_percent / 100)
+                final_price += discounted_rate * tier_units
+                remaining_units -= tier_units
+
         return final_price
 
+    def get_discount_breakdown(self, base_rate, units):
+        """Get detailed breakdown of discount calculation."""
+        breakdown = []
+        remaining_units = units
+
+        discount_tiers = self.tiers.all().order_by("min_units")
+
+        for tier in discount_tiers:
+            if remaining_units <= 0:
+                break
+
+            tier_min = tier.min_units
+            tier_max = tier.max_units if tier.max_units else float("inf")
+
+            if units < tier_min:
+                continue
+
+            units_start = max(0, units - remaining_units)
+            units_end = min(units, tier_max if tier.max_units else units)
+            tier_units = max(0, units_end - max(units_start, tier_min - 1))
+
+            if tier_units > 0:
+                discounted_rate = base_rate * (1 - tier.discount_percent / 100)
+                tier_total = discounted_rate * tier_units
+
+                breakdown.append(
+                    {
+                        "tier_range": f"{tier_min}-{tier_max-1 if tier.max_units else '∞'}",
+                        "units": tier_units,
+                        "discount_percent": tier.discount_percent,
+                        "rate": discounted_rate,
+                        "subtotal": tier_total,
+                    }
+                )
+
+                remaining_units -= tier_units
+
+        return breakdown
+
 
 class DiscountTier(models.Model):
     discount_model = models.ForeignKey(
         ProgressiveDiscountModel, on_delete=models.CASCADE, related_name="tiers"
     )
-    threshold = models.PositiveIntegerField(
-        help_text="Starting unit count for this tier"
+    min_units = models.PositiveIntegerField(
+        help_text="Minimum unit count for this tier (inclusive)", default=0
+    )
+    max_units = models.PositiveIntegerField(
+        null=True,
+        blank=True,
+        help_text="Maximum unit count for this tier (exclusive). Leave blank for unlimited.",
     )
     discount_percent = models.DecimalField(
         max_digits=5, decimal_places=2, help_text="Percentage discount applied (0-100)"
     )
 
     class Meta:
-        ordering = ["threshold"]
-        unique_together = ["discount_model", "threshold"]
+        ordering = ["min_units"]
+        unique_together = ["discount_model", "min_units"]
 
     def __str__(self):
-        return f"{self.discount_model.name}: {self.threshold}+ units → {self.discount_percent}% discount"
+        if self.max_units:
+            return f"{self.discount_model.name}: {self.min_units}-{self.max_units-1} units → {self.discount_percent}% discount"
+        else:
+            return f"{self.discount_model.name}: {self.min_units}+ units → {self.discount_percent}% discount"
 
 
 class VSHNAppCatBaseFee(models.Model):