feat(promotion code): Promotion code system done

I added the features for users to use promotion code
and for promoters to create on their events.
May be rewrite to discount code?

app/models/event.rb

@@ -21,6 +21,7 @@ class Event < ApplicationRecord
   has_many :ticket_types
   has_many :tickets, through: :ticket_types
   has_many :orders
+  has_many :promotion_codes
 
   # === Callbacks ===
   before_validation :geocode_address, if: :should_geocode_address?

app/models/order.rb

@@ -90,10 +90,34 @@ class Order < ApplicationRecord
     end
   end
 
-  # Calculate total from ticket prices only (platform fee deducted from promoter payout)
+  # Calculate total from ticket prices minus promotion code discounts
   def calculate_total!
     ticket_total = tickets.sum(:price_cents)
-    update!(total_amount_cents: ticket_total)
+    discount_total = promotion_codes.sum(:discount_amount_cents)
+
+    # Ensure total doesn't go below zero
+    final_total = [ticket_total - discount_total, 0].max
+    update!(total_amount_cents: final_total)
+  end
+
+  # Subtotal amount before discounts
+  def subtotal_amount_cents
+    tickets.sum(:price_cents)
+  end
+
+  # Subtotal amount in euros
+  def subtotal_amount_euros
+    subtotal_amount_cents / 100.0
+  end
+
+  # Total discount amount from all promotion codes
+  def discount_amount_cents
+    promotion_codes.sum(:discount_amount_cents)
+  end
+
+  # Discount amount in euros
+  def discount_amount_euros
+    discount_amount_cents / 100.0
   end
 
   # Platform fee: €0.50 fixed + 1.5% of ticket price, per ticket

app/models/promotion_code.rb

@@ -12,9 +12,28 @@ class PromotionCode < ApplicationRecord
   before_create :increment_uses_count
 
   # Associations
+  belongs_to :user
+  belongs_to :event
   has_many :order_promotion_codes
   has_many :orders, through: :order_promotion_codes
 
+  # Instance methods
+  def discount_amount_euros
+    discount_amount_cents / 100.0
+  end
+
+  def active?
+    active && (expires_at.nil? || expires_at > Time.current)
+  end
+
+  def expired?
+    expires_at.present? && expires_at < Time.current
+  end
+
+  def can_be_used?
+    active? && (usage_limit.nil? || uses_count < usage_limit)
+  end
+
   private
 
   def increment_uses_count