feat: Add promotion code functionality to ticket orders

app/models/order.rb

@@ -7,6 +7,8 @@ class Order < ApplicationRecord
   belongs_to :user
   belongs_to :event
   has_many :tickets, dependent: :destroy
+  has_many :order_promotion_codes, dependent: :destroy
+  has_many :promotion_codes, through: :order_promotion_codes
 
   # === Validations ===
   validates :user_id, presence: true

app/models/order_promotion_code.rb

@@ -0,0 +1,26 @@
+class OrderPromotionCode < ApplicationRecord
+  # Associations
+  belongs_to :order
+  belongs_to :promotion_code
+
+  # Validations
+  validates :order, presence: true
+  validates :promotion_code, presence: true
+
+  # Callbacks
+  after_create :apply_discount
+  after_create :increment_promotion_code_uses
+
+  private
+
+  def apply_discount
+    # Apply the discount to the order
+    discount_amount = promotion_code.discount_amount_cents
+    order.update!(total_amount_cents: [ order.total_amount_cents - discount_amount, 0 ].max)
+  end
+
+  def increment_promotion_code_uses
+    # Increment the uses count on the promotion code
+    promotion_code.increment!(:uses_count)
+  end
+end

app/models/promotion_code.rb

@@ -0,0 +1,23 @@
+class PromotionCode < ApplicationRecord
+  # Validations
+  validates :code, presence: true, uniqueness: true
+  validates :discount_amount_cents, numericality: { greater_than_or_equal_to: 0 }
+
+  # Scopes
+  scope :active, -> { where(active: true) }
+  scope :expired, -> { where("expires_at < ? OR active = ?", Time.current, false) }
+  scope :valid, -> { active.where("expires_at > ? OR expires_at IS NULL", Time.current) }
+
+  # Callbacks
+  before_create :increment_uses_count
+
+  # Associations
+  has_many :order_promotion_codes
+  has_many :orders, through: :order_promotion_codes
+
+  private
+
+  def increment_uses_count
+    self.uses_count ||= 0
+  end
+end