fix(promotion code): Cap the minimum invoice for Stripe

Stripe does not support negative invoices, so to
allow correct invoice generation, we apply dismiss
negative invoices.

app/controllers/orders_controller.rb

@@ -130,11 +130,16 @@ class OrdersController < ApplicationController
     if params[:promotion_code].present?
       promotion_code = PromotionCode.valid.find_by(code: params[:promotion_code].upcase)
       if promotion_code
-        # Apply the promotion code to the order
-        @order.promotion_codes << promotion_code
-        @order.calculate_total!
-        @total_amount = @order.total_amount_cents
-        flash.now[:notice] = "Code promotionnel appliqué: #{promotion_code.code}"
+        # Check if promotion code is already applied to this order
+        if @order.promotion_codes.include?(promotion_code)
+          flash.now[:alert] = "Ce code promotionnel est déjà appliqué à cette commande"
+        else
+          # Apply the promotion code to the order
+          @order.promotion_codes << promotion_code
+          @order.calculate_total!
+          @total_amount = @order.total_amount_cents
+          flash.now[:notice] = "Code promotionnel appliqué: #{promotion_code.code}"
+        end
       else
         flash.now[:alert] = "Code promotionnel invalide"
       end
@@ -302,7 +307,14 @@ class OrdersController < ApplicationController
   end
 
   def create_stripe_session
+    # Calculate the discount amount per ticket to distribute the promotion evenly
+    total_tickets = @order.tickets.count
+    discount_per_ticket = @order.discount_amount_cents / total_tickets if total_tickets > 0
+
     line_items = @order.tickets.map do |ticket|
+      # Apply discount proportionally to each ticket
+      discounted_price = [ticket.price_cents - discount_per_ticket.to_i, 0].max
+
       {
         price_data: {
           currency: "eur",
@@ -310,7 +322,7 @@ class OrdersController < ApplicationController
             name: "#{@order.event.name} - #{ticket.ticket_type.name}",
             description: ticket.ticket_type.description
           },
-          unit_amount: ticket.price_cents
+          unit_amount: discounted_price
         },
         quantity: 1
       }

app/models/order.rb

@@ -21,6 +21,9 @@ class Order < ApplicationRecord
   validates :payment_attempts, presence: true,
     numericality: { greater_than_or_equal_to: 0 }
 
+  # Custom validation to prevent duplicate promotion codes
+  validate :no_duplicate_promotion_codes
+
   # Stripe invoice ID for accounting records
   attr_accessor :stripe_invoice_id
 
@@ -188,4 +191,12 @@ class Order < ApplicationRecord
   def draft?
     status == "draft"
   end
+
+  # Prevent duplicate promotion codes on the same order
+  def no_duplicate_promotion_codes
+    promotion_code_ids = promotion_codes.map(&:id)
+    if promotion_code_ids.size != promotion_code_ids.uniq.size
+      errors.add(:promotion_codes, "ne peuvent pas contenir de codes en double")
+    end
+  end
 end