[ongoing] using cash coupon in reservation logic

app/models/invoice.rb

@@ -149,7 +149,12 @@ class Invoice < ActiveRecord::Base
     end
     # handle coupon
     unless avoir.coupon_id.nil?
-      discount = avoir.total  * avoir.coupon.percent_off / 100.0
+      discount = avoir.total
+      if avoir.coupon.type == 'percent_off'
+        discount = avoir.total * avoir.coupon.percent_off / 100.0
+      elsif avoir.coupon.type == 'amount_off'
+        discount = avoit.coupon.amount_off
+      end
       avoir.total -= discount
     end
     avoir

app/models/price.rb

@@ -45,7 +45,7 @@ class Price < ActiveRecord::Base
           if machine_credit
             hours_available = machine_credit.hours
             if !new_plan_being_bought
-              user_credit = user.users_credits.find_by_credit_id(machine_credit.id)
+              user_credit = user.users_credits.find_by(credit_id: machine_credit.id)
               if user_credit
                 hours_available = machine_credit.hours - user_credit.hours_used
               end
@@ -111,10 +111,7 @@ class Price < ActiveRecord::Base
     end
 
     # === apply Coupon if any ===
-    unless coupon_code.nil?
-      _coupon = Coupon.find_by_code(coupon_code)
-      _amount = _amount - (_amount  * _coupon.percent_off / 100.0)
-    end
+    _amount = CouponApplyService.new.(_amount, coupon_code)
 
     # return result
     {elements: _elements, total: _amount}

app/services/coupon_apply_service.rb

@@ -0,0 +1,22 @@
+class CouponApplyService
+  def call(total, coupon_code)
+    price = total
+
+    # if no coupon code or if code does not match, return origin price without change
+    unless coupon_code.nil?
+      _coupon = Coupon.find_by(code: coupon_code)
+      if _coupon
+        if _coupon.type == 'percent_off'
+          price = price - (price * _coupon.percent_off / 100.0)
+        elsif _coupon.type == 'amount_off'
+          # do not apply cash coupon unless it has a lower amount that the total price
+          if _coupon.amount_off <= price
+            price -= _coupon.amount_off
+          end
+        end
+      end
+    end
+
+    price
+  end
+end