Refactor: Refactored the bill inventory in the hope of making it less

error prone and more understandable.
Refactor: Also upgrade path to moving from Price/FullPrice to HasHappyHour/
          IsHappyHour
Must have a few errors.

Tanshu.Accounts.Contracts/Data Contracts/InventoryBO.cs

@@ -41,6 +41,50 @@ namespace Tanshu.Accounts.Entities
             }
             set { }
         }
+
+        public virtual decimal ServiceTaxAmount
+        {
+            get
+            {
+                if (IsScTaxable)
+                    return Quantity * Price * (1 - Discount) * (1 + ServiceCharge) * ServiceTaxRate;
+                return Quantity * Price * (1 - Discount) * ServiceTaxRate;
+            }
+        }
+
+        public virtual decimal VatAmount
+        {
+            get
+            {
+                if (IsScTaxable)
+                    return Quantity * Price * (1 - Discount) * (1 + ServiceCharge) * VatRate;
+                return Quantity * Price * (1 - Discount) * VatRate;
+            }
+        }
+
+        public virtual decimal ServiceChargeAmount
+        {
+            get
+            {
+                return Quantity * Price * (1 - Discount) * ServiceCharge;
+            }
+        }
+
+        public virtual decimal DiscountAmount
+        {
+            get
+            {
+                return Quantity * Price * Discount;
+            }
+        }
+
+        public virtual decimal Net
+        {
+            get
+            {
+                return Quantity * Price * (1 - Discount);
+            }
+        }
     }
     public class InventoryMap : ClassMapping<Inventory>
     {