Remove old version and udpate to use reflection to load rules

DesignPatternsInCSharp/RulesEngine/Discounts/DiscountCalculator.cs

@@ -1,62 +1,127 @@
 using System;
+using System.Collections;
+using System.Collections.Generic;
+using System.Diagnostics.Contracts;
+using System.Linq;
 
 namespace DesignPatternsInCSharp.RulesEngine.Discounts
 {
-    public class DiscountCalculator
+    // View History
+    // https://github.githistory.xyz/ardalis/DesignPatternsInCSharp/blob/master/DesignPatternsInCSharp/RulesEngine/Discounts/DiscountCalculator.cs
+    public interface IDiscountRule
     {
-        public decimal CalculateDiscountPercentage(Customer customer)
+        decimal CalculateDiscount(Customer customer, decimal currentDiscount);
+    }
+
+    public class FirstTimeCustomerRule : IDiscountRule
+    {
+        public decimal CalculateDiscount(Customer customer, decimal currentDiscount)
         {
-            bool isBirthday = customer.DateOfBirth.HasValue && customer.DateOfBirth.Value.Month == DateTime.Today.Month && customer.DateOfBirth.Value.Day == DateTime.Today.Day;
             if (!customer.DateOfFirstPurchase.HasValue)
             {
                 return .15m;
             }
-            else
+            return 0;
+        }
+    }
+
+    public class LoyalCustomerRule : IDiscountRule
+    {
+        public decimal CalculateDiscount(Customer customer, decimal currentDiscount)
+        {
+            if (customer.DateOfFirstPurchase.HasValue)
             {
                 if (customer.DateOfFirstPurchase.Value < DateTime.Now.AddYears(-15))
                 {
-                    if (isBirthday) return .25m;
                     return .15m;
                 }
                 if (customer.DateOfFirstPurchase.Value < DateTime.Now.AddYears(-10))
                 {
-                    if (isBirthday) return .22m;
                     return .12m;
                 }
                 if (customer.DateOfFirstPurchase.Value < DateTime.Now.AddYears(-5))
                 {
-                    if (isBirthday) return .20m;
                     return .10m;
                 }
-                if (customer.DateOfFirstPurchase.Value < DateTime.Now.AddYears(-2) &&
-                    !customer.IsVeteran)
+                if (customer.DateOfFirstPurchase.Value < DateTime.Now.AddYears(-2))
                 {
-                    if (isBirthday) return .18m;
                     return .08m;
                 }
-                if (customer.DateOfFirstPurchase.Value < DateTime.Now.AddYears(-1) &&
-                    !customer.IsVeteran)
+                if (customer.DateOfFirstPurchase.Value < DateTime.Now.AddYears(-1))
                 {
-                    if (isBirthday) return .15m;
                     return .05m;
                 }
             }
+            return 0;
+        }
+    }
 
+    public class VeteranRule : IDiscountRule
+    {
+        public decimal CalculateDiscount(Customer customer, decimal currentDiscount)
+        {
             if (customer.IsVeteran)
             {
-                if (isBirthday) return .20m;
                 return .10m;
             }
-
-            if(customer.DateOfBirth < DateTime.Now.AddYears(-65))
+            return 0;
+        }
+    }
+    public class SeniorRule : IDiscountRule
+    {
+        public decimal CalculateDiscount(Customer customer, decimal currentDiscount)
+        {
+            if (customer.DateOfBirth < DateTime.Now.AddYears(-65))
             {
-                if (isBirthday) return .15m;
                 return .05m;
             }
+            return 0;
+        }
+    }
 
-            if (isBirthday) return .10m;
+    public class BirthdayRule : IDiscountRule
+    {
+        public decimal CalculateDiscount(Customer customer, decimal currentDiscount)
+        {
+            bool isBirthday = customer.DateOfBirth.HasValue && customer.DateOfBirth.Value.Month == DateTime.Today.Month && customer.DateOfBirth.Value.Day == DateTime.Today.Day;
 
-            return 0;
+            if (isBirthday) return currentDiscount + 0.10m;
+            return currentDiscount;
+        }
+    }
+
+    public class DiscountRuleEngine
+    {
+        List<IDiscountRule> _rules = new List<IDiscountRule>();
+
+        public DiscountRuleEngine(IEnumerable<IDiscountRule> rules)
+        {
+            _rules.AddRange(rules);
+        }
+
+        public decimal CalculateDiscountPercentage(Customer customer)
+        {
+            decimal discount = 0m;
+            foreach(var rule in _rules)
+            {
+                discount = Math.Max(discount, rule.CalculateDiscount(customer, discount));
+            }
+            return discount;
+        }
+    }
+
+    public class DiscountCalculator
+    {
+        public decimal CalculateDiscountPercentage(Customer customer)
+        {
+            var ruleType = typeof(IDiscountRule);
+            IEnumerable<IDiscountRule> rules = this.GetType().Assembly.GetTypes()
+                .Where(p => ruleType.IsAssignableFrom(p) && !p.IsInterface)
+                .Select(r => Activator.CreateInstance(r) as IDiscountRule);
+
+            var engine = new DiscountRuleEngine(rules);
+
+            return engine.CalculateDiscountPercentage(customer);
         }
     }
 }