Move DailyUpdate of each type to DailyUpdaterHierarchy and add a simple factory method to get the appropriate updater to use.

csharpcore/GildedRose/DailyUpdater.cs

@@ -0,0 +1,94 @@
+using System.Data;
+
+namespace GildedRoseKata;
+
+public abstract class DailyUpdater
+{
+    protected const int MinQuality = 0;
+    protected const int MaxQuality = 50;
+
+    public void DailyUpdate(Item item)
+    {
+        UpdateSellIn(item);
+        UpdateQuality(item);
+    }
+
+    public abstract void UpdateQuality(Item item);
+    public virtual void UpdateSellIn(Item item) => item.SellIn -= 1;
+
+    protected static bool IsExpired(Item item) => item.SellIn < 0;
+
+    protected static void IncreaseQuality(Item item, int byValue)
+    {
+        item.Quality = int.Min(item.Quality + byValue, MaxQuality);
+    }
+
+    protected static void DecreaseQuality(Item item, int byValue)
+    {
+        item.Quality = int.Max(item.Quality - byValue, MinQuality);
+    }
+    
+    
+}
+
+public class DailyUpdaterForRegularItems : DailyUpdater
+{
+    public override void UpdateQuality(Item item)
+    {
+        DecreaseQuality(item, 1);
+        if (IsExpired(item))
+        {
+            DecreaseQuality(item, 1);
+        }
+    }
+}
+
+public class DailyUpdaterForBetterWithAgeItems : DailyUpdater
+{
+    public override void UpdateQuality(Item item)
+    {
+        IncreaseQuality(item, 1);
+        if (IsExpired(item))
+        {
+            IncreaseQuality(item, 1);
+        }
+    }
+}
+
+
+public class DailyUpdaterForBackstagePassesItems : DailyUpdater
+{
+    public override void UpdateQuality(Item item)
+    {
+        if (item.SellIn > 9)
+        {
+            IncreaseQuality(item, 1);
+        }
+        else if (item.SellIn > 4)
+        {
+            IncreaseQuality(item, 2);
+        }
+        else if (!IsExpired(item))
+        {
+            IncreaseQuality(item, 3);
+        }
+        else //Expired
+        {
+            DecreaseQuality(item, item.Quality);
+        }
+    }
+}
+
+public class DailyUpdaterForLegendaryItems : DailyUpdater
+{
+    public override void UpdateSellIn(Item item)
+    {
+        // Legendary Items don't change over time
+    }
+    public override void UpdateQuality(Item item)
+    {
+        // Legendary Items don't change over time
+    }
+}
+
+

csharpcore/GildedRose/GildedRose.cs

@@ -17,7 +17,8 @@ public class GildedRose
     {
         foreach (var item in _items)
         {
-            DailyItemUpdate(item);
+            DailyUpdater dailyUpdater = getDailyUpdater(item);
+            dailyUpdater.DailyUpdate(item);
         }
     }
 
@@ -26,67 +27,24 @@ public class GildedRose
     private static bool IsBackstagePassesItem(Item item) => item.Name.ToLower().Contains("backstage passes");
 
     private static bool IsBetterWithAgeItem(Item item) => item.Name.ToLower().Equals("aged brie");
-
-    private static bool IsRegularItem(Item item) => (!IsLegendaryItem(item) &&
-                                                     !IsBackstagePassesItem(item) &&
-                                                     !IsBetterWithAgeItem(item));
-
-    private static bool IsExpired(Item item) => item.SellIn < 0;
     
-    private static void IncreaseQuality(Item item, int byValue)
+    private DailyUpdater getDailyUpdater(Item item)
     {
-        item.Quality = int.Min(item.Quality + byValue, MaxQuality);
-    }
-    
-    private static void DecreaseQuality(Item item, int byValue)
-    {
-        item.Quality = int.Max(item.Quality - byValue, MinQuality);
-    }
-
-
-    private void DailyItemUpdate(Item item)
-    {
-        if (IsLegendaryItem(item)) return;
-        
-        item.SellIn -= 1;
-        
-        if (IsRegularItem(item))
+        if (IsLegendaryItem(item))
         {
-            DecreaseQuality(item, 1);
-            if (IsExpired(item))
-            {
-                DecreaseQuality(item, 1);
-            }
+            return new DailyUpdaterForLegendaryItems();
         }
 
         if (IsBetterWithAgeItem(item))
         {
-            IncreaseQuality(item, 1);
-            if (IsExpired(item))
-            {
-                IncreaseQuality(item, 1);
-            }
+            return new DailyUpdaterForBetterWithAgeItems();
         }
 
-        if(IsBackstagePassesItem(item))
+        if (IsBackstagePassesItem(item))
         {
-            if (item.SellIn > 9)
-            {
-                IncreaseQuality(item, 1);
-            }
-            else if (item.SellIn > 4)
-            {
-                IncreaseQuality(item, 2);
-            }
-            else if (!IsExpired(item))
-            {
-                IncreaseQuality(item, 3);
-            }
-            else //Expired
-            {
-                DecreaseQuality(item, item.Quality);
-            }
+            return new DailyUpdaterForBackstagePassesItems();
         }
 
+        return new DailyUpdaterForRegularItems();
     }
 }

csharpcore/GildedRose/RefactoringDiary.md

@@ -12,11 +12,20 @@ Some of the tests failed due to bugs I discovered in the code/existing tests (e.
 I decorated these tests with `[Ignore]` until I get to a stage in the refactoring where I can easily fix the issues and re-introduce the tests.   
 2. small refactorings of the UpdateQuality() method to make it more readable and separate the different (unrelated) handling of the different types.<br>
 3. Extract Increasing/Decreasing Quality into a method.<br>  
-It feels like Quality should have been a TinyType that manages its own limits. However, since we're not allowed to change Item, I'm just extracting a method.
 4. Separated the processing of the different types from each other.<br>
+5. Used the `Template` design pattern to create DailyUpdater abstract class and derived classes to handle the DailyUpdate's steps for the different types of items.<br>
+The different derived classes will be moved to their own files in the next PR. Left them together for now to show the steps.
+6. Created a `Simple Factory` method to return the appropriate DailyUpdater object for the item type.<br>
+For this PR, I left this method in the GildedRose.cp to show the steps. But in the next PR I'll move it into its own class.
 
 
 This is the state of the code now
 
 
+### Considered but dropped
+This is all the design ideas/patterns I've considered but decided against
+- It feels like Quality should have been a `TinyType` that manages its own limits. However, since we're not allowed to change Item I'm not implementing this.
+- 
+
+