Refactor code structure and implement Conjured items support

Refactoring improvements:
- Extract complex nested if-else logic into well-named private methods
- Separate concerns: each item type has its own update method
- Use constants for item names and quality limits
- Add comprehensive docstrings for all methods
- Improve code readability and maintainability

Conjured items implementation:
- Conjured items degrade in quality twice as fast as normal items
- After sell-by date, Conjured items degrade 4x faster (2x normal rate * 2x after sell-by)
- Quality never goes below 0
- Uses prefix matching for flexibility ('Conjured' prefix)

All tests pass, including the new Conjured items tests.

python/gilded_rose.py

@@ -1,42 +1,114 @@
 # -*- coding: utf-8 -*-
 
+
 class GildedRose(object):
+    """Manages the inventory of items at the Gilded Rose inn."""
+    
+    # Item type constants
+    AGED_BRIE = "Aged Brie"
+    BACKSTAGE_PASSES = "Backstage passes to a TAFKAL80ETC concert"
+    SULFURAS = "Sulfuras, Hand of Ragnaros"
+    CONJURED_PREFIX = "Conjured"
+    
+    # Quality constraints
+    MAX_QUALITY = 50
+    MIN_QUALITY = 0
+    SULFURAS_QUALITY = 80
 
     def __init__(self, items):
         self.items = items
 
     def update_quality(self):
+        """Updates the quality and sell_in values for all items."""
         for item in self.items:
-            if item.name != "Aged Brie" and item.name != "Backstage passes to a TAFKAL80ETC concert":
+            self._update_item(item)
-                if item.quality > 0:
+
-                    if item.name != "Sulfuras, Hand of Ragnaros":
+    def _update_item(self, item):
-                        item.quality = item.quality - 1
+        """Updates a single item's quality and sell_in values."""
-            else:
+        if self._is_sulfuras(item):
-                if item.quality < 50:
+            # Sulfuras never changes
-                    item.quality = item.quality + 1
+            return
-                    if item.name == "Backstage passes to a TAFKAL80ETC concert":
+        
-                        if item.sell_in < 11:
+        # Update sell_in date
-                            if item.quality < 50:
+        item.sell_in -= 1
-                                item.quality = item.quality + 1
+        
-                        if item.sell_in < 6:
+        # Update quality based on item type
-                            if item.quality < 50:
+        if self._is_aged_brie(item):
-                                item.quality = item.quality + 1
+            self._update_aged_brie(item)
-            if item.name != "Sulfuras, Hand of Ragnaros":
+        elif self._is_backstage_passes(item):
-                item.sell_in = item.sell_in - 1
+            self._update_backstage_passes(item)
-            if item.sell_in < 0:
+        elif self._is_conjured(item):
-                if item.name != "Aged Brie":
+            self._update_conjured_item(item)
-                    if item.name != "Backstage passes to a TAFKAL80ETC concert":
+        else:
-                        if item.quality > 0:
+            self._update_normal_item(item)
-                            if item.name != "Sulfuras, Hand of Ragnaros":
+
-                                item.quality = item.quality - 1
+    def _is_sulfuras(self, item):
-                    else:
+        """Check if item is Sulfuras."""
-                        item.quality = item.quality - item.quality
+        return item.name == self.SULFURAS
-                else:
+
-                    if item.quality < 50:
+    def _is_aged_brie(self, item):
-                        item.quality = item.quality + 1
+        """Check if item is Aged Brie."""
+        return item.name == self.AGED_BRIE
+
+    def _is_backstage_passes(self, item):
+        """Check if item is Backstage passes."""
+        return item.name == self.BACKSTAGE_PASSES
+
+    def _is_conjured(self, item):
+        """Check if item is a Conjured item."""
+        return item.name.startswith(self.CONJURED_PREFIX)
+
+    def _update_normal_item(self, item):
+        """Update quality for normal items."""
+        degradation_rate = self._get_degradation_rate(item)
+        self._decrease_quality(item, degradation_rate)
+
+    def _update_conjured_item(self, item):
+        """Update quality for Conjured items (degrade twice as fast)."""
+        degradation_rate = self._get_degradation_rate(item) * 2
+        self._decrease_quality(item, degradation_rate)
+
+    def _update_aged_brie(self, item):
+        """Update quality for Aged Brie (increases with age)."""
+        self._increase_quality(item)
+        if self._is_past_sell_by_date(item):
+            self._increase_quality(item)
+
+    def _update_backstage_passes(self, item):
+        """Update quality for Backstage passes."""
+        if self._is_past_sell_by_date(item):
+            # Quality drops to 0 after the concert
+            item.quality = 0
+        else:
+            self._increase_quality(item)
+            if item.sell_in < 10:
+                self._increase_quality(item)
+            if item.sell_in < 5:
+                self._increase_quality(item)
+
+    def _get_degradation_rate(self, item):
+        """Get the degradation rate based on sell_in date."""
+        if self._is_past_sell_by_date(item):
+            return 2  # Degrades twice as fast after sell by date
+        return 1  # Normal degradation rate
+
+    def _is_past_sell_by_date(self, item):
+        """Check if item is past its sell by date."""
+        return item.sell_in < 0
+
+    def _increase_quality(self, item):
+        """Increase item quality by 1, respecting maximum quality cap."""
+        if item.quality < self.MAX_QUALITY:
+            item.quality += 1
+
+    def _decrease_quality(self, item, amount):
+        """Decrease item quality by specified amount, respecting minimum quality."""
+        item.quality = max(self.MIN_QUALITY, item.quality - amount)
 
 
 class Item:
+    """Represents an item in the inventory."""
+    
     def __init__(self, name, sell_in, quality):
         self.name = name
         self.sell_in = sell_in