Gilded Rose Kata

The objective of this kata is to practice refactoring. This kata motivates the need for refactoring as follows:

• The implementation is spaghetti code, and difficult to glean context.
• The tests of the current implementation pass, but there are a number of pending tests.
• You are asked to implement the code to get the pending tests to pass.
• This isn't easy, because the implementation is so messy.
• Consider using the passing tests to refactor the code to make it more habitable before implementing new functionality. Also known as a preparatory refactoring.

It may help you to understand the problem domain if you know that the Gilded Rose is an inn from the World of Warcraft.

Problem description

Hi and welcome to team Gilded Rose. As you know, we are a small inn with a prime location in a prominent city run by a friendly innkeeper named Allison. We also buy and sell only the finest goods. Unfortunately, our goods are constantly degrading in quality as they approach their sell by date. We have a system in place that updates our inventory for us. It was developed by a no-nonsense type named Leeroy, who has moved on to new adventures. Your task is to add the new feature to our system so that we can begin selling a new category of items. First an introduction to our system:

• All items have a sell_in value which denotes the number of days we have to sell the item
• All items have a quality value which denotes how valuable the item is
• At the end of each day our system lowers both values for every item

Pretty simple, right? Well, this is where it gets interesting:

• Once the sell by date has passed, Quality degrades twice as fast
• The Quality of an item is never negative
• "Aged Brie" actually increases in Quality the older it gets
• The Quality of an item is never more than 50
• "Sulfuras", being a legendary item, never has to be sold or decreases in Quality
• "Backstage passes", like aged brie, increases in Quality as its sell by date approaches; Quality increases by 2 when there are 10 days or less and by 3 when there are 5 days or less but Quality drops to 0 after the concert

We have recently signed a supplier of conjured items. This requires an update to our system:

• "Conjured" items degrade in Quality twice as fast as normal items

Feel free to make any changes to the update_quality method and add any new functions, as long as everything still works correctly. However, do not alter the Item class or the items property as those belong to the goblin in the corner who will insta-rage and one-shot you as he doesn't believe in shared code ownership. Your work needs to be completed by Friday, February 18, 2011 08:00:00 AM PST.

Just for clarification, an item can never have its Quality increase above 50, however "Sulfuras" is a legendary item and as such its Quality is 80 and it never alters.