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The Gilded Rose Code Kata in elm

This is an elm version of the Gilded Rose Kata, found here.

This is a refactoring kata, so you will be starting with a legacy code base.
Clone this repository, read the description below for the rules and start hacking right away!

Installation and running tests

Assuming you already installed node.js and npm you have to install elm and elm-test:

# install prerequisites. depending on your setup, you may want to use `sudo`.
npm install -g elm elm-test

# run the tests
elm-test

If the tests pass, you are all set up to work the kata. After making familiar with the original description you may start hacking at src/GildedRose.elm!

Afterwards

Whenever you have a solution, please do not hesitate to make a PR. It will not be merged but may be an inspiration for the fellow elmish.
You also might want to have a look at my solution by checking out solution1.

Changes from the original

This elm version follows the original code closely, but has the following changes:

  • The original had no tests. Since this is a refactoring kata, I feel the tests are important and provide a fairly complete test suite. Just delete the tests if you wish to "go it alone".

  • The original used a hard coded set of "items", presumably for testing the code. Since I added a test suite, the hard coded values were not of much use. I also changed the interface to accept a list of items as a parameter rather than a hard coded constant.

Original Description of the Gilded Rose

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 SellIn 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 it's SellIn value 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 UpdateQuality method and add any new code as long as everything still works correctly. However, do not alter the Item class or 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 (you can make the UpdateQuality method and Items property static if you like, we'll cover for you). 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.

Props

This README has mostly been copied from Jim Weinrich's Ruby version.