Arnold Clark's coding challenge done by Csaba Nagy (@icnagy).
# run tests with
rspec
The task is to write a small utility site that will get a vehicle’s registration plate and stock reference from the user and then display all the images available for a vehicle.
- A website written using Ruby on Rails
- Test Driven Development
- No bugs
- A good user experience
- Clean code and good engineering practices throughout
The task is to create a site where by entering registration numnber and a reference number we would get back the images from the cache for the car represented by the registration and reference number. To accomplish this, we do not need to store any kind of data, the site will be a kind of "through-and-through" site, where the user enters two ids and gets back the result from a different server.
USER <==> RAILS APP <==> [http://vcache.arnoldclark.com/imageserver]
The user should see a form with two inputs, registration and stock reference number. After sanitizing the user input, using JQuery the server respond will populate the image area.
According to the documentation stock-ref = "ARNFC-U-7276".
- Stock reference number is at least 9 characters long (the 9th character has to be used to create the obfuscated stock reference number)
- Might have dashes
- Has numbers and letters
- Letters are uppercase
According to documentation registration = “YT61BXJ".
- 7 character long
- Numbers and letters
- Uppercase letters
The Rails application should take the user input and show the user the photos of corresponding car.
The image cache takes an obfuscated stock reference number, a resolution/size and a camera id as parameter and returns an image.
- A car can have 12 pictures. Usually it's less than that.
- Recently added cars usually don't have any images at all
- If an image is not available, a default image is sent back.
The obfuscated stock reference is calculated by interleaving the stock reference with the reversal of the registration plate and appending the 9th character of the stock reference and taking the shortest possible solution (i.e. ignore any unused characters from the stock reference)
Quick typing in irb yields the first approach:
reference.ch
7374
ars.take(registration.length).zip(registration.reverse.chars).flatten.compact.join << reference.chars[8]
or without compact
reference.chars.take(registration.length).zip(registration.reverse.chars).flatten.join << reference.chars[8]
Take the first 7 characters of stock reference, interleave it with the revers of the registartion, flatten the array of two's, then join the array to a string, and add the 9th character of the reference number.
As presumed earlier, the Rails app does not need any database to store information. So I create a new Rails app without ActiveRecord:
rails new arnoldc -O
I have ruby 2.2.0 and Rails 4.2.0 installed, so I will just use that. I use RVM, so I just let it install the .rvmrc, .ruby-version and .version.conf files:
$ rvm --rvmrc 2.2.0@arnoldc
$ rvm --create --ruby-version use 2.2.0@arnoldc
$ rvm --create --versions-conf use 2.2.0@arnoldc
Time to initialize git:
git init
I use IntelliJ's RubyMine for IDE so I update the .gitignore file.
See architecture.md
While working on caching I noticed that some registration numbers will work with different combination of stock reference numbers. I started swapping the letters/number for the cache url and got to that each even letter has no contribution:
XAXBXCXDXEXFXGX
where X can be anything 0-9, a-z, A-Z or '-'.
These:
- http://vcache.arnoldclark.com/imageserver/XDXTXYX6X5XKXRX/350/f
- http://vcache.arnoldclark.com/imageserver/zDzTzYz6z5zKzRz/350/f
- http://vcache.arnoldclark.com/imageserver/0D0T0Y06050K0R0/350/f
- http://vcache.arnoldclark.com/imageserver/-D-T-Y-6-5-K-R-/350/f
return the same image.