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Shop ABCD 
By P. Mark Anderson

This code sample demonstrates a basic point-of-sale scanning API that accepts an arbitrary ordering of products (similar to what would happen when actually at a checkout line) and returns the correct total price for an entire shopping cart based on the per unit prices or the volume prices as applicable.

This implementation is written in Ruby and consists of four classes and a utility module. There are two ways to test this code as an API.

1) Run the command line test program.

    $ ruby cli/shop_abcd.rb


2) Copy and paste the code in run_online/shop_abcd_combined.rb into this online Ruby editor.

    http://www.compileonline.com/execute_ruby_online.php


BONUS

On reading the instructions again I noticed that they clearly state not to spend time on a UI. I certainly want to follow direction, but after completing the command line implementation I knew that making this code a Sinatra app hosted on AppFog with a Redis backend was a fairly minor task, so here's an additional way to test my work.

    http://shop.martianrover.com/


Below is a sample execution of the POS terminal test program being run from the command line. Thanks for your time!
Mark



$ ruby cli/shop_abcd.rb


[SHOP] Welcome to Shop ABCD
[SHOP] Initializing catalog

[CATALOG] New product: A $1.25
[CATALOG] New product: B $4.25
[CATALOG] New product: C $1.00
[CATALOG] New product: D $0.75
[CATALOG] New discount: 3 product A for $3.00
[CATALOG] New discount: 6 product C for $5.00


- - - - - - - - - - - - - - - -
[SHOP] Executing order 1: ABCDABA should be $13.25

[ORDER] Added product: A
[POS] TOTAL:  $1.25

[ORDER] Added product: B
[POS] TOTAL:  $5.50

[ORDER] Added product: C
[POS] TOTAL:  $6.50

[ORDER] Added product: D
[POS] TOTAL:  $7.25

[ORDER] Added product: A
[POS] TOTAL:  $8.50

[ORDER] Added product: B
[POS] TOTAL:  $12.75

[ORDER] Added product: A
[POS] SUBTOTAL:  $14.00
[POS] DISCOUNT: -$0.75
[POS] TOTAL:  $13.25



- - - - - - - - - - - - - - - -
[SHOP] Executing order 2: CCCCCCC should be $6.00

[ORDER] Added product: C
[POS] TOTAL:  $1.00

[ORDER] Added product: C
[POS] TOTAL:  $2.00

[ORDER] Added product: C
[POS] TOTAL:  $3.00

[ORDER] Added product: C
[POS] TOTAL:  $4.00

[ORDER] Added product: C
[POS] TOTAL:  $5.00

[ORDER] Added product: C
[POS] SUBTOTAL:  $6.00
[POS] DISCOUNT: -$1.00
[POS] TOTAL:  $5.00

[ORDER] Added product: C
[POS] SUBTOTAL:  $7.00
[POS] DISCOUNT: -$1.00
[POS] TOTAL:  $6.00



- - - - - - - - - - - - - - - -
[SHOP] Executing order 3: ABCD should be $7.25

[ORDER] Added product: A
[POS] TOTAL:  $1.25

[ORDER] Added product: B
[POS] TOTAL:  $5.50

[ORDER] Added product: C
[POS] TOTAL:  $6.50

[ORDER] Added product: D
[POS] TOTAL:  $7.25