instat test

test.rb

require 'awesome_print'
class Item
	attr_reader :code, :name
	def initialize( code, name )
		@code, @name = code, name
	end
	def to_s
		"#{ @code } #{ @name }"
	end
end
class Rule
	def process( records )
		records .each do |rec|
			price = get_price( rec .item .code .to_sym )
			rec .price = price if price != nil
		end
	end
	protected
	def get_price( code )
		throw :abstract
	end
end
class Base < Rule
	def initialize( prices )
		@prices = prices
	end
	protected
	def get_price( code )
		@prices[ code ]
	end
end
class BuyOneGetOneFree < Rule
	def initialize( code )
		@code = code
	end
	def process( records )
		@free = false
		super( records )
	end
	protected
	def get_price( code )
		return nil unless code == @code
		res = @free ? 0 : nil
		@free = ! @free
		res
	end
end
class BulkDiscount < Rule
	def initialize( code, quantity, price )
		@code, @quantity, @price = code, quantity, price
	end
	def process( records )
		count = records .inject( 0 )do |sum, rec|
			rec .item .code .to_sym == @code ? sum + 1 : sum
		end
		return if count < @quantity
		super( records )
	end
	protected
	def get_price( code )
		return nil unless code == @code
		@price
	end
end

class Record
	attr_accessor :price
	attr_reader :item
	def initialize( item )
		@item = item
		@price = 0
	end
end
class Checkout
	attr_reader :records
	def initialize( pricing_rules )
		@pricing_rules = pricing_rules
		@records = []
	end
	def scan( item )
		@records << Record .new( item )
		@pricing_rules .each{ |rule| rule .process( @records ) }
	end
	def total
		@records .inject( 0 ){ |sum, rec| sum + rec .price }
	end
end
class Test
	def initialize
		i1 = Item .new 'FR1', 'Fruit tea'
		i2 = Item .new 'AP1', 'Apple'
		i3 = Item .new 'CF1', 'Coffee'
		@items = [ i1, i2, i3 ] .inject( {} ){ |hash, item| hash[ item .code .to_sym ] = item; hash }
		#print i1, ' ', i2, ' ', i3, "\n"
		@pricing_rules = [ Base .new( { FR1: 3.11, AP1: 5.0, CF1: 11.23 } ) ]
		@pricing_rules << BuyOneGetOneFree .new( :FR1 )
		@pricing_rules << BulkDiscount .new( :AP1, 3, 4.50 )

		self .class .instance_methods(false) .each do |m|
			matched = /^test(.+)$/ .match( m .to_s )
			if matched
				print "\n\ntest #{ matched[ 1 ] }\n"
				setup
				send m
			end
		end
	end
	def assert( value, expected, msg = '' )
		res = value == expected ? 'PASSED' : 'FAILED'
		print "#{ msg } #{ expected } #{ value } #{ res }"
	end
	def setup
		@co = Checkout .new( @pricing_rules )
	end
	def test1
		%i[ FR1 AP1 FR1 CF1 ] .each{ |code| @co .scan( @items[ code ] ) }
		assert @co .total, 22.25, 'FR1 AP1 FR1 CF1'
	end
	def test2
		%i[ FR1 FR1 ] .each{ |code| @co .scan( @items[ code ] ) }
		assert @co .total, 3.11, 'FR1 FR1'
	end
	def test3
		%i[ AP1 AP1 FR1 AP1 ] .each{ |code| @co .scan( @items[ code ] ) }
		assert @co .total, 16.61, 'AP1 AP1 FR1 AP1'
	end
end
Test .new

=begin
InStat's quest for global domination has prompted us to open a supermarket - we sell only three products:

+--------------|--------------|---------+
| Product Code |     Name     |  Price  |
+--------------|--------------|---------+
|     FR1      |   Fruit tea  |  $3.11  |
|     AP1      |   Apple      |  $5.00  |
|     CF1      |   Coffee     | $11.23  |
+--------------|--------------|---------+

Our CEO is a big fan of buy-one-get-one-free offers and of fruit tea. He wants us to add a rule to do this.

The COO, though, likes low prices and wants people buying apple to get a price discount for bulk purchases. 
If you buy 3 or more apple, the price should drop to $4.50. Our check-out can scan items in any order, and because the CEO and COO change their minds often, it needs to be flexible regarding our pricing rules.

The interface to our checkout looks like this (shown in Ruby):

co = Checkout.new(pricing_rules)
co.scan(item)
co.scan(item)
price = co.total

Implement a checkout system that fulfils these requirements in Ruby.

Here are some test data:

Basket: FR1, AP1, FR1, CF1
Total price expected: $22.25

Basket: FR1, FR1
Total price expected: $3.11

Basket: AP1, AP1, FR1, AP1
Total price expected: $16.61

PS: Here at InStat, we love specs ;)
=end