sales_tax.rb

require 'yaml'

module Tax
  SALES_TAX = 10
  SALES_TAX_EXEMPTIONS = ['book', 'chocolate', 'pills' ]
  IMPORT_DUTY = 5
end

# There is no standard method that rounds off a float to 2 decimals.
class Float
  def round_to(x)
    (self * 10**x).round.to_f / 10**x
  end
end

class Item
  def initialize(attributes)
    return if attributes.length < 0
    attributes.each do |name, value|
      instance_variable_set "@#{name}", value
    end
  end
  
  def exempted?
    Tax::SALES_TAX_EXEMPTIONS.any?{|i| @item.downcase.include?(i.downcase)}
  end
  
  def imported?
    [email protected](/imported/i).empty?
  end
  
  def sales_tax
    base_tax = exempted? ? 0 : Tax::SALES_TAX
    import_duty = imported? ? Tax::IMPORT_DUTY : 0
    tax_rate = base_tax + import_duty
    total_tax = (@price.to_f*tax_rate)/100
    total_tax.round_to(2)
  end
  
  def price
    (@price.to_f + sales_tax).round_to(2)
  end
  
  def print_receipt
    puts "Item: #{@item}, Quantity: #{@quantity}, Price: #{price}"
  end
  alias_method :p, :print_receipt
  
end

inputs = YAML.load(File.open('inputs.yml'))

inputs.sort.each do |label, values|
  puts "Processing #{label.gsub('_',' ').capitalize}:"
  totals = values.collect do |item, value|
    item, price = value.split(/\s+at\s+/)
    quantity, item = item.split(/\s/, 2)
    billed_item = Item.new(:item => item, :quantity => quantity, :price => price)
    billed_item.p
    [billed_item.price, billed_item.sales_tax]
  end
  t = totals.inject do |sum, v|
    [sum[0] + v[0], sum[1] + v[1]]
  end
  puts "-----------------------"
  puts "Total Sales Taxes: #{t[1]}"
  puts "Total: #{t[0]}", ""
end