Bill Splitter

bill_splitter.rb

class BillSplitter
  attr_reader :total, :people, :tip

  def initialize(options={})
    @total = options.fetch(:total).to_f
    @people = options.fetch(:people, 2)
    @tip = options.fetch(:tip, 10)
  end

  def calculate
    "The cost is $%.2f per person " \
    "(including a $%.2f tip)" \
      % [price_per_person, tip_per_person]
  end

  private

  def price_per_person
    total / people + tip_per_person
  end

  def tip_per_person
    calculated_tip / people
  end

  def calculated_tip
    total / 100 * tip
  end
end

#-~-~-~-~-~-#

# calculates the tip
p BillSplitter.new({ total: 104.80, people: 3, tip: 12 }).calculate
# => "The cost is $39.13 per person (including a $4.19 tip)"

# uses defaults of two people and a tip of 10%
p BillSplitter.new({ total: 104.80 }).calculate
# => "The cost is $57.64 per person (including a $5.24 tip)"

# if you don't provide a required key the error is helpful
p BillSplitter.new({ people: 3, tip: 8 }).calculate
# => `fetch': key not found: :total (KeyError)