translation of erlang_program.prompt.erl to ruby

erlang_program_in_ruby.rb

#############################################################################
# title: erlang_program_in_ruby.rb
# desc: translation of erlang_program.prompt.erl to ruby
# author: gianna fusaro
# date: october 20, 2015
#############################################################################


# WeightItem: item with label, weight, and unit
class WeightItem
  LBS_PER_KG = 0.45359237

  attr_reader :label, :unit

  def initialize(item)
    @label, @unit, @weight = item
  end

  # force weight to float
  def weight
    @weight.to_f
  end

  # convert weight from lbs to kg, or kg to kg
  def to_kg
    case @unit
    when 'l' then WeightItem.new [@label, 'k', weight*LBS_PER_KG]
    when 'k' then self
    else fail "unsupported conversion from #{@unit} to kilograms"
    end
  end

  def to_s
    "#{@label.ljust(14)} #{weight} #{@unit}"
  end
end

# KWeightItemCollection: collection of WeightItems in kg
class KWeightItemCollection

  def initialize(items)
    @items = items.map { |item| WeightItem.new(item).to_kg }
  end

  # returns items with min and max weight
  def minmax
    @items.minmax { |a, b| a.weight <=> b.weight }
  end

  # print each item in kg
  # print item information for max and min weights
  def summarize
    @items.each { |item| puts item }

    min, max = minmax
    puts "Max weight was #{max.weight} #{max.unit} in #{max.label}"
    puts "Min weight was #{min.weight} #{min.unit} in #{min.label}"
  end
end

# handle user input
unless ARGV.empty?
  # parse arguments and display summary
  inputs = ARGV.collect { |arg| arg.split }
  KWeightItemCollection.new(inputs).summarize
else
  # display usage information
  puts <<-END
  Usage: erlang_program_in_ruby.rb \
  'name1 unit1 value1' 'name2 unit2 value2' ... \n\
  Example: erlang_program_in_ruby.rb 'Penny l 0.00551156' 'Dime l 0.005004493'

  END
end