A simple application to calculate an e-liquid mixture

liquid-calc.rb

# @example
#     vapey = Vapey.new
#     vapey.read_amounts
#     puts vapey
class Vapey
  Valid = {
    "ml"      => ->(ml) { Integer(ml, 10) rescue false },
    "mg"      => ->(mg) { Integer(mg, 10) rescue false },
    "percent" => ->(pc) { Float(pc).between?(0, 1) rescue false },
  }
  Convert = {
    'ml'      => ->(ml) { Integer(ml) },
    'mg'      => ->(mg) { Integer(mg) },
    'percent' => ->(pc) { Float(pc) },
  }
  PrintableTemplate = <<~EOS
    Total amount: %dml
    Base Amount:  %fml(total) %fml(VG) %fml(PG)
    Aroma Amount: %fml
    Amount Shot:  %fml
  EOS

  def initialize
    @out                = $stdout
    @in                 = $stdin
    @ml_total           = 100
    @aroma_percent      = 0.05
    @nicotin_per_ml     = 3
    @shot_concentration = 18
    @target_vg          = 0.75
  end

  def read_amounts
    @ml_total           = read_unit('total', 'ml')
    @aroma_percent      = read_unit('aroma', 'percent')
    @nicotin_per_ml     = read_unit('target nicotine content', 'mg')
    @shot_concentration = read_unit('shot nicotine content', 'mg')
    @target_vg          = read_unit('target VG', 'percent')
  end

  def to_s
    amount_shot  = @ml_total.fdiv(@shot_concentration) * @nicotin_per_ml
    amount_aroma = @ml_total * @aroma_percent
    amount_base  = @ml_total - amount_shot - amount_aroma
    base_vg      = (amount_base) - (amount_shot+amount_aroma) / 2.0
    base_pg      = amount_base - base_vg

    sprintf(
      PrintableTemplate,
      @ml_total,
      base_vg+base_pg,
      base_vg, base_pg,
      amount_aroma,
      amount_shot
    )
  end

  private def read_unit(name, unit)
    @out.print "Enter #{name} in #{unit}: "
    @out.flush

    begin
      input = @in.gets.chomp
      valid_input = Valid[unit].call(input)
      @out.puts "invalid input" unless valid_input
    end until valid_input

    Convert[unit].call(input)
  end
end