# In order to give the user maximum flexibility with
# units, we create classes Quantity, Length and Angle
class Quantity
  def initialize
    @conversions = {}
  end

  def normalize(mag, units = nil)
    units ||= default_units
    units = units.strip.downcase
    raise "Invalid unit #{units}" unless @conversions.has_key? units
    mag.to_f * @conversions[units]
  end

  def parse(args)
    num = nil
    units = nil

    # does it look like a number with a unit suffix?
    front = args.shift
    if front =~ /^(-?[0-9\.]+)([a-zA-Z-]+)$/
      num = $1.to_f
      units = $2.strip.downcase

    # Just a number?
    elsif front =~ /^(-?[0-9\.]+)$/
      num = $1.to_f

    # A non-blank, non-null junk value?
    elsif front and front !~ /^\s*$/
      $stderr.puts "Error: invalid quantity #{front}"
      usage!

    end

    # Perhaps they put a space before the unit
    if !units and !args.empty? and @conversions.has_key? args.first
      units = args.shift.strip.downcase
    end

    @last_units ||= default_units
    units ||= @last_units
    @last_units = units

    return normalize(num,units)
  end

  def input
    parse( $stdin.readline.strip.split )
  end

  def supported_units
    @conversions.keys
  end
end


class Length < Quantity

  CM_PER_IN = 2.54
  IN_PER_CM = 1.0 / CM_PER_IN
  IN_PER_FT = 12.0
  PTS_PER_IN = 72.0
  CENTI = 100.0
  MILLI = 1000.0

  def initialize
    super
    @conversions = {   'in' =>                                              PTS_PER_IN,
                       'ft' =>                                  IN_PER_FT * PTS_PER_IN,
                       'mm' =>                  CENTI / MILLI * IN_PER_CM * PTS_PER_IN,
                       'cm' =>                                  IN_PER_CM * PTS_PER_IN,
                        'm' =>                          CENTI * IN_PER_CM * PTS_PER_IN }
  end

  def default_units
    'in'
  end

end


class Diameter < Length
  DIAM_PER_CIRC = 1.0 / Math::PI
  DIAM_PER_RAD  = 2.0

  def initialize
    super
    @conversions.keys.each do |key|
      @conversions[key + '-circ'] = DIAM_PER_CIRC * @conversions[key]
      @conversions[key + '-rad']  = DIAM_PER_RAD  * @conversions[key]
    end
  end
end

class Angle < Quantity
  TWOPI = 2.0 * Math::PI

  def initialize
    super
    @conversions = {'deg'     =>  TWOPI / 360.0,
                    'degrees' =>  TWOPI / 360.0,
                    'rad'     =>  1.0,
                    'radians' =>  1.0}
  end

  def default_units
    'degrees'
  end
end

ANGLE = Angle.new
LENGTH = Length.new
DIAMETER = Diameter.new