# Interactive RGB Color Hex Convert
# usage:
# $ ruby rgb_to_hex.rb
# r g b > 255 51 234
# hex: #ff33aa
# r g b > 0
# ### Please type 3 int values: red green blue
# r g b > 132 256 -1
# ### Please type 3 int values: (0 <= x <= 255)
# r g b > quit
# bye

# rgb is Integer Array etc [r, g, b] (0 <= n <= 255)
def conv(rgb)
  msg = '### Please type 3 int values'
  return "#{msg}:: red green blue" if rgb.length < 3
  return "#{msg}:: (0 <= x <= 255)" unless rgb.all? {|i| (0..255).include? i }
  "hex: ##{rgb.map {|i| '%02x' % i }.join '' }"
end

def prompt
  print 'r g b > '
  gets.strip
end

# main loop
def main
  input = prompt()
  until input == 'quit'
    puts conv(input.split.map &:to_i)
    input = prompt()
  end
  puts 'bye'
end

if $0 == __FILE__
  main
end