ColorContrast.rb

class Color
  attr_reader :r, :g, :b

  def initialize(r,g,b)
    @r = r
    @g = g
    @b = b
  end

  def brightness_index
    # Brightness index is 
    # ( 299*R1 + 587*G1 + 114*B1) / 1000
    (299*@r + 587*@g + 114*@b) / 1000
  end

  def brightness_difference(another_color)
    # Brightness difference is absolute difference in brightness indices
    (brightness_index - another_color.brightness_index).abs
  end

  def hue_difference(another_color)
    # Hue difference is R1 - R2 + G1 - G2 + B1 - B2
    ((@r - another_color.r).abs + (@g - another_color.g).abs + (@b - another_color.b).abs)
  end

  def enough_contrast?(another_color)
    (brightness_difference(another_color) > 125 && hue_difference(another_color) > 500)
  end
end