class Rainbow::Color

def self.build(ground, values)
  unless [1, 3].include?(values.size)
    raise ArgumentError,
          "Wrong number of arguments for color definition, should be 1 or 3"
  end
  color = values.size == 1 ? values.first : values
  case color
  # NOTE: Properly handle versions before/after Ruby 2.4.0.
  # Ruby 2.4+ unifies Fixnum & Bignum into Integer.
  # However previous versions would still use Fixnum.
  # To avoid missing `Fixnum` input, call `0.class` which would
  # return either `Integer` or `Fixnum`.
  when 0.class
    Indexed.new(ground, color)
  when Symbol
    if Named.color_names.include?(color)
      Named.new(ground, color)
    elsif X11Named.color_names.include?(color)
      X11Named.new(ground, color)
    else
      raise ArgumentError,
            "Unknown color name, valid names: " +
            (Named.color_names + X11Named.color_names).join(', ')
    end
  when Array
    RGB.new(ground, *color)
  when String
    RGB.new(ground, *parse_hex_color(color))
  end
end

def self.parse_hex_color(hex)
  unless hex =~ /^#?[a-f0-9]{6}/i
    raise ArgumentError,
          "Invalid hexadecimal RGB triplet. Valid format: /^#?[a-f0-9]{6}/i"
  end
  hex = hex.sub(/^#/, '')
  r   = hex[0..1].to_i(16)
  g   = hex[2..3].to_i(16)
  b   = hex[4..5].to_i(16)
  [r, g, b]
end