256-color hex intepretation for terminal colorization

256color.rb

#!/usr/bin/env ruby
# frozen_string_literal: true

# 256-color hex interpretation for terminal colorization
#
# Usage
# "text".color256(foreground, background)
#
# print "Colorize this".color256('#f7921e', '#666')

# String category
module Color256
  def fg(fgc)
    "\x1b[38;2;#{fgc.rgb}m"
  end

  def bg(bgc)
    "\x1b[48;2;#{bgc.rgb}m"
  end

  def reset
    "\x1b[0m"
  end

  def rgb
    hex_string = sub(/^#?/, '')

    hex_string = hex_string.split(//).map { |a| a * 2 }.join('') if hex_string =~ /^#?[a-f0-9]{3}$/i

    parts = hex_string.match(/#?(?<r>..)(?<g>..)(?<b>..)/)
    t = []
    %w[r g b].each do |e|
      t << parts[e].hex
    end
    t.join(';')
  end

  def color256(fgc, bgc = nil)
    out = ''
    out += fg(fgc)
    out += bg(bgc) if bgc
    out += self
    out + reset
  end
end

class ::String
  include Color256
end

def test
  256.times do |r|
    256.times do |g|
      256.times do |b|
        c = ''
        [r, g, b].each { |comp| c += format('%02x', comp) }
        print ' '.color256('000', c)
      end
    end
  end
end

if __FILE__ == $0
  print ARGV[0].color256(ARGV[1], ARGV[2])
end