coolline.rb

require 'io/console'

class Coolline
  # Creates a new cool line
  # @param [IO] input  Input to read from. This has to be an actual IO object.
  # @param [IO] output Output. This can be an object of any kind.
  #
  # @yield after each character entered
  # @yieldparam [String] line
  # @yieldreturn [String] string to print for this input
  def initialize(input = STDIN, output = $stdout, &block)
    @input  = input
    @output = output

    @transform = block
  end

  # Reads a line from the terminal
  # @param [String] prompt Characters to print before each line
  def readline(prompt = ">> ")
    @line       = ""
    @pos        = 0
    @max_length = 0

    print prompt

    until (char = @input.getch) == "\r"
      handle(char)

      line = fill_line(transform(@line))

      print "\r"
      print prompt + fill_line(transform(@line))
      print "\e[#{prompt.size + @pos + 1}G"
    end

    print "\n"

    @line
  end

  def gets
    readline ""
  end

  private
  def transform(line)
    ret = @transform ? @transform.call(line) : line
    @max_length = ret.length if ret.length > @max_length
    ret
  end

  def handle(char)
    case char
    when "\b", "\x7F"
      if @pos != 0
        @line[@pos - 1] = ''
        @pos -= 1
      end
    when "\C-a"
      @pos = 0
    when "\C-e"
      @pos = @line.size
    when "\C-k"
      @line[@pos..-1] = ""
    when "\C-f"
      if @pos != @line.size
        @pos += 1
      end
    when "\C-b"
      if @pos != 0
        @pos -= 1
      end
    when "\C-d"
      if @pos != @line.size
        @line[@pos] = ""
      end
    when "\C-c"
      raise Interrupt
    when "\C-w"
      if @pos != 0
        pos = @pos - 1
        pos -= 1 if pos != -1 and word_boundary? @line[pos]
        pos -= 1 until pos == -1 or word_boundary? @line[pos]
        @line[(pos + 1)..@pos] = ""
        @pos = pos + 1
      end
    when "\C-a".."\C-z"
      # ignore other control codes
    else
      @line.insert @pos, char
      @pos += char.size
    end
  end

  def fill_line(line)
    line.ljust(@max_length)
  end

  def word_boundary?(char)
    char =~ /[ _-]/
  end
end

require 'coderay'

cool = Coolline.new do |line|
  CodeRay.scan(line, :ruby).term
end

loop do
  cool.readline
end