editor.rb

require 'curses'
include Curses

class Editor
  LOG = File.open('editor.log', 'w')

  def initialize
    @x = 1
    @y = 1
  end

  def move
    print "\033[#{@y};#{@x}f"
  end

  def act(key)
    case key
      when "\e[A"
        @y -= 1
        move
      when "\e[B"
        @y += 1
        move
      when "\e[C"
        @x += 1
        move
      when "\e[D"
        @x -= 1
        move
      when "\r"
        @x = 1
        @y += 1
        move
      else
        print key
        @x += 1
        move
    end
    LOG.puts([@y, @x].inspect)
    LOG.puts(key.inspect); LOG.flush
  end

  def loop
    key = ''
    in_escape = false
    begin
      char = STDIN.getc
      in_escape = true if char == "\e"
      key += char
      if in_escape
        if key.length == 3
          act(key)
          key = ''
          in_escape = false
        end
      else
        act(key)
        key = ''
      end
    end until key == 'Q'
  end
end

begin
  clear; refresh
  cbreak; noecho #; curs_set(0)
  editor = Editor.new
  editor.loop
ensure
  nocbreak; echo; curs_set(1)
end