editor.rb

#! /usr/bin/env ruby
# adapted from https://gist.github.com/gabehollombe/064a90351c204381832d749ca6b569e0
# but it actually edits a file!
# `editor.rb [filename]`
# arrows, letters, backspace... Just the basics.

require 'curses'
include Curses
include Curses::Key

class Integer
  def clamp(low, high)
    v = self
    v = low if self < low
    v = high if self > high
    v
  end
end

class Cursor
  attr_reader :row, :col

  def initialize(row = 0, col = 0)
    @row = row
    @col = col
  end

  def right
    Cursor.new @row, @col + 1
  end

  def left
    Cursor.new @row, @col - 1
  end

  def down
    Cursor.new @row + 1, @col
  end

  def up
    Cursor.new @row - 1, @col
  end
end

class Buffer
  attr_reader :lines, :cursor

  def initialize(lines = [], cursor = Cursor.new)
    @lines = lines
    @cursor = cursor
  end

  def cur_row
    @cursor.row
  end

  def cur_col
    @cursor.col
  end

  def current_line
    @lines[cur_row]
  end

  def add_char(char)
    lines = @lines.dup
    line = lines[cur_row] || []
    line.insert cur_col, char
    lines[cur_row] = line

    Buffer.new lines, @cursor.right
  end

  def remove_char_before_cursor
    return Buffer.new @lines, @cursor if cur_col == 0

    lines = @lines.dup
    line = lines[cur_row] || []
    line.delete_at(cur_col - 1)
    lines[@cursor.row] = line

    Buffer.new lines, @cursor.left
  end

  def new_line
    lines = @lines.dup
    line, next_line = current_line.partition.with_index { |_, i| i < cur_col }
    lines[cur_row] = line
    lines = lines.insert cur_row + 1, next_line
    Buffer.new lines, Cursor.new(cur_row + 1, 0)
  end

  def beginning_of_line
    Buffer.new lines, Cursor.new(cur_row, 0)
  end

  def end_of_line
    Buffer.new lines, Cursor.new(cur_row, current_line.length)
  end

  def cursor_left
    Buffer.new lines, clamp(@cursor.left)
  end

  def cursor_right
    Buffer.new lines, clamp(@cursor.right)
  end

  def cursor_up
    Buffer.new lines, clamp(@cursor.up)
  end

  def cursor_down
    Buffer.new lines, clamp(@cursor.down)
  end

  def clamp(cursor)
    r = cursor.row.clamp(0, @lines.count - 1)
    c = cursor.col.clamp(0, @lines[r].length)

    Cursor.new r, c
  end
end

class Editor
  BACKSPACE = 127
  CTRLA = 1
  CTRLC = 3
  CTRLE = 5
  CTRLX = 24
  ENTER = 13

  def main(buffer = nil)
    raw
    noecho
    nonl
    stdscr.keypad = true
    init_screen

    buffer ||= Buffer.new
    render buffer

    begin
      loop do
        char = getch
        buffer =
          case char
          when CTRLX then break
          when CTRLC then exit
          when CTRLA then buffer.beginning_of_line
          when CTRLE then buffer.end_of_line
          when KEY_UP then buffer.cursor_up
          when KEY_DOWN then buffer.cursor_down
          when KEY_LEFT then buffer.cursor_left
          when KEY_RIGHT then buffer.cursor_right
          when BACKSPACE then buffer.remove_char_before_cursor
          when ENTER then buffer.new_line
          when /[[:print:]]/ then buffer.add_char(char)
          else buffer
          end

        render buffer
      end
    ensure
      close_screen
    end
    buffer
  end

  def render(buffer)
    clear
    buffer.lines.each_with_index do |line, index|
      setpos index, 0
      addstr(line.join)
    end
    setpos buffer.cursor.row, buffer.cursor.col
    refresh
  end
end

buf = Buffer.new File.read(ARGV[0]).lines.to_a.map { |r| r.scan(/[[:print:]]/) }, Cursor.new(0, 0) unless ARGV[0].nil?

buf = Editor.new.main buf

if ARGV[0].nil?
  print "file name? ('q' to exit without save): "
  filename = gets.strip
else
  filename = ARGV[0]
end
File.write(filename, buf.lines.map { |line| line.join('') }.join("\n")) unless filename == 'q'