A toy text editor written in CoffeeScript

editor.coffee

# =========================================
# A toy text editor written in CoffeeScript
# =========================================
#
# Requires ncurses bindings for node.js:
#   npm install ncurses
#
# Usage:
#   coffee editor.coffee FILENAME
#
#   Ctrl+w saves
#   Ctrl+x exits
#
# =========================================

fs = require 'fs'
ncurses = require 'ncurses'

class Position
  constructor: ->
    @x = 0
    @y = 0
    
  set: (content, index) ->
    lines = content[0...index].split "\n"
    @x = lines[lines.length - 1].length
    @y = lines.length - 1
    
  index: (content) ->
    lines = content.split "\n"
    index = lines[0...@y].join("\n").length + @x
    index += 1 if @y > 0
    index
    
  move: (content, dx, dy) ->
    lines = content.split "\n"
    @y = Math.min Math.max(@y + dy, 0), lines.length - 1
    @x = Math.min Math.max(@x + dx, 0), (lines[@y] || '').length
    
class Viewport
  constructor: (@width, @height) ->
    @offset = { x: 0, y: 0 }
    @cursor = { x: 0, y: 0 }

  adjust: (position) ->
    @reposition position
    @scroll position
    @reposition position

  scroll: (position) ->
    if @cursor.x >= @width
      @offset.x = position.x - @width + 1
    @offset.x = Math.min Math.max(@offset.x, 0), position.x
    if @cursor.y >= @height
      @offset.y = position.y - @height + 1
    @offset.y = Math.min Math.max(@offset.y, 0), position.y

  reposition: (position) ->
    @cursor.x = position.x - @offset.x
    @cursor.y = position.y - @offset.y

  crop: (content) ->
    lines = content.split "\n"
    line[@offset.x...@offset.x + @width] for line in lines[@offset.y...@offset.y + @height]

class Editor
  constructor: (@viewport, @content) ->
    @position = new Position()
    
  view: ->
    @viewport.crop @content
    
  move: (dx, dy) ->
    @position.move @content, dx, dy
    @viewport.adjust @position
    
  insert: (text) ->
    index = @position.index @content
    @content = @content[0...index] + text + @content[index...]
    newlines = text.split "\n"
    @move newlines[newlines.length - 1].length, newlines.length - 1
    
  backspace: (count) ->
    index = @position.index(@content) - count
    if index < 0
      count += index
      index = 0
    @content = @content[0...index] + @content[index + count...]
    @position.set @content, index
    @viewport.adjust @position

class Application
  constructor: (@file) ->
    @window = new ncurses.Window
    @viewport = new Viewport @window.width, @window.height
    @editor = new Editor @viewport, fs.readFileSync @file, 'utf8'

    @window.on 'inputChar', (c, i) =>
      switch i
        when ncurses.keys.UP
          @editor.move 0, -1
        when ncurses.keys.RIGHT
          @editor.move 1, 0
        when ncurses.keys.DOWN
          @editor.move 0, 1
        when ncurses.keys.LEFT
          @editor.move -1, 0
        when ncurses.keys.NEWLINE
          @editor.insert "\n"
        when ncurses.keys.BACKSPACE, 127
          @editor.backspace 1
        when 23 # Ctrl+w
          fs.writeFileSync @file, @editor.content
        when 24 # Ctrl+x
          @window.close()
          return
        else
          if i in [32..126]
            @editor.insert c
      @refresh()

    @refresh()
    @window.refresh()

  refresh: ->
    for line, i in @editor.view()
      padding = Array(@viewport.width - line.length + 1).join ' '
      @window.addstr i, 0, line + padding
    @window.cursor @viewport.cursor.y, @viewport.cursor.x

do ->
  file = process.argv[2]
  unless file?
    console.warn 'Must specify a file'
  else
    app = new Application file