Swap the left and right sides of an image

swaprl.js

#!/usr/bin/env node

var lwip = require('lwip');
var path = require('path');
var file = path.resolve(process.argv[2]);
var newfile = path.join(path.dirname(file),
  path.basename(file, path.extname(file))+'_SWAPPED'+path.extname(file) )

lwip.open(file, swaplr)

function swaplr (err, img) {
  if (err) throw err;

  var h = img.height(), w = img.width();

  img.extract(1, 1, w/2, h, function (err, left) {
    if (err) throw err;

    img.extract(w/2+1, 1, w, h, function (err, right) {
      if (err) throw err;

      img.paste(0, 0, right, function (err, img) {
        if (err) throw err;

        img.paste(img.width()/2, 0, left, function (err, img) {
          if (err) throw err;

          img.writeFile(newfile, function (err) {
            if (err) throw err;
          })
        })
      })
    })
  })
}