var fs = require("fs");
var path = require("path");

var walk = function (start, callback) {
  fs.lstat(start, function (err, stat) {
    if (err) return callback(err)

    if (stat.isDirectory() && !stat.isSymbolicLink()) {
      fs.readdir(start, function (err, files) {
        if (err) return callback(err)
        var dirs = []
          , notDirs = []
          , IL = files.length

        for (i = 0; i < IL; i++) {
          var abspath = path.join(start, files[i]);
          var _stat = fs.lstatSync(abspath);

          if (_stat.isDirectory() && !_stat.isSymbolicLink()) {
            dirs.push(abspath);
            walk(abspath, callback);
          } else {
            notDirs.push(abspath);
          }
        }

        return callback(null, start, dirs, notDirs);
      });
    } else {
      return callback(new Error("path: " + start + " is not a directory"));
    }
  });
};