var Promise = require('native-or-bluebird')

module.exports = function mz_promisify(name, fn) {
  return eval('(function ' + name + '() {\n'
    + 'var len = arguments.length\n'
    + 'var args = new Array(len + 1)\n'
    + 'for (var i = 0; i < len; ++i) args[i] = arguments[i]\n'
    + 'var lastIndex = i\n'
    + 'return new Promise(function (resolve, reject) {\n'
      + 'args[lastIndex] = makeCallback(resolve, reject)\n'
      + 'fn.apply(null, args)\n'
    + '})\n'
  + '})')
}

function makeCallback(resolve, reject) {
  return function(err, value) {
    if (err) {
      reject(err)
    } else {
      var len = arguments.length
      if (len > 2) {
        var values = new Array(len - 1)
        for (var i = 1; i < len; ++i) {
          values[i - 1] = arguments[i]
        }
        resolve(values)
      } else {
        resolve(value)
      }
    }
  }
}