config -> object mapping keys to stat & uri

config.json

{
    "foo": "/path/to/foo"
  , "bar": "/path/to/bar"
}

index.js

const fs          = require('fs')
    , path        = require('path')
    , execute     = require('execute')

function transform (fn) {
  return function transformer (value, callback) {
    if (typeof fn == 'function')
      return fn(value, callback)
    callback(null, fn)
  }
}

function pluckConfigProperty (config) {
  return transform(function (prop, callback) {
    if (typeof config[prop] != 'string')
      return callback('Required configuration property not set: ' + prop)
    return callback(null, config[prop])
  })
}

function toUri (root) {
  return transform(function (p, callback) {
    callback(null, path.resolve(root, p))
  })
}

function toStatAndUri () {
  return transform(function (uri, callback) {
    fs.stat(uri, function (err, stat) {
      if (err)
        return callback(err)
      return callback(null, { uri: uri, stat: stat })
    })
  })
}

function eachTransform () {
  var transforms = Array.prototype.slice.call(arguments)
  return function (value, callback) {
    var i = 0
      , execute = function () {
          if (i == transforms.length)
            return callback(null, value)

          transforms[i++](value, function (err, _value) {
            if (err)
              return callback(err)
            value = _value
            execute()
          })
        }
    execute()
  }
}

function configToStat (root, config, properties, callback) {
  var transforms = eachTransform(
      pluckConfigProperty(config)
    , toUri(root)
    , toStatAndUri()
  )
  execute(
      properties.reduce(function (p, k) {
        p[k] = transforms.bind(null, k)
        return p
      }, {})
    , callback
  )
}

function loadFiles (root, config) {
  configToStat(root, config, [ 'foo', 'bar' ], function (err, result) {
    if (err)
      return console.error('Error:', err)
    console.log(result)
  })
}

resuilt.js

// expected result:

{ foo: 
   { stat: 
      { dev: 2065,
        mode: 16893,
        nlink: 2,
        uid: 1000,
        gid: 1000,
        rdev: 0,
        blksize: 4096,
        ino: 11701430,
        size: 4096,
        blocks: 8,
        atime: Tue Apr 30 2013 14:49:26 GMT+1000 (EST),
        mtime: Tue Apr 30 2013 14:49:26 GMT+1000 (EST),
        ctime: Tue Apr 30 2013 14:49:26 GMT+1000 (EST) },
     uri: '/path/to/foo' },
  bar: 
   { stat: 
      { dev: 2065,
        mode: 16893,
        nlink: 2,
        uid: 1000,
        gid: 1000,
        rdev: 0,
        blksize: 4096,
        ino: 11817511,
        size: 4096,
        blocks: 8,
        atime: Tue Apr 30 2013 14:49:33 GMT+1000 (EST),
        mtime: Tue Apr 30 2013 14:49:33 GMT+1000 (EST),
        ctime: Tue Apr 30 2013 14:49:33 GMT+1000 (EST) },
     uri: '/path/to/bar' } }