var fs = require ('graceful-fs')
var dz = require ('dezalgo')
var once = require ('once')
var path = require ('path')
var debug = require ('debuglog') ('rds')

module . exports = readdir

function readdir (dir, cb) {
  fs . readdir (dir, function (er, kids) {
    if (er)
      return cb (er)

    debug ('dir=%j, kids=%j', dir, kids)
    readScopes (dir, kids, function (er, data) {
      if (er)
        return cb (er)

      // Sort for bonus consistency points
      data = data . sort (function (a, b) {
        return a > b ? 1 : -1
      })

      return cb (null, data)
    })
  })
}

// Turn [ 'a', '@scope' ] into
// ['a', '@scope/foo', '@scope/bar']
function readScopes (root, kids, cb) {
  var scopes = kids . filter (function (kid) {
    return kid . charAt (0) === '@'
  })

  kids = kids . filter (function (kid) {
    return kid . charAt (0) !== '@'
  })

  debug ('scopes=%j', scopes)

  if (scopes . length === 0)
    dz (cb) (null, kids) // prevent maybe-sync zalgo release

  cb = once (cb)
  var l = scopes . length
  scopes . forEach (function (scope) {
    var scopedir = path . resolve (root, scope)
    debug ('root=%j scope=%j scopedir=%j', root, scope, scopedir)
    fs . readdir (scopedir, then . bind (null, scope))
  })

  function then (scope, er, scopekids) {
    if (er)
      return cb (er)

    // XXX: Not sure how old this node bug is. Maybe superstition?
    scopekids = scopekids . filter (function (scopekid) {
      return !(scopekid === '.' || scopekid === '..' || !scopekid)
    })

    kids . push . apply (kids, scopekids . map (function (scopekid) {
      return scope + '/' + scopekid
    }))

    debug ('scope=%j scopekids=%j kids=%j', scope, scopekids, kids)

    if (--l === 0)
      cb (null, kids)
  }
}