var fs = require('fs')
var polyfills = require('./polyfills.js')
var legacy = require('./legacy-streams.js')
var queue = []

var util = require('util')

function noop () {}

var debug = noop
if (util.debuglog)
  debug = util.debuglog('gfs4')
else if (/\bgfs4\b/i.test(process.env.NODE_DEBUG || ''))
  debug = function() {
    var m = util.format.apply(util, arguments)
    m = 'GFS4: ' + m.split(/\n/).join('\nGFS4: ')
    console.error(m)
  }

if (/\bgfs4\b/i.test(process.env.NODE_DEBUG || '')) {
  process.on('exit', function() {
    debug(queue)
    require('assert').equal(queue.length, 0)
  })
}

module.exports = patch(require('./fs.js'))
if (process.env.TEST_GRACEFUL_FS_GLOBAL_PATCH) {
  module.exports = patch(fs)
}

// Always patch fs.close/closeSync, because we want to
// retry() whenever a close happens *anywhere* in the program.
// This is essential when multiple graceful-fs instances are
// in play at the same time.
module.exports.close =
fs.close = (function (fs$close) { return function (fd, cb) {
  return fs$close.call(fs, fd, function (err) {
    if (!err)
      retry()

    if (typeof cb === 'function')
      cb.apply(this, arguments)
  })
}})(fs.close)

module.exports.closeSync =
fs.closeSync = (function (fs$closeSync) { return function (fd) {
  // Note that graceful-fs also retries when fs.closeSync() fails.
  // Looks like a bug to me, although it's probably a harmless one.
  var rval = fs$closeSync.apply(fs, arguments)
  retry()
  return rval
}})(fs.closeSync)

function patch (fs) {
  // Everything that references the open() function needs to be in here
  polyfills(fs)
  fs.gracefulify = patch
  fs.FileReadStream = ReadStream;  // Legacy name.
  fs.FileWriteStream = WriteStream;  // Legacy name.
  fs.createReadStream = createReadStream
  fs.createWriteStream = createWriteStream
  var fs$readFile = fs.readFile
  fs.readFile = readFile
  function readFile (path, options, cb) {
    if (typeof options === 'function')
      cb = options, options = null

    return go$readFile(path, options, cb)

    function go$readFile (path, options, cb) {
      return fs$readFile(path, options, function (err) {
        if (err && (err.code === 'EMFILE' || err.code === 'ENFILE'))
          enqueue([go$readFile, [path, options, cb]])
        else {
          if (typeof cb === 'function')
            cb.apply(this, arguments)
          retry()
        }
      })
    }
  }

  var fs$writeFile = fs.writeFile
  fs.writeFile = writeFile
  function writeFile (path, data, options, cb) {
    if (typeof options === 'function')
      cb = options, options = null

    return go$writeFile(path, data, options, cb)

    function go$writeFile (path, data, options, cb) {
      return fs$writeFile(path, data, options, function (err) {
        if (err && (err.code === 'EMFILE' || err.code === 'ENFILE'))
          enqueue([go$writeFile, [path, data, options, cb]])
        else {
          if (typeof cb === 'function')
            cb.apply(this, arguments)
          retry()
        }
      })
    }
  }

  var fs$appendFile = fs.appendFile
  if (fs$appendFile)
    fs.appendFile = appendFile
  function appendFile (path, data, options, cb) {
    if (typeof options === 'function')
      cb = options, options = null

    return go$appendFile(path, data, options, cb)

    function go$appendFile (path, data, options, cb) {
      return fs$appendFile(path, data, options, function (err) {
        if (err && (err.code === 'EMFILE' || err.code === 'ENFILE'))
          enqueue([go$appendFile, [path, data, options, cb]])
        else {
          if (typeof cb === 'function')
            cb.apply(this, arguments)
          retry()
        }
      })
    }
  }

  var fs$readdir = fs.readdir
  fs.readdir = readdir
  function readdir (path, cb) {
    return go$readdir(path, cb)

    function go$readdir () {
      return fs$readdir(path, function (err, files) {
        if (files && files.sort)
          files.sort();  // Backwards compatibility with graceful-fs.

        if (err && (err.code === 'EMFILE' || err.code === 'ENFILE'))
          enqueue([go$readdir, [path, cb]])
        else {
          if (typeof cb === 'function')
            cb.apply(this, arguments)
          retry()
        }
      })
    }
  }


  if (process.version.substr(0, 4) === 'v0.8') {
    var legStreams = legacy(fs)
    ReadStream = legStreams.ReadStream
    WriteStream = legStreams.WriteStream
  }

  var fs$ReadStream = fs.ReadStream
  ReadStream.prototype = Object.create(fs$ReadStream.prototype)
  ReadStream.prototype.open = ReadStream$open

  var fs$WriteStream = fs.WriteStream
  WriteStream.prototype = Object.create(fs$WriteStream.prototype)
  WriteStream.prototype.open = WriteStream$open

  fs.ReadStream = ReadStream
  fs.WriteStream = WriteStream

  function ReadStream (path, options) {
    if (this instanceof ReadStream)
      return fs$ReadStream.apply(this, arguments), this
    else
      return ReadStream.apply(Object.create(ReadStream.prototype), arguments)
  }

  function ReadStream$open () {
    var that = this
    open(that.path, that.flags, that.mode, function (err, fd) {
      if (err) {
        if (that.autoClose)
          that.destroy()

        that.emit('error', err)
      } else {
        that.fd = fd
        that.emit('open', fd)
        that.read()
      }
    })
  }

  function WriteStream (path, options) {
    if (this instanceof WriteStream)
      return fs$WriteStream.apply(this, arguments), this
    else
      return WriteStream.apply(Object.create(WriteStream.prototype), arguments)
  }

  function WriteStream$open () {
    var that = this
    open(that.path, that.flags, that.mode, function (err, fd) {
      if (err) {
        that.destroy()
        that.emit('error', err)
      } else {
        that.fd = fd
        that.emit('open', fd)
      }
    })
  }

  function createReadStream (path, options) {
    return new ReadStream(path, options)
  }

  function createWriteStream (path, options) {
    return new WriteStream(path, options)
  }

  var fs$open = fs.open
  fs.open = open
  function open (path, flags, mode, cb) {
    if (typeof mode === 'function')
      cb = mode, mode = null

    return go$open(path, flags, mode, cb)

    function go$open (path, flags, mode, cb) {
      return fs$open(path, flags, mode, function (err, fd) {
        if (err && (err.code === 'EMFILE' || err.code === 'ENFILE'))
          enqueue([go$open, [path, flags, mode, cb]])
        else {
          if (typeof cb === 'function')
            cb.apply(this, arguments)
          retry()
        }
      })
    }
  }

  return fs
}

function enqueue (elem) {
  debug('ENQUEUE', elem[0].name, elem[1])
  queue.push(elem)
}

function retry () {
  var elem = queue.shift()
  if (elem) {
    debug('RETRY', elem[0].name, elem[1])
    elem[0].apply(null, elem[1])
  }
}
