// this keeps a queue of opened file descriptors, and will make
// fs operations wait until some have closed before trying to open more.

var fs = require("fs")

// there is such a thing as TOO graceful.
if (fs.open === gracefulOpen) return

var queue = []
  , constants = require("constants")

exports = module.exports = fs
fs._curOpen = 0

fs.MIN_MAX_OPEN = 64
fs.MAX_OPEN = 1024

var originalOpen = fs.open
  , originalOpenSync = fs.openSync
  , originalClose = fs.close
  , originalCloseSync = fs.closeSync


// prevent EMFILE errors
function OpenReq (path, flags, mode, cb) {
  this.path = path
  this.flags = flags
  this.mode = mode
  this.cb = cb
}

function noop () {}

fs.open = gracefulOpen

function gracefulOpen (path, flags, mode, cb) {
  if (typeof mode === "function") cb = mode, mode = null
  if (typeof cb !== "function") cb = noop

  if (fs._curOpen >= fs.MAX_OPEN) {
    queue.push(new OpenReq(path, flags, mode, cb))
    setTimeout(flush)
    return
  }
  open(path, flags, mode, function (er, fd) {
    if (er && er.code === "EMFILE" && fs._curOpen > fs.MIN_MAX_OPEN) {
      // that was too many.  reduce max, get back in queue.
      // this should only happen once in a great while, and only
      // if the ulimit -n is set lower than 1024.
      fs.MAX_OPEN = fs._curOpen - 1
      return fs.open(path, flags, mode, cb)
    }
    cb(er, fd)
  })
}

function open (path, flags, mode, cb) {
  cb = cb || noop
  fs._curOpen ++
  originalOpen.call(fs, path, flags, mode, function (er, fd) {
    if (er) onclose()
    cb(er, fd)
  })
}

fs.openSync = function (path, flags, mode) {
  var ret
  ret = originalOpenSync.call(fs, path, flags, mode)
  fs._curOpen ++
  return ret
}

function onclose () {
  fs._curOpen --
  flush()
}

function flush () {
  while (fs._curOpen < fs.MAX_OPEN) {
    var req = queue.shift()
    if (!req) return
    open(req.path, req.flags || "r", req.mode || 0777, req.cb)
  }
}

fs.close = function (fd, cb) {
  cb = cb || noop
  originalClose.call(fs, fd, function (er) {
    onclose()
    cb(er)
  })
}

fs.closeSync = function (fd) {
  onclose()
  return originalCloseSync.call(fs, fd)
}


// (re-)implement some things that are known busted or missing.

var constants = require("constants")

// lchmod, broken prior to 0.6.2
// back-port the fix here.
if (constants.hasOwnProperty('O_SYMLINK') &&
    process.version.match(/^v0\.6\.[0-2]|^v0\.5\./)) {
  fs.lchmod = function (path, mode, callback) {
    callback = callback || noop
    fs.open( path
           , constants.O_WRONLY | constants.O_SYMLINK
           , mode
           , function (err, fd) {
      if (err) {
        callback(err)
        return
      }
      // prefer to return the chmod error, if one occurs,
      // but still try to close, and report closing errors if they occur.
      fs.fchmod(fd, mode, function (err) {
        fs.close(fd, function(err2) {
          callback(err || err2)
        })
      })
    })
  }

  fs.lchmodSync = function (path, mode) {
    var fd = fs.openSync(path, constants.O_WRONLY | constants.O_SYMLINK, mode)

    // prefer to return the chmod error, if one occurs,
    // but still try to close, and report closing errors if they occur.
    var err, err2
    try {
      var ret = fs.fchmodSync(fd, mode)
    } catch (er) {
      err = er
    }
    try {
      fs.closeSync(fd)
    } catch (er) {
      err2 = er
    }
    if (err || err2) throw (err || err2)
    return ret
  }
}


// lutimes implementation, or no-op
if (!fs.lutimes) {
  if (constants.hasOwnProperty("O_SYMLINK")) {
    fs.lutimes = function (path, at, mt, cb) {
      fs.open(path, constants.O_SYMLINK, function (er, fd) {
        cb = cb || noop
        if (er) return cb(er)
        fs.futimes(fd, at, mt, function (er) {
          fs.close(fd, function (er2) {
            return cb(er || er2)
          })
        })
      })
    }

    fs.lutimesSync = function (path, at, mt) {
      var fd = fs.openSync(path, constants.O_SYMLINK)
        , err
        , err2
        , ret

      try {
        var ret = fs.futimesSync(fd, at, mt)
      } catch (er) {
        err = er
      }
      try {
        fs.closeSync(fd)
      } catch (er) {
        err2 = er
      }
      if (err || err2) throw (err || err2)
      return ret
    }

  } else if (fs.utimensat && constants.hasOwnProperty("AT_SYMLINK_NOFOLLOW")) {
    // maybe utimensat will be bound soonish?
    fs.lutimes = function (path, at, mt, cb) {
      fs.utimensat(path, at, mt, constants.AT_SYMLINK_NOFOLLOW, cb)
    }

    fs.lutimesSync = function (path, at, mt) {
      return fs.utimensatSync(path, at, mt, constants.AT_SYMLINK_NOFOLLOW)
    }

  } else {
    fs.lutimes = function (_a, _b, _c, cb) { process.nextTick(cb) }
    fs.lutimesSync = function () {}
  }
}


// https://github.com/isaacs/node-graceful-fs/issues/4
// Chown should not fail on einval or eperm if non-root.

fs.chown = chownFix(fs.chown)
fs.fchown = chownFix(fs.fchown)
fs.lchown = chownFix(fs.lchown)

fs.chownSync = chownFixSync(fs.chownSync)
fs.fchownSync = chownFixSync(fs.fchownSync)
fs.lchownSync = chownFixSync(fs.lchownSync)

function chownFix (orig) {
  if (!orig) return orig
  return function (target, uid, gid, cb) {
    return orig.call(fs, target, uid, gid, function (er, res) {
      if (chownErOk(er)) er = null
      cb(er, res)
    })
  }
}

function chownFixSync (orig) {
  if (!orig) return orig
  return function (target, uid, gid) {
    try {
      return orig.call(fs, target, uid, gid)
    } catch (er) {
      if (!chownErOk(er)) throw er
    }
  }
}

function chownErOk (er) {
  // if there's no getuid, or if getuid() is something other than 0,
  // and the error is EINVAL or EPERM, then just ignore it.
  // This specific case is a silent failure in cp, install, tar,
  // and most other unix tools that manage permissions.
  // When running as root, or if other types of errors are encountered,
  // then it's strict.
  if (!er || (!process.getuid || process.getuid() !== 0)
      && (er.code === "EINVAL" || er.code === "EPERM")) return true
}


// if lchmod/lchown do not exist, then make them no-ops
if (!fs.lchmod) {
  fs.lchmod = function (path, mode, cb) {
    process.nextTick(cb)
  }
  fs.lchmodSync = function () {}
}
if (!fs.lchown) {
  fs.lchown = function (path, uid, gid, cb) {
    process.nextTick(cb)
  }
  fs.lchownSync = function () {}
}



// on Windows, A/V software can lock the directory, causing this
// to fail with an EACCES or EPERM if the directory contains newly
// created files.  Try again on failure, for up to 1 second.
if (process.platform === "win32") {
  var rename_ = fs.rename
  fs.rename = function rename (from, to, cb) {
    var start = Date.now()
    rename_(from, to, function CB (er) {
      if (er
          && (er.code === "EACCES" || er.code === "EPERM")
          && Date.now() - start < 1000) {
        return rename_(from, to, CB)
      }
      cb(er)
    })
  }
}


// if read() returns EAGAIN, then just try it again.
var read = fs.read
fs.read = function (fd, buffer, offset, length, position, callback_) {
  var callback
  if (callback_ && typeof callback_ === 'function') {
    var eagCounter = 0
    callback = function (er, _, __) {
      if (er && er.code === 'EAGAIN' && eagCounter < 10) {
        eagCounter ++
        return read.call(fs, fd, buffer, offset, length, position, callback)
      }
      callback_.apply(this, arguments)
    }
  }
  return read.call(fs, fd, buffer, offset, length, position, callback)
}

var readSync = fs.readSync
fs.readSync = function (fd, buffer, offset, length, position) {
  var eagCounter = 0
  while (true) {
    try {
      return readSync.call(fs, fd, buffer, offset, length, position)
    } catch (er) {
      if (er.code === 'EAGAIN' && eagCounter < 10) {
        eagCounter ++
        continue
      }
      throw er
    }
  }
}
