// Copyright 2019 The Go Authors. All rights reserved.

// Use of this source code is governed by a BSD-style

// license that can be found in the LICENSE file.

// +build darwin,go1.13

package unix

import "unsafe"

//sys	closedir(dir uintptr) (err error)

//sys	readdir_r(dir uintptr, entry *Dirent, result **Dirent) (res Errno)

func fdopendir(fd int) (dir uintptr, err error) {

	r0, _, e1 := syscall_syscallPtr(funcPC(libc_fdopendir_trampoline), uintptr(fd), 0, 0)

	dir = uintptr(r0)

	if e1 != 0 {

		err = errnoErr(e1)

	}

	return

}

func libc_fdopendir_trampoline()

//go:linkname libc_fdopendir libc_fdopendir

//go:cgo_import_dynamic libc_fdopendir fdopendir "/usr/lib/libSystem.B.dylib"

func Getdirentries(fd int, buf []byte, basep *uintptr) (n int, err error) {

	// Simulate Getdirentries using fdopendir/readdir_r/closedir.

	// We store the number of entries to skip in the seek

	// offset of fd. See issue #31368.

	// It's not the full required semantics, but should handle the case

	// of calling Getdirentries or ReadDirent repeatedly.

	// It won't handle assigning the results of lseek to *basep, or handle

	// the directory being edited underfoot.

	skip, err := Seek(fd, 0, 1 /* SEEK_CUR */)

	if err != nil {

		return 0, err

	}

	// We need to duplicate the incoming file descriptor

	// because the caller expects to retain control of it, but

	// fdopendir expects to take control of its argument.

	// Just Dup'ing the file descriptor is not enough, as the

	// result shares underlying state. Use Openat to make a really

	// new file descriptor referring to the same directory.

	fd2, err := Openat(fd, ".", O_RDONLY, 0)

	if err != nil {

		return 0, err

	}

	d, err := fdopendir(fd2)

	if err != nil {

		Close(fd2)

		return 0, err

	}

	defer closedir(d)

	var cnt int64

	for {

		var entry Dirent

		var entryp *Dirent

		e := readdir_r(d, &entry, &entryp)

		if e != 0 {

			return n, errnoErr(e)

		}

		if entryp == nil {

			break

		}

		if skip > 0 {

			skip--

			cnt++

			continue

		}

		reclen := int(entry.Reclen)

		if reclen > len(buf) {

			// Not enough room. Return for now.

			// The counter will let us know where we should start up again.

			// Note: this strategy for suspending in the middle and

			// restarting is O(n^2) in the length of the directory. Oh well.

			break

		}

		// Copy entry into return buffer.

		s := struct {

			ptr unsafe.Pointer

			siz int

			cap int

		}{ptr: unsafe.Pointer(&entry), siz: reclen, cap: reclen}

		copy(buf, *(*[]byte)(unsafe.Pointer(&s)))

		buf = buf[reclen:]

		n += reclen

		cnt++

	}

	// Set the seek offset of the input fd to record

	// how many files we've already returned.

	_, err = Seek(fd, cnt, 0 /* SEEK_SET */)

	if err != nil {

		return n, err

	}

	return n, nil

}