// Copyright (c) 2026 Petr Balvín <opensource@petrbalvin.org> (https://petrbalvin.org)
// SPDX-License-Identifier: MIT

//go:build freebsd

package nfsfs

import (
	"os"
	"strings"
	"syscall"
	"unsafe"
)

// xattrNamespace is the only namespace this backend serves: RFC 8276
// section 3.3 names the attributes with their namespace, and the local
// mapping of the FreeBSD server is the extattr user namespace.
const xattrNamespace = "user."

// extattrNamespaceUser is EXTATTR_NAMESPACE_USER of sys/sys/extattr.h,
// the numeric namespace the extattr family of system calls takes. The
// syscall package of FreeBSD exports the traps of the family but not
// this constant.
const extattrNamespaceUser = 0x1

// xattrPath resolves a handle for the extattr family: the registered path
// must still name the handle's device, inode and kind. A symlink is
// refused the way the kernel refuses the user namespace on one, so the
// path calls never follow a link out of the export.
func (l *Local) xattrPath(h Handle) (string, error) {
	_, path, fi, err := l.revalidate(h)
	if err != nil {
		return "", err
	}
	if fi.Mode()&os.ModeSymlink != 0 {
		return "", syscall.EPERM
	}
	return path, nil
}

// GetXattr reads one named attribute of the object.
func (l *Local) GetXattr(h Handle, name string, max int) ([]byte, error) {
	path, err := l.xattrPath(h)
	if err != nil {
		return nil, err
	}
	attr, ok := strings.CutPrefix(name, xattrNamespace)
	if !ok {
		return nil, ErrNoXattr
	}
	buf := make([]byte, maxOr(max, 256))
	for {
		n, err := extattrGetFile(path, attr, buf)
		if err == syscall.ERANGE {
			if len(buf) > 1<<20 {
				return nil, syscall.ERANGE
			}
			buf = make([]byte, len(buf)*2)
			continue
		}
		if err == syscall.ENOATTR {
			return nil, ErrNoXattr
		}
		if err != nil {
			return nil, err
		}
		return buf[:n], nil
	}
}

// SetXattr writes one named attribute under the RFC 8276 mode. The
// extattr interface of FreeBSD carries no create and replace flags, so
// the two strict modes ask for the attribute first and write it after:
// a create of an existing name answers EEXIST and a replace of a
// missing one ENOATTR, the same answers the flags of Linux produce.
func (l *Local) SetXattr(h Handle, name string, value []byte, mode uint32) error {
	path, err := l.xattrPath(h)
	if err != nil {
		return err
	}
	attr, ok := strings.CutPrefix(name, xattrNamespace)
	if !ok {
		return syscall.EOPNOTSUPP
	}
	switch mode {
	case XattrModeCreate, XattrModeReplace:
		_, err := extattrGetFile(path, attr, nil)
		switch {
		case err == nil && mode == XattrModeCreate:
			return syscall.EEXIST
		case err == syscall.ENOATTR && mode == XattrModeReplace:
			return syscall.ENOATTR
		case err != nil && err != syscall.ENOATTR:
			return err
		}
	}
	return extattrSetFile(path, attr, value)
}

// ListXattr names the user namespace attributes of the object. The list
// of extattr_list_file is a sequence of one length byte and name pairs
// with no separators, extattr(2), and its names carry no namespace, so
// each name is dressed with the namespace prefix the protocol speaks.
func (l *Local) ListXattr(h Handle, max int) ([]string, error) {
	path, err := l.xattrPath(h)
	if err != nil {
		return nil, err
	}
	buf := make([]byte, maxOr(max, 1024))
	for {
		n, err := extattrListFile(path, buf)
		if err == syscall.ERANGE {
			if len(buf) > 1<<20 {
				return nil, syscall.ERANGE
			}
			buf = make([]byte, len(buf)*2)
			continue
		}
		if err != nil {
			return nil, err
		}
		buf = buf[:n]
		break
	}
	var names []string
	for len(buf) > 0 {
		size := int(buf[0])
		if size+1 > len(buf) {
			break
		}
		names = append(names, xattrNamespace+string(buf[1:1+size]))
		buf = buf[1+size:]
	}
	return names, nil
}

// RemoveXattr deletes one named attribute.
func (l *Local) RemoveXattr(h Handle, name string) error {
	path, err := l.xattrPath(h)
	if err != nil {
		return err
	}
	attr, ok := strings.CutPrefix(name, xattrNamespace)
	if !ok {
		return ErrNoXattr
	}
	if err := extattrDeleteFile(path, attr); err == syscall.ENOATTR {
		return ErrNoXattr
	} else if err != nil {
		return err
	}
	return nil
}

// maxOr replaces a zero budget with the given default.
func maxOr(max, def int) int {
	if max == 0 || max > 1<<20 {
		return def
	}
	return max
}

// extattrGetFile reads the attribute attr of path into buf, or names its
// size when buf is nil, extattr(2).
func extattrGetFile(path, attr string, buf []byte) (int, error) {
	name, err := syscall.ByteSliceFromString(attr)
	if err != nil {
		return 0, err
	}
	// SAFETY: the kernel reads the buffer for the length of the call
	// only, and data stays alive through the unsafe pointer until the
	// system call returns.
	var data unsafe.Pointer
	if len(buf) > 0 {
		data = unsafe.Pointer(&buf[0])
	}
	n, _, errno := syscall.Syscall6(syscall.SYS_EXTATTR_GET_FILE,
		uintptr(unsafe.Pointer(syscall.StringBytePtr(path))),
		extattrNamespaceUser,
		uintptr(unsafe.Pointer(&name[0])),
		uintptr(data),
		uintptr(len(buf)),
		0)
	if errno != 0 {
		return 0, errno
	}
	return int(n), nil
}

// extattrSetFile writes value into the attribute attr of path,
// extattr(2).
func extattrSetFile(path, attr string, value []byte) error {
	name, err := syscall.ByteSliceFromString(attr)
	if err != nil {
		return err
	}
	// SAFETY: the kernel reads the buffer for the length of the call
	// only, and value stays alive through the unsafe pointer until the
	// system call returns.
	var data unsafe.Pointer
	if len(value) > 0 {
		data = unsafe.Pointer(&value[0])
	}
	_, _, errno := syscall.Syscall6(syscall.SYS_EXTATTR_SET_FILE,
		uintptr(unsafe.Pointer(syscall.StringBytePtr(path))),
		extattrNamespaceUser,
		uintptr(unsafe.Pointer(&name[0])),
		uintptr(data),
		uintptr(len(value)),
		0)
	if errno != 0 {
		return errno
	}
	return nil
}

// extattrListFile names the user namespace attributes of path into buf,
// or names the size of the list when buf is nil, extattr(2).
func extattrListFile(path string, buf []byte) (int, error) {
	// SAFETY: the kernel writes the buffer for the length of the call
	// only, and buf stays alive through the unsafe pointer until the
	// system call returns.
	var data unsafe.Pointer
	if len(buf) > 0 {
		data = unsafe.Pointer(&buf[0])
	}
	n, _, errno := syscall.Syscall6(syscall.SYS_EXTATTR_LIST_FILE,
		uintptr(unsafe.Pointer(syscall.StringBytePtr(path))),
		extattrNamespaceUser,
		uintptr(data),
		uintptr(len(buf)),
		0, 0)
	if errno != 0 {
		return 0, errno
	}
	return int(n), nil
}

// extattrDeleteFile takes the attribute attr off path, extattr(2).
func extattrDeleteFile(path, attr string) error {
	name, err := syscall.ByteSliceFromString(attr)
	if err != nil {
		return err
	}
	_, _, errno := syscall.Syscall(syscall.SYS_EXTATTR_DELETE_FILE,
		uintptr(unsafe.Pointer(syscall.StringBytePtr(path))),
		extattrNamespaceUser,
		uintptr(unsafe.Pointer(&name[0])))
	if errno != 0 {
		return errno
	}
	return nil
}