//go:build linux && !fstree_generic

package fstree

import (
	"errors"
	"io/fs"
	"strconv"

	"git.frostfs.info/TrueCloudLab/frostfs-node/pkg/local_object_storage/blobstor/common"
	"git.frostfs.info/TrueCloudLab/frostfs-node/pkg/local_object_storage/util/logicerr"
	apistatus "git.frostfs.info/TrueCloudLab/frostfs-sdk-go/client/status"
	"golang.org/x/sys/unix"
)

type linuxWriter struct {
	root  string
	perm  uint32
	flags int

	counter FileCounter
}

func newSpecificWriteData(c FileCounter, root string, perm fs.FileMode, noSync bool) writer {
	flags := unix.O_WRONLY | unix.O_TMPFILE | unix.O_CLOEXEC
	if !noSync {
		flags |= unix.O_DSYNC
	}
	fd, err := unix.Open(root, flags, uint32(perm))
	if err != nil {
		// Which means that OS-specific writeData can't be created
		// and FSTree should use the generic one.
		return nil
	}
	_ = unix.Close(fd) // Don't care about error.
	w := &linuxWriter{
		root:    root,
		perm:    uint32(perm),
		flags:   flags,
		counter: c,
	}
	return w
}

func (w *linuxWriter) writeData(p string, data []byte) error {
	err := w.writeFile(p, data)
	if errors.Is(err, unix.ENOSPC) {
		return common.ErrNoSpace
	}
	return err
}

func (w *linuxWriter) writeFile(p string, data []byte) error {
	fd, err := unix.Open(w.root, w.flags, w.perm)
	if err != nil {
		return err
	}
	tmpPath := "/proc/self/fd/" + strconv.FormatUint(uint64(fd), 10)
	n, err := unix.Write(fd, data)
	if err == nil {
		if n == len(data) {
			err = unix.Linkat(unix.AT_FDCWD, tmpPath, unix.AT_FDCWD, p, unix.AT_SYMLINK_FOLLOW)
			if err == nil {
				w.counter.Inc()
			}
			if errors.Is(err, unix.EEXIST) {
				err = nil
			}
		} else {
			err = errors.New("incomplete write")
		}
	}
	errClose := unix.Close(fd)
	if err != nil {
		return err // Close() error is ignored, we have a better one.
	}
	return errClose
}

func (w *linuxWriter) removeFile(p string) error {
	err := unix.Unlink(p)
	if err != nil && err == unix.ENOENT {
		return logicerr.Wrap(new(apistatus.ObjectNotFound))
	}
	if err == nil {
		w.counter.Dec()
	}
	return err
}