//go:build !windows

package safeio

import (
	"errors"
	"io"
	"os"
	"sort"
	"time"

	"golang.org/x/sys/unix"
)

type unixPrivateDirectory struct {
	descriptor int
}

func openPrivateDirectory(path string, ensure bool) (PrivateDirectoryHandle, bool, error) {
	parents, err := openCanonicalUnixParent(path)
	if err != nil {
		return nil, false, ErrUnsafeFile
	}
	defer parents.Close()
	return openPrivateUnixDirectoryAt(parents.parent, parents.target, ensure)
}

func openPrivateUnixDirectoryAt(parent int, name string, ensure bool) (PrivateDirectoryHandle, bool, error) {
	if parent < 0 || !validPrivateLeafName(name) {
		return nil, false, ErrUnsafeFile
	}
	for attempt := 0; attempt < 2; attempt++ {
		descriptor, err := unix.Openat(parent, name, unix.O_RDONLY|unix.O_CLOEXEC|unix.O_DIRECTORY|unix.O_NOFOLLOW, 0)
		if err == nil {
			value := &unixPrivateDirectory{descriptor: descriptor}
			if value.Validate() != nil {
				_ = value.Close()
				return nil, false, ErrUnsafeFile
			}
			return value, true, nil
		}
		if !errors.Is(err, unix.ENOENT) {
			return nil, false, ErrUnsafeFile
		}
		if !ensure {
			if unix.Faccessat(parent, ".", unix.W_OK|unix.X_OK, unix.AT_EACCESS) != nil {
				return nil, false, ErrUnsafeFile
			}
			return nil, false, nil
		}
		if err := unix.Mkdirat(parent, name, 0o700); err != nil && !errors.Is(err, unix.EEXIST) {
			return nil, false, ErrUnsafeFile
		}
	}
	return nil, false, ErrUnsafeFile
}

func (directory *unixPrivateDirectory) Close() error {
	if directory == nil || directory.descriptor < 0 {
		return nil
	}
	err := unix.Close(directory.descriptor)
	directory.descriptor = -1
	if err != nil {
		return ErrUnsafeFile
	}
	return nil
}

func (directory *unixPrivateDirectory) Validate() error {
	if directory == nil || directory.descriptor < 0 {
		return ErrUnsafeFile
	}
	var stat unix.Stat_t
	if err := unix.Fstat(directory.descriptor, &stat); err != nil || !privateUnixDirectoryStat(&stat) {
		return ErrUnsafeFile
	}
	return nil
}

func (directory *unixPrivateDirectory) OpenChild(name string, ensure bool) (PrivateDirectoryHandle, bool, error) {
	if directory.Validate() != nil || !validPrivateLeafName(name) {
		return nil, false, ErrUnsafeFile
	}
	child, found, err := openPrivateUnixDirectoryAt(directory.descriptor, name, ensure)
	if err != nil || directory.Validate() != nil {
		if child != nil {
			_ = child.Close()
		}
		return nil, false, ErrUnsafeFile
	}
	return child, found, nil
}

func privateUnixRootRegular(stat *unix.Stat_t, links uint64) bool {
	return stat != nil && stat.Mode&unix.S_IFMT == unix.S_IFREG && uint64(stat.Nlink) == links &&
		stat.Uid == uint32(os.Geteuid()) && stat.Mode&0o7777 == 0o600
}

func sameUnixRootRegular(left, right unix.Stat_t) bool {
	return left.Dev == right.Dev && left.Ino == right.Ino && left.Size == right.Size &&
		left.Mtim == right.Mtim && left.Ctim == right.Ctim && left.Mode == right.Mode && left.Nlink == right.Nlink
}

func requirePrivateUnixRootRegularAt(directory int, name string, links uint64) (unix.Stat_t, error) {
	var stat unix.Stat_t
	if err := unix.Fstatat(directory, name, &stat, unix.AT_SYMLINK_NOFOLLOW); err != nil || !privateUnixRootRegular(&stat, links) {
		return unix.Stat_t{}, ErrUnsafeFile
	}
	return stat, nil
}

func privateUnixRootRegularAtAllowedLinks(directory int, name string, allowed ...uint64) error {
	var stat unix.Stat_t
	if err := unix.Fstatat(directory, name, &stat, unix.AT_SYMLINK_NOFOLLOW); err != nil {
		return ErrUnsafeFile
	}
	for _, links := range allowed {
		if privateUnixRootRegular(&stat, links) {
			return nil
		}
	}
	return ErrUnsafeFile
}

func requireSamePrivateUnixRootPairAt(directory int, source, claim string) error {
	left, err := requirePrivateUnixRootRegularAt(directory, source, 2)
	if err != nil {
		return ErrUnsafeFile
	}
	right, err := requirePrivateUnixRootRegularAt(directory, claim, 2)
	if err != nil || !sameUnixPrivateFile(left, right) {
		return ErrUnsafeFile
	}
	return nil
}

func isPrivateUnixRootClaimAbsentOrOrphanAt(directory int, source, claim string) bool {
	var sourceStat, claimStat unix.Stat_t
	sourceErr := unix.Fstatat(directory, source, &sourceStat, unix.AT_SYMLINK_NOFOLLOW)
	claimErr := unix.Fstatat(directory, claim, &claimStat, unix.AT_SYMLINK_NOFOLLOW)
	if errors.Is(sourceErr, unix.ENOENT) && errors.Is(claimErr, unix.ENOENT) {
		return true
	}
	return errors.Is(sourceErr, unix.ENOENT) && claimErr == nil && privateUnixRootRegular(&claimStat, 1)
}

func writeAllPrivateRoot(file *os.File, contents []byte) error {
	for written := 0; written < len(contents); {
		count, err := file.Write(contents[written:])
		written += count
		if err != nil {
			return err
		}
		if count == 0 {
			return io.ErrShortWrite
		}
	}
	return file.Sync()
}

func (directory *unixPrivateDirectory) CreateRegular(name string, contents []byte) (bool, error) {
	if directory.Validate() != nil || !validPrivateLeafName(name) || len(contents) == 0 {
		return false, ErrUnsafeFile
	}
	descriptor, err := unix.Openat(directory.descriptor, name,
		unix.O_WRONLY|unix.O_CREAT|unix.O_EXCL|unix.O_CLOEXEC|unix.O_NOFOLLOW, 0o600)
	if errors.Is(err, unix.EEXIST) {
		if _, existingErr := requirePrivateUnixRootRegularAt(directory.descriptor, name, 1); existingErr != nil || directory.Validate() != nil {
			return false, ErrUnsafeFile
		}
		return false, nil
	}
	if err != nil {
		return false, ErrUnsafeFile
	}
	file := os.NewFile(uintptr(descriptor), "tht-safeio-private-root-create")
	if file == nil {
		_ = unix.Close(descriptor)
		_ = unix.Unlinkat(directory.descriptor, name, 0)
		return false, ErrUnsafeFile
	}
	failed := true
	defer func() {
		if failed {
			_ = unix.Unlinkat(directory.descriptor, name, 0)
		}
	}()
	if unix.Fchmod(descriptor, 0o600) != nil {
		_ = file.Close()
		return false, ErrUnsafeFile
	}
	var stat unix.Stat_t
	if unix.Fstat(descriptor, &stat) != nil || !privateUnixRootRegular(&stat, 1) || writeAllPrivateRoot(file, contents) != nil || file.Close() != nil {
		return false, ErrUnsafeFile
	}
	if directory.Validate() != nil || unix.Fsync(directory.descriptor) != nil {
		return false, ErrUnsafeFile
	}
	failed = false
	return true, nil
}

func (directory *unixPrivateDirectory) CreateRegularFile(name string) (*os.File, bool, error) {
	if directory.Validate() != nil || !validPrivateLeafName(name) {
		return nil, false, ErrUnsafeFile
	}
	descriptor, err := unix.Openat(directory.descriptor, name,
		unix.O_RDWR|unix.O_CREAT|unix.O_EXCL|unix.O_CLOEXEC|unix.O_NOFOLLOW, 0o600)
	if errors.Is(err, unix.EEXIST) {
		if _, existingErr := requirePrivateUnixRootRegularAt(directory.descriptor, name, 1); existingErr != nil || directory.Validate() != nil {
			return nil, false, ErrUnsafeFile
		}
		return nil, false, nil
	}
	if err != nil {
		return nil, false, ErrUnsafeFile
	}
	file := os.NewFile(uintptr(descriptor), "tht-safeio-private-root-stream")
	if file == nil {
		_ = unix.Close(descriptor)
		_ = unix.Unlinkat(directory.descriptor, name, 0)
		return nil, false, ErrUnsafeFile
	}
	failed := true
	defer func() {
		if failed {
			_ = file.Close()
			_ = unix.Unlinkat(directory.descriptor, name, 0)
		}
	}()
	if unix.Fchmod(descriptor, 0o600) != nil {
		return nil, false, ErrUnsafeFile
	}
	var stat unix.Stat_t
	if unix.Fstat(descriptor, &stat) != nil || !privateUnixRootRegular(&stat, 1) {
		return nil, false, ErrUnsafeFile
	}
	if directory.Validate() != nil || unix.Fsync(directory.descriptor) != nil {
		return nil, false, ErrUnsafeFile
	}
	failed = false
	return file, true, nil
}

func (directory *unixPrivateDirectory) ReadRegular(name string, maximum int64) ([]byte, bool, error) {
	if directory.Validate() != nil || !validPrivateLeafName(name) || maximum < 0 || maximum == int64(^uint64(0)>>1) {
		return nil, false, ErrUnsafeFile
	}
	before, err := requirePrivateUnixRootRegularAt(directory.descriptor, name, 1)
	if err != nil {
		var stat unix.Stat_t
		if statErr := unix.Fstatat(directory.descriptor, name, &stat, unix.AT_SYMLINK_NOFOLLOW); errors.Is(statErr, unix.ENOENT) {
			return nil, false, nil
		}
		return nil, false, ErrUnsafeFile
	}
	descriptor, err := unix.Openat(directory.descriptor, name, unix.O_RDONLY|unix.O_CLOEXEC|unix.O_NOFOLLOW|unix.O_NONBLOCK, 0)
	if err != nil {
		return nil, false, ErrUnsafeFile
	}
	file := os.NewFile(uintptr(descriptor), "tht-safeio-private-root-read")
	if file == nil {
		_ = unix.Close(descriptor)
		return nil, false, ErrUnsafeFile
	}
	contents, readErr := io.ReadAll(io.LimitReader(file, maximum+1))
	var opened unix.Stat_t
	statErr := unix.Fstat(descriptor, &opened)
	closeErr := file.Close()
	var current unix.Stat_t
	currentErr := unix.Fstatat(directory.descriptor, name, &current, unix.AT_SYMLINK_NOFOLLOW)
	if readErr != nil || statErr != nil || closeErr != nil || currentErr != nil || int64(len(contents)) > maximum ||
		!privateUnixRootRegular(&opened, 1) || !privateUnixRootRegular(&current, 1) ||
		!sameUnixRootRegular(before, opened) || !sameUnixRootRegular(opened, current) || directory.Validate() != nil {
		return nil, false, ErrUnsafeFile
	}
	return contents, true, nil
}

func (directory *unixPrivateDirectory) ReplaceRegular(name string, contents []byte) error {
	if directory.Validate() != nil || !validPrivateLeafName(name) || len(contents) == 0 {
		return ErrUnsafeFile
	}
	if _, err := requirePrivateUnixRootRegularAt(directory.descriptor, name, 1); err != nil {
		return ErrUnsafeFile
	}
	temporary, err := writePrivateTemporaryAt(directory.descriptor, contents)
	if err != nil {
		return ErrUnsafeFile
	}
	defer func() { _ = unix.Unlinkat(directory.descriptor, temporary, 0) }()
	if _, err := requirePrivateUnixRootRegularAt(directory.descriptor, name, 1); err != nil || directory.Validate() != nil {
		return ErrUnsafeFile
	}
	if err := unix.Renameat(directory.descriptor, temporary, directory.descriptor, name); err != nil || unix.Fsync(directory.descriptor) != nil || directory.Validate() != nil {
		return ErrUnsafeFile
	}
	return nil
}

func (directory *unixPrivateDirectory) RemoveRegular(name string) (bool, error) {
	if directory.Validate() != nil || !validPrivateLeafName(name) {
		return false, ErrUnsafeFile
	}
	if _, err := requirePrivateUnixRootRegularAt(directory.descriptor, name, 1); err != nil {
		var stat unix.Stat_t
		if statErr := unix.Fstatat(directory.descriptor, name, &stat, unix.AT_SYMLINK_NOFOLLOW); errors.Is(statErr, unix.ENOENT) {
			return false, nil
		}
		return false, ErrUnsafeFile
	}
	if err := unix.Unlinkat(directory.descriptor, name, 0); err != nil || unix.Fsync(directory.descriptor) != nil || directory.Validate() != nil {
		return false, ErrUnsafeFile
	}
	return true, nil
}

func (directory *unixPrivateDirectory) ListPage(
	maximumEntries int,
	afterName string,
	validName func(string) bool,
	validLinks func(string, uint64) bool,
) (PrivateDirectoryPage, error) {
	if directory.Validate() != nil || maximumEntries < 1 || maximumEntries > 4096 || validName == nil || validLinks == nil || (afterName != "" && !validName(afterName)) {
		return PrivateDirectoryPage{}, ErrUnsafeFile
	}
	var before unix.Stat_t
	if unix.Fstat(directory.descriptor, &before) != nil || !privateUnixDirectoryStat(&before) {
		return PrivateDirectoryPage{}, ErrUnsafeFile
	}
	duplicate, err := unix.Dup(directory.descriptor)
	if err != nil {
		return PrivateDirectoryPage{}, ErrUnsafeFile
	}
	file := os.NewFile(uintptr(duplicate), "tht-safeio-private-root-list")
	if file == nil {
		_ = unix.Close(duplicate)
		return PrivateDirectoryPage{}, ErrUnsafeFile
	}
	defer file.Close()
	seen := make(map[string]struct{}, maximumEntries+1)
	selected := make([]PrivateDirectoryEntry, 0, maximumEntries+1)
	scanned := 0
	for {
		entries, readErr := file.ReadDir(1)
		if readErr != nil && !errors.Is(readErr, io.EOF) {
			return PrivateDirectoryPage{}, ErrUnsafeFile
		}
		if len(entries) == 0 {
			break
		}
		if len(entries) != 1 {
			return PrivateDirectoryPage{}, ErrUnsafeFile
		}
		scanned++
		if scanned > maximumPrivateDirectoryPageScanEntries {
			return PrivateDirectoryPage{}, ErrUnsafeFile
		}
		name := entries[0].Name()
		if !validPrivateLeafName(name) || !validName(name) {
			return PrivateDirectoryPage{}, ErrUnsafeFile
		}
		if _, duplicate := seen[name]; duplicate {
			return PrivateDirectoryPage{}, ErrUnsafeFile
		}
		seen[name] = struct{}{}
		var stat unix.Stat_t
		if unix.Fstatat(directory.descriptor, name, &stat, unix.AT_SYMLINK_NOFOLLOW) != nil ||
			!privateUnixRootRegular(&stat, uint64(stat.Nlink)) || !validLinks(name, uint64(stat.Nlink)) {
			return PrivateDirectoryPage{}, ErrUnsafeFile
		}
		if name > afterName {
			selected = appendBoundedPrivateDirectoryEntry(selected, PrivateDirectoryEntry{
				Name: name, ModifiedUnixMs: time.Unix(stat.Mtim.Sec, stat.Mtim.Nsec).UnixMilli(),
			}, maximumEntries+1)
		}
		if errors.Is(readErr, io.EOF) {
			break
		}
	}
	var after unix.Stat_t
	if unix.Fstat(directory.descriptor, &after) != nil || !privateUnixDirectoryStat(&after) ||
		before.Dev != after.Dev || before.Ino != after.Ino || before.Mode != after.Mode || before.Mtim != after.Mtim || before.Ctim != after.Ctim || directory.Validate() != nil {
		return PrivateDirectoryPage{}, ErrUnsafeFile
	}
	sort.Slice(selected, func(left, right int) bool { return selected[left].Name < selected[right].Name })
	more := len(selected) > maximumEntries
	if more {
		selected = selected[:maximumEntries]
	}
	return PrivateDirectoryPage{Entries: selected, More: more}, nil
}

func (directory *unixPrivateDirectory) ClaimRegular(source, claim string) (bool, error) {
	if directory.Validate() != nil || !validPrivateLeafName(source) || !validPrivateLeafName(claim) {
		return false, ErrUnsafeFile
	}
	if err := privateUnixRootRegularAtAllowedLinks(directory.descriptor, source, 1); err != nil {
		if requireSamePrivateUnixRootPairAt(directory.descriptor, source, claim) == nil || isPrivateUnixRootClaimAbsentOrOrphanAt(directory.descriptor, source, claim) {
			return false, nil
		}
		return false, ErrUnsafeFile
	}
	if err := unix.Linkat(directory.descriptor, source, directory.descriptor, claim, 0); err != nil {
		if errors.Is(err, unix.EEXIST) && privateUnixRootRegularAtAllowedLinks(directory.descriptor, claim, 1, 2) == nil {
			return false, nil
		}
		return false, ErrUnsafeFile
	}
	if err := requireSamePrivateUnixRootPairAt(directory.descriptor, source, claim); err != nil || unix.Fsync(directory.descriptor) != nil || directory.Validate() != nil {
		return false, ErrUnsafeFile
	}
	return true, nil
}

func (directory *unixPrivateDirectory) ReadClaim(source, claim string, maximum int64) ([]byte, bool, error) {
	if directory.Validate() != nil || !validPrivateLeafName(source) || !validPrivateLeafName(claim) || maximum < 0 || maximum == int64(^uint64(0)>>1) {
		return nil, false, ErrUnsafeFile
	}
	if err := requireSamePrivateUnixRootPairAt(directory.descriptor, source, claim); err != nil {
		if isPrivateUnixRootClaimAbsentOrOrphanAt(directory.descriptor, source, claim) {
			return nil, false, nil
		}
		return nil, false, ErrUnsafeFile
	}
	descriptor, err := unix.Openat(directory.descriptor, source, unix.O_RDONLY|unix.O_CLOEXEC|unix.O_NOFOLLOW|unix.O_NONBLOCK, 0)
	if err != nil {
		return nil, false, ErrUnsafeFile
	}
	file := os.NewFile(uintptr(descriptor), "tht-safeio-private-root-claim")
	if file == nil {
		_ = unix.Close(descriptor)
		return nil, false, ErrUnsafeFile
	}
	contents, readErr := io.ReadAll(io.LimitReader(file, maximum+1))
	var after unix.Stat_t
	statErr := unix.Fstat(descriptor, &after)
	closeErr := file.Close()
	if readErr != nil || statErr != nil || closeErr != nil || int64(len(contents)) > maximum || !privateUnixRootRegular(&after, 2) ||
		requireSamePrivateUnixRootPairAt(directory.descriptor, source, claim) != nil || directory.Validate() != nil {
		return nil, false, ErrUnsafeFile
	}
	return contents, true, nil
}

func (directory *unixPrivateDirectory) RemoveClaim(source, claim string) (bool, error) {
	if directory.Validate() != nil || !validPrivateLeafName(source) || !validPrivateLeafName(claim) {
		return false, ErrUnsafeFile
	}
	if err := requireSamePrivateUnixRootPairAt(directory.descriptor, source, claim); err != nil {
		if isPrivateUnixRootClaimAbsentOrOrphanAt(directory.descriptor, source, claim) {
			return false, nil
		}
		return false, ErrUnsafeFile
	}
	if err := unix.Unlinkat(directory.descriptor, source, 0); err != nil || privateUnixRootRegularAtAllowedLinks(directory.descriptor, claim, 1) != nil ||
		unix.Unlinkat(directory.descriptor, claim, 0) != nil || unix.Fsync(directory.descriptor) != nil || directory.Validate() != nil {
		return false, ErrUnsafeFile
	}
	return true, nil
}