//go:build windows

package safeio

import (
	"errors"
	"io"
	"os"
	"path/filepath"

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

const windowsReplaceMoveFlags = windows.MOVEFILE_REPLACE_EXISTING | windows.MOVEFILE_WRITE_THROUGH

func replaceCanonicalRegular(path string, contents []byte) error {
	directory := filepath.Dir(path)
	if err := requireCanonicalDirectory(directory); err != nil || !safeExistingRegular(path) {
		return ErrUnsafeFile
	}
	temporary, err := writePrivateTemporary(directory, contents)
	if err != nil {
		return ErrUnsafeFile
	}
	defer func() { _ = os.Remove(temporary) }()
	if !safeExistingRegular(path) {
		return ErrUnsafeFile
	}
	from, err := windows.UTF16PtrFromString(temporary)
	if err != nil {
		return ErrUnsafeFile
	}
	to, err := windows.UTF16PtrFromString(path)
	if err != nil {
		return ErrUnsafeFile
	}
	if err := windows.MoveFileEx(from, to, windowsReplaceMoveFlags); err != nil {
		return ErrUnsafeFile
	}
	return nil
}

func safeExistingRegular(path string) bool {
	handle, err := openWindowsComponent(path, false)
	if err != nil {
		return false
	}
	return windows.CloseHandle(handle) == nil
}

func writePrivateTemporary(directory string, contents []byte) (string, error) {
	for attempt := 0; attempt < 16; attempt++ {
		name, err := randomTemporaryName()
		if err != nil {
			return "", err
		}
		path := filepath.Join(directory, name)
		file, err := os.OpenFile(path, os.O_WRONLY|os.O_CREATE|os.O_EXCL, 0o600)
		if errors.Is(err, os.ErrExist) {
			continue
		}
		if err != nil {
			return "", err
		}
		if err := file.Chmod(0o600); err == nil {
			var written int
			written, err = file.Write(contents)
			if err == nil && written != len(contents) {
				err = io.ErrShortWrite
			}
		}
		if err == nil {
			err = file.Sync()
		}
		closeErr := file.Close()
		if err == nil {
			err = closeErr
		}
		if err != nil {
			_ = os.Remove(path)
			return "", err
		}
		return path, nil
	}
	return "", ErrUnsafeFile
}