//go:build windows && !go1.26

package sequential

import (
	"os"
	"unsafe"

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

func openFileSequential(name string, flag int, _ os.FileMode) (file *os.File, err error) {
	if name == "" {
		return nil, &os.PathError{Op: "open", Path: name, Err: windows.ERROR_FILE_NOT_FOUND}
	}
	r, e := openSequential(name, flag|windows.O_CLOEXEC)
	if e != nil {
		return nil, &os.PathError{Op: "open", Path: name, Err: e}
	}
	return os.NewFile(uintptr(r), name), nil
}

func makeInheritSa() *windows.SecurityAttributes {
	var sa windows.SecurityAttributes
	sa.Length = uint32(unsafe.Sizeof(sa))
	sa.InheritHandle = 1
	return &sa
}

func openSequential(path string, mode int) (fd windows.Handle, err error) {
	if len(path) == 0 {
		return windows.InvalidHandle, windows.ERROR_FILE_NOT_FOUND
	}
	pathp, err := windows.UTF16PtrFromString(path)
	if err != nil {
		return windows.InvalidHandle, err
	}
	var access uint32
	switch mode & (windows.O_RDONLY | windows.O_WRONLY | windows.O_RDWR) {
	case windows.O_RDONLY:
		access = windows.GENERIC_READ
	case windows.O_WRONLY:
		access = windows.GENERIC_WRITE
	case windows.O_RDWR:
		access = windows.GENERIC_READ | windows.GENERIC_WRITE
	}
	if mode&windows.O_CREAT != 0 {
		access |= windows.GENERIC_WRITE
	}
	if mode&windows.O_APPEND != 0 {
		access &^= windows.GENERIC_WRITE
		access |= windows.FILE_APPEND_DATA
	}
	sharemode := uint32(windows.FILE_SHARE_READ | windows.FILE_SHARE_WRITE)
	var sa *windows.SecurityAttributes
	if mode&windows.O_CLOEXEC == 0 {
		sa = makeInheritSa()
	}
	var createmode uint32
	switch {
	case mode&(windows.O_CREAT|windows.O_EXCL) == (windows.O_CREAT | windows.O_EXCL):
		createmode = windows.CREATE_NEW
	case mode&(windows.O_CREAT|windows.O_TRUNC) == (windows.O_CREAT | windows.O_TRUNC):
		createmode = windows.CREATE_ALWAYS
	case mode&windows.O_CREAT == windows.O_CREAT:
		createmode = windows.OPEN_ALWAYS
	case mode&windows.O_TRUNC == windows.O_TRUNC:
		createmode = windows.TRUNCATE_EXISTING
	default:
		createmode = windows.OPEN_EXISTING
	}
	// Use FILE_FLAG_SEQUENTIAL_SCAN rather than FILE_ATTRIBUTE_NORMAL as implemented in golang.
	// https://learn.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-createfilea#FILE_FLAG_SEQUENTIAL_SCAN
	h, e := windows.CreateFile(pathp, access, sharemode, sa, createmode, windows.FILE_FLAG_SEQUENTIAL_SCAN, 0)
	return h, e
}