// Copyright (C) 2019 Storj Labs, Inc.
// See LICENSE for copying information.

// +build windows

package filestore

import (
	"errors"
	"fmt"
	"os"
	"path/filepath"
	"unsafe"

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

var errSharingViolation = windows.Errno(32)

func isBusy(err error) bool {
	err = underlyingError(err)
	return errors.Is(err, errSharingViolation)
}

func diskInfoFromPath(path string) (info DiskInfo, err error) {
	absPath, err := filepath.Abs(path)
	if err != nil {
		absPath = path
	}
	var filesystemID string
	var availableSpace int64

	availableSpace, err = getDiskFreeSpace(absPath)
	if err != nil {
		return DiskInfo{"", -1}, err
	}

	filesystemID, err = getVolumeSerialNumber(absPath)
	if err != nil {
		return DiskInfo{"", availableSpace}, err
	}

	return DiskInfo{filesystemID, availableSpace}, nil
}

var (
	kernel32             = windows.MustLoadDLL("kernel32.dll")
	procGetDiskFreeSpace = kernel32.MustFindProc("GetDiskFreeSpaceExW")
)

func getDiskFreeSpace(path string) (int64, error) {
	path16, err := windows.UTF16PtrFromString(path)
	if err != nil {
		return -1, err
	}

	var bytes int64
	_, _, err = procGetDiskFreeSpace.Call(uintptr(unsafe.Pointer(path16)), uintptr(unsafe.Pointer(&bytes)), 0, 0)
	err = ignoreSuccess(err)
	return bytes, err
}

func getVolumeSerialNumber(path string) (string, error) {
	path16, err := windows.UTF16PtrFromString(path)
	if err != nil {
		return "", err
	}

	var volumePath [1024]uint16
	err = windows.GetVolumePathName(path16, &volumePath[0], uint32(len(volumePath)))
	if err != nil {
		return "", err
	}

	var volumeSerial uint32

	err = windows.GetVolumeInformation(
		&volumePath[0],
		nil, 0, // volume name buffer
		&volumeSerial,
		nil,    // maximum component length
		nil,    // filesystem flags
		nil, 0, // filesystem name buffer
	)
	err = ignoreSuccess(err)
	if err != nil {
		return "", err
	}

	return fmt.Sprintf("%08x", volumeSerial), nil
}

// windows api occasionally returns.
func ignoreSuccess(err error) error {
	if errors.Is(err, windows.Errno(0)) {
		return nil
	}
	return err
}

// Adds `\\?` prefix to ensure that API recognizes it as a long path.
// see https://msdn.microsoft.com/en-us/library/windows/desktop/aa365247(v=vs.85).aspx#maxpath
func tryFixLongPath(path string) string {
	abspath, err := filepath.Abs(path)
	if err != nil {
		return path
	}
	return `\\?\` + abspath
}

// rename implements atomic file rename on windows.
func rename(oldpath, newpath string) error {
	oldpathp, err := windows.UTF16PtrFromString(tryFixLongPath(oldpath))
	if err != nil {
		return &os.LinkError{Op: "replace", Old: oldpath, New: newpath, Err: err}
	}
	newpathp, err := windows.UTF16PtrFromString(tryFixLongPath(newpath))
	if err != nil {
		return &os.LinkError{Op: "replace", Old: oldpath, New: newpath, Err: err}
	}

	err = windows.MoveFileEx(oldpathp, newpathp, windows.MOVEFILE_REPLACE_EXISTING|windows.MOVEFILE_WRITE_THROUGH)
	if err != nil {
		return &os.LinkError{Op: "replace", Old: oldpath, New: newpath, Err: err}
	}

	return nil
}

// openFileReadOnly opens the file with read only.
// Custom implementation, because os.Open doesn't support specifying FILE_SHARE_DELETE.
func openFileReadOnly(path string, perm os.FileMode) (*os.File, error) {
	pathp, err := windows.UTF16PtrFromString(tryFixLongPath(path))
	if err != nil {
		return nil, err
	}

	access := uint32(windows.GENERIC_READ)
	sharemode := uint32(windows.FILE_SHARE_READ | windows.FILE_SHARE_WRITE | windows.FILE_SHARE_DELETE)

	var sa windows.SecurityAttributes
	sa.Length = uint32(unsafe.Sizeof(sa))
	sa.InheritHandle = 1

	createmode := uint32(windows.OPEN_EXISTING)

	handle, err := windows.CreateFile(pathp, access, sharemode, &sa, createmode, windows.FILE_ATTRIBUTE_NORMAL, 0)
	if err != nil {
		return nil, err
	}

	return os.NewFile(uintptr(handle), path), nil
}