package fileops

import (
	"crypto/rand"
	"encoding/hex"
	"fmt"
	"os"
	"path/filepath"
	"strings"
)

// createPrivateTemp follows CreateTemp's pattern syntax while installing native
// private permissions at creation, rather than inheriting a shared Windows DACL.
func createPrivateTemp(dir, pattern string) (*os.File, error) {
	if pattern != "" && filepath.Base(pattern) != pattern {
		return nil, fmt.Errorf("temporary pattern contains a path separator: %s", pattern)
	}
	if dir == "" {
		dir = os.TempDir()
	}
	prefix, suffix := pattern, ""
	if index := strings.LastIndexByte(pattern, '*'); index >= 0 {
		prefix, suffix = pattern[:index], pattern[index+1:]
	}
	for attempt := 0; attempt < 10; attempt++ {
		var nonce [16]byte
		if _, err := rand.Read(nonce[:]); err != nil {
			return nil, err
		}
		path := filepath.Join(dir, prefix+hex.EncodeToString(nonce[:])+suffix)
		file, err := CreatePrivateFile(path)
		if os.IsExist(err) {
			continue
		}
		return file, err
	}
	return nil, fmt.Errorf("could not reserve a unique private file")
}