// Package tempdir allocates disposable storage outside a source worktree.
package tempdir

import (
	"fmt"
	"os"
	"path/filepath"
	"strings"
)

// Outside uses the system temporary directory and leaves cleanup to its caller.
func Outside(repositoryDir, pattern string) (string, error) {
	directory, err := os.MkdirTemp("", pattern)
	if err != nil {
		return "", err
	}
	absolute, err := filepath.Abs(directory)
	if err != nil {
		os.RemoveAll(directory)
		return "", err
	}
	directory = absolute
	repository, err := filepath.Abs(repositoryDir)
	if err == nil && !strings.EqualFold(filepath.VolumeName(repository), filepath.VolumeName(directory)) {
		return directory, nil
	}
	if err == nil {
		var relative string
		relative, err = filepath.Rel(repository, directory)
		if err == nil && (relative == "." || relative != ".." && !strings.HasPrefix(relative, ".."+string(filepath.Separator))) {
			err = fmt.Errorf("temporary storage %q is inside repository %q; select an external temporary directory", directory, repository)
		}
	}
	if err != nil {
		os.RemoveAll(directory)
		return "", err
	}
	return directory, nil
}