package fsx

import (
	"errors"
	"path/filepath"
	"strings"
)

func CleanURLLike(p string) string {
	p = strings.TrimSpace(p)
	if p == "" || p == "/" {
		return "/"
	}
	parts := []string{}
	for _, seg := range strings.Split(strings.ReplaceAll(p, "\\", "/"), "/") {
		switch seg {
		case "", ".":
			continue
		case "..":
			if len(parts) > 0 {
				parts = parts[:len(parts)-1]
			}
		default:
			parts = append(parts, seg)
		}
	}
	return "/" + strings.Join(parts, "/")
}

func SafeRel(root, requested string) (string, error) {
	s := CleanURLLike(requested)
	if strings.HasPrefix(s, "/") {
		s = strings.TrimPrefix(s, "/")
	}
	full := filepath.Join(root, filepath.FromSlash(s))
	rel, err := filepath.Rel(root, full)
	if err != nil {
		return "", err
	}
	if rel == "." {
		return "/", nil
	}
	sep := string(filepath.Separator)
	if strings.HasPrefix(rel, "..") || strings.Contains(rel, ".."+sep) {
		return "", errors.New("path escapes root")
	}
	return "/" + filepath.ToSlash(rel), nil
}

func ResponsePath(root, full string) string {
	rel, err := filepath.Rel(root, full)
	if err != nil || rel == "." {
		return "/"
	}
	return "/" + filepath.ToSlash(rel)
}