package api

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

func toHostPath(containerRoot, hostRoot, containerPath string) (string, error) {
	if !filepath.IsAbs(containerRoot) || !filepath.IsAbs(hostRoot) || !filepath.IsAbs(containerPath) {
		return "", errors.New("absolute storage paths required")
	}
	rel, err := filepath.Rel(containerRoot, containerPath)
	if err != nil || rel == ".." || strings.HasPrefix(rel, ".."+string(filepath.Separator)) {
		return "", errors.New("storage path escapes root")
	}
	return filepath.Join(hostRoot, rel), nil
}