export interface RouteMatch {
  ns: string;
  id: string;
  rest: string;
}

const NAMESPACE = /^\/[^/\s]+$/;

export function validateNamespace(ns: string): string {
  if (!NAMESPACE.test(ns)) {
    throw new Error(
      `namespace must be '/' plus a single path segment: ${JSON.stringify(ns)}`,
    );
  }
  return ns;
}

// ids are client-generated names, not capabilities; restricting them to the
// unreserved URI charset closes weird-key/path-confusion holes at the boundary.
const ID_CHARSET = /^[A-Za-z0-9._~-]+$/;
const ID_MAX_LENGTH = 256;

export function invalidIdReason(id: string): string | null {
  if (id === "") return "id must be non-empty";
  if (id.length > ID_MAX_LENGTH) {
    return `id must be at most ${ID_MAX_LENGTH} characters`;
  }
  if (!ID_CHARSET.test(id)) return "id must contain only [A-Za-z0-9._~-]";
  return null;
}

export function parseRoute(pathname: string): RouteMatch | null {
  if (!pathname.startsWith("/")) return null;
  const idStart = pathname.indexOf("/", 1);
  if (idStart <= 1) return null;
  const ns = pathname.slice(0, idStart);
  const remainder = pathname.slice(idStart);
  const idEnd = remainder.indexOf("/", 1);
  const id = idEnd === -1 ? remainder.slice(1) : remainder.slice(1, idEnd);
  const rest = idEnd === -1 ? "" : remainder.slice(idEnd);
  return { ns, id, rest };
}