/**
 * Stable public identity for a large-course module.
 *
 * The persisted classroom id is an operations-side source identifier. It must
 * never double as the learner-facing courseware id, otherwise a manifest leaks
 * a direct route to the mutable source classroom and bypasses its version/hash
 * pin. Keeping this derivation deterministic also means a course re-publish
 * creates the next immutable version of the same public module.
 */
export function courseModuleCoursewareId(courseId: string, moduleIndex: number): string {
  if (!/^[a-zA-Z0-9_-]+$/.test(courseId)) {
    throw new Error(`Invalid course id: ${courseId}`);
  }
  if (!Number.isInteger(moduleIndex) || moduleIndex < 1) {
    throw new Error(`Invalid module index: ${moduleIndex}`);
  }
  return `course_${courseId}_module_${moduleIndex}`;
}