import path from 'path';

const COURSEWARE_ID_PATTERN = /^[a-zA-Z0-9_-]+$/;

export function isValidCoursewareId(value: unknown): value is string {
  return typeof value === 'string' && COURSEWARE_ID_PATTERN.test(value);
}

export function assertCoursewareId(value: unknown): asserts value is string {
  if (!isValidCoursewareId(value)) {
    throw new Error('Invalid coursewareId');
  }
}

export function isValidCoursewareVersion(value: unknown): value is number {
  return typeof value === 'number' && Number.isSafeInteger(value) && value >= 1;
}

export function assertCoursewareVersion(value: unknown): asserts value is number {
  if (!isValidCoursewareVersion(value)) {
    throw new Error('Invalid courseware version');
  }
}

/** Resolve exactly one direct child without allowing absolute paths or traversal. */
export function resolveDirectChildPath(rootDir: string, childName: string): string {
  if (!childName || path.basename(childName) !== childName) {
    throw new Error('Invalid courseware storage path');
  }
  const root = path.resolve(rootDir);
  const child = path.resolve(root, childName);
  if (path.dirname(child) !== root) {
    throw new Error('Invalid courseware storage path');
  }
  return child;
}