// Stable server-side pagination — Phase 4.1 §16. Shared by every list endpoint that could
// otherwise grow unbounded (audit log, attempt histories, assessment session history, scenario
// analytics). Simple offset/limit, not cursor-based — this admin/instructor scale (hundreds to
// low thousands of rows, not a high-frequency infinite-scroll feed) doesn't need more than
// that, and offset pagination is what every other query in this codebase already reads like.

const DEFAULT_PAGE_SIZE = 50;
const MAX_PAGE_SIZE = 200;

// Reads ?page=&page_size= from a request, clamped to sane bounds — never trusts the client for
// an unbounded page_size (that would defeat the entire point).
function parsePagination(req) {
  const page = Math.max(1, parseInt(req.query.page, 10) || 1);
  const pageSize = Math.min(MAX_PAGE_SIZE, Math.max(1, parseInt(req.query.page_size, 10) || DEFAULT_PAGE_SIZE));
  return { page, pageSize, offset: (page - 1) * pageSize };
}

function paginatedResponse(rows, total, { page, pageSize }) {
  return { items: rows, page, page_size: pageSize, total, total_pages: Math.max(1, Math.ceil(total / pageSize)) };
}

module.exports = { parsePagination, paginatedResponse, DEFAULT_PAGE_SIZE, MAX_PAGE_SIZE };