import { sql } from "drizzle-orm";
import type { PayloadRequest } from "payload";

/**
 * Acquires a Postgres transaction-scoped advisory lock so that two
 * concurrent requests confirming a booking for the same day can't both pass
 * the "is this slot free?" check before either has committed (Payload's
 * default transaction isolation is READ COMMITTED, which alone would allow
 * that race). The lock is automatically released when the transaction ends.
 *
 * Must be called from inside a Payload hook/operation that already has an
 * active `req.transactionID` (true for collection create/update by default).
 */
export async function acquireBookingDayLock(req: PayloadRequest, dateKey: string): Promise<void> {
  const txID = req.transactionID ? String(await req.transactionID) : undefined;
  if (!txID) return; // No active transaction — nothing to lock against.

  const adapter = req.payload.db as unknown as {
    sessions?: Record<string, { db: { execute: (query: unknown) => Promise<unknown> } }>;
    drizzle: { execute: (query: unknown) => Promise<unknown> };
  };
  const tx = adapter.sessions?.[txID]?.db ?? adapter.drizzle;

  await tx.execute(sql`SELECT pg_advisory_xact_lock(hashtext(${dateKey}))`);
}