import type { Pool } from 'pg';

const STUCK_TIMEOUT_MINUTES = 5;

export type EventRow = {
  event_id: number;
  uuid: string;
  name: string;
  data: unknown;
  status: string;
  created_at: string;
  started_at: string | null;
  completed_at: string | null;
};

/**
 * Wraps all PostgreSQL interactions for the event queue.
 * Accepts a pg Pool so it can be replaced with a mock in tests.
 */
export class EventStorage {
  private pool: Pool;

  constructor(pool: Pool) {
    this.pool = pool;
  }

  /**
   * Atomically claims up to `batchSize` pending events using a single CTE
   * query — no BEGIN/COMMIT/ROLLBACK needed, eliminating the pg multi-query
   * deprecation warning entirely.
   */
  async claimBatch(batchSize: number): Promise<EventRow[]> {
    const result = await this.pool.query<EventRow>(
      `WITH claimed AS (
         SELECT uuid FROM event
         WHERE status = 'pending'
         ORDER BY event_id ASC
         LIMIT $1
         FOR UPDATE SKIP LOCKED
       )
       UPDATE event SET status = 'processing', started_at = NOW()
       WHERE uuid IN (SELECT uuid FROM claimed)
       RETURNING *`,
      [batchSize]
    );
    return result.rows;
  }

  /**
   * Marks an event as successfully completed and removes it from the table.
   * Updates status first so a failed DELETE doesn't leave the event as pending.
   */
  async markDoneAndDelete(uuid: string): Promise<void> {
    await this.pool.query(
      `UPDATE event SET status = 'done', completed_at = NOW() WHERE uuid = $1`,
      [uuid]
    );
    await this.pool.query(`DELETE FROM event WHERE uuid = $1`, [uuid]);
  }

  /**
   * At startup: mark any events that were stuck as 'processing' during a
   * prior crash as 'failed'. At-most-once delivery — subscribers are never
   * called twice. Returns the number of events marked failed.
   */
  async markStuckAsFailed(): Promise<number> {
    const result = await this.pool.query(
      `UPDATE event SET status = 'failed'
       WHERE status = 'processing'
         AND started_at < NOW() - INTERVAL '${STUCK_TIMEOUT_MINUTES} minutes'`
    );
    return result.rowCount ?? 0;
  }
}