import crypto from 'node:crypto';

function safeJsonParse(value, fallback = null) {
  try {
    return JSON.parse(value);
  } catch {
    return fallback;
  }
}

export function createSessionStreamStore({ pool }) {
  if (!pool) {
    throw new Error('createSessionStreamStore requires pool');
  }

  async function appendEvent({
    userId,
    sessionId,
    payload,
    id = crypto.randomUUID(),
    upstreamEventId = null,
  } = {}) {
    if (!userId || !sessionId || !payload) {
      throw new Error('appendEvent requires userId, sessionId, and payload');
    }
    const createdAt = Date.now();
    const eventType = String(payload?.type ?? 'unknown').slice(0, 64);
    await pool.query(
      `INSERT INTO h5_session_stream_events
         (id, user_id, agent_session_id, event_type, payload_json, upstream_event_id, created_at)
       VALUES (?, ?, ?, ?, ?, ?, ?)`,
      [
        id,
        userId,
        sessionId,
        eventType,
        JSON.stringify(payload),
        upstreamEventId || null,
        createdAt,
      ],
    );
    return {
      id,
      createdAt,
      eventType,
      payload,
    };
  }

  async function listEventsForUser(userId, sessionId, { afterEventId = null, limit = 500 } = {}) {
    if (!userId || !sessionId) return null;

    let afterCreatedAt = null;
    let cursorMiss = false;
    if (afterEventId) {
      const [cursorRows] = await pool.query(
        `SELECT created_at
         FROM h5_session_stream_events
         WHERE id = ? AND agent_session_id = ? AND user_id = ?
         LIMIT 1`,
        [afterEventId, sessionId, userId],
      );
      if (!cursorRows[0]) {
        cursorMiss = true;
      } else {
        afterCreatedAt = Number(cursorRows[0].created_at);
      }
    }

    const [rows] = await pool.query(
      afterCreatedAt == null
        ? `SELECT id, event_type, payload_json, upstream_event_id, created_at
           FROM h5_session_stream_events
           WHERE agent_session_id = ? AND user_id = ?
           ORDER BY created_at ASC, id ASC
           LIMIT ?`
        : `SELECT id, event_type, payload_json, upstream_event_id, created_at
           FROM h5_session_stream_events
           WHERE agent_session_id = ? AND user_id = ? AND created_at > ?
           ORDER BY created_at ASC, id ASC
           LIMIT ?`,
      afterCreatedAt == null
        ? [sessionId, userId, limit]
        : [sessionId, userId, afterCreatedAt, limit],
    );

    return {
      events: rows.map((row) => ({
        id: row.id,
        eventType: row.event_type,
        payload: safeJsonParse(row.payload_json, null),
        upstreamEventId: row.upstream_event_id ?? null,
        createdAt: Number(row.created_at),
      })),
      cursorMiss,
    };
  }

  async function getLatestEventForUser(userId, sessionId) {
    const [rows] = await pool.query(
      `SELECT id, event_type, payload_json, upstream_event_id, created_at
       FROM h5_session_stream_events
       WHERE agent_session_id = ? AND user_id = ?
       ORDER BY created_at DESC, id DESC
       LIMIT 1`,
      [sessionId, userId],
    );
    const row = rows[0];
    if (!row) return null;
    return {
      id: row.id,
      eventType: row.event_type,
      payload: safeJsonParse(row.payload_json, null),
      upstreamEventId: row.upstream_event_id ?? null,
      createdAt: Number(row.created_at),
    };
  }

  return {
    appendEvent,
    listEventsForUser,
    getLatestEventForUser,
  };
}