/**
 * @fileoverview NATS + JetStream connection lifecycle.
 * @module nats/connection
 */

import { createDebugger } from '../debug/logger.js';
import { config } from '../config.js';
import { SUBJECTS, STREAMS } from './subjects.js';

const log = createDebugger('nats');

/** @type {import('nats').NatsConnection|null} */
let nc = null;
/** @type {import('nats').JetStreamClient|null} */
let js = null;
/** @type {import('nats').JetStreamManager|null} */
let jsm = null;

/**
 * Connect to NATS and return JetStream handles.
 *
 * @param {string} [url=config.natsUrl]
 * @returns {Promise<{ nc: import('nats').NatsConnection, js: import('nats').JetStreamClient, jsm: import('nats').JetStreamManager }>}
 */
export async function connectNats(url = config.natsUrl) {
  if (!config.natsEnabled && process.env.NATS_FORCE_CONNECT !== '1') {
    log.debug('connect skipped — NATS_ENABLED=false');
    throw new Error('NATS is disabled (NATS_ENABLED=false)');
  }

  if (nc && js && jsm) {
    return { nc, js, jsm };
  }

  log.info('connecting to NATS', { url });

  const { connect } = await import('nats');
  nc = await connect({ servers: url, name: 'verae-zapier-middleware' });
  js = nc.jetstream();
  jsm = await nc.jetstreamManager();

  log.info('NATS connected', { url });
  return { nc, js, jsm };
}

/** @returns {import('nats').NatsConnection|null} */
export function getNatsConnection() {
  return nc;
}

/**
 * Idempotently create JetStream streams required by this middleware.
 *
 * @param {import('nats').JetStreamManager} [manager]
 * @returns {Promise<void>}
 */
export async function ensureStreams(manager) {
  const m = manager ?? jsm;
  if (!m) {
    throw new Error('JetStream manager not available — call connectNats first');
  }

  /** @type {Array<{ name: string, subjects: string[] }>} */
  const defs = [
    { name: STREAMS.ZAPIER_JOBS, subjects: [SUBJECTS.JOBS_WATCH] },
    { name: STREAMS.ZAPIER_EVENTS, subjects: [SUBJECTS.JOBS_EVENTS] },
    { name: STREAMS.ZAPIER_WEBHOOKS, subjects: [SUBJECTS.WEBHOOKS_DELIVER] },
  ];

  for (const def of defs) {
    try {
      await m.streams.info(def.name);
      log.debug('stream exists', { stream: def.name });
    } catch {
      await m.streams.add({
        name: def.name,
        subjects: def.subjects,
        retention: 'limits',
        storage: 'file',
        max_age: 24 * 60 * 60 * 1e9, // 24h in ns
        num_replicas: 1,
      });
      log.info('stream created', { stream: def.name, subjects: def.subjects });
    }
  }
}

/**
 * Close the shared NATS connection if open.
 * @returns {Promise<void>}
 */
export async function closeNats() {
  if (!nc) {
    log.debug('closeNats: no active connection');
    return;
  }
  log.info('closing NATS connection');
  await nc.drain();
  nc = null;
  js = null;
  jsm = null;
}

/**
 * @returns {import('nats').JetStreamClient|null}
 */
export function getJetStream() {
  return js;
}

/**
 * @returns {boolean}
 */
export function isNatsConnected() {
  return Boolean(nc && !nc.isClosed());
}