import type { INestApplicationContext } from '@nestjs/common';
import { IoAdapter } from '@nestjs/platform-socket.io';
import { createAdapter } from '@socket.io/redis-adapter';
import Redis from 'ioredis';
import type { ServerOptions } from 'socket.io';
import { LoggerService } from './logger.service';

const CONTEXT = 'RedisIoAdapter';

/**
 * Socket.IO adapter backed by Redis pub/sub so WebSocket broadcasts
 * fan out across every API instance.
 *
 * Falls back to the in-memory IoAdapter when Redis cannot be reached,
 * so local dev without Redis and single-node deployments still work.
 */
export class RedisIoAdapter extends IoAdapter {
  private adapterConstructor: ReturnType<typeof createAdapter> | null = null;
  private pubClient: Redis | null = null;
  private subClient: Redis | null = null;
  private readonly logger: LoggerService;

  constructor(app: INestApplicationContext) {
    super(app);
    this.logger = app.get(LoggerService);
  }

  async connectToRedis(): Promise<void> {
    const host = process.env['REDIS_HOST'] ?? 'localhost';
    const port = Number(process.env['REDIS_PORT'] ?? 6379);
    const password = process.env['REDIS_PASSWORD'] ?? undefined;

    const pub = new Redis({
      host,
      port,
      password,
      lazyConnect: true,
      enableReadyCheck: false,
      maxRetriesPerRequest: 1,
      retryStrategy: (times) => Math.min(times * 1000, 5000),
    });
    const sub = pub.duplicate();

    try {
      await Promise.all([pub.connect(), sub.connect()]);
    } catch (error) {
      this.logger.warn(
        `Redis pub/sub unavailable — falling back to in-memory adapter: ${
          error instanceof Error ? error.message : String(error)
        }`,
        CONTEXT,
      );
      await Promise.allSettled([pub.quit(), sub.quit()]);
      return;
    }

    this.pubClient = pub;
    this.subClient = sub;
    this.adapterConstructor = createAdapter(pub, sub);
    this.logger.log(
      `Redis pub/sub adapter connected (${host}:${port})`,
      CONTEXT,
    );
  }

  override createIOServer(port: number, options?: ServerOptions): unknown {
    const server = super.createIOServer(port, options) as {
      adapter: (constructor: unknown) => void;
    };
    if (this.adapterConstructor) {
      server.adapter(this.adapterConstructor);
    }
    return server;
  }

  override async close(): Promise<void> {
    await Promise.allSettled([
      this.pubClient?.quit(),
      this.subClient?.quit(),
    ]);
    this.pubClient = null;
    this.subClient = null;
    this.adapterConstructor = null;
  }
}