import type { Response } from 'express';
import { logger } from '../../utils/logger';

interface SSEClient {
  id: string;
  userId: string;
  res: Response;
  connectedAt: Date;
}

/** In-memory SSE connection manager (single-node) */
class SSEService {
  private clients = new Map<string, SSEClient[]>(); // userId → client connections
  private heartbeatInterval: NodeJS.Timeout | null = null;

  /** Start heartbeat interval (30s keep-alive) */
  startHeartbeat() {
    if (this.heartbeatInterval) return;
    this.heartbeatInterval = setInterval(() => {
      let total = 0;
      for (const [, clients] of this.clients) {
        for (const client of clients) {
          try {
            client.res.write(': heartbeat\n\n');
            total++;
          } catch {
            this.removeClient(client.id);
          }
        }
      }
      if (total > 0) {
        logger.debug(`SSE heartbeat sent to ${total} clients`);
      }
    }, 30_000);
  }

  /** Stop heartbeat */
  stopHeartbeat() {
    if (this.heartbeatInterval) {
      clearInterval(this.heartbeatInterval);
      this.heartbeatInterval = null;
    }
  }

  /** Add an SSE client */
  addClient(userId: string, res: Response): string {
    const id = `${userId}-${Date.now()}-${Math.random().toString(36).slice(2, 8)}`;

    const client: SSEClient = { id, userId, res, connectedAt: new Date() };

    if (!this.clients.has(userId)) {
      this.clients.set(userId, []);
    }
    this.clients.get(userId)!.push(client);

    logger.info(`SSE client connected: ${id} (user: ${userId})`);
    return id;
  }

  /** Remove an SSE client by connection ID */
  removeClient(connectionId: string) {
    for (const [userId, clients] of this.clients) {
      const idx = clients.findIndex((c) => c.id === connectionId);
      if (idx >= 0) {
        clients.splice(idx, 1);
        if (clients.length === 0) {
          this.clients.delete(userId);
        }
        logger.info(`SSE client disconnected: ${connectionId} (user: ${userId})`);
        return userId;
      }
    }
    return null;
  }

  /** Send an event to a specific user (all connections) */
  sendToUser(userId: string, event: string, data: unknown) {
    const clients = this.clients.get(userId);
    if (!clients || clients.length === 0) return false;

    const payload = `event: ${event}\ndata: ${JSON.stringify(data)}\n\n`;

    for (const client of clients) {
      try {
        client.res.write(payload);
      } catch {
        this.removeClient(client.id);
      }
    }
    return true;
  }

  /** Broadcast an event to a list of user IDs */
  sendToUsers(userIds: string[], event: string, data: unknown) {
    for (const userId of userIds) {
      this.sendToUser(userId, event, data);
    }
  }

  /** Check if a user has any active SSE connections */
  isConnected(userId: string): boolean {
    const clients = this.clients.get(userId);
    return !!clients && clients.length > 0;
  }

  /** Get all currently connected user IDs */
  getConnectedUserIds(): string[] {
    return Array.from(this.clients.keys());
  }

  /** Get connection count */
  getConnectionCount(): number {
    let count = 0;
    for (const clients of this.clients.values()) {
      count += clients.length;
    }
    return count;
  }

  /** Get connection count for a specific user */
  getConnectionCountForUser(userId: string): number {
    return this.clients.get(userId)?.length ?? 0;
  }

  /** Close all connections (graceful shutdown) */
  closeAll() {
    this.stopHeartbeat();
    for (const [, clients] of this.clients) {
      for (const client of clients) {
        try { client.res.end(); } catch {}
      }
    }
    this.clients.clear();
    logger.info('SSE: All connections closed');
  }
}

export const sseService = new SSEService();