import { Injectable } from '@nestjs/common';

export interface Presence {
  userId: string;
  online: boolean;
  lastSeen: number;
}

/**
 * 在线状态管理：开发期使用内存 Map（可分布式广播）。
 * 后续接入 Redis 时替换为 Redis Hash + Pub/Sub 实现，接口保持一致。
 */
@Injectable()
export class PresenceService {
  private readonly map = new Map<string, Presence>();
  /** userId -> Set<socketId>，同一用户多端登录 */
  private readonly sockets = new Map<string, Set<string>>();

  markOnline(userId: string, socketId: string) {
    const set = this.sockets.get(userId) ?? new Set<string>();
    set.add(socketId);
    this.sockets.set(userId, set);
    const p: Presence = { userId, online: true, lastSeen: Date.now() };
    this.map.set(userId, p);
    return p;
  }

  markOffline(userId: string, socketId: string): Presence | null {
    const set = this.sockets.get(userId);
    if (set) {
      set.delete(socketId);
      if (set.size > 0) return this.map.get(userId) ?? null;
      this.sockets.delete(userId);
    }
    const p: Presence = { userId, online: false, lastSeen: Date.now() };
    this.map.set(userId, p);
    return p;
  }

  get(userId: string): Presence {
    return this.map.get(userId) ?? { userId, online: false, lastSeen: 0 };
  }

  getAll(): Presence[] {
    return [...this.map.values()];
  }
}