import { Injectable, MessageEvent, OnModuleDestroy } from '@nestjs/common';
import { Observable, Subject, interval, merge, takeUntil } from 'rxjs';
import { map } from 'rxjs/operators';

export type CardRealtimeEventType =
  | 'card.created'
  | 'card.updated'
  | 'card.deleted'
  | 'response.added'
  | 'heartbeat';

export interface CardRealtimePayload {
  event: CardRealtimeEventType;
  card_id?: string;
  data?: unknown;
  at: string;
}

/**
 * Bus SSE in-memory par utilisateur (V1 mono-instance).
 * Rooms = userId (audience carte).
 */
@Injectable()
export class CardsRealtimeService implements OnModuleDestroy {
  private readonly byUser = new Map<string, Set<Subject<CardRealtimePayload>>>();
  private readonly destroy$ = new Subject<void>();

  onModuleDestroy(): void {
    this.destroy$.next();
    this.destroy$.complete();
    for (const set of this.byUser.values()) {
      for (const s of set) s.complete();
    }
    this.byUser.clear();
  }

  /** Flux SSE pour un utilisateur authentifié. */
  streamFor(userId: string): Observable<MessageEvent> {
    const subject = new Subject<CardRealtimePayload>();
    let set = this.byUser.get(userId);
    if (!set) {
      set = new Set();
      this.byUser.set(userId, set);
    }
    set.add(subject);

    const heartbeat$ = interval(25_000).pipe(
      map(
        (): CardRealtimePayload => ({
          event: 'heartbeat',
          at: new Date().toISOString(),
        }),
      ),
    );

    return new Observable<MessageEvent>((observer) => {
      const sub = merge(subject, heartbeat$)
        .pipe(takeUntil(this.destroy$))
        .subscribe({
          next: (payload) =>
            observer.next({
              type: payload.event,
              data: payload,
            } as MessageEvent),
          error: (err) => observer.error(err),
          complete: () => observer.complete(),
        });

      // ping initial
      subject.next({
        event: 'heartbeat',
        at: new Date().toISOString(),
      });

      return () => {
        sub.unsubscribe();
        set!.delete(subject);
        subject.complete();
        if (set!.size === 0) this.byUser.delete(userId);
      };
    });
  }

  emitToUsers(
    userIds: string[],
    event: Exclude<CardRealtimeEventType, 'heartbeat'>,
    cardId: string | undefined,
    data?: unknown,
  ): void {
    const unique = [...new Set(userIds.filter(Boolean))];
    const payload: CardRealtimePayload = {
      event,
      card_id: cardId,
      data,
      at: new Date().toISOString(),
    };
    for (const uid of unique) {
      const set = this.byUser.get(uid);
      if (!set) continue;
      for (const s of set) s.next(payload);
    }
  }

  /** Test / debug : nombre d’abonnés actifs. */
  subscriberCount(userId?: string): number {
    if (userId) return this.byUser.get(userId)?.size ?? 0;
    let n = 0;
    for (const s of this.byUser.values()) n += s.size;
    return n;
  }
}