/**
 * Center-scoped admin cache.
 *
 * Holds the at-most-one admin user (email + userId) fetched from Center.
 * Used to decide who to deliver triage messages to as a silent observer
 * (wake=false), regardless of on-duty / mention status.
 *
 * Refresh policy (per spec, 2026-05-22):
 *   • TTL = 1 day. Center admin changes are rare; agents tolerate a
 *     day's stale cache without surprises
 *   • on first lookup the cache lazy-fetches
 *   • cli `admin refresh` forces an out-of-band refresh without waiting
 *     for TTL expiry
 *
 * Failure mode: a Center fetch error is treated identically to "no
 * admin" — guild keeps operating without an observer. The cache holds
 * the failed-fetch decision for the same TTL so we don't hammer Center.
 */

import { Injectable, Logger } from '@nestjs/common';
import { fetchAdminEmail } from './center-auth.js';

const ADMIN_CACHE_TTL_MS = 24 * 60 * 60 * 1000;

export interface CachedAdmin {
  email: string;
  userId: string;
}

@Injectable()
export class AdminCacheService {
  private readonly logger = new Logger(AdminCacheService.name);
  private cached: CachedAdmin | null = null;
  private cachedAt = 0;
  private inflight: Promise<CachedAdmin | null> | null = null;

  /**
   * Return the cached admin, fetching from Center if the cache is empty
   * or older than the TTL. Returns null if no admin is set.
   *
   * `force=true` bypasses the cache and refreshes immediately — used by
   * the cli refresh command.
   */
  async get(force = false): Promise<CachedAdmin | null> {
    const fresh = Date.now() - this.cachedAt < ADMIN_CACHE_TTL_MS;
    if (!force && this.cachedAt > 0 && fresh) {
      return this.cached;
    }
    if (this.inflight) return this.inflight;

    this.inflight = (async () => {
      try {
        const result = await fetchAdminEmail();
        this.cached = result;
        this.cachedAt = Date.now();
        this.logger.log(
          `admin cache refreshed: ${result ? `${result.email} (${result.userId})` : 'no admin set'}`,
        );
        return result;
      } finally {
        this.inflight = null;
      }
    })();
    return this.inflight;
  }

  /** Snapshot of the cached admin (no fetch). Returns null if not yet
   *  populated. Used by the hot delivery path which doesn't want to
   *  block on a Center round-trip. */
  snapshot(): CachedAdmin | null {
    return this.cached;
  }
}