import { Injectable, Inject } from '@nestjs/common';
import { CACHE_MANAGER } from '@nestjs/cache-manager';
import { Cache } from 'cache-manager';
import { ConfigService } from '@nestjs/config';

@Injectable()
export class CacheService {
  constructor(
    @Inject(CACHE_MANAGER) private cacheManager: Cache,
    private configService: ConfigService,
  ) {}

  async get<T>(key: string): Promise<T | undefined> {
    return this.cacheManager.get<T>(key);
  }

  async set(key: string, value: unknown, ttl?: number): Promise<void> {
    await this.cacheManager.set(key, value, ttl);
  }

  private buildKey(...parts: string[]): string {
    return parts.join(':');
  }

  async getOrFetch<T>(
    keyPrefix: string,
    keyParts: string[],
    fetchFn: () => Promise<T>,
    ttlConfigKey: string,
  ): Promise<{ data: T; fromCache: boolean; cachedAt: string | null }> {
    const key = this.buildKey(keyPrefix, ...keyParts);
    const ttl = this.configService.get<number>(`app.cache.${ttlConfigKey}`, 900);

    const cached = await this.get<T>(key);
    if (cached !== undefined) {
      return { data: cached, fromCache: true, cachedAt: null };
    }

    const data = await fetchFn();
    await this.set(key, data, ttl);

    return { data, fromCache: false, cachedAt: new Date().toISOString() };
  }
}