src/features/discovery/services/featured-creators-cache.service.ts

// Story 7.3: Redis caching service for featured creators
// Implements stale-while-revalidate pattern from Story 7.2

import { redis } from '@/lib/redis';
import type { FeaturedCreator, CachedFeaturedCreators } from '../types/discovery.types';

// Dual-key caching strategy (same pattern as trending)
const CACHE_TTL_PRIMARY = 7200; // 2 hours in seconds
const CACHE_TTL_STALE = 14400; // 4 hours in seconds
const CACHE_KEY = 'featured:creators:v1';
const CACHE_KEY_STALE_SUFFIX = ':stale';

/**
 * Get cached featured creators with stale-while-revalidate pattern
 * 
 * Flow:
 * 1. Check primary cache first (2-hour TTL)
 * 2. If miss, check stale cache (4-hour TTL)
 * 3. If stale hit, return stale data (caller should trigger background refresh)
 * 4. If both miss, return null
 * 
 * Returns: { data, isStale } where isStale indicates if serving from stale cache
 */
export async function getCachedFeaturedCreators(): Promise<{ data: FeaturedCreator[]; isStale: boolean } | null> {
  try {
    // Try primary cache first
    const primaryCached = await redis.get<CachedFeaturedCreators>(CACHE_KEY);
    
    if (primaryCached) {
      return { data: primaryCached.data, isStale: false };
    }

    // Primary cache miss - try stale cache
    const staleCached = await redis.get<CachedFeaturedCreators>(
      `${CACHE_KEY}${CACHE_KEY_STALE_SUFFIX}`
    );
    
    if (staleCached) {
      // Serving stale data - caller should trigger background revalidation
      return { data: staleCached.data, isStale: true };
    }

    // Both caches missed
    return null;
  } catch (error) {
    console.error('Error reading from Redis cache:', error);
    // Gracefully degrade to database on Redis failure
    return null;
  }
}

/**
 * Set cached featured creators with dual-key strategy
 * Writes to both primary (2h TTL) and stale (4h TTL) caches
 */
export async function setCachedFeaturedCreators(data: FeaturedCreator[]): Promise<void> {
  try {
    const now = Date.now();
    const cachedData: CachedFeaturedCreators = {
      data,
      cachedAt: now,
      expiresAt: now + (CACHE_TTL_PRIMARY * 1000),
    };

    // Write to primary cache (2 hour TTL)
    await redis.set(CACHE_KEY, cachedData, {
      ex: CACHE_TTL_PRIMARY,
    });

    // Write to stale cache (4 hour TTL)
    await redis.set(
      `${CACHE_KEY}${CACHE_KEY_STALE_SUFFIX}`,
      cachedData,
      {
        ex: CACHE_TTL_STALE,
      }
    );
  } catch (error) {
    console.error('Error writing to Redis cache:', error);
    // Don't throw - caching is optional, app should work without it
  }
}

/**
 * Invalidate featured creators cache (both primary and stale)
 * Useful for manual cache busting or after data updates
 */
export async function invalidateFeaturedCreatorsCache(): Promise<void> {
  try {
    await redis.del(CACHE_KEY);
    await redis.del(`${CACHE_KEY}${CACHE_KEY_STALE_SUFFIX}`);
  } catch (error) {
    console.error('Error invalidating Redis cache:', error);
  }
}

/**
 * Check if primary cache exists and is fresh
 */
export async function isCacheFresh(): Promise<boolean> {
  try {
    const cached = await redis.get<CachedFeaturedCreators>(CACHE_KEY);
    
    if (!cached) {
      return false;
    }

    const now = Date.now();
    return now <= cached.expiresAt;
  } catch (error) {
    console.error('Error checking cache freshness:', error);
    return false;
  }
}