/**
 * Cache Service for Award Progress
 *
 * Provides in-memory caching for award progress calculations to avoid
 * expensive database aggregations on every request.
 *
 * Cache TTL: 5 minutes (balances freshness with performance)
 *
 * Usage:
 *   - Check cache before calculating award progress
 *   - Invalidate cache when QSOs are synced/updated
 *   - Automatic expiry after TTL
 */

const awardCache = new Map();
const CACHE_TTL = 5 * 60 * 1000; // 5 minutes

/**
 * Get cached award progress if available and not expired
 * @param {number} userId - User ID
 * @param {string} awardId - Award ID
 * @returns {object|null} Cached progress data or null if not found/expired
 */
export function getCachedAwardProgress(userId, awardId) {
  const key = `${userId}:${awardId}`;
  const cached = awardCache.get(key);

  if (!cached) {
    return null;
  }

  // Check if cache has expired
  const age = Date.now() - cached.timestamp;
  if (age > CACHE_TTL) {
    awardCache.delete(key);
    return null;
  }

  return cached.data;
}

/**
 * Set award progress in cache
 * @param {number} userId - User ID
 * @param {string} awardId - Award ID
 * @param {object} data - Award progress data to cache
 */
export function setCachedAwardProgress(userId, awardId, data) {
  const key = `${userId}:${awardId}`;
  awardCache.set(key, {
    data,
    timestamp: Date.now()
  });
}

/**
 * Invalidate all cached awards for a specific user
 * Call this after syncing or updating QSOs
 * @param {number} userId - User ID
 */
export function invalidateUserCache(userId) {
  const prefix = `${userId}:`;
  let deleted = 0;

  for (const [key] of awardCache) {
    if (key.startsWith(prefix)) {
      awardCache.delete(key);
      deleted++;
    }
  }

  return deleted;
}

/**
 * Clear all cached awards (use sparingly)
 *主要用于测试或紧急情况
 */
export function clearAllCache() {
  const size = awardCache.size;
  awardCache.clear();
  return size;
}

/**
 * Get cache statistics (for monitoring/debugging)
 * @returns {object} Cache stats
 */
export function getCacheStats() {
  const now = Date.now();
  let expired = 0;
  let valid = 0;

  for (const [, value] of awardCache) {
    const age = now - value.timestamp;
    if (age > CACHE_TTL) {
      expired++;
    } else {
      valid++;
    }
  }

  return {
    total: awardCache.size,
    valid,
    expired,
    ttl: CACHE_TTL
  };
}

/**
 * Clean up expired cache entries (maintenance function)
 * Can be called periodically to free memory
 * @returns {number} Number of entries cleaned up
 */
export function cleanupExpiredCache() {
  const now = Date.now();
  let cleaned = 0;

  for (const [key, value] of awardCache) {
    const age = now - value.timestamp;
    if (age > CACHE_TTL) {
      awardCache.delete(key);
      cleaned++;
    }
  }

  return cleaned;
}