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* Stale-While-Revalidate (SWR) Cache
*
* Implements the stale-while-revalidate caching strategy:
* 1. Fresh data (<staleTime): Return cached data immediately
* 2. Stale data (<maxStaleTime): Return cached data, revalidate in background
* 3. Expired data (>maxStaleTime): Fetch fresh data
*
* Benefits:
* - Fast responses for users (serve from cache)
* - Fresh data (background revalidation)
* - Resilience (serve stale on fetch failure)
*/
import { cacheService } from './cache-service';
import { logger } from '@/lib/logging';
// ============================================================================
// Types
// ============================================================================
interface SWRCacheEntry<T> {
data: T;
timestamp: number;
isRevalidating?: boolean;
}
interface SWROptions<T> {
/** Time in seconds data is considered fresh */
staleTime: number;
/** Maximum time in seconds stale data can be served */
maxStaleTime: number;
/** Function to fetch fresh data */
fetcher: () => Promise<T>;
/** Optional callback on successful revalidation */
onSuccess?: (data: T) => void;
/** Optional callback on revalidation error */
onError?: (error: Error) => void;
}
interface SWRResult<T> {
data: T | null;
isStale: boolean;
isRevalidating: boolean;
}
// ============================================================================
// SWR Cache Implementation
// ============================================================================
/**
* Get data with stale-while-revalidate strategy
*
* @example
* ```typescript
* const products = await getWithSWR('products:featured', {
* staleTime: 60, // Fresh for 1 minute
* maxStaleTime: 3600, // Serve stale up to 1 hour
* fetcher: () => fetchFeaturedProducts(),
* });
* ```
*/
export async function getWithSWR<T>(
key: string,
options: SWROptions<T>
): Promise<SWRResult<T>> {
const { staleTime, maxStaleTime, fetcher, onSuccess, onError } = options;
const now = Date.now();
// Try to get from cache
const cached = cacheService.get<SWRCacheEntry<T>>(key);
if (cached) {
const ageSeconds = (now - cached.timestamp) / 1000;
// Data is fresh - return immediately
if (ageSeconds < staleTime) {
return {
data: cached.data,
isStale: false,
isRevalidating: false,
};
}
// Data is stale but within max stale time
if (ageSeconds < maxStaleTime) {
// Return stale data immediately
const result: SWRResult<T> = {
data: cached.data,
isStale: true,
isRevalidating: !cached.isRevalidating,
};
// Revalidate in background if not already revalidating
if (!cached.isRevalidating) {
// Mark as revalidating to prevent duplicate fetches
cacheService.set(key, { ...cached, isRevalidating: true });
// Start background revalidation
revalidateInBackground(key, fetcher, maxStaleTime, onSuccess, onError);
}
return result;
}
// Data is too old - need fresh data
logger.debug(`Cache expired for ${key}`, { category: 'PERFORMANCE', ageSeconds, maxStaleTime });
}
// No cache or expired - fetch fresh data
try {
const freshData = await fetcher();
// Cache the fresh data
const entry: SWRCacheEntry<T> = {
data: freshData,
timestamp: now,
isRevalidating: false,
};
cacheService.set(key, entry, maxStaleTime);
onSuccess?.(freshData);
return {
data: freshData,
isStale: false,
isRevalidating: false,
};
} catch (error) {
// If fetch fails and we have stale data, return it
if (cached) {
logger.warn(`Fetch failed for ${key}, returning stale data`, {
category: 'PERFORMANCE',
error: (error as Error).message,
});
onError?.(error as Error);
return {
data: cached.data,
isStale: true,
isRevalidating: false,
};
}
// No stale data to fall back to
onError?.(error as Error);
throw error;
}
}
/**
* Background revalidation helper
*/
async function revalidateInBackground<T>(
key: string,
fetcher: () => Promise<T>,
ttl: number,
onSuccess?: (data: T) => void,
onError?: (error: Error) => void
): Promise<void> {
try {
const freshData = await fetcher();
const entry: SWRCacheEntry<T> = {
data: freshData,
timestamp: Date.now(),
isRevalidating: false,
};
cacheService.set(key, entry, ttl);
logger.debug(`Background revalidation complete for ${key}`, { category: 'PERFORMANCE' });
onSuccess?.(freshData);
} catch (error) {
// Clear revalidating flag on error
const cached = cacheService.get<SWRCacheEntry<T>>(key);
if (cached) {
cacheService.set(key, { ...cached, isRevalidating: false });
}
logger.warn(`Background revalidation failed for ${key}`, {
category: 'PERFORMANCE',
error: (error as Error).message,
});
onError?.(error as Error);
}
}
// ============================================================================
// SWR Cache Presets
// ============================================================================
/**
* Preset configurations for common use cases
*/
export const SWRPresets = {
/** For frequently updated data (e.g., product prices, stock) */
frequent: {
staleTime: 30, // Fresh for 30 seconds
maxStaleTime: 300, // Serve stale up to 5 minutes
},
/** For moderately updated data (e.g., product lists, categories) */
moderate: {
staleTime: 300, // Fresh for 5 minutes
maxStaleTime: 1800, // Serve stale up to 30 minutes
},
/** For rarely updated data (e.g., hero content, testimonials) */
static: {
staleTime: 1800, // Fresh for 30 minutes
maxStaleTime: 7200, // Serve stale up to 2 hours
},
/** For user-specific data (e.g., cart, wishlist) */
user: {
staleTime: 10, // Fresh for 10 seconds
maxStaleTime: 60, // Serve stale up to 1 minute
},
} as const;
// ============================================================================
// Convenience Functions
// ============================================================================
/**
* Simple SWR wrapper with moderate preset
*/
export async function swrFetch<T>(
key: string,
fetcher: () => Promise<T>
): Promise<T | null> {
const result = await getWithSWR(key, {
...SWRPresets.moderate,
fetcher,
});
return result.data;
}
/**
* SWR fetch with custom stale times
*/
export async function swrFetchWithTimes<T>(
key: string,
fetcher: () => Promise<T>,
staleTime: number,
maxStaleTime: number
): Promise<T | null> {
const result = await getWithSWR(key, {
staleTime,
maxStaleTime,
fetcher,
});
return result.data;
}
/**
* Invalidate an SWR cache entry and optionally trigger immediate revalidation
*/
export async function invalidateSWR<T>(
key: string,
fetcher?: () => Promise<T>
): Promise<void> {
cacheService.delete(key);
// Optionally warm the cache with fresh data
if (fetcher) {
try {
const freshData = await fetcher();
const entry: SWRCacheEntry<T> = {
data: freshData,
timestamp: Date.now(),
isRevalidating: false,
};
cacheService.set(key, entry);
} catch (error) {
logger.warn(`Failed to warm cache for ${key}`, {
category: 'PERFORMANCE',
error: (error as Error).message,
});
}
}
}
/**
* Prefetch data into SWR cache (cache warming)
*/
export async function prefetchSWR<T>(
key: string,
fetcher: () => Promise<T>,
ttl: number = SWRPresets.moderate.maxStaleTime
): Promise<void> {
try {
const data = await fetcher();
const entry: SWRCacheEntry<T> = {
data,
timestamp: Date.now(),
isRevalidating: false,
};
cacheService.set(key, entry, ttl);
logger.debug(`Prefetched ${key}`, { category: 'PERFORMANCE' });
} catch (error) {
logger.warn(`Prefetch failed for ${key}`, {
category: 'PERFORMANCE',
error: (error as Error).message,
});
}
}
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