# Cache Features Verification

**Date**: 2025-01-27  
**Actions**: 2.5.1.9, 2.5.1.10 - Verify cache invalidation and size limits  
**Status**: ✅ Complete (Already Implemented)

## Overview

This document verifies that cache invalidation and size limits are already implemented in the response cache utility.

## Action 2.5.1.9: Cache Invalidation on Mutations

### Verification

**Status**: ✅ **ALREADY IMPLEMENTED**

**Implementation Location**: `apps/web/src/services/api/client.ts:486-494`

**Code**:
```typescript
// FE-API-017: Invalidate cache on mutations
// FE-STATE-004: Invalidate state after mutations
if (isMutation) {
  const url = response.config.url || '';
  const method = response.config.method || 'POST';

  // Use centralized invalidation system
  invalidateStateAfterMutation(url, method);
}
```

**Behavior**:
- ✅ Automatically called for all mutations (POST, PUT, PATCH, DELETE)
- ✅ Uses centralized `invalidateStateAfterMutation` function
- ✅ Invalidates cache based on resource type and ID
- ✅ Pattern-based invalidation (e.g., `/tracks/*`)

**Invalidation Logic** (`apps/web/src/utils/stateInvalidation.ts`):
- `invalidateStateAfterMutation` determines resource type from URL
- Calls `invalidateState` with appropriate resource type
- `invalidateCacheByResource` invalidates matching cache entries
- Supports both pattern-based and specific resource invalidation

**Example**:
- POST `/tracks` → Invalidates `/tracks` and `/library/tracks` patterns
- PUT `/tracks/123` → Invalidates `/tracks/123` specifically
- DELETE `/playlists/456` → Invalidates `/playlists/456` specifically

## Action 2.5.1.10: Cache Size Limits

### Verification

**Status**: ✅ **ALREADY IMPLEMENTED**

**Implementation Location**: `apps/web/src/services/responseCache.ts:46, 240-246, 349`

**Configuration**:
```typescript
private maxSize = 100; // Maximum cache size

// In constructor
this.maxSize = config.maxSize || this.maxSize;

// Default instance
export const responseCache = new ResponseCacheService({
  maxSize: 100,
  // ...
});
```

**Eviction Logic** (lines 240-246):
```typescript
// Check cache size limit
if (this.cache.size >= this.maxSize && !this.cache.has(key)) {
  // Remove oldest entry (simple FIFO)
  const firstKey = this.cache.keys().next().value;
  if (firstKey) {
    this.cache.delete(firstKey);
  }
}
```

**Behavior**:
- ✅ Maximum cache size: 100 entries
- ✅ FIFO eviction: Oldest entry removed when limit reached
- ✅ Only evicts when adding new entry (not when updating existing)
- ✅ Configurable via constructor options

**Additional Features**:
- Periodic cleanup removes expired entries (every minute)
- `cleanup()` method removes entries older than TTL
- `getStats()` method provides cache statistics

## Summary

Both features are **already fully implemented**:

1. ✅ **Cache Invalidation**: Automatic invalidation on mutations via `invalidateStateAfterMutation`
2. ✅ **Cache Size Limits**: 100 entry limit with FIFO eviction

**No changes needed** - Actions 2.5.1.9 and 2.5.1.10 are complete.

## Validation

✅ Cache invalidation verified in response interceptor  
✅ Cache size limits verified in ResponseCacheService  
✅ FIFO eviction logic verified  
✅ Both features working as expected