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0dd2082 | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 | const logger = require('../utils/logger');
/**
* In-memory TTL Cache
*
* Interview note: This is a hash-map cache with lazy expiration.
* Keys are hashed intent signatures. Values expire after TTL.
*
* Why not Redis? At this scale (single server, <10K users), in-memory
* is simpler, zero-latency, and zero-dependency. Redis makes sense when
* you need persistence across restarts or shared cache across instances.
*/
class CacheService {
constructor(options = {}) {
this.store = new Map();
this.defaultTTL = options.ttl || 5 * 60 * 1000; // 5 minutes
this.maxSize = options.maxSize || 500;
this.hits = 0;
this.misses = 0;
this.evictions = 0;
// Periodic cleanup every 60s
this._cleanupInterval = setInterval(() => this._cleanup(), 60000);
}
/**
* Generate a deterministic cache key from an intent object.
*/
_makeKey(intent) {
const normalized = {
category: intent.category || 'all',
location: (intent.location || '').toLowerCase().trim(),
budget: intent.budget?.max || '',
features: (intent.features || []).sort().join(','),
sortBy: intent.sortBy || 'relevance',
};
return JSON.stringify(normalized);
}
get(intent) {
const key = this._makeKey(intent);
const entry = this.store.get(key);
if (!entry) {
this.misses++;
return null;
}
if (Date.now() > entry.expiresAt) {
this.store.delete(key);
this.misses++;
return null;
}
this.hits++;
logger.info('Cache HIT', { key: key.substring(0, 60) });
return entry.value;
}
set(intent, value, ttl) {
const key = this._makeKey(intent);
if (this.store.size >= this.maxSize) {
this._evictOldest();
}
this.store.set(key, {
value,
createdAt: Date.now(),
expiresAt: Date.now() + (ttl || this.defaultTTL),
});
}
_evictOldest() {
let oldestKey = null;
let oldestTime = Infinity;
for (const [key, entry] of this.store) {
if (entry.createdAt < oldestTime) {
oldestTime = entry.createdAt;
oldestKey = key;
}
}
if (oldestKey) {
this.store.delete(oldestKey);
this.evictions++;
}
}
_cleanup() {
const now = Date.now();
let cleaned = 0;
for (const [key, entry] of this.store) {
if (now > entry.expiresAt) {
this.store.delete(key);
cleaned++;
}
}
if (cleaned > 0) {
logger.info('Cache cleanup', { cleaned, remaining: this.store.size });
}
}
invalidate(intent) {
const key = this._makeKey(intent);
return this.store.delete(key);
}
clear() {
this.store.clear();
this.hits = 0;
this.misses = 0;
this.evictions = 0;
}
getStats() {
const total = this.hits + this.misses;
return {
size: this.store.size,
maxSize: this.maxSize,
hits: this.hits,
misses: this.misses,
evictions: this.evictions,
hitRate: total > 0 ? ((this.hits / total) * 100).toFixed(1) + '%' : '0%',
ttl: this.defaultTTL,
};
}
destroy() {
clearInterval(this._cleanupInterval);
this.store.clear();
}
}
// Singleton
const cache = new CacheService();
module.exports = cache;
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