cache categories:cid and cid:<cid>:children

these rarely change, no need to go to db for them

src/cache.js

@@ -0,0 +1,56 @@
+'use strict';
+
+var LRU = require('lru-cache');
+var pubsub = require('./pubsub');
+
+var cache = LRU({
+	max: 1000,
+	maxAge: 0,
+});
+cache.hits = 0;
+cache.misses = 0;
+
+const cacheGet = cache.get;
+const cacheDel = cache.del;
+const cacheReset = cache.reset;
+
+cache.get = function (key) {
+	const data = cacheGet.apply(cache, [key]);
+	if (data === undefined) {
+		cache.misses += 1;
+	} else {
+		cache.hits += 1;
+	}
+	return data;
+};
+
+cache.del = function (key) {
+	if (!Array.isArray(key)) {
+		key = [key];
+	}
+	pubsub.publish('local:cache:del', key);
+	key.forEach(key => cacheDel.apply(cache, [key]));
+};
+
+cache.reset = function () {
+	pubsub.publish('local:cache:reset');
+	localReset();
+};
+
+function localReset() {
+	cacheReset.apply(cache);
+	cache.hits = 0;
+	cache.misses = 0;
+}
+
+pubsub.on('local:cache:reset', function () {
+	localReset();
+});
+
+pubsub.on('local:cache:del', function (keys) {
+	if (Array.isArray(keys)) {
+		keys.forEach(key => cacheDel.apply(cache, [key]));
+	}
+});
+
+module.exports = cache;