Added ttl

Author: mcollina

index.js

@@ -4,11 +4,15 @@ const kValues = require('./symbol')
 const stringify = require('safe-stable-stringify')
 const LRUCache = require('mnemonist/lru-cache')
 
+const kCacheSize = Symbol('kCacheSize')
+const kTTL = Symbol('kTTL')
+
 class Cache {
   constructor (opts) {
     opts = opts || {}
     this[kValues] = {}
-    this._cacheSize = opts.cacheSize || 1024
+    this[kCacheSize] = opts.cacheSize || 1024
+    this[kTTL] = opts.ttl || 0
   }
 
   define (key, opts, func) {
@@ -28,23 +32,40 @@ class Cache {
       throw new TypeError('serialize must be a function')
     }
 
-    const cacheSize = opts.cacheSize || this._cacheSize
+    const cacheSize = opts.cacheSize || this[kCacheSize]
+    const ttl = opts.ttl || this[kTTL]
 
-    const wrapper = new Wrapper(func, key, serialize, cacheSize)
+    const wrapper = new Wrapper(func, key, serialize, cacheSize, ttl)
 
     this[kValues][key] = wrapper
     this[key] = wrapper.add.bind(wrapper)
   }
 }
 
+let _currentSecond
+
+function currentSecond () {
+  if (_currentSecond !== undefined) {
+    return _currentSecond
+  }
+  _currentSecond = Math.floor(Date.now() / 1000)
+  setTimeout(_clearSecond, 1000).unref()
+  return _currentSecond
+}
+
+function _clearSecond () {
+  _currentSecond = undefined
+}
+
 class Wrapper {
-  constructor (func, key, serialize, cacheSize) {
+  constructor (func, key, serialize, cacheSize, ttl) {
     this.ids = new LRUCache(cacheSize)
     this.error = null
     this.started = false
     this.func = func
     this.key = key
     this.serialize = serialize
+    this.ttl = ttl
   }
 
   add (args) {
@@ -55,8 +76,15 @@ class Wrapper {
     if (!query) {
       query = new Query(id, args, this.func)
       this.ids.set(key, query)
+    } else if (this.ttl > 0) {
+      if (currentSecond() - query.lastAccessed > this.ttl) {
+        // restart
+        query.promise = this.func.call(null, args)
+      }
     }
 
+    query.touch()
+
     return query.promise
   }
 }
@@ -65,6 +93,11 @@ class Query {
   constructor (id, args, func) {
     this.id = id
     this.promise = func(args)
+    this.lastAccessed = null
+  }
+
+  touch () {
+    this.lastAccessed = currentSecond()
   }
 }
 

test.js

@@ -2,6 +2,9 @@
 
 const { test } = require('tap')
 const { Cache } = require('.')
+const { promisify } = require('util')
+
+const sleep = promisify(setTimeout)
 
 const kValues = require('./symbol')
 
@@ -214,3 +217,23 @@ test('cacheSize on constructor', async (t) => {
     { k: 42 }
   ])
 })
+
+test('ttl', async (t) => {
+  t.plan(5)
+
+  const cache = new Cache({
+    ttl: 1 // seconds
+  })
+
+  cache.define('fetchSomething', async (query) => {
+    t.equal(query, 42)
+    return { k: query }
+  })
+
+  t.same(await cache.fetchSomething(42), { k: 42 })
+  t.same(await cache.fetchSomething(42), { k: 42 })
+
+  await sleep(2000)
+
+  t.same(await cache.fetchSomething(42), { k: 42 })
+})