1//
 2// Copyright (c) 2019 Ted Unangst <tedu@tedunangst.com>
 3//
 4// Permission to use, copy, modify, and distribute this software for any
 5// purpose with or without fee is hereby granted, provided that the above
 6// copyright notice and this permission notice appear in all copies.
 7//
 8// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 9// WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
10// MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
11// ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
12// WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
13// ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
14// OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
15
16package main
17
18import (
19	"reflect"
20	"sync"
21	"time"
22)
23
24type cacheFiller func(key interface{}) (interface{}, bool)
25
26type cacheOptions struct {
27	Filler   interface{}
28	Duration time.Duration
29}
30
31type Cache struct {
32	cache    map[interface{}]interface{}
33	filler   cacheFiller
34	lock     sync.Mutex
35	stale    time.Time
36	duration time.Duration
37}
38
39func cacheNew(options cacheOptions) *Cache {
40	c := new(Cache)
41	c.cache = make(map[interface{}]interface{})
42	fillfn := options.Filler
43	ftype := reflect.TypeOf(fillfn)
44	if ftype.Kind() != reflect.Func {
45		panic("cache filler is not function")
46	}
47	if ftype.NumIn() != 1 || ftype.NumOut() != 2 {
48		panic("cache filler has wrong argument count")
49	}
50	c.filler = func(key interface{}) (interface{}, bool) {
51		vfn := reflect.ValueOf(fillfn)
52		args := []reflect.Value{reflect.ValueOf(key)}
53		rv := vfn.Call(args)
54		return rv[0].Interface(), rv[1].Bool()
55	}
56	if options.Duration != 0 {
57		c.duration = options.Duration
58		c.stale = time.Now().Add(c.duration)
59	}
60	return c
61}
62
63func (cache *Cache) Get(key interface{}, value interface{}) bool {
64	cache.lock.Lock()
65	defer cache.lock.Unlock()
66	if !cache.stale.IsZero() && cache.stale.Before(time.Now()) {
67		cache.stale = time.Now().Add(cache.duration)
68		cache.cache = make(map[interface{}]interface{})
69	}
70	v, ok := cache.cache[key]
71	if !ok {
72		v, ok = cache.filler(key)
73		if ok {
74			cache.cache[key] = v
75		}
76	}
77	if ok {
78		ptr := reflect.ValueOf(v)
79		reflect.ValueOf(value).Elem().Set(ptr)
80	}
81	return ok
82}
83
84func (cache *Cache) Clear(key interface{}) {
85	cache.lock.Lock()
86	defer cache.lock.Unlock()
87	delete(cache.cache, key)
88}
89
90func (cache *Cache) Flush() {
91	cache.lock.Lock()
92	defer cache.lock.Unlock()
93	cache.cache = make(map[interface{}]interface{})
94}