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)
22
23type cacheFiller func(key interface{}) (interface{}, bool)
24
25type cacheOptions struct {
26	Filler interface{}
27}
28
29type Cache struct {
30	cache  map[interface{}]interface{}
31	filler cacheFiller
32	lock   sync.Mutex
33}
34
35func cacheNew(options cacheOptions) *Cache {
36	c := new(Cache)
37	c.cache = make(map[interface{}]interface{})
38	fillfn := options.Filler
39	ftype := reflect.TypeOf(fillfn)
40	if ftype.Kind() != reflect.Func {
41		panic("cache filler is not function")
42	}
43	if ftype.NumIn() != 1 || ftype.NumOut() != 2 {
44		panic("cache filler has wrong argument count")
45	}
46	c.filler = func(key interface{}) (interface{}, bool) {
47		vfn := reflect.ValueOf(fillfn)
48		args := []reflect.Value{reflect.ValueOf(key)}
49		rv := vfn.Call(args)
50		return rv[0].Interface(), rv[1].Bool()
51	}
52	return c
53}
54
55func (cache *Cache) Get(key interface{}, value interface{}) bool {
56	cache.lock.Lock()
57	defer cache.lock.Unlock()
58	v, ok := cache.cache[key]
59	if !ok {
60		v, ok = cache.filler(key)
61		if ok {
62			cache.cache[key] = v
63		}
64	}
65	if ok {
66		ptr := reflect.ValueOf(v)
67		reflect.ValueOf(value).Elem().Set(ptr)
68	}
69	return ok
70}
71
72func (cache *Cache) Clear(key interface{}) {
73	cache.lock.Lock()
74	defer cache.lock.Unlock()
75	delete(cache.cache, key)
76}
77
78func (cache *Cache) Flush() {
79	cache.lock.Lock()
80	defer cache.lock.Unlock()
81	cache.cache = make(map[interface{}]interface{})
82}