1package spent
 2
 3import (
 4	"sync"
 5	"time"
 6)
 7
 8type Set struct {
 9	mu sync.Mutex
10	m  map[string]time.Time
11}
12
13func New() *Set {
14	return &Set{m: map[string]time.Time{}}
15}
16
17func (s *Set) Spend(key string, until, now time.Time) bool {
18	s.mu.Lock()
19	defer s.mu.Unlock()
20	for k, exp := range s.m {
21		if now.After(exp) {
22			delete(s.m, k)
23		}
24	}
25	if _, used := s.m[key]; used {
26		return false
27	}
28	s.m[key] = until
29	return true
30}
31
32func (s *Set) Len() int {
33	s.mu.Lock()
34	defer s.mu.Unlock()
35	return len(s.m)
36}