1 files changed, 92 insertions, 0 deletions
diff --git a/src/pow/store.go b/src/pow/store.go
new file mode 100644
index 0000000..0b5e7d0
--- /dev/null
+++ b/src/pow/store.go
@@ -0,0 +1,92 @@
+package pow
+
+import (
+	"errors"
+	"sync"
+	"time"
+
+	"github.com/tilinna/clock"
+)
+
+// ErrSeedSolved is used to indicate a seed has already been solved.
+var ErrSeedSolved = errors.New("seed already solved")
+
+// Store is used to track information related to proof-of-work challenges and
+// solutions.
+type Store interface {
+
+	// MarkSolved will return ErrSeedSolved if the seed was already marked. The
+	// seed will be cleared from the Store once expiresAt is reached.
+	MarkSolved(seed []byte, expiresAt time.Time) error
+
+	Close() error
+}
+
+type inMemStore struct {
+	clock clock.Clock
+
+	m          map[string]time.Time
+	l          sync.Mutex
+	closeCh    chan struct{}
+	spinLoopCh chan struct{} // only used by tests
+}
+
+const inMemStoreGCPeriod = 5 * time.Second
+
+// NewMemoryStore initializes and returns an in-memory Store implementation.
+func NewMemoryStore(clock clock.Clock) Store {
+	s := &inMemStore{
+		clock:      clock,
+		m:          map[string]time.Time{},
+		closeCh:    make(chan struct{}),
+		spinLoopCh: make(chan struct{}, 1),
+	}
+	go s.spin(s.clock.NewTicker(inMemStoreGCPeriod))
+	return s
+}
+
+func (s *inMemStore) spin(ticker *clock.Ticker) {
+	defer ticker.Stop()
+
+	for {
+		select {
+		case <-ticker.C:
+			now := s.clock.Now()
+
+			s.l.Lock()
+			for seed, expiresAt := range s.m {
+				if !now.Before(expiresAt) {
+					delete(s.m, seed)
+				}
+			}
+			s.l.Unlock()
+
+		case <-s.closeCh:
+			return
+		}
+
+		select {
+		case s.spinLoopCh <- struct{}{}:
+		default:
+		}
+	}
+}
+
+func (s *inMemStore) MarkSolved(seed []byte, expiresAt time.Time) error {
+	seedStr := string(seed)
+
+	s.l.Lock()
+	defer s.l.Unlock()
+
+	if _, ok := s.m[seedStr]; ok {
+		return ErrSeedSolved
+	}
+
+	s.m[seedStr] = expiresAt
+	return nil
+}
+
+func (s *inMemStore) Close() error {
+	close(s.closeCh)
+	return nil
+}