Refactor Store into SessionStore; move domain SQL onto User/Question/Answer.

internal/store/sessions.go

@@ -26,13 +26,28 @@ type sessionStopper interface {
 	StopCleanup()
 }
 
-// SessionStore returns the scs store backed by this database.
-func (s *Store) SessionStore() scs.Store {
-	return s.sessionStore
+// SessionStore wraps scs Postgres session persistence and cleanup.
+type SessionStore struct {
+	store   scs.Store
+	stopper sessionStopper
 }
 
-func (s *Store) initSessionStore(cleanupInterval time.Duration) {
-	ps := postgresstore.NewWithCleanupInterval(s.db, cleanupInterval)
-	s.sessionStore = ps
-	s.sessionStopper = ps
+// NewSessionStore starts a postgresstore with the given cleanup interval.
+func NewSessionStore(db *sql.DB, cleanupInterval time.Duration) *SessionStore {
+	ps := postgresstore.NewWithCleanupInterval(db, cleanupInterval)
+	return &SessionStore{store: ps, stopper: ps}
+}
+
+// Store returns the scs.Store implementation.
+func (s *SessionStore) Store() scs.Store {
+	return s.store
+}
+
+// Close stops background session cleanup.
+func (s *SessionStore) Close() {
+	if s == nil || s.stopper == nil {
+		return
+	}
+	s.stopper.StopCleanup()
+	s.stopper = nil
 }