import java.util.HashMap;
import java.util.Map;
+import java.util.Optional;
public class SumBusinessLogic
{
+ private final Map<String, Long> state;
+
+
public SumBusinessLogic()
{
+ this(new HashMap<>());
}
+ public SumBusinessLogic(Map<String, Long> state)
+ {
+ this.state = state;
+ }
+
+
public synchronized void startSum(String user)
{
+ if (state.containsKey(user))
+ throw new IllegalStateException("Sumation for " + user + " already in progress, state: " + state.get(user));
+
+ state.put(user, 0l);
+ }
+
+ public synchronized Optional<Long> getSum(String user)
+ {
+ return Optional.ofNullable(state.get(user));
+ }
+
+ public synchronized Long endSum(String user)
+ {
+ return null;
}
}