+ 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 void addToSum(String user, Integer value)
+ {
+ if (!state.containsKey(user))
+ throw new IllegalStateException("No sumation for " + user + " in progress");
+ if (value == null || value < 1)
+ throw new IllegalArgumentException("Not a positive number: " + value);
+
+ long result = state.get(user) + value;
+ state.put(user, result);
+ }
+
+ public synchronized Long endSum(String user)
+ {
+ if (!state.containsKey(user))
+ throw new IllegalStateException("No sumation for " + user + " in progress");
+
+ return state.remove(user);
+ }
+
+ protected Map<String, Long> getState()
+ {
+ return state;