using System;
using System.Collections.Generic;
public class TCP
{
   
        private class State
        {
            //TcpFSM state name
            public string Name { get; set; }

            // list of trasitions for this state
            public Dictionary<string, State> Transitions { get; set; } = new Dictionary<string, State>();

            public State GetNextState(string eventName)
            {
              if (Transitions.TryGetValue(eventName, out var result))
              {
                return result;
              }
              return null;
            }
        }



        public static string TraverseStates(string[] events)
        {
            var state = "CLOSED"; // initial state, always
                                  // Your code here!
            var tcpStateMachine = Init();
            var currentState = tcpStateMachine;
            foreach (var e in events)
            {
                currentState = currentState.GetNextState(e);
                if (currentState is null)
                {
                    state = "ERROR";
                    break;
                }
                state = currentState.Name;
            }

            return state;
        }

        private static State Init()
        {
            State initialState = new State()
            {
                Name = "CLOSED"
            };
            State listen = new State()
            {
                Name = "LISTEN",
            };
            State synSent = new State()
            {
                Name = "SYN_SENT",
            };
            State synRcvd = new State()
            {
                Name = "SYN_RCVD",
            };

            State established = new State()
            {
                Name = "ESTABLISHED",
            };

            State closeWait = new State()
            {
                Name = "CLOSE_WAIT"
            };
            State lastAck = new State()
            {
                Name = "LAST_ACK"
            };


            State finWait1 = new State()
            {
                Name = "FIN_WAIT_1"
            };
            State finWait2 = new State()
            {
                Name = "FIN_WAIT_2"
            };

            State timeWait = new State()
            {
                Name = "TIME_WAIT"
            };

            State closing = new State()
            {
                Name = "CLOSING"
            };

            initialState.Transitions["APP_PASSIVE_OPEN"] = listen;
            initialState.Transitions["APP_ACTIVE_OPEN"] = synSent;

            listen.Transitions["RCV_SYN"] = synRcvd;
            listen.Transitions["APP_SEND"] = synSent;
            listen.Transitions["APP_CLOSE"] = initialState;

            synRcvd.Transitions["APP_CLOSE"] = finWait1;
            synRcvd.Transitions["RCV_ACK"] = established;
            
            synSent.Transitions["RCV_SYN"] = synRcvd;
            synSent.Transitions["RCV_SYN_ACK"] = established;
            synSent.Transitions["APP_CLOSE"] = initialState;

            established.Transitions["APP_CLOSE"] = finWait1;
            established.Transitions["RCV_FIN"] = closeWait;

            finWait1.Transitions["RCV_FIN"] = closing;
            finWait1.Transitions["RCV_FIN_ACK"] = timeWait;
            finWait1.Transitions["RCV_ACK"] = finWait2;

            closing.Transitions["RCV_ACK"] = timeWait;
            finWait2.Transitions["RCV_FIN"] = timeWait;

            timeWait.Transitions["APP_TIMEOUT"] = initialState;

            closeWait.Transitions["APP_CLOSE"] = lastAck;

            lastAck.Transitions["RCV_ACK"] = initialState;

            return initialState;
        }
}