Public Class TCP
    Public Shared Function TraverseStates(ByVal r As String()) As String
        Dim dict = ParseStates()

        Dim currentState = "CLOSED"
        For Each el As String In r
            If Not dict.ContainsKey(currentState)Then Return "ERROR"
            Dim currentDict = dict(currentState)
            If Not currentDict.ContainsKey(el) Then Return "ERROR"
            currentState = currentDict(el)
        Next

        Return currentState

    End Function



    '                                           init state            event       new_state
    Public Shared Function ParseStates() As Dictionary(Of String, Dictionary(Of String, String))
        Dim parsedStates = states.Split(Environment.NewLine).
            Select(Function(s) ParseStateLine(s)).
            ToList()

        Dim results = New Dictionary(Of String, Dictionary(Of String, String))

        For Each line As Tuple(Of String, String, String) In parsedStates
            If Not results.ContainsKey(line.Item1) Then results.Add(line.Item1, New Dictionary(Of String, String))
            Dim subdict = results(line.Item1)
            subdict(line.Item2) = line.Item3
        Next

        Return results
    End Function

    Public Shared Function ParseStateLine(line As String) As Tuple(Of String, String, String)
        Dim parts = line.Split(":")
        Dim initialState = parts(0).Trim()
        parts = parts(1).Split("->")
        Dim [event] = parts(0).Trim()
        Dim resultingState = parts(1).Trim()

        Return New Tuple(Of String, String, String)(initialState, [event], resultingState)

    End Function

    Class State
        Public InitialState As String
        Public EventName As String
        Public NewState As String
    End Class

    Dim Shared states As String = "CLOSED: APP_PASSIVE_OPEN -> LISTEN
    CLOSED: APP_ACTIVE_OPEN  -> SYN_SENT
    LISTEN: RCV_SYN          -> SYN_RCVD
    LISTEN: APP_SEND         -> SYN_SENT
    LISTEN: APP_CLOSE        -> CLOSED
    SYN_RCVD: APP_CLOSE      -> FIN_WAIT_1
    SYN_RCVD: RCV_ACK        -> ESTABLISHED
    SYN_SENT: RCV_SYN        -> SYN_RCVD
    SYN_SENT: RCV_SYN_ACK    -> ESTABLISHED
    SYN_SENT: APP_CLOSE      -> CLOSED
    ESTABLISHED: APP_CLOSE   -> FIN_WAIT_1
    ESTABLISHED: RCV_FIN     -> CLOSE_WAIT
    FIN_WAIT_1: RCV_FIN      -> CLOSING
    FIN_WAIT_1: RCV_FIN_ACK  -> TIME_WAIT
    FIN_WAIT_1: RCV_ACK      -> FIN_WAIT_2
    CLOSING: RCV_ACK         -> TIME_WAIT
    FIN_WAIT_2: RCV_FIN      -> TIME_WAIT
    TIME_WAIT: APP_TIMEOUT   -> CLOSED
    CLOSE_WAIT: APP_CLOSE    -> LAST_ACK
    LAST_ACK: RCV_ACK        -> CLOSED"
End Class