/// <summary>
/// Performs single computation step of finite state machine.
/// </summary>
/// <param name="inputSymbol">Input transition symbol.</param>
/// <returns></returns>
public State <TInSymbol, TOutSymbol> MoveNext(TInSymbol inputSymbol)
{
Transition <TInSymbol, TOutSymbol> t;
_status = AutomataStatus.Running;
// Check if symbol is null
if (inputSymbol is null)
{
SetError();
throw new ArgumentNullException();
}
// Check if input symbol is invalid and proceed accordingly
else if (!InputSymbols().Contains(inputSymbol))
{
return(TryHandleInvalidInput());
}
// Check if transition function exist and proceed accordingly
else if ((t = GetTransition(_currentState, inputSymbol)) is null)
{
return(TryHandleMissingTransition());
}
// Process valid program step
else
{
TryCallExitAction(_currentState, inputSymbol);
TryCallTransitionAction(t, inputSymbol);
_currentState = t.TargetState;
TryCallEntryAction(_currentState, inputSymbol);
return(_currentState);
}
}
/// <summary>
/// Performs attempt to reset DFA. Reset is performed if ResetOnTrapState option is eneabled.
/// </summary>
private void TryEscapeTrapState()
{
if ((_options & FiniteAutomataOptions.ResetOnTrapState) != 0)
{
Reset();
}
else
{
_status = AutomataStatus.Trapped;
}
}
/// <summary>
/// Returns instance of DFA.
/// </summary>
/// <param name="transitions">Collection of DFA transitions.</param>
/// <param name="startState">Reference to start state.</param>
/// <param name="errorState">Reference to error state.</param>
/// <param name="options">DFA options.</param>
public DFA(IEnumerable <Transition <TInSymbol, TOutSymbol> > transitions,
State <TInSymbol, TOutSymbol> startState,
State <TInSymbol, TOutSymbol> errorState,
FiniteAutomataOptions options = FiniteAutomataOptions.None)
{
_transitions = transitions ?? throw new ArgumentNullException();
_startState = startState ?? throw new ArgumentNullException();
_errorState = errorState ?? throw new ArgumentNullException();
_currentState = _startState;
_options = options;
_status = AutomataStatus.Ready;
if (!IsDeterministic())
{
throw new ArgumentOutOfRangeException("Non deterministic transitions passed to DFA class constructor");
}
}
/// <summary>
/// Sets DFA to error state.
/// </summary>
private void SetError()
{
_status = AutomataStatus.Error;
_currentState = _errorState;
}
/// <summary>
/// Resets DFA. Calling this method resets internal program counter (next step will be processed from statring state) and clears internal buffer if ClearBufferOnReset option is eneabled.
/// </summary>
public void Reset()
{
_status = AutomataStatus.Ready;
_currentState = _startState;
}
