import java.util.HashMap;

/* Control unit of Turing machine.
 * 
 */

public class Control {
    private HashMap<String, State> states;             // list of states
    private HashMap<String, Transition> transitions;   // list of transitions
    private State state;                               // current state

    public Control() {
        states      = new HashMap<String, State>();
        transitions = new HashMap<String, Transition>();
    }

    // get and set the current state
    public State getState()           { return state;       }
    public void setState(State state) { this.state = state; }

    // add a state to the control unit
    public void addState(String name, String type) {
        State s = new State(name, type);
        states.put(name, s);
        if (state == null) state = s;   // start state
    }
	
    // find and return state with given name
    private State findState(String name) {
       return states.get(name);
    }
	

    // add a transition
    public void addTransition(String f, String t, String read, String write) {
        State from = findState(f);
        State to = findState(t);
        Transition transition = new Transition(from, to, read, write);
        if (transitions.get(f + Transition.DELIMITER + read) != null)
            throw new RuntimeException("Nondeterministic Turing machine");
        transitions.put(f + Transition.DELIMITER + read, transition);
    }
	
    // Return appropriate transition, null if no matching transition
    public Transition getTransition(String read) {
        Transition t = transitions.get(state.getName() + Transition.DELIMITER + read);
        return t;
    }
	
	
}