statemachine.h

/* ScummVM - Graphic Adventure Engine
 *
 * ScummVM is the legal property of its developers, whose names
 * are too numerous to list here. Please refer to the COPYRIGHT
 * file distributed with this source distribution.
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 *
 */

#ifndef MEDIASTATION_STATEMACHINE_H
#define MEDIASTATION_STATEMACHINE_H

#include "common/textconsole.h"
#include "common/queue.h"

namespace MediaStation {

template<typename EventType>
struct StateMachineEvent {
    EventType eventType;
};

// The original had a very generalized finite state machine supported by state matrix, function pointer,
// and other classes, but that was judged needlessly complex to reimplement here. The state transition logic
// is embedded directly into this class.
template<typename StateType, typename EventType>
class StateMachine {
public:
    virtual ~StateMachine() {};

    void queueEvent(EventType event);
    void runIfNotNested();
    void executeForever();

protected:
    StateType _currentState = StateType();
    Common::Queue<EventType> _events;
    bool _handlingEvents = false;
    virtual void executeNextState(EventType eventType) = 0;
    void warnOnInvalidTransition(EventType eventType);
};

template<typename StateType, typename EventType>
void StateMachine<StateType, EventType>::queueEvent(EventType event) {
    _events.push(event);
}

template<typename StateType, typename EventType>
void StateMachine<StateType, EventType>::runIfNotNested() {
    if (!_handlingEvents) {
        _handlingEvents = true;
        executeForever();
        _handlingEvents = false;
    }
}

template<typename StateType, typename EventType>
void StateMachine<StateType, EventType>::executeForever() {
    while (!_events.empty()) {
        EventType eventType = _events.pop();
        executeNextState(eventType);
    }
}

template<typename StateType, typename EventType>
void StateMachine<StateType, EventType>::warnOnInvalidTransition(EventType eventType) {
    warning("Got invalid event %d for state %d", static_cast<uint>(eventType), static_cast<uint>(_currentState));
}

} // End of namespace MediaStation

#endif