#ifndef GHOST_ABSTRACT_H
#define GHOST_ABSTRACT_H

template <class A, class B>
class Map {
public:
	Link<A, Map<A, B> > a;
	Link<B, Map<A, B> > b;

	enum { none, b_out, b_out_a_in,
	             a_out, a_out_b_in } state;

	Map(A& a, B& b) : a(a, this, &Map::push_a, &Map::pull_a), b(b, this, &Map::push_b, &Map::pull_b), state(none) {}

	virtual void a_to_b() = 0;

	virtual void b_to_a() = 0;

	void _a_to_b() {
		a_to_b();
		state = b_out;
		b.push();
		a.pull();
	}

	void _b_to_a() {
		b_to_a();
		state = a_out;
		a.push();
		b.pull();
	}

	// TODO - I could make this class a template over M for efficiency?
	// Doubtful that it would help any - can try later.

	void push_a() {
		assert(state == none || state == b_out);
		if (state == none) _a_to_b();
		else state = b_out_a_in;
	}

	void push_b() {
		assert(state == none || state == a_out);
		if (state == none) _b_to_a();
		else state = a_out_b_in;
	}

	void pull_a() {
		assert(state == a_out || state == a_out_b_in);
		if (state == a_out) state = none;
		else _b_to_a();
	}

	void pull_b() {
		assert(state == b_out || state == b_out_a_in);
		if (state == b_out) state = none;
		else _a_to_b();
	}
};

#endif