using System;



namespace fsm;



public record class Context : imm.Recorded<Context>
{

}

public record class State<T, CTX> : imm.Recorded<State<T, CTX>>
	where T: State<T, CTX>
	where CTX: Context
{
	virtual public (CTX, T) onEnter(CTX ctx, State<T, CTX> oldState)
	{
		return (ctx, (T)this);
	}

	virtual public (CTX, T) onExit(CTX ctx, State<T, CTX> newState)
	{
		return (ctx, (T)this);
	}
}

public record class FSM<T, CTX, ST> : imm.Recorded<FSM<T, CTX, ST>>
	where T: FSM<T, CTX, ST>
	where CTX: Context
	where ST: State<ST, CTX>
{
	public CTX Context { get; private set; }
	public ST  State   { get; private set; }

	public FSM(CTX context, ST state)
	{
		Context = context;
		State = state;
	}

	public FSM<T, CTX, ST> Transition(ST newState)
	{
		var (newOldCTX, oldState) = State.onExit(Context, newState);

		var (newCTX, storeState) = newState.onEnter(newOldCTX, oldState);

		return this with
		{
			Context = newCTX,
			State = storeState,
		};
	}



}