architecture specification of traffic_light_controller is

	signal Present_State : State := Highway_Light_Green;
	signal Timed_Out_Long : Boolean := FALSE ;
	signal Start_Timer : Boolean := FALSE ;
	
	begin -- specification
	      --process statement which implements the state machine
	Controller_Process:
	process
	begin
	  case Present_State is

		when Highway_Light_Green =>
		    if Car_On_Farmroad and Timed_Out_Long then
			 Start_Timer <= not Start_Timer;
			 Present_State <= Highway_Light_Yellow;
		    end if ;
	

		when Highway_Light_Yellow =>
		    if Timed_Out_Short then
			 Start_Timer <= not Start_Timer;
			 Present_State <= Farmroad_Light_Green;
		    end if ;


		when Farmroad_Light_Green =>
		    if not Car_On_Farmroad or Timed_Out_Long then
			 Start_Timer <= not Start_Timer;
			 Present_State <= Farmroad_Light_Yellow;
		    end if ;

		when Farmroad_Light_Yellow =>
		    if Timed_Out_Short then
			 Start_Timer <= not Start_Timer;
			 Present_State <= Highway_Light_Green;
		    end if ;
	end case;
	wait on
	  Car_On_Farmroad, Timed_Out_Long, Timed_Out_Short;
	end process;


   -- Conditional signal assignment to set highway light

	Highway_Light_Set:
	 with Present_State select 
	   Highway_Light <=
		Green when Highway_Light_Green,
		Yellow when Highway_Light_Yellow,
		Red when
                  Farmroad_Light_Green | Farmroad_Light_Yellow;

   -- Conditional signal assignment to set farm road light

	Farmroad_Light_Set:
	  with Present_State select
		Farmroad_Light <=
		  Green when Farmroad_Light_Green,
		  Yellow when Farmroad_Light_Yellow,
		  Red when
			Highway_Light_Green | Highway_Light_Yellow;

-- process statement to implement timing mechanism

	Timer_Process:
	process
	begin
	  Timed_Out_Long <= FALSE, TRUE after Long_Time;
	  Timed_Out_Short <= FALSE, TRUE after Short_Time;
	wait on Start_Timer;
	end process;

end specification;