% plug_on_wire example

assemble1_wire_switch :-               % level 1
        fabricate_plug_on_wire,
        assemble2_wire_switch,
        print('job completed'),!.

fabricate_plug_on_wire :-              % level 2
        consume([wire,plug]),
        use(inject_mold),
        produce(plug_on_wire),
        release(inject_mold),
        print('fabrication complete'),!.

assemble2_wire_switch :-               % level 2   
        use(assembly_area),
        consume([plug_on_wire]),
        produce(wire_switch),
        release(assembly_area),
        print('assembly complete'),!.

% use and release apply to reusable resources
use(What) :-
        reusable(What,available),
        retract(reusable(What,available)),
        assert(reusable(What,in_use)).        
release(What) :-
        reusable(What,in_use),
        retract(reusable(What,in_use)),
        assert(reusable(What,available)).        

% consume and produce apply to consumable resources
consume([]) :- !.
consume([What|Rest]) :-
        consumable(What,Qty),
        Qty > 0,                               % need at least one unit
        retract(consumable(What,Qty)),
        NewQty is Qty - 1,
        assert(consumable(What,NewQty)),
	consume(Rest).
produce(What) :-
        consumable(What,Qty),
        retract(consumable(What,Qty)),
        NewQty is Qty + 1,
        assert(consumable(What,NewQty)).

% resource database (specifies initial conditions on resources)

% reusable resources (facilities, tooling, etc.) -- reusable(What,Status)
reusable(assembly_area, available).
reusable(inject_mold,available).

% consumables (parts, supplies, etc.) -- consumable(What,Qty)
consumable(wire,5).
consumable(plug,4).
consumable(plug_on_wire,0).
consumable(wire_switch,0).

% test
test :- assemble1_wire_switch.

% if your prolog interpreter does not support print, then uncomment next line
% print(X) :- write(X),nl.