% requirement definition for Meeting Scheduler System (MSS)

meeting_date_OK(Date,Location) :- 
	exclusion_OK(Date),
	preference_OK(Date),
	location_OK(Date,Location),
	equipment_OK(Location),
	print('Date=',Date,' Location=',Location),!.
meeting_date_OK(Date,_) :-
	print('Date=',Date,' not available').

nonpreference_meeting_date_OK(Date,Location) :- 
	exclusion_OK(Date),
	location_OK(Date,Location),
	equipment_OK(Location),
	print('Date=',Date,' Location=',Location),!.
nonpreference_meeting_date_OK(Date,_) :-
	print('Date=',Date,' not available').

exclusion_OK(Date) :- exclusion_list(EL), 
	nonmember(Date,EL).
preference_OK(Date) :- preference_list(PL), 
	memberchk(Date,PL).
location_OK(Date,Location) :- location_preference_list(LP),
	memberchk(Location,LP), location_availability(Location,AV),
	memberchk(Date,AV).
equipment_OK(Location) :- equipment_list(EQ),
	equipment_at_location(Location, EAL),
	subset(EQ,EAL).

exclusion_list(EL) :- findall(X,attendee_exclusion(Y,X),L),
	list_union(L,EL).
preference_list(PL) :- findall(X,attendee_preference(Y,X),L),
	list_intersection(L,PL).
location_preference_list(LP) :- findall(X,attendee_location_preference(Y,X),L),
	list_intersection(L,LP).
equipment_list(QL):- findall(X,attendee_equipment(Y,X),L),
	list_union(L,QL).

% set operations

member(Element,[Element|_]).
member(Element,[_|Rest]) :- member(Element,Rest).

memberchk(Element, [Element|_]) :- !.
memberchk(Element, [_|Rest]) :-
	memberchk(Element, Rest).

nonmember(_,[]).
nonmember(X,[H|T]) :- X /= H,nonmember(X,T).

subset([], _).
subset([Element|Residue], Set) :-
	memberchk(Element, Set), !,
	subset(Residue, Set).

subtract([], _, []).
subtract([Element|Residue], Set, Difference) :-
	memberchk(Element, Set), !,
	subtract(Residue, Set, Difference).
subtract([Element|Residue], Set, [Element|Difference]) :-
	subtract(Residue, Set, Difference).

union([], Set2, Set2).
union([Element|Residue], Set, Union) :-
	memberchk(Element, Set), !,
	union(Residue, Set, Union).
union([Element|Residue], Set, [Element|Union]) :-
	union(Residue, Set, Union).

list_union([First|Rest],Out) :-
	union1(First,[],Rest,Out).
union1(First,Second,[],Out) :-
        union(First,Second,Out).
union1(First,Second,[Next|Rest1],Union) :-
        union(First,Second,Un),
        union1(Next,Un,Rest1,Union).

intersect([],_,[]).
intersect([Element|Residue], Set, Result) :- member(Element, Set),!,
   Result = [Element|Intersection],intersect(Residue,Set,Intersection).
intersect([_|Rest],Set,Intersection) :- intersect(Rest,Set,Intersection).

list_intersection([First|Rest],Out) :-
	intersection1(First,First,Rest,Out).
intersection1(First,Second,[],Out) :-
        intersect(First,Second,Out).
intersection1(First,Second,[Next|Rest1],Intersection) :-
        intersect(First,Second,Inter),
        intersection1(Next,Inter,Rest1,Intersection).

% tests

range_check(Start,End,Location) :-
	Start <= End,
	meeting_date_OK(Start,Location),
	N is Start + 1,
	range_check(N,End,Location).

nonpreference_range_check(Start,End,Location) :-
	Start <= End,
	nonpreference_meeting_date_OK(Start,Location),
	N is Start + 1,
	nonpreference_range_check(N,End,Location).

test_lists(EL,PL,LP,QL) :-
	exclusion_list(EL),
	preference_list(PL),
	location_preference_list(LP),
	equipment_list(QL).

% test database

meeting_initiator(secretary).
attendee_exclusion(jim,[1,5,9]).
attendee_exclusion(joe,[1,6,10]).
attendee_preference(jim,[3,4]).
attendee_preference(joe,[2,3,4]).
attendee_equipment(jim,[projector]).
attendee_equipment(joe,[video]).
attendee_location_preference(jim,[london,paris,berlin]).
attendee_location_preference(joe,[paris]).
location_availability(paris,[1,2,3,4]).
equipment_at_location(paris,[projector,video,telephone]).