%{ knowledge starts from here
%% the database knows these people
person('Mary Brod').
person('Carl Stuckart').
person('Rudolf Fisher').
person('Amanda Least').
person('Minority Report').

%% when they are born
born('Mary Brod', date(1988, 3, 11)).
born('Carl Stuckart', date(1978, 5, 10)).
born('Rudolf Fisher', date(1978, 5, 10)).
born('Amanda Least', date(1988, 11, 3)).
born('Minority Report', date(1997, 11, 3)).

%% their gender
gender('Mary Brod', female).
gender('Carl Stuckart', male).
gender('Rudolf Fisher', male).
gender('Amanda Least', female).
gender('Minority Report', male).

%% their sex orientation
likesGender('Mary Brod', [female, male]).
likesGender('Carl Stuckart', [female]).
likesGender('Rudolf Fisher', [female]).
likesGender('Amanda Least', [male]).
likesGender('Minority Report', [female]).

%% who knows who (reciprocal)
knows('Mary Brod', 'Amanda Least').
knows('Mary Brod', 'Carl Stuckart').
knows('Mary Brod', 'Minority Report').
knows('Carl Stuckart', 'Mary Brod').
knows('Carl Stuckart', 'Rudolf Fisher').
knows('Carl Stuckart', 'Minority Report').
knows('Rudolf Fisher', 'Carl Stuckart').
knows('Rudolf Fisher', 'Amanda Least').
knows('Rudolf Fisher', 'Minority Report').
knows('Amanda Least', 'Mary Brod').
knows('Amanda Least', 'Rudolf Fisher').
knows('Amanda Least', 'Minority Report').
knows('Minority Report', 'Mary Brod').
knows('Minority Report', 'Carl Stuckart').
knows('Minority Report', 'Rudolf Fisher').
knows('Minority Report', 'Amanda Least').

%% who knows who (unidirectional)
knows('Carl Stuckart', 'Amanda Least').
knows('Rudolf Fisher', 'Mary Brod').

%% people like people (or maybe not); a rather broad term
likes('Mary Brod', 'Carl Stuckart').
likes('Carl Stuckart', 'Mary Brod').
likes('Carl Stuckart', 'Rudolf Fisher').
likes('Rudolf Fisher', 'Amanda Least').
likes('Amanda Least', 'Mary Brod').
likes('Amanda Least', 'Rudolf Fisher').
likes('Mary Brod', 'Minority Report').
likes('Carl Stuckart', 'Minority Report').
likes('Rudolf Fisher', 'Minority Report').
likes('Amanda Least', 'Minority Report').
likes('Minority Report', 'Mary Brod').
likes('Minority Report', 'Carl Stuckart').
likes('Minority Report', 'Rudolf Fisher').
likes('Minority Report', 'Amanda Least').


%% people may be in love (unrequited or not), and even with
%% more than one person.
loves('Mary Brod', 'Amanda Least').
loves('Carl Stuckart', 'Amanda Least').
loves('Rudolf Fisher', 'Mary Brod').
loves('Rudolf Fisher', 'Amanda Least').
loves('Amanda Least', 'Rudolf Fisher').

%} knowledge ends here

%% friendship is reciprocal knowledge
friends(P1, P2) :- knows(P1, P2), knows(P2, P1).

%% get year from gprolog dt struct given by date_time
get_year(Y, dt(Y, _, _, _, _, _)).

%% compute the current age of a person (simplified)
age(Person, AgeYear) :-
	person(Person),
	date_time(Dt),
	get_year(Yc, Dt),
	born(Person, date(Yb, _, _)),
	AgeYear is Yc - Yb.


%% two persons could have sex if they like/love each other and their
%% sex orientations match the gender of the probable partner,
%% and if they are in age for each other or, if underaged,
%% the difference is not more than 5
canHaveSex(P1, P2) :-
	(likes(P1, P2) ; loves(P1, P2)),
	(likes(P2, P1) ; loves(P2, P1)),
	gender(P1, G1), gender(P2, G2),
	likesGender(P1, L1), likesGender(P2, L2),
	member(G1, L2), member(G2, L1),
	age(P1, Age1), age(P2, Age2),
	( (Age1 >= 18, Age2 >= 18) ;
	  ( abs(Age1 - Age2) < 6, (Age1 > 13, Age2 > 13) )
	).