% Library Model
% Borrower's View
print(A) :- prin(A),nl.
get_book(Card_ID,Call_ID) :-
	print(["Borrower-> ",Card_ID," wants to check out book: ",Call_ID]),
	check_out(Card_ID,Call_ID),!.
return_book(Call_ID) :-
	print(["Borrower-> Book: ",Call_ID," is returned to library"]),
	check_in(Call_ID),!.
% Clerk's View
check_out(Card_ID,Call_ID) :-
	card_OK(Card_ID),
	call_ID_OK(Call_ID),
	book_OK(Call_ID),
	print(["Clerk-> Book ",Call_ID," checked out by: ",Card_ID]),
	catalog_out(Card_ID,Call_ID),!.
check_out(_,_) :-
	print("Incomplete checkout").
check_in(Call_ID) :-
	print(["Clerk-> Book ",Call_ID," returned to library"]),
	catalog_in(Call_ID),
	shelve(Call_ID),!.
card_OK(Card_ID) :-
	borrower(Card_ID),!.
card_OK(Card_ID) :-
	print(["Clerk-> Invalid card"]),
	fail.
book_OK(Call_ID) :-
	book_status(Call_ID,in,_),
	book_info(Call_ID,circulating,_),!.
book_OK(Call_ID) :-
	book_status(Call_ID,out,_), 
	print(["Clerk-> Requested book is out"]),
	fail,!.
book_OK(Call_ID) :- 
	book_info(Call_ID,reference,_),
	print(["Clerk-> Requested book does not circulate"]),
	fail.
%Librarian's View
shelve(Call_ID) :-
	print(["Librarian-> Book is returned to shelf. Call Number:
",Call_ID]).
% Book Catalog View
catalog_out(Card_ID,Call_ID) :-
	retract(book_status(Call_ID,_,_)),
	assert(book_status(Call_ID,out,Card_ID)),
	print(["Catalog-> Book ",Call_ID," is signed out to: ",Card_ID]).
catalog_in(Call_ID) :-
	retract(book_status(Call_ID,_,_)),
	assert(book_status(Call_ID,in,0)),
	print(["Catalog-> Book ",Call_ID," returned to library."]).
call_ID_OK(Call_ID) :-
	book_info(Call_ID,_,_),!.
call_ID_OK(Call_ID) :-
	print(["Catalog-> Invalid call number"]),
	fail.
% Knowledge-base
% book information
book_info(1111,circulating,"Mystery").
book_info(2222,reference,"English-German dictionary").
% book status
book_status(1111,in,_).
book_status(2222,in,_).
% Borrowers
borrower(joe).
borrower(jane).
% test
test :-
	get_book(joe,1111),
	get_book(jane,2222),
	return_book(1111),
	get_book(jane,1111),
	get_book(joe,3333).