:- use_module(library(lists), [reverse/2]).
:- use_module(contestlib, [write_elements/1]).

snake(Pattern,Cols,Rows) :-
	infinite_snake(Pattern,InfSnake,InfSnake),
	produce_snake(Rows,Cols,InfSnake,Snake),
	coil_it(Snake,odd).

infinite_snake([],S,S).
infinite_snake([A|R],[A|T],S) :-
	infinite_snake(R,T,S).

produce_snake([],_,_,[]).
produce_snake([_|Rows],Cols,InfSnake,[Part|Tail]) :-
	part_of_snake(Cols,InfSnake,NewInfSnake,Part),
	produce_snake(Rows,Cols,NewInfSnake,Tail).

part_of_snake([],RestSnake,RestSnake,[]).
part_of_snake([_|R],[Ring|Rings],RestSnake,[Ring|RestRings]) :-
	part_of_snake(R,Rings,RestSnake,RestRings).

coil_it([],_).
coil_it([Line|Lines],odd) :-
	write_elements(Line), nl,
	coil_it(Lines,even).
coil_it([Line|Lines],even) :-
	reverse(Line,Line1),
        write_elements(Line1), nl,
        coil_it(Lines,odd).