-module(day4).

-export([solve/1]).

solve(InputData) ->
	Lines = binary:split(InputData, <<$\n>>, [trim_all, global]),
	solver(Lines, {0, 0}).

solver([], Acc) -> Acc;
solver([Entry | Rest], {Part1, Part2}) ->
	Ranges = binary:split(Entry, <<",">>, [trim_all, global]),
	[[F1, F2], [S1, S2]] = lists:map(fun(Range) -> binary:split(Range, <<"-">>, [trim_all, global]) end, Ranges),
	First = {binary_to_integer(F1), binary_to_integer(F2)},
	Second = {binary_to_integer(S1), binary_to_integer(S2)},
	Intersection = range_intersect(First, Second),
	{P1Flag, P2Flag} =
	case Intersection of
		First -> {1, 1};
		Second -> {1, 1};
		SomethingElse ->
			case range_is_empty(Intersection) of
				false -> {0, 1};
				true -> {0, 0}
			end
	end,
	solver(Rest, {Part1+P1Flag, Part2+P2Flag}).

range_is_empty({Bottom, Top}) -> Top < Bottom.
range_intersect({B1, T1}, {B2, T2}) -> {max(B1, B2), min(T1, T2)}.