-module(day7).

-export([solve/1]).

solve(InputData) ->
	Input = binary:split(InputData, <<"\n">>, [trim_all, global]),
	#{sizes := Sizes} = lists:foldl(fun execute/2, #{cwd => [], sizes => #{}}, Input),
	{maps:fold(fun adder/3, 0, Sizes), none}.

adder(_Path, Size, Total) when Size > 100000 -> Total;
adder(_Path, Size, Total) -> Size + Total.

execute(<<"$ cd /">>, State) -> State#{cwd := []};
execute(<<"$ cd ..">>, #{cwd := [_Cwd | Parent]} = State) -> State#{cwd := Parent};
execute(<<"$ cd ", Dir/binary>>, #{cwd := Cwd} = State) -> State#{cwd := [Dir | Cwd]};
execute(<<"$ ls">>, State) -> State;
execute(<<"dir ", Dir/binary>>, #{cwd := Cwd} = State) -> State#{[Dir | Cwd] => 0};
execute(FileCommand ,#{cwd := Cwd, sizes := Sizes} = State) ->
	{Filename, Size} = parse_file_command(FileCommand),
	State#{sizes := add_sizes(Cwd, Size, Sizes)}.

parse_file_command(Command) -> parse_file_command(Command, 0).

parse_file_command(<<$\s, Name/binary>>, Size) -> {Name, Size};
parse_file_command(<<Digit, Rest/binary>>, Size) -> parse_file_command(Rest, (Size*10) + (Digit - $0)).

add_sizes(Path, Size, Sizes) ->
	NewSizes = maps:update_with(Path, fun(OldSize) -> OldSize + Size end, Size, Sizes),
	case Path of
		[] -> NewSizes;
		[_Head| Parent] -> add_sizes(Parent, Size, NewSizes)
	end.