-module(day10).

-export([solve/1]).

solve(Input) ->
    {part1(Input), io:format("~s~n", [part2(Input)])}.

part1(Input) ->
    History = run(Input, [{1, 1}]),
    Interesting = [20, 60, 100, 140, 180, 220],
    Score = fun(Key) ->
                    Key * element(2, lists:keyfind(Key, 1, History))
            end,
    lists:sum(lists:map(Score, Interesting)).
part2(Input) ->
    History = run(Input, [{1, 1}]),
    render(History, []).

render([{Cycle, X}|Rest], Acc) ->
    Prefix =
        case Cycle rem 40 == 0 of
            true -> "\n";
            false -> []
        end,
    Symbol = 
    if
        X + 2 < Cycle rem 40 -> $.;
        X > Cycle rem 40 -> $.;
        true -> $#
    end,
    render(Rest, [Symbol|Prefix] ++ Acc);
render([], Acc) -> Acc.

run(<<"\n", Rest/binary>>, StateIn) ->
    run(Rest, StateIn);
run(<<"noop", Rest/binary>>, [{Cycle, X}|_]=History) ->
    run(Rest, [{Cycle+1, X} | History]);
run(<<"addx ", RestIn/binary>>, [{Cycle, X}|_]=History) ->
    {Value, RestOut} = parse_int(RestIn),
    run(RestOut, [{Cycle+2, X+Value}, {Cycle+1, X} | History]);
run(<<>>, State) ->
    State.

parse_int(<<$-, Rest/binary>>) ->
    {AbsoluteValue, Binary} = parse_int0(Rest, 0),
    {-1 * AbsoluteValue, Binary};
parse_int(Binary) ->
    parse_int0(Binary, 0).

parse_int0(<<Digit, Rest/binary>>, Acc) when Digit >= $0 andalso Digit =< $9 ->
    parse_int0(Rest, Acc*10 + Digit - $0);
parse_int0(Binary, Acc) when is_binary(Binary) -> {Acc, Binary}.