-module(day_3).
-export([part_1/0, part_2/0]).
-export([parse/1]).

%% mul\((\d{1,3}),(\d{1,3})\)

part_1() ->
    Filename = filename:absname("./priv/input/3.txt"),
    part_1(Filename).

part_1(Filename) ->
    Input = read_input(Filename),
    Pairs = parse(Input),
    io:format("~p~n", [Pairs]),
    Products = lists:map(fun({A, B}) -> A * B end, Pairs),
    lists:sum(Products).

part_2() ->
    Filename = filename:absname("./priv/input/3.txt"),
    part_2(Filename).

part_2(Filename) ->
    Input = read_input(Filename),
    0.

%% Private Functions

read_input(Filename) ->
    {ok, Binary} = file:read_file(Filename),
    Binary.

parse(Binary) ->
    parse(Binary, []).

parse(<<"mul(",A:1/binary,",",B:1/binary,")",Rest/binary>>, Pairs) -> parse(Rest, [make_pair(A, B) | Pairs]);
parse(<<"mul(",A:1/binary,",",B:2/binary,")",Rest/binary>>, Pairs) -> parse(Rest, [make_pair(A, B) | Pairs]);
parse(<<"mul(",A:1/binary,",",B:3/binary,")",Rest/binary>>, Pairs) -> parse(Rest, [make_pair(A, B) | Pairs]);
parse(<<"mul(",A:2/binary,",",B:1/binary,")",Rest/binary>>, Pairs) -> parse(Rest, [make_pair(A, B) | Pairs]);
parse(<<"mul(",A:2/binary,",",B:2/binary,")",Rest/binary>>, Pairs) -> parse(Rest, [make_pair(A, B) | Pairs]);
parse(<<"mul(",A:2/binary,",",B:3/binary,")",Rest/binary>>, Pairs) -> parse(Rest, [make_pair(A, B) | Pairs]);
parse(<<"mul(",A:3/binary,",",B:1/binary,")",Rest/binary>>, Pairs) -> parse(Rest, [make_pair(A, B) | Pairs]);
parse(<<"mul(",A:3/binary,",",B:2/binary,")",Rest/binary>>, Pairs) -> parse(Rest, [make_pair(A, B) | Pairs]);
parse(<<"mul(",A:3/binary,",",B:3/binary,")",Rest/binary>>, Pairs) -> parse(Rest, [make_pair(A, B) | Pairs]);
parse(<<_:8,Rest/binary>>, Pairs) ->
    parse(Rest, Pairs);
parse(<<_Whatever:8>>, Pairs) ->
    Pairs;
parse(<<"">>, Pairs) ->
    Pairs.

make_pair(A, B) -> {binary_to_integer(A), binary_to_integer(B)}.


%% TESTS

-ifdef(TEST).
-include_lib("eunit/include/eunit.hrl").

part_1_test() ->
    TestFile = test_data(),
    ?assertEqual(161, part_1(TestFile)).

%% part_2_test() ->
%%     TestFile = test_data(),
%%     ?assertEqual(4, part_2(TestFile)).

test_data() ->
    filename:absname("./priv/test_input/3.txt").
-endif.