-module(day1_part2).
-export([main/0]).

% Main entry point
main() ->
    {ok, Content} = file:read_file("input.txt"),
    Lines = string:split(string:trim(Content), "\n", all),
    {List1, List2} = lists:foldl(fun parse_line/2, {[], []}, Lines),
    CountMap = build_count_map(List2),
    SimilarityScore = calculate_similarity_score(List1, CountMap),
    io:format("Result: ~p~n", [SimilarityScore]).

% Parse a single line into two integers and accumulate them into lists
parse_line(Line, {Acc1, Acc2}) ->
    [Str1, Str2] = string:split(string:trim(Line), "   ", all),
    {Num1, _} = string:to_integer(Str1),
    {Num2, _} = string:to_integer(Str2),
    {[Num1 | Acc1], [Num2 | Acc2]}.

% Build a map of counts for elements in List2
build_count_map(List) ->
    lists:foldl(fun(Elem, Acc) ->
        maps:update_with(Elem, fun(Count) -> Count + 1 end, 1, Acc)
    end, #{}, List).

% Calculate the total similarity score
calculate_similarity_score(List1, CountMap) ->
    lists:foldl(fun(Elem, Acc) ->
        Acc + Elem * maps:get(Elem, CountMap, 0)
    end, 0, List1).