-module(birdie@internal@diff).
-compile([no_auto_import, nowarn_unused_vars, nowarn_unused_function, nowarn_nomatch]).

-export([line_by_line/2]).
-export_type([diff_line/0, diff_line_kind/0]).

-type diff_line() :: {diff_line, integer(), binary(), diff_line_kind()}.

-type diff_line_kind() :: old | new | shared.

-spec do_map2_index(
    list(IDZ),
    list(IEB),
    fun((IDZ, IEB, integer()) -> IED),
    list(IED),
    integer()
) -> {list(IED), list(IDZ), list(IEB), integer()}.
do_map2_index(One, Other, Fun, Acc, Index) ->
    case {One, Other} of
        {Rest_one, []} ->
            {gleam@list:reverse(Acc), Rest_one, [], Index};

        {[], Rest_other} ->
            {gleam@list:reverse(Acc), [], Rest_other, Index};

        {[One@1 | Rest_one@1], [Other@1 | Rest_other@1]} ->
            _pipe = [Fun(One@1, Other@1, Index) | Acc],
            do_map2_index(Rest_one@1, Rest_other@1, Fun, _pipe, Index + 1)
    end.

-spec map2_index(list(IDR), list(IDT), fun((IDR, IDT, integer()) -> IDV)) -> {list(IDV),
    list(IDR),
    list(IDT),
    integer()}.
map2_index(One, Other, Fun) ->
    do_map2_index(One, Other, Fun, [], 1).

-spec line_by_line(binary(), binary()) -> list(diff_line()).
line_by_line(Old, New) ->
    Old_lines = gleam@string:split(Old, <<"\n"/utf8>>),
    New_lines = gleam@string:split(New, <<"\n"/utf8>>),
    {Diffs, Rest_old, Rest_new, Line_number} = (map2_index(
        Old_lines,
        New_lines,
        fun(Old_line, New_line, Line) ->
            Equal_lines = Old_line =:= New_line,
            Shared_diff_line = {diff_line, Line, Old_line, shared},
            gleam@bool:guard(
                Equal_lines,
                [Shared_diff_line],
                fun() ->
                    Comparison = begin
                        _pipe = gap:compare_strings(New_line, Old_line),
                        _pipe@1 = gap@styling:from_comparison(_pipe),
                        _pipe@2 = gap@styling:highlight(
                            _pipe@1,
                            fun gleam_community@ansi:underline/1,
                            fun gleam_community@ansi:underline/1,
                            fun gap@styling:no_highlight/1
                        ),
                        gap@styling:to_styled_comparison(_pipe@2)
                    end,
                    [{diff_line, Line, erlang:element(3, Comparison), old},
                        {diff_line, Line, erlang:element(2, Comparison), new}]
                end
            )
        end
    )),
    _pipe@3 = gleam@list:concat(Diffs),
    _pipe@4 = gleam@list:append(
        _pipe@3,
        gleam@list:index_map(
            Rest_old,
            fun(Line@1, I) ->
                {diff_line, (Line_number + I) + 1, Line@1, old}
            end
        )
    ),
    gleam@list:append(
        _pipe@4,
        gleam@list:index_map(
            Rest_new,
            fun(Line@2, I@1) ->
                {diff_line, (Line_number + I@1) + 1, Line@2, new}
            end
        )
    ).