glanoid

-module(glanoid).
-compile([no_auto_import, nowarn_unused_vars, nowarn_unused_function, nowarn_nomatch]).

-export([make_generator/1]).

-spec fix4(fun((fun((FNB, FNC, FND, FNE) -> FNK), FNB, FNC, FND, FNE) -> FNK)) -> fun((FNB, FNC, FND, FNE) -> FNK).
fix4(F) ->
    fun(A, B, C, D) -> F(fix4(F), A, B, C, D) end.

-spec do_bit_size(integer(), integer()) -> integer().
do_bit_size(N, Acc) ->
    case N of
        0 ->
            Acc;

        _ ->
            do_bit_size(erlang:'bsr'(N, 1), Acc + 1)
    end.

-spec bit_size(integer()) -> integer().
bit_size(N) ->
    do_bit_size(N, 0).

-spec make_generator(binary()) -> {ok, fun((integer()) -> binary())} |
    {error, nil}.
make_generator(Alphabet) ->
    gleam@bool:guard(
        gleam@string:length(Alphabet) =:= 0,
        {error, nil},
        fun() ->
            Bit_mask = begin
                _pipe = Alphabet,
                _pipe@1 = gleam@string:length(_pipe),
                _pipe@2 = gleam@int:subtract(_pipe@1, 1),
                _pipe@3 = bit_size(_pipe@2),
                _pipe@4 = erlang:'bsl'(2, _pipe@3),
                gleam@int:subtract(_pipe@4, 1)
            end,
            To_alphabet@1 = fix4(
                fun(To_alphabet, Bits, Size, Alphabet@1, Acc) ->
                    case {gleam@string:length(Acc) =:= Size, Bits} of
                        {true, _} ->
                            Acc;

                        {false, <<X:8, Rest/bitstring>>} ->
                            Index = erlang:'band'(X, Bit_mask),
                            Letter = gleam@string:slice(Alphabet@1, Index, 1),
                            case Letter of
                                <<""/utf8>> ->
                                    To_alphabet(Rest, Size, Alphabet@1, Acc);

                                _ ->
                                    To_alphabet(
                                        Rest,
                                        Size,
                                        Alphabet@1,
                                        <<Acc/binary, Letter/binary>>
                                    )
                            end;

                        {false, <<>>} ->
                            To_alphabet(
                                crypto:strong_rand_bytes(Size * 2),
                                Size,
                                Alphabet@1,
                                Acc
                            );

                        {_, _} ->
                            erlang:error(#{gleam_error => panic,
                                    message => <<"panic expression evaluated"/utf8>>,
                                    module => <<"glanoid"/utf8>>,
                                    function => <<"make_generator"/utf8>>,
                                    line => 48})
                    end
                end
            ),
            {ok, fun(Size@1) -> _pipe@5 = crypto:strong_rand_bytes(Size@1 * 2),
                    To_alphabet@1(_pipe@5, Size@1, Alphabet, <<""/utf8>>) end}
        end
    ).