-module(pinkdf2).
-compile([no_auto_import, nowarn_unused_vars, nowarn_unused_function, nowarn_nomatch]).

-export([get_salt/0, with_config/5, with_defaults/2]).
-export_type([pbkdf2_keys/0, pbkdf2_error/0]).

-if(?OTP_RELEASE >= 27).
-define(MODULEDOC(Str), -moduledoc(Str)).
-define(DOC(Str), -doc(Str)).
-else.
-define(MODULEDOC(Str), -compile([])).
-define(DOC(Str), -compile([])).
-endif.

?MODULEDOC(
    " Password-Based Key Derivation Function 2 in Gleam for Erlang as defined in RFC 2898\n"
    " https://datatracker.ietf.org/doc/html/rfc2898\n"
).

-type pbkdf2_keys() :: {pbkdf2_keys, bitstring(), binary()}.

-type pbkdf2_error() :: {unsupported_algorithm, binary()} |
    key_derived_length_too_long.

-file("src/pinkdf2.gleam", 81).
?DOC(
    " Generates a base64-encoded salt with a minimum size of 64 bytes.\n"
    " It is provided here for convenience, but it is based on the same underlying Erlang function as `crypto.strong_rand_bytes`.\n"
).
-spec get_salt() -> binary().
get_salt() ->
    extern:get_salt().

-file("src/pinkdf2.gleam", 152).
-spec new_prf(gleam@crypto:hash_algorithm()) -> fun((bitstring(), bitstring()) -> bitstring()).
new_prf(Alg) ->
    fun(Key, Data) -> gleam_crypto_ffi:hmac(Data, Alg, Key) end.

-file("src/pinkdf2.gleam", 156).
-spec max_key_length() -> integer().
max_key_length() ->
    _pipe = erlang:'bsl'(1, 32),
    gleam@int:subtract(_pipe, 1).

-file("src/pinkdf2.gleam", 160).
-spec d_len_too_long(integer(), integer()) -> boolean().
d_len_too_long(H_len, D_len) ->
    Max_len = begin
        _pipe = max_key_length(),
        gleam@int:multiply(_pipe, H_len)
    end,
    D_len > Max_len.

-file("src/pinkdf2.gleam", 167).
-spec allowed_algorithm(gleam@crypto:hash_algorithm()) -> {ok,
        gleam@crypto:hash_algorithm()} |
    {error, pbkdf2_error()}.
allowed_algorithm(Alg) ->
    case Alg of
        md5 ->
            {error,
                {unsupported_algorithm,
                    <<"Insecure algorithm. Please select Sha224, Sha256, Sha384, or Sha512."/utf8>>}};

        sha1 ->
            {error,
                {unsupported_algorithm,
                    <<"Insecure algorithm. Please select Sha224, Sha256, Sha384, or Sha512."/utf8>>}};

        _ ->
            {ok, Alg}
    end.

-file("src/pinkdf2.gleam", 120).
-spec compute_block(
    fun((bitstring(), bitstring()) -> bitstring()),
    bitstring(),
    bitstring(),
    integer(),
    integer(),
    integer(),
    bitstring(),
    bitstring()
) -> bitstring().
compute_block(Prf, Password, Salt, Iterations, Block_idx, Count, Prev, Acc) ->
    case Count of
        Count@1 when Count@1 > Iterations ->
            Acc;

        1 ->
            Init = Prf(Password, <<Salt/bitstring, Block_idx:32/integer-big>>),
            compute_block(
                Prf,
                Password,
                Salt,
                Iterations,
                Block_idx,
                2,
                Init,
                Init
            );

        _ ->
            Next = Prf(Password, Prev),
            compute_block(
                Prf,
                Password,
                Salt,
                Iterations,
                Block_idx,
                Count + 1,
                Next,
                crypto:exor(Next, Acc)
            )
    end.

-file("src/pinkdf2.gleam", 94).
-spec compute_key(
    fun((bitstring(), bitstring()) -> bitstring()),
    bitstring(),
    bitstring(),
    integer(),
    integer(),
    integer(),
    bitstring()
) -> bitstring().
compute_key(Prf, Password, Salt, Iterations, D_len, Block_idx, Acc) ->
    case erlang:byte_size(Acc) > D_len of
        true ->
            Bit_len = D_len * 8,
            <<Key:Bit_len/bitstring, _/bitstring>> = case Acc of
                <<_:Bit_len/bitstring, _/bitstring>> -> Acc;
                _assert_fail ->
                    erlang:error(#{gleam_error => let_assert,
                                message => <<"Pattern match failed, no pattern matched the value."/utf8>>,
                                value => _assert_fail,
                                module => <<"pinkdf2"/utf8>>,
                                function => <<"compute_key"/utf8>>,
                                line => 106})
            end,
            Key;

        false ->
            Block = compute_block(
                Prf,
                Password,
                Salt,
                Iterations,
                Block_idx,
                1,
                <<>>,
                <<>>
            ),
            compute_key(
                Prf,
                Password,
                Salt,
                Iterations,
                D_len,
                Block_idx + 1,
                <<Block/bitstring, Acc/bitstring>>
            )
    end.

-file("src/pinkdf2.gleam", 42).
?DOC(
    " Derives a key using the provided configuration.\n"
    "\n"
    " `alg` may be any algorithm from `crypto.HashAlgorithm` except for `Md5` and `Sha1`.\n"
    " 'd_len' is the targeted derived key length in bytes.\n"
    "\n"
    " ## Examples\n"
    "\n"
    " ```gleam\n"
    " import gleam/crypto\n"
    " import pinkdf2\n"
    "\n"
    " let salt = pinkdf2.get_salt()\n"
    " let assert Ok(key) = pinkdf2.with_config(crypto.Sha512, \"password\", salt, 210_000, 32)\n"
    " ```\n"
).
-spec with_config(
    gleam@crypto:hash_algorithm(),
    binary(),
    binary(),
    integer(),
    integer()
) -> {ok, pbkdf2_keys()} | {error, pbkdf2_error()}.
with_config(Alg, Password, Salt, Iterations, D_len) ->
    case allowed_algorithm(Alg) of
        {error, E} ->
            {error, E};

        {ok, _} ->
            Prf = new_prf(Alg),
            case d_len_too_long(
                begin
                    _pipe = Prf(<<Password/binary>>, <<Salt/binary>>),
                    erlang:byte_size(_pipe)
                end,
                D_len
            ) of
                true ->
                    {error, key_derived_length_too_long};

                false ->
                    Raw = compute_key(
                        Prf,
                        <<Password/binary>>,
                        <<Salt/binary>>,
                        Iterations,
                        D_len,
                        1,
                        <<>>
                    ),
                    {ok,
                        {pbkdf2_keys,
                            Raw,
                            gleam_stdlib:bit_array_base64_encode(Raw, false)}}
            end
    end.

-file("src/pinkdf2.gleam", 83).
-spec with_defaults_(
    gleam@crypto:hash_algorithm(),
    bitstring(),
    bitstring(),
    integer()
) -> bitstring().
with_defaults_(Alg, Password, Salt, Iterations) ->
    Prf = new_prf(Alg),
    D_len = begin
        _pipe = Prf(Password, Salt),
        erlang:byte_size(_pipe)
    end,
    compute_key(Prf, Password, Salt, Iterations, D_len, 1, <<>>).

-file("src/pinkdf2.gleam", 19).
?DOC(
    " Derives a key from a password and salt with default settings based on the\n"
    " (OWASP recommendations)[https://cheatsheetseries.owasp.org/cheatsheets/Password_Storage_Cheat_Sheet.html#pbkdf2].\n"
).
-spec with_defaults(binary(), binary()) -> {ok, pbkdf2_keys()} |
    {error, pbkdf2_error()}.
with_defaults(Password, Salt) ->
    Raw = with_defaults_(sha256, <<Password/binary>>, <<Salt/binary>>, 600000),
    {ok, {pbkdf2_keys, Raw, gleam_stdlib:bit_array_base64_encode(Raw, false)}}.