-module(totp).

-include_lib("hotp/include/hotp_extra_params.hrl").
-include("totp_extra_params.hrl").

-export(
    [ cons/1
    , cons/2
    ]).

cons(<<Secret/binary>>) ->
    TimeNow = time_now(),
    cons(Secret, #totp_extra_params{time_now = TimeNow}).

cons(<<Secret/binary>>, #totp_extra_params
    { hash_algo = HashAlgo
    , length    = Length
    , time_zero = TimeZero
    , time_now  = TimeNow
    , time_step = TimeStep
    }
) ->
    Time = time_interval(TimeZero, TimeNow, TimeStep),
    HOTPExtraParams = #hotp_extra_params
        { hash_algo = HashAlgo
        , length    = Length
        },
    hotp:cons(Secret, Time, HOTPExtraParams).

time_interval(TimeZero, TimeNow, TimeStep) ->
    trunc((TimeNow - TimeZero) / TimeStep).

time_now() ->
    {MegaSeconds, Seconds, _} = os:timestamp(),
    MegaSeconds * 1000000 + Seconds.

%% ============================================================================
%% Tests from RFC 6238 (https://tools.ietf.org/html/rfc6238#appendix-B)
%% ============================================================================

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

-record(test_case,
    { secret      :: binary()
    , time_step   :: integer()
    , t0          :: integer()
    , time        :: integer()
    , t_in_hex    :: binary()
    , mode        :: hmac:hash_algo()
    , totp_digits :: integer()
    , totp_value  :: integer()
    }).

rfc6238_test_() ->
    lists:map(fun test_case_to_tests/1, test_cases_from_rfc6238()).

test_case_to_tests(#test_case
    { secret      = Secret1
    , time_step   = TimeStep
    , t0          = TimeZero
    , time        = TimeNow
    , t_in_hex    = THexPadded
    , mode        = HashAlgo
    , totp_digits = Length
    , totp_value  = TOTPValue
    }
) ->
    [
        {
            "Time interval",
            ?_assertEqual(
                THexPadded,
                t_to_padded_hex(time_interval(TimeZero, TimeNow, TimeStep))
            )
        },
        {
            "TOTP value",
            ?_assertEqual(
                TOTPValue,
                cons(
                    Secret1,
                    #totp_extra_params
                    { hash_algo = HashAlgo
                    , length    = Length
                    , time_zero = TimeZero
                    , time_now  = TimeNow
                    , time_step = TimeStep
                    }
                )
            )
        }
    ].

-spec t_to_padded_hex(integer()) ->
    binary().
t_to_padded_hex(T) ->
    THex = integer_to_list(T, 16),
    THexPad = lists:duplicate(16 - length(THex), $0),
    list_to_binary([THexPad, THex]).

test_cases_from_rfc6238() ->
    Secret20 = <<"12345678901234567890">>,
    Secret32 = <<"12345678901234567890123456789012">>,
    Secret64 = <<"1234567890123456789012345678901234567890123456789012345678901234">>,
    TimeStep = 30,
    T0       = 0,
    [ #test_case{secret = Secret20, time_step = TimeStep, t0 = T0, time =          59 , t_in_hex = <<"0000000000000001">> , mode = sha    , totp_digits = 8 , totp_value = 94287082}
    , #test_case{secret = Secret32, time_step = TimeStep, t0 = T0, time =          59 , t_in_hex = <<"0000000000000001">> , mode = sha256 , totp_digits = 8 , totp_value = 46119246}
    , #test_case{secret = Secret64, time_step = TimeStep, t0 = T0, time =          59 , t_in_hex = <<"0000000000000001">> , mode = sha512 , totp_digits = 8 , totp_value = 90693936}
    , #test_case{secret = Secret20, time_step = TimeStep, t0 = T0, time =  1111111109 , t_in_hex = <<"00000000023523EC">> , mode = sha    , totp_digits = 8 , totp_value = 07081804}
    , #test_case{secret = Secret32, time_step = TimeStep, t0 = T0, time =  1111111109 , t_in_hex = <<"00000000023523EC">> , mode = sha256 , totp_digits = 8 , totp_value = 68084774}
    , #test_case{secret = Secret64, time_step = TimeStep, t0 = T0, time =  1111111109 , t_in_hex = <<"00000000023523EC">> , mode = sha512 , totp_digits = 8 , totp_value = 25091201}
    , #test_case{secret = Secret20, time_step = TimeStep, t0 = T0, time =  1111111111 , t_in_hex = <<"00000000023523ED">> , mode = sha    , totp_digits = 8 , totp_value = 14050471}
    , #test_case{secret = Secret32, time_step = TimeStep, t0 = T0, time =  1111111111 , t_in_hex = <<"00000000023523ED">> , mode = sha256 , totp_digits = 8 , totp_value = 67062674}
    , #test_case{secret = Secret64, time_step = TimeStep, t0 = T0, time =  1111111111 , t_in_hex = <<"00000000023523ED">> , mode = sha512 , totp_digits = 8 , totp_value = 99943326}
    , #test_case{secret = Secret20, time_step = TimeStep, t0 = T0, time =  1234567890 , t_in_hex = <<"000000000273EF07">> , mode = sha    , totp_digits = 8 , totp_value = 89005924}
    , #test_case{secret = Secret32, time_step = TimeStep, t0 = T0, time =  1234567890 , t_in_hex = <<"000000000273EF07">> , mode = sha256 , totp_digits = 8 , totp_value = 91819424}
    , #test_case{secret = Secret64, time_step = TimeStep, t0 = T0, time =  1234567890 , t_in_hex = <<"000000000273EF07">> , mode = sha512 , totp_digits = 8 , totp_value = 93441116}
    , #test_case{secret = Secret20, time_step = TimeStep, t0 = T0, time =  2000000000 , t_in_hex = <<"0000000003F940AA">> , mode = sha    , totp_digits = 8 , totp_value = 69279037}
    , #test_case{secret = Secret32, time_step = TimeStep, t0 = T0, time =  2000000000 , t_in_hex = <<"0000000003F940AA">> , mode = sha256 , totp_digits = 8 , totp_value = 90698825}
    , #test_case{secret = Secret64, time_step = TimeStep, t0 = T0, time =  2000000000 , t_in_hex = <<"0000000003F940AA">> , mode = sha512 , totp_digits = 8 , totp_value = 38618901}
    , #test_case{secret = Secret20, time_step = TimeStep, t0 = T0, time = 20000000000 , t_in_hex = <<"0000000027BC86AA">> , mode = sha    , totp_digits = 8 , totp_value = 65353130}
    , #test_case{secret = Secret32, time_step = TimeStep, t0 = T0, time = 20000000000 , t_in_hex = <<"0000000027BC86AA">> , mode = sha256 , totp_digits = 8 , totp_value = 77737706}
    , #test_case{secret = Secret64, time_step = TimeStep, t0 = T0, time = 20000000000 , t_in_hex = <<"0000000027BC86AA">> , mode = sha512 , totp_digits = 8 , totp_value = 47863826}
    ].

-endif.