  Copyright ( c ) 2014 - 2017 Yüce Tekol
%
%% Permission is hereby granted, free of charge, to any person obtaining a copy of this software
  and associated documentation files ( the " Software " ) , to deal in the Software without
%% restriction, including without limitation the rights to use, copy, modify, merge, publish,
  distribute , sublicense , and/or sell copies of the Software , and to permit persons to whom the
%% Software is furnished to do so, subject to the following conditions:
%
%% The above copyright notice and this permission notice shall be included in all copies or
  substantial portions of the Software .
%
  THE SOFTWARE IS PROVIDED " AS IS " , WITHOUT WARRANTY OF ANY KIND , EXPRESS OR IMPLIED , INCLUDING
%% BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
%% NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
  DAMAGES OR OTHER LIABILITY , WHETHER IN AN ACTION OF CONTRACT , TORT OR OTHERWISE , ARISING FROM ,
%% OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

-module(pot).

% API
-export([hotp/2, hotp/3]).
-export([totp/1, totp/2]).

-export([valid_token/1, valid_token/2]).
-export([valid_hotp/2, valid_hotp/3]).
-export([valid_totp/2, valid_totp/3]).

% Internal API
-export([time_interval/1]).

% Types
-export_type([token/0, secret/0, interval/0]).

-export_type([valid_token_options/0,
              hotp_options/0,
              totp_options/0,
              valid_hotp_options/0,
              valid_totp_options/0,
              time_interval_options/0]).

%%==============================================================================
%% Types
%%==============================================================================

-type interval() :: integer().
-type secret() :: binary().
-type token() :: binary().

-type token_option() :: {token_length, pos_integer()}.

-type time_interval_option() :: {addwindow, integer()} |
                                {interval_length, pos_integer()} |
                                {timestamp, erlang:timestamp()}.

-type hotp_option() :: token_option() |
                       {digest_method, atom()}.

-type totp_option() :: hotp_option() | time_interval_option().

-type valid_hotp_option() :: hotp_option() |
                             {last, interval()} |
                             return_interval | {return_interval, boolean()} |
                             {trials, pos_integer()}.

-type valid_totp_option() :: totp_option() |
                             {window, non_neg_integer()}.

-type hotp_options() :: [hotp_option() | proplists:property()].
-type totp_options() :: [totp_option() | proplists:property()].

-type valid_token_options() :: [token_option() | proplists:property()].
-type valid_hotp_options() :: [valid_hotp_option() | proplists:property()].
-type valid_totp_options() :: [valid_totp_option() | proplists:property()].

-type time_interval_options() :: [time_interval_option() | proplists:property()].

-type valid_hotp_return() :: boolean() | {true, LastInterval :: interval()}.

%%==============================================================================
%% Token generation
%%==============================================================================

-spec hotp(secret(), interval()) -> token().
hotp(Secret, IntervalsNo) ->
    hotp(Secret, IntervalsNo, []).

-spec hotp(secret(), interval(), hotp_options()) -> token().
hotp(Secret, IntervalsNo, Opts) ->
    DigestMethod = proplists:get_value(digest_method, Opts, sha),
    TokenLength = proplists:get_value(token_length, Opts, 6),
    Key = pot_base32:decode(Secret),
    Msg = <<IntervalsNo:8/big-unsigned-integer-unit:8>>,
    Digest = hmac(DigestMethod, Key, Msg),
    <<Ob:8>> = binary:part(Digest, {byte_size(Digest), -1}),
    O = Ob band 15,
    <<TokenBase0:4/integer-unit:8>> = binary:part(Digest, O, 4),
    TokenBase = TokenBase0 band 16#7fffffff,
    Token0 = TokenBase rem trunc(math:pow(10, TokenLength)),
    Token1 = integer_to_binary(Token0),
    prepend_zeros(Token1, TokenLength - byte_size(Token1)).

-spec totp(secret()) -> token().
totp(Secret) ->
    totp(Secret, []).

-spec totp(secret(), totp_options()) -> token().
totp(Secret, Opts) ->
    IntervalsNo = time_interval(Opts),
    hotp(Secret, IntervalsNo, Opts).

%%==============================================================================
%% Token validation
%%==============================================================================

-spec valid_token(token()) -> boolean().
valid_token(Token) ->
    valid_token(Token, []).

-spec valid_token(token(), valid_token_options()) -> boolean().
valid_token(Token, Opts) when is_binary(Token) ->
    Length = proplists:get_value(token_length, Opts, 6),
    case byte_size(Token) == Length of
        true ->
            lists:all(fun(X) -> X >= $0 andalso X =< $9 end, binary_to_list(Token));
        false ->
            false
    end.

-spec valid_hotp(token(), secret()) -> boolean().
valid_hotp(Token, Secret) ->
    valid_hotp(Token, Secret, []).

-spec valid_hotp(token(), secret(), valid_hotp_options()) -> valid_hotp_return().
valid_hotp(Token, Secret, Opts) ->
    Last = proplists:get_value(last, Opts, 1),
    Trials = proplists:get_value(trials, Opts, 1000),
    TokenLength = proplists:get_value(token_length, Opts, 6),
    case valid_token(Token, [{token_length, TokenLength}]) of
        true ->
            case check_candidate(Token, Secret, Last + 1, Last + Trials, Opts) of
                false ->
                    false;
                LastInterval ->
                    valid_hotp_return(LastInterval, proplists:get_value(return_interval, Opts, false))
            end;
        _ ->
            false
    end.

-spec valid_totp(token(), secret()) -> boolean().
valid_totp(Token, Secret) ->
    valid_totp(Token, Secret, []).

-spec valid_totp(token(), secret(), valid_totp_options()) -> boolean().
valid_totp(Token, Secret, Opts) ->
    case valid_token(Token, Opts) of
        true ->
            IntervalsNo = time_interval(Opts),
            case totp(Secret, Opts) of
                Token ->
                    true;
                _ ->
                    Window = proplists:get_value(window, Opts, 0),
                    case check_candidate(Token, Secret, IntervalsNo - Window, IntervalsNo + Window, Opts) of
                        false ->
                            false;
                        _ ->
                            true
                    end
            end;
        _ ->
            false
    end.

%%==============================================================================
  Internal functions
%%==============================================================================

-spec time_interval(time_interval_options()) -> interval().
time_interval(Opts) ->
  IntervalLength = proplists:get_value(interval_length, Opts, 30),
  AddSeconds = proplists:get_value(addwindow, Opts, 0) * proplists:get_value(interval_length, Opts, 30),
  {MegaSecs, Secs, _} = proplists:get_value(timestamp, Opts, os:timestamp()),
  trunc((MegaSecs * 1000000 + (Secs + AddSeconds)) / IntervalLength).

-spec check_candidate(token(), secret(), interval(), interval(), hotp_options()) ->
    interval() | false.
check_candidate(Token, Secret, Current, Last, Opts) when Current =< Last ->
    case hotp(Secret, Current, Opts) of
        Token ->
            Current;
        _ ->
            check_candidate(Token, Secret, Current + 1, Last, Opts)
    end;
check_candidate(_Token, _Secret, _Current, _Last, _Opts) ->
    false.

-spec prepend_zeros(token(), non_neg_integer()) -> token().
prepend_zeros(Token, N) ->
    Padding = << <<48:8>> || _ <- lists:seq(1, N) >>,
    <<Padding/binary, Token/binary>>.

-spec valid_hotp_return(interval(), boolean()) -> valid_hotp_return().
valid_hotp_return(LastInterval, true = _ReturnInterval) ->
    {true, LastInterval};
valid_hotp_return(_LastInterval, _ReturnInterval) ->
    true.

-ifdef(OTP_RELEASE).
-if(?OTP_RELEASE >= 23).
hmac(DigestMethod, Key, Msg) ->
    crypto:mac(hmac, DigestMethod, Key, Msg).
-else.
hmac(DigestMethod, K, S) ->
    crypto:hmac(DigestMethod, K, S).
-endif.
-else.
hmac(DigestMethod, K, S) ->
    crypto:hmac(DigestMethod, K, S).
-endif.


 Permission is hereby granted, free of charge, to any person obtaining a copy of this software
 restriction, including without limitation the rights to use, copy, modify, merge, publish,
 Software is furnished to do so, subject to the following conditions:

 The above copyright notice and this permission notice shall be included in all copies or

 BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
 OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 API
 Internal API
 Types
==============================================================================
 Types
==============================================================================
==============================================================================
 Token generation
==============================================================================
==============================================================================
 Token validation
==============================================================================
==============================================================================
==============================================================================
  Copyright ( c ) 2014 - 2017 Yüce Tekol
  and associated documentation files ( the " Software " ) , to deal in the Software without
  distribute , sublicense , and/or sell copies of the Software , and to permit persons to whom the
  substantial portions of the Software .
  THE SOFTWARE IS PROVIDED " AS IS " , WITHOUT WARRANTY OF ANY KIND , EXPRESS OR IMPLIED , INCLUDING
  DAMAGES OR OTHER LIABILITY , WHETHER IN AN ACTION OF CONTRACT , TORT OR OTHERWISE , ARISING FROM ,

-module(pot).

-export([hotp/2, hotp/3]).
-export([totp/1, totp/2]).

-export([valid_token/1, valid_token/2]).
-export([valid_hotp/2, valid_hotp/3]).
-export([valid_totp/2, valid_totp/3]).

-export([time_interval/1]).

-export_type([token/0, secret/0, interval/0]).

-export_type([valid_token_options/0,
              hotp_options/0,
              totp_options/0,
              valid_hotp_options/0,
              valid_totp_options/0,
              time_interval_options/0]).


-type interval() :: integer().
-type secret() :: binary().
-type token() :: binary().

-type token_option() :: {token_length, pos_integer()}.

-type time_interval_option() :: {addwindow, integer()} |
                                {interval_length, pos_integer()} |
                                {timestamp, erlang:timestamp()}.

-type hotp_option() :: token_option() |
                       {digest_method, atom()}.

-type totp_option() :: hotp_option() | time_interval_option().

-type valid_hotp_option() :: hotp_option() |
                             {last, interval()} |
                             return_interval | {return_interval, boolean()} |
                             {trials, pos_integer()}.

-type valid_totp_option() :: totp_option() |
                             {window, non_neg_integer()}.

-type hotp_options() :: [hotp_option() | proplists:property()].
-type totp_options() :: [totp_option() | proplists:property()].

-type valid_token_options() :: [token_option() | proplists:property()].
-type valid_hotp_options() :: [valid_hotp_option() | proplists:property()].
-type valid_totp_options() :: [valid_totp_option() | proplists:property()].

-type time_interval_options() :: [time_interval_option() | proplists:property()].

-type valid_hotp_return() :: boolean() | {true, LastInterval :: interval()}.


-spec hotp(secret(), interval()) -> token().
hotp(Secret, IntervalsNo) ->
    hotp(Secret, IntervalsNo, []).

-spec hotp(secret(), interval(), hotp_options()) -> token().
hotp(Secret, IntervalsNo, Opts) ->
    DigestMethod = proplists:get_value(digest_method, Opts, sha),
    TokenLength = proplists:get_value(token_length, Opts, 6),
    Key = pot_base32:decode(Secret),
    Msg = <<IntervalsNo:8/big-unsigned-integer-unit:8>>,
    Digest = hmac(DigestMethod, Key, Msg),
    <<Ob:8>> = binary:part(Digest, {byte_size(Digest), -1}),
    O = Ob band 15,
    <<TokenBase0:4/integer-unit:8>> = binary:part(Digest, O, 4),
    TokenBase = TokenBase0 band 16#7fffffff,
    Token0 = TokenBase rem trunc(math:pow(10, TokenLength)),
    Token1 = integer_to_binary(Token0),
    prepend_zeros(Token1, TokenLength - byte_size(Token1)).

-spec totp(secret()) -> token().
totp(Secret) ->
    totp(Secret, []).

-spec totp(secret(), totp_options()) -> token().
totp(Secret, Opts) ->
    IntervalsNo = time_interval(Opts),
    hotp(Secret, IntervalsNo, Opts).


-spec valid_token(token()) -> boolean().
valid_token(Token) ->
    valid_token(Token, []).

-spec valid_token(token(), valid_token_options()) -> boolean().
valid_token(Token, Opts) when is_binary(Token) ->
    Length = proplists:get_value(token_length, Opts, 6),
    case byte_size(Token) == Length of
        true ->
            lists:all(fun(X) -> X >= $0 andalso X =< $9 end, binary_to_list(Token));
        false ->
            false
    end.

-spec valid_hotp(token(), secret()) -> boolean().
valid_hotp(Token, Secret) ->
    valid_hotp(Token, Secret, []).

-spec valid_hotp(token(), secret(), valid_hotp_options()) -> valid_hotp_return().
valid_hotp(Token, Secret, Opts) ->
    Last = proplists:get_value(last, Opts, 1),
    Trials = proplists:get_value(trials, Opts, 1000),
    TokenLength = proplists:get_value(token_length, Opts, 6),
    case valid_token(Token, [{token_length, TokenLength}]) of
        true ->
            case check_candidate(Token, Secret, Last + 1, Last + Trials, Opts) of
                false ->
                    false;
                LastInterval ->
                    valid_hotp_return(LastInterval, proplists:get_value(return_interval, Opts, false))
            end;
        _ ->
            false
    end.

-spec valid_totp(token(), secret()) -> boolean().
valid_totp(Token, Secret) ->
    valid_totp(Token, Secret, []).

-spec valid_totp(token(), secret(), valid_totp_options()) -> boolean().
valid_totp(Token, Secret, Opts) ->
    case valid_token(Token, Opts) of
        true ->
            IntervalsNo = time_interval(Opts),
            case totp(Secret, Opts) of
                Token ->
                    true;
                _ ->
                    Window = proplists:get_value(window, Opts, 0),
                    case check_candidate(Token, Secret, IntervalsNo - Window, IntervalsNo + Window, Opts) of
                        false ->
                            false;
                        _ ->
                            true
                    end
            end;
        _ ->
            false
    end.

  Internal functions

-spec time_interval(time_interval_options()) -> interval().
time_interval(Opts) ->
  IntervalLength = proplists:get_value(interval_length, Opts, 30),
  AddSeconds = proplists:get_value(addwindow, Opts, 0) * proplists:get_value(interval_length, Opts, 30),
  {MegaSecs, Secs, _} = proplists:get_value(timestamp, Opts, os:timestamp()),
  trunc((MegaSecs * 1000000 + (Secs + AddSeconds)) / IntervalLength).

-spec check_candidate(token(), secret(), interval(), interval(), hotp_options()) ->
    interval() | false.
check_candidate(Token, Secret, Current, Last, Opts) when Current =< Last ->
    case hotp(Secret, Current, Opts) of
        Token ->
            Current;
        _ ->
            check_candidate(Token, Secret, Current + 1, Last, Opts)
    end;
check_candidate(_Token, _Secret, _Current, _Last, _Opts) ->
    false.

-spec prepend_zeros(token(), non_neg_integer()) -> token().
prepend_zeros(Token, N) ->
    Padding = << <<48:8>> || _ <- lists:seq(1, N) >>,
    <<Padding/binary, Token/binary>>.

-spec valid_hotp_return(interval(), boolean()) -> valid_hotp_return().
valid_hotp_return(LastInterval, true = _ReturnInterval) ->
    {true, LastInterval};
valid_hotp_return(_LastInterval, _ReturnInterval) ->
    true.

-ifdef(OTP_RELEASE).
-if(?OTP_RELEASE >= 23).
hmac(DigestMethod, Key, Msg) ->
    crypto:mac(hmac, DigestMethod, Key, Msg).
-else.
hmac(DigestMethod, K, S) ->
    crypto:hmac(DigestMethod, K, S).
-endif.
-else.
hmac(DigestMethod, K, S) ->
    crypto:hmac(DigestMethod, K, S).
-endif.
