%% @copyright 2014 Jean Parpaillon
%% @author Jean Parpaillon <jean.parpaillon@free.fr>
%% @doc
%%
%% @end
-module(dbus_hex).

%%--------------------------------------------------------------------
%% External exports
%%--------------------------------------------------------------------
-export([to/1,
	 from/1]).

%%====================================================================
%% External functions
%%====================================================================

%% @doc Convert a binary (for example the result of erlang:md5/1)
%% to a hex binary.
%% @end
-spec to(binary()) -> binary().
to(Binary) when is_binary(Binary) ->
    bin_to_hex(Binary, <<>>).


%% @doc Convert hex string into an integer.
%% @end
-spec from(binary()) -> integer().
from(<< $\s, Rest/binary >>) ->
    from(Rest);

from(Bin) ->
    case parse(Bin, 0) of
	invalid -> throw(invalid_encoding);
	I when is_integer(I) -> I
    end.

%%%
%%% Priv
%%%

%% N keeps the current acumulated value, each new char encountered when
%% scaning to the right, is added and N is shifted 4 bits to the left
%% Note: "N * 16" could be replaced by "N bsl 4"

parse(<<>>, N) ->
    N;

parse(<< C:8, _Rest/binary >>, N) when C =:= $\s; C =:= $\r; C =:= $\n->
    N;

parse(<<C:8, Rest/binary>>, N) when C >= $0, C =< $9 ->
    M = N * 16 + (C - $0),
    parse(Rest, M);

parse(<<C:8, Rest/binary>>, N) when C >= $a, C =< $f ->
    M = N * 16 + (C - $a + 10),
    parse(Rest, M);

parse(<<C:8, Rest/binary>>, N) when C >= $A, C =< $F ->
    M = N * 16 + (C - $A + 10),
    parse(Rest, M);

parse(_, _) ->
    invalid.

-define(H(X), (hex(X)):16).

bin_to_hex(<<>>, Acc) -> Acc;
bin_to_hex(Bin, Acc) when byte_size(Bin) band 7 =:= 0 ->
    bin_to_hex_(Bin, Acc);
bin_to_hex(<<X:8, Rest/binary>>, Acc) ->
    bin_to_hex(Rest, <<Acc/binary, ?H(X)>>).

bin_to_hex_(<<>>, Acc) -> Acc;
bin_to_hex_(<<A:8, B:8, C:8, D:8, E:8, F:8, G:8, H:8, Rest/binary>>, Acc) ->
    bin_to_hex_(
      Rest,
      <<Acc/binary,
	?H(A), ?H(B), ?H(C), ?H(D), ?H(E), ?H(F), ?H(G), ?H(H)>>).

%%-compile({inline, [hex/1]}).
hex(X) ->
    element(
      X+1, {16#3030, 16#3031, 16#3032, 16#3033, 16#3034, 16#3035, 16#3036,
	    16#3037, 16#3038, 16#3039, 16#3041, 16#3042, 16#3043, 16#3044,
	    16#3045, 16#3046, 16#3130, 16#3131, 16#3132, 16#3133, 16#3134,
	    16#3135, 16#3136, 16#3137, 16#3138, 16#3139, 16#3141, 16#3142,
	    16#3143, 16#3144, 16#3145, 16#3146, 16#3230, 16#3231, 16#3232,
	    16#3233, 16#3234, 16#3235, 16#3236, 16#3237, 16#3238, 16#3239,
	    16#3241, 16#3242, 16#3243, 16#3244, 16#3245, 16#3246, 16#3330,
	    16#3331, 16#3332, 16#3333, 16#3334, 16#3335, 16#3336, 16#3337,
	    16#3338, 16#3339, 16#3341, 16#3342, 16#3343, 16#3344, 16#3345,
	    16#3346, 16#3430, 16#3431, 16#3432, 16#3433, 16#3434, 16#3435,
	    16#3436, 16#3437, 16#3438, 16#3439, 16#3441, 16#3442, 16#3443,
	    16#3444, 16#3445, 16#3446, 16#3530, 16#3531, 16#3532, 16#3533,
	    16#3534, 16#3535, 16#3536, 16#3537, 16#3538, 16#3539, 16#3541,
	    16#3542, 16#3543, 16#3544, 16#3545, 16#3546, 16#3630, 16#3631,
	    16#3632, 16#3633, 16#3634, 16#3635, 16#3636, 16#3637, 16#3638,
	    16#3639, 16#3641, 16#3642, 16#3643, 16#3644, 16#3645, 16#3646,
	    16#3730, 16#3731, 16#3732, 16#3733, 16#3734, 16#3735, 16#3736,
	    16#3737, 16#3738, 16#3739, 16#3741, 16#3742, 16#3743, 16#3744,
	    16#3745, 16#3746, 16#3830, 16#3831, 16#3832, 16#3833, 16#3834,
	    16#3835, 16#3836, 16#3837, 16#3838, 16#3839, 16#3841, 16#3842,
	    16#3843, 16#3844, 16#3845, 16#3846, 16#3930, 16#3931, 16#3932,
	    16#3933, 16#3934, 16#3935, 16#3936, 16#3937, 16#3938, 16#3939,
	    16#3941, 16#3942, 16#3943, 16#3944, 16#3945, 16#3946, 16#4130,
	    16#4131, 16#4132, 16#4133, 16#4134, 16#4135, 16#4136, 16#4137,
	    16#4138, 16#4139, 16#4141, 16#4142, 16#4143, 16#4144, 16#4145,
	    16#4146, 16#4230, 16#4231, 16#4232, 16#4233, 16#4234, 16#4235,
	    16#4236, 16#4237, 16#4238, 16#4239, 16#4241, 16#4242, 16#4243,
	    16#4244, 16#4245, 16#4246, 16#4330, 16#4331, 16#4332, 16#4333,
	    16#4334, 16#4335, 16#4336, 16#4337, 16#4338, 16#4339, 16#4341,
	    16#4342, 16#4343, 16#4344, 16#4345, 16#4346, 16#4430, 16#4431,
	    16#4432, 16#4433, 16#4434, 16#4435, 16#4436, 16#4437, 16#4438,
	    16#4439, 16#4441, 16#4442, 16#4443, 16#4444, 16#4445, 16#4446,
	    16#4530, 16#4531, 16#4532, 16#4533, 16#4534, 16#4535, 16#4536,
	    16#4537, 16#4538, 16#4539, 16#4541, 16#4542, 16#4543, 16#4544,
	    16#4545, 16#4546, 16#4630, 16#4631, 16#4632, 16#4633, 16#4634,
	    16#4635, 16#4636, 16#4637, 16#4638, 16#4639, 16#4641, 16#4642,
	    16#4643, 16#4644, 16#4645, 16#4646}).