-module(ataxia_id).

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%% TYPES %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
-type type() :: binary().

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%% EXPORTS %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
-export_type([type/0]).

%%%% Actual Interface
-export
(
   [
      null/0,
      next/1
   ]
).

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%% LOCAL FUNCTIONS %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
-spec next_char (integer()) -> integer().
next_char ($9) -> $a;
next_char ($z) -> $A;
next_char ($Z) -> $0;
next_char (C) -> (C + 1).

-spec next_id_internal
   (
      list(integer()),
      boolean(),
      list(integer())
   )
   -> list(integer()).
next_id_internal ([], true, Result) -> [$0|Result];
next_id_internal ([], false, Result) -> Result;
next_id_internal ([$Z|Next], true, Result) ->
   next_id_internal(Next, true, [$0|Result]);
next_id_internal ([Char|Next], true, Result) ->
   next_id_internal(Next, false, [next_char(Char)|Result]);
next_id_internal ([Char|Next], false, Result) ->
   next_id_internal(Next, false, [Char|Result]).


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%% EXPORTED FUNCTIONS %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
-spec next (type()) -> type().
next (ID) ->
   list_to_binary
   (
      next_id_internal
      (
         lists:reverse(binary:bin_to_list(ID)),
         true,
         []
      )
   ).

-spec null () -> type().
null () -> <<"">>.