-module(shr_orddict_util).

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%% TYPES %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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%% EXPORTS %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
-export
(
   [
      compute_next_non_neg_integer_index/1
   ]
).

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%% LOCAL FUNCTIONS %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%% EXPORTED FUNCTIONS %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
-spec compute_next_non_neg_integer_index
   (
      orddict:orddict(non_neg_integer(), any())
   )
   -> non_neg_integer().
compute_next_non_neg_integer_index (Collection) ->
   CollectionSize = orddict:size(Collection),
   Candidates = lists:seq(0, CollectionSize),

   Result =
      lists:foldr
      (
         fun (Candidate, CurrentResult) ->
            case is_integer(CurrentResult) of
               true -> CurrentResult;
               false ->
                  case orddict:is_key(Candidate, Collection) of
                     true -> none;
                     false -> Candidate
                  end
            end
         end,
         none,
         Candidates
      ),

   Result.