Support preprocess SQL with place holders

src/emqx_rule_utils.erl

@@ -16,7 +16,9 @@
 
 %% preprocess and process tempalte string with place holders
 -export([ preproc_tmpl/1
-        , proc_tmpl/2]).
+        , proc_tmpl/2
+        , preproc_sql/1
+        , preproc_sql/2]).
 
 %% type converting
 -export([ str/1
@@ -31,6 +33,10 @@
 
 -type(tmpl_token() :: list({var, fun()} | {str, binary()})).
 
+-type(prepare_statement() :: binary()).
+
+-type(prepare_params() :: fun((binary()) -> list())).
+
 %% preprocess template string with place holders
 -spec(preproc_tmpl(binary()) -> tmpl_token()).
 preproc_tmpl(Str) ->
@@ -54,6 +60,38 @@ proc_tmpl(Tokens, Data) ->
                 ({var, GetVal}) -> GetVal(Data)
             end, Tokens)).
 
+%% preprocess SQL with place holders
+-spec(preproc_sql(Sql::binary()) -> {prepare_statement(), prepare_params()}).
+preproc_sql(Sql) ->
+    preproc_sql(Sql, '?').
+
+-spec(preproc_sql(Sql::binary(), '?' | '$n') -> {prepare_statement(), prepare_params()}).
+preproc_sql(Sql, ReplaceWith) ->
+    case re:run(Sql, ?EX_PLACE_HOLDER, [{capture, all_but_first, binary}, global]) of
+        {match, PlaceHolders} ->
+            NewSql = 
+                case ReplaceWith of
+                    '?' ->
+                        re:replace(Sql, ?EX_PLACE_HOLDER, "?", [{return, binary}, global]);
+                    '$n' ->
+                        Parts = re:split(Sql, ?EX_PLACE_HOLDER, [{return,binary}, trim, group]),
+                        {Sql1, _} = 
+                            lists:foldl(fun([Tkn, _Phld], {Acc, Seq}) ->
+                                            Seq1 = erlang:integer_to_binary(Seq),
+                                            {<<Acc/binary, Tkn/binary, "$", Seq1/binary>>, Seq + 1};
+                                        ([Tkn], {Acc, Seq}) ->
+                                            {<<Acc/binary, Tkn/binary>>, Seq}
+                                        end, {<<>>, 1}, Parts),
+                        binary_to_list(Sql1)
+                end,
+            {NewSql, fun(Data) ->
+                         [maps:get(atom_key(Key), Data, undefined)
+                          || Key <- [var(hd(PH)) || PH <- PlaceHolders]]
+                     end};
+        nomatch ->
+            {Sql, []}
+    end.
+
 atom_key(Key) when is_atom(Key) ->
     Key;
 atom_key(Key) when is_list(Key) ->