Check for group as argument (expandable)

I want to check whether an argument of a command is fully contained in a pair of curly braces without using any extra packages. For this I define two macros containing { and } with catcode 12, respectively. Then I turn the input into a string using \detokenize and compare the first and the last token I find.

The macro should either ignore leading and trailing spaces around the group or treat them as false (ignoring has higher priority -- two versions one ignoring one not would be best).

So the following should be outputted for the ignoring version:

\MyIfGroup{{}}{true}{false}   -> true\MyIfGroup{ {}}{true}{false}  -> true\MyIfGroup{{} }{true}{false}  -> true\MyIfGroup{ {} }{true}{false} -> true\MyIfGroup{ }{true}{false}    -> false\MyIfGroup{a}{true}{false}    -> false\MyIfGroup{{}a}{true}{false}  -> false

The not ignoring version should return true only for the first of the above cases. Anything inside the inner pair of braces (even nested braces) shouldn't make a difference (except for unmatched braces). The case \MyIfGroup{{}{}} is considered an edge case (by myself) and doesn't have to be detected correctly -- it would be nice though.

The following code is an ignoring version which detects everything except {}{} (that's ok) and if there is space after the pair of braces, in which case it throws a "Runaway argument"-error.

\documentclass[]{article}\makeatletter\newcommand\MyIfEmptyTF[1]  {%    \if\relax\detokenize{#1}\relax      \expandafter\@firstoftwo    \else      \expandafter\@secondoftwo    \fi  }\newcommand\MyIfGroupTF[1]  {%    \MyIfEmptyTF{#1}{\@secondoftwo}      {%        \expandafter\MyIfGroup@preopen\expandafter{\detokenize{#1}}%      }%  }\newcommand\MyIfGroup@preopen[1]  {%    \MyIfDetSpaceTF{#1}      {\@secondoftwo}      {\MyIfGroup@open#1\end@MyIfGroup}%  }\long\def\MyIfGroup@open#1#2\end@MyIfGroup%  {%    \if\Mylbraceother#1%      \expandafter\@firstoftwo    \else      \expandafter\@secondoftwo    \fi    {\MyIfGroup@close#2\end@MyIfGroup}    {\@secondoftwo}%  }\long\def\MyIfGroup@close#1#2\end@MyIfGroup  {%    \MyIfEmptyTF{#2}      {%        \MyIfDetSpaceTF{#1}          {\@secondoftwo}          {%            \if\Myrbraceother#1%              \expandafter\@firstoftwo            \else              \expandafter\@secondoftwo            \fi          }%      }      {\MyIfGroup@close#2\end@MyIfGroup}  }\newcommand\MyIfDetSpaceTF[1]  {%    \if#1\detokenize{ }%      \expandafter\@firstoftwo    \else      \expandafter\@secondoftwo    \fi  }\bgroup\catcode`\{=12\catcode`\}=12\catcode`\(=1\catcode`\)=2\gdef\Mylbraceother({)\gdef\Myrbraceother(})\egroup\makeatother\begin{document}Works: \MyIfGroupTF{{i}}{true}{false}.Works: \MyIfGroupTF{ {}}{true}{false}.Works: \MyIfGroupTF{ }{true}{false}.Works: \MyIfGroupTF{ a }{true}{false}.Works: \MyIfGroupTF{a}{true}{false}.Wrong: \MyIfGroupTF{{}{}}{true}{false}.%Doesn't compile (fails in @close): \MyIfGroupTF{{} }{true}{false}.\end{document}