Nested environment: same counter value before and after

Question

I'd like to generate "labels" to use at the beginning and at the end of an environment. Unfortunately the value of the counter is modified between the start and the end of the environment:

Any idea how I could avoid that issue?

\documentclass[a4paper,12pt]{article}

\newcounter{nextMarkId}

\newenvironment{subproof}{\thenextMarkId\stepcounter{nextMarkId}}{\thenextMarkId}

\begin{document}

\begin{subproof}
  \begin{subproof}
    blabla
  \end{subproof}
\end{subproof}

I'd like to have: 0 1 blabla 1 0

\end{document}

EDIT

The proposed answer does not work because I want the label of each environment to be unique:

\documentclass[a4paper,12pt]{article}

\newcounter{nextMarkId}

\newenvironment{subproof}
{\thenextMarkId\stepcounter{nextMarkId}}
{\addtocounter{nextMarkId}{-1}\thenextMarkId}

\begin{document}

\begin{subproof}
  \begin{subproof}
    blabla
  \end{subproof}
  \begin{subproof}
    blabla
  \end{subproof}
\end{subproof}

I'd like to have: 0 1 blabla 1 2 blabla 2 0

\end{document}

I was thinking to use some sort of stack... but it seems quite ugly.

Answer 1

Store the current value and use it at the end of the environment. Since environments form groups, this will do the right thing.

\documentclass[a4paper,12pt]{article}

\newcounter{nextMarkId}

\newenvironment{subproof}
  {\thenextMarkId\edef\thisMarkId{\thenextMarkId}\stepcounter{nextMarkId}}
  {\thisMarkId}

\begin{document}

\begin{subproof}
  \begin{subproof}
    blabla
  \end{subproof}
\end{subproof}

I'd like to have: 0 1 blabla 1 0

\begin{subproof}
  \begin{subproof}
    blabla
    \begin{subproof}
      blabla
    \end{subproof}
  \end{subproof}
  \begin{subproof}
    blabla
  \end{subproof}
\end{subproof}

\end{document}