How to count the number of items in enumerate when nesting and [resume]

Question

As question Count and use the number of items in advance mentioned, I have the same demand, but mine is more advanced.

Here I have some enumerates, some of them begin with [resume] paramater, some of them have nested enumerate. I want to compute the number of the first level items of each enumerate. For example

I wrote codes below:

\documentclass{article}
\usepackage{enumitem}
\makeatletter
\newcounter{totalitems}
\newcounter{beginitems}
\newcounter{enditems}
\let\@numerate\enumerate
\def\enumerate{%
    \setcounter{beginitems}{\arabic{enumi}}
    @numerate
}
\let\end@numerate\endenumerate
\def\endenumerate{
    \end@numerate%
    \setcounter{enditems}{\arabic{enumi}}
    \setcounter{totalitems}{\numexpr \c@enditems - \c@beginitems \relax}
}
\makeatother
\begin{document}
    \begin{enumerate}
        \item one
        \item two
    \end{enumerate}
    total = \thetotalitems, begin = \thebeginitems, end = \theenditems
\begin{enumerate}[resume]
    \item three
    \begin{enumerate}
        \item a nested enumerate
    \end{enumerate}
\end{enumerate}
total = \thetotalitems, begin = \thebeginitems, end = \theenditems

\begin{enumerate}
    \item one 
    \item two 
\end{enumerate}
total = \thetotalitems, begin = \thebeginitems, end = \theenditems


\end{document}

it produced:

As we can see there are some things goes wrong

1. When there is nested enumerate, the beginitems counter is wrong
2. When there is no [resume] paramater, the beginitems counter didn't been reset to 0.

Where should I change to reach my demand?

Answer 1

You need to postpone \setcounter{beginitems}{\arabic{enumi}} to after the enumerate environment was initiated, so essentially after \begin{enumerate} or \begin{enumerate}[resume] respectively. You need to take into account that \begin{environment} may have one optional argument.

I am not totally sure, but I think, using \LetLtxMacro instead of a plain \let and \renewcommand instead of \def is a bit more secure here:

\documentclass{article}
\usepackage{enumitem}
\makeatletter
\newcounter{totalitems}
\newcounter{beginitems}
\newcounter{enditems}
\usepackage{letltxmacro}
\LetLtxMacro{@numerate}{\enumerate}
\LetLtxMacro{\end@numerate}{\endenumerate}
\renewcommand{\enumerate}[1][]{%
    @numerate[#1]%
    \setcounter{beginitems}{\arabic{enumi}}
}
\renewcommand{\endenumerate}{
    \end@numerate%
    \setcounter{enditems}{\arabic{enumi}}
    \setcounter{totalitems}{\numexpr \c@enditems - \c@beginitems \relax}
}
\makeatother
\begin{document}
\begin{enumerate}
    \item one
    \item two
\end{enumerate}
total = \thetotalitems, begin = \thebeginitems, end = \theenditems

\begin{enumerate}[resume]
    \item three
    \begin{enumerate}
        \item a nested enumerate
    \end{enumerate}
\end{enumerate}
total = \thetotalitems, begin = \thebeginitems, end = \theenditems

\begin{enumerate}
    \item one 
    \item two 
\end{enumerate}
total = \thetotalitems, begin = \thebeginitems, end = \theenditems


\end{document}

Now, you still may have the problem that the counters are affected every time, an enumerate environment starts, which may cause wrong results when enumerate environments are nested. I did not test this thouroughly.

Answer 2

THANKS FOR @JohnKormylo and @JasperHabicht

method from @JasperHabicht

I found a control sequence \enit@depth which show the enumerate depth. So I can use \if to test if I'm in the first level, like this:

\renewcommand{\enumerate}[1][]{%
    \@numerate[#1]%
    \ifnum\enit@depth=\@ne
        \setcounter{beginitems}{\arabic{enumi}}
    \fi
}
\renewcommand{\endenumerate}{
    \ifnum\enit@depth=\@ne
        \setcounter{enditems}{\arabic{enumi}}
        \setcounter{totalitems}{\numexpr \c@enditems - \c@beginitems \relax}
    \fi
    \end@numerate%
}

If we do this, when we aren't in the first level, \setcounters won't work. The whole codes are:

\documentclass{article}
\usepackage{enumitem}
\makeatletter
\newcounter{totalitems}
\newcounter{beginitems}
\newcounter{enditems}
\usepackage{letltxmacro}
\LetLtxMacro{@numerate}{\enumerate}
\LetLtxMacro{\end@numerate}{\endenumerate}
\renewcommand{\enumerate}[1][]{%
    @numerate[#1]%
    \ifnum\enit@depth=@ne
        \setcounter{beginitems}{\arabic{enumi}}
    \fi
}
\renewcommand{\endenumerate}{
    \ifnum\enit@depth=@ne
        \setcounter{enditems}{\arabic{enumi}}
        \setcounter{totalitems}{\numexpr \c@enditems - \c@beginitems \relax}
    \fi
    \end@numerate%
}
\makeatother
\begin{document}
\begin{enumerate}
    \item one
    \item two
\end{enumerate}
total = \thetotalitems, begin = \thebeginitems, end = \theenditems

\begin{enumerate}[resume]
    \item three
    \begin{enumerate}
        \item a nested enumerate
    \end{enumerate}
\end{enumerate}
total = \thetotalitems, begin = \thebeginitems, end = \theenditems

\begin{enumerate}
    \item one 
    \item two 
\end{enumerate}
total = \thetotalitems, begin = \thebeginitems, end = \theenditems


\end{document}

my new method

In this method, I renew the \item command, let the conter plus 1 when \item appears in the top level:

1. first, we create a newif \ifenum to test if we are in the top level, we create a counter and save the macros:

\newif\ifenum
\newcounter{totalitems}
\usepackage{letltxmacro}
\LetLtxMacro{@numerate}{\enumerate}
\LetLtxMacro{\end@numerate}{\endenumerate}
\LetLtxMacro{\it@m}{\item}

2. use xparse to renew the \item command, when this \item is in the top level, step the counter totalitems. Also we can let it have some new features, like \item* for not count, \item[<paramater>] for a user-defined label as the previous definition but also count, \item*[paramater] for a user-defined label without count:

\DeclareDocumentCommand{\item}{ s o }{
    \IfNoValueTF{#2}{\it@m}{\it@m[#2]}  
    \ifenum
        \IfBooleanT{#1}{\addtocounter{totalitems}{-1}}%
        \stepcounter{totalitems}
    \fi
}

3. Then we judge when should we true the \ifenum: after \begin{enumerate}, we test if we are in the top level, if true, set totalitems to 0, and set \enumtrue, if not, set \enumfalse; before \end{enumerate} act oppositely. It doesn't matter when nested list appears, because \ifenum always truns false when the second or deeper level begins.

\renewcommand{\enumerate}[1][]{%
    \@numerate[#1]
    \ifnum\enit@depth=\@ne
        \setcounter{totalitems}{0}
        \enumtrue
    \else
        \enumfalse
    \fi
}
\renewcommand{\endenumerate}{
    \ifnum\enit@depth=\@ne 
        \enumfalse
    \else
        \enumtrue
    \fi
    \end@numerate%
}

Now we can get the number of the top level items:

\documentclass{article}
\usepackage{enumitem}
\newif\ifenum
\makeatletter
\newcounter{totalitems}
\usepackage{letltxmacro}
\LetLtxMacro{@numerate}{\enumerate}
\LetLtxMacro{\end@numerate}{\endenumerate}
\LetLtxMacro{\it@m}{\item}
\DeclareDocumentCommand{\item}{ s o }{
    \IfNoValueTF{#2}{\it@m}{\it@m[#2]}
    \ifenum
        \IfBooleanT{#1}{\addtocounter{totalitems}{-1}}%
        \stepcounter{totalitems}
    \fi
}
\renewcommand{\enumerate}[1][]{%
    @numerate[#1]
    \ifnum\enit@depth=@ne
        \setcounter{totalitems}{0}
        \enumtrue
    \else
        \enumfalse
    \fi
}
\renewcommand{\endenumerate}{
    \ifnum\enit@depth=@ne 
        \enumfalse
    \else
        \enumtrue
    \fi
    \end@numerate%
}
\makeatother
\begin{document}
\begin{enumerate}
    \item one
    \item two
\end{enumerate}
total = \thetotalitems

\begin{enumerate}[resume]
    \item three
    \begin{enumerate}
        \item a nested enumerate
        \item* a star nest
    \end{enumerate}
    \item item after nested
\end{enumerate}
total = \thetotalitems

\begin{enumerate}
    \item* a star version 
    \item[paramater] the only item which is counted
    \item*[paramater] a star version with paramater
\end{enumerate}
total = \thetotalitems


\end{document}