#!/usr/bin/perl -w
# closetex [-v] [-a] - print the next closing LaTeX tag (or all)

use v5.16;
use Getopt::Std;

our ($opt_a, $opt_v);
getopts('av');

my (@tags, @ind);

while (<<>>) {
    print  if $opt_v;
    while (/(^\s*)\\(begin|end)\{(.*?)\}/g) {
        if ($2 eq "begin") {
            push @tags, $3;
            push @ind, $1;
        } elsif ($2 eq "end") {
            die "error: line $.: wanted $_, got $3\n"  if $3 ne ($_ = pop @tags);
            pop @ind;
        }
    }
}

for (reverse @tags) {
    say pop @ind, "\\end{$_}";
    last  unless $opt_a;
}

__END__

# kakoune
define-command lc %{
    exec 'ZGG<A-:><A-!>closetex 2>&1<ret>zdgl'
}

# vim
command! Lc k` | exe "1,.!closetex -v" | norm ``