my $g_nested_brackets;
$g_nested_brackets = qr{
    (?>                             # Atomic matching
       [^\[\]]+                     # Anything other than brackets
     | 
       \[
         (??{ $g_nested_brackets }) # Recursive set of nested brackets
       \]
    )*
}x;
my $anchors = qr{
    (                # wrap whole match in $1
      \[
        ($g_nested_brackets)    # link text = $2
      \]
      \(            # literal paren
        [ \t]*
        <?(.*?)>?   # href = $3
        [ \t]*
        (           # $4
          (['"])    # quote char = $5
          (.*?)     # Title = $6
          \5        # matching quote
        )?          # title is optional
      \)
    )
}xs;

##</code><code>##

use warnings;
use strict;

my $anchors = qr{
	(?(DEFINE) (?<nested_brackets>
		(?> [^\[\]]+ | \[ (?&nested_brackets) \] )*
	) )
	\[ (?<text> (?&nested_brackets) ) \]
	\( (?<link>
		[ \t]* <? .*? >? [ \t]*
		(?: (?<titlequote>['"]) .*? \k<titlequote> )?
	) \)
}xs;

my $input = <<'END';
blah blah [click me](click me) more stuff
blah [link here](link here) blah blah
END
my $expect = <<'END';
blah blah [click me](/click-me) more stuff
blah [link here](/link-here) blah blah
END
(my $output = $input) =~
	s{$anchors}{
		my ($t, $l) = @+{qw/ text link /};
		$l =~ s/\s+/-/g;
		"[$t](/$l)"
	}ge;

use Test::More tests=>1;
is $output, $expect;