use warnings;
use strict;

use Regexp::Common;


my $text = q{start \chapter{argument1}{argument2} end};

print "INPUT: '$text' \n";

# macro name and replacement pattern taken from a file, sans newlines.
chomp(my $macro_name          = <DATA>);
chomp(my $replacement_pattern = <DATA>);

my $parens = '{}';
my $arg    = qr{ $RE{balanced}{-parens => $parens} }xms;
my $intro  = qr{ \\ }xms;

my $inpattern = qr{ $intro $macro_name \s* ($arg) \s* ($arg) }xms;

# print "inpattern $inpattern \n";  # FOR DEBUG

$text =~
    # s{ $inpattern }
    s{ $intro $macro_name \s* ($arg) \s* ($arg) }
     {  my ($body, $tag) = ($1, $2);  # nail down captures soonest
        validate_paired($parens, $body, $tag);
        trim_paired    ($parens, $body, $tag);
        eval qq{ qq{$replacement_pattern} }
            or die "replacement failed: '$replacement_pattern'";
     }xmsge;

print "OUTPUT: '$text' \n";
print "\n";


sub trim_paired {

    my $pair = shift;  # opening/closing pair of chars to trim

    my ($opener, $closer) = $pair =~ m{ \S }xmsg;

    die "pair of opening and closing chars not supplied: $pair"
        unless defined $opener and defined $closer;

    s{ \A $opener | $closer \z }''xmsg for @_;

    }


sub validate_paired {

    my $pair = shift;  # opening/closing pair of bracing chars

    my ($opener, $closer) = $pair =~ m{ \S }xmsg;

    die "pair of opening and closing chars not supplied"
        unless defined $opener and defined $closer;

    m{ \A $opener .* $closer \z }xms or die "not braced: '$_'" for @_;

    }


__DATA__
chapter
<h1 tag="$tag">$body</h1>