#!/usr/bin/perl
#
# droplinebreak: remove newlines before/after lines containing regex.
#
# 2006-12-13: Written by Steven J. DeRose, sderose\@acm.org.
# 2008-08-31 sjd: BSD.
#
# To do:
#     Option to *replace* the linebreaks instead of just dropping them,
#         such as to put in a field-delimiter.

use strict;
use Getopt::Long;

my $version = "2008-08-31";

my $expr = "";
my $dropPreceding = 0;
my $dropFollowing = 1;
my $help = 0;
my $lineends = "U";
my $quiet = 0;
my $replace ="";
my $verbose = 0;

# Process options
Getopt::Long::Configure ("ignore_case");
my $result = GetOptions(
	"b"                 => sub { $dropPreceding = 1; $dropFollowing = 1; },
	"f"                 => sub { $dropPreceding = 0; $dropFollowing = 1; },
	"p"                 => sub { $dropPreceding = 1; $dropFollowing = 0; },
	"linends=s"         => sub { $lineends = uc(substr($ARGV[0]."U",0,1)); },
	"h|help|?"          => \$help,
	"q|quiet!"          => \$quiet,
	"replace=s"         => \$replace,
	"v|verbose+"        => \$verbose,
    "version"           => sub {
		die "Version of $version, by Steven J. DeRose, sderose\@acm.org.\n";
	}
	);

if ($help) { showUsage(); exit; }
($result) || die "Bad options.\n";


# Validate and default options

$lineends = substr($lineends."U",0,1);
(index("MDU",$lineends) >= 0) ||
	die "Unknown line-end type $lineends.\n";

my $expr = shift;;
($expr) || die "No regex specified.\n";


################################################################################

my $last = 0; # No pending line-break from prior line.
open my $fh, "<&STDIN";
while (my $l = <$fh>) {
	chomp($l);

	if ($l !~ m/$expr/) { # If this line does not match
		if ($last) { printBreak(); }
		print $l;
		$last = 1;
	}
	else { # If this line does match
        if ($last) { # Prior line did *not* drop intervening line break
			if ($dropPreceding) { 
				if ($replace) { print "$replace"; }				
			}
			else {
				printBreak();
			}
		}
        print $l;
		if ($dropFollowing) {
			$last = 0; # Definitely drop this trailing one
			if ($replace) { print "$replace"; }
		}
		else {
			$last = 1; # keep following newline, unless next line pre drops it.
		}
	}
} # while not EOF
if ($last) { printBreak(); }
close $fh;

exit;


################################################################################

sub printBreak {
	if    ($lineends eq "M") { print "\r";   }
	elsif ($lineends eq "D") { print "\r\n"; }
	else                     { print "\n";   }
}


################################################################################

sub showUsage() {
	print "
Usage: droplinebreak [options] 'regex'
    Delete the linebreak at the end of lines that match the (Perl-style) regex.
    (the line need not match in its entirety -- use ^ and \$ if you want that).
Options:
    -b           Drop line-ends preceding *and* following each matched line.
    -f           Drop line-end following each matched line (the default).
    -linends t   Output M (mac), D (dos), or U (*nix default) line-ends.
    -p           Drop line-end preceding each matched line.
    -q           Suppress most messages.
    -r 'string'  Put in this string in place of the dropped line breaks.
    -version     Display version info and exit ($version, sjd).
Known bugs and limitations:
    The -r option is not fully tested.
";
}