#!/usr/bin/perl
use strict;
use warnings;
use Getopt::Long ();

process( init() );
exit;

sub process {
	my $opts = shift;

	my @buffer = ();
	my $wait = 0;
	while ( <> ) {

		if ( ( scalar @buffer ) > $opts->{ 'b' } ) {
			print ( shift @buffer );
		}

		if ( $wait ) {
			$wait--;
			next unless $opts->{ 'nest' };
		} else {
			push @buffer, $_;
		}

		if ( /$opts->{ 'pattern' }/ ) {
			@buffer = ();
			$wait = $opts->{ 'a' };
		}
	}
	print @buffer;
}

sub init {
	my %options = (
		'help'    => 0,
		'a'       => 1,
		'b'       => 1,
		'c'       => 0,
		'nest'    => 0,
		'pattern' => '',
	);
	Getopt::Long::Configure( 'gnu_getopt' );
	Getopt::Long::GetOptions( \%options, 'help+', 'a=i', 'b=i', 'c=i', 'nest+', 'pattern=s' );
	if ( $options{ 'c' } ) {
		$options{ 'a' } = $options{ 'b' } = $options{ 'c' };
	}
	if ( $options{ 'help' } ) {
		warn "Usage: $0 [[--help]|[[-a <n>] [-b <n>]|[-c <n>]] [--nest] --pattern <s>\n\n"
		. "Print the input file excluding the matched line provided by the -p argument and as many lines before and after that line as specified.\n\n"
		. "\t--help\t\t\tthis help message\n"
		. "\t-a <number>\t\texclude <number> lines after the matched line\n"
		. "\t-b <number>\t\texclude <number> lines before the matched line\n"
		. "\t-c <number>\t\texclude <number> lines before and after the matched line, overriding -a and -b in the process\n"
		. "\t--nest\t\t\tmatch lines already excluded by a preceding match, and exclude the following lines accordingly\n"
		. "\t--pattern <string>\texclude the line matching this pattern (may be a regular expression) and other lines as specified by the other options\n\n";
		exit 0;
	}

	return \%options;
}