#!/usr/bin/perl -w

# Extract or update a section from a combined patch + documentation +
# meta information file.

use FileHandle;
use Getopt::Long;
use strict;

my $select;
my $update;

if (!GetOptions("s|select=s" => \$select,
		"u|update=s" => \$update) ||
    (!defined $select && !defined $update)) {
	print STDERR "USAGE: $0 {-s|-u} section file [< replacement]\n";
	exit 1;
}

foreach my $arg (@ARGV) {
	my $fh;

	if ($arg =~ /\.gz$/) {
		$fh = new FileHandle("gzip -cd $arg |");
	} elsif ($arg =~ /\.bz2$/) {
		$fh = new FileHandle("bzip2 -cd $arg |");
	} else {
		$fh = new FileHandle("< $arg");
	}

	unless ($fh) {
		print STDERR "$arg: $!\n";
		next;
	}

	if (defined $select) {
		my $section = "head";
		my $newline = "";
		while (<$fh>) {
			if (/^%(.*)/) {
				last if $section eq $select;
				$section = $1;
				next;
			}
			if ($section eq $select) {
				print $newline;
				if ($_ eq "\n") {
					$newline = $_;
				} else {
					$newline="";
					print;
				}
			}
		}
	} elsif (defined $update) {
		my $fh2;
		if ($arg =~ /\.gz$/) {
			$fh2 = new FileHandle("| gzip -c > $arg.parse");
		} elsif ($arg =~ /\.bz2$/) {
			$fh2 = new FileHandle("| bzip2 -c > $arg.parse");
		} else {
			$fh2 = new FileHandle("$arg.parse", O_CREAT|O_WRONLY);
		}
		unless ($fh2) {
			die "$arg.parse: $!\n";
		}

		# Copy things before updated section
		while (<$fh>) {
			if (/^%(.*)/ && $1 eq $update) {
				last;
			}
			print $fh2 $_;
		}
		# Create/replace updated section
		print $fh2 "%$update\n";
		while (<STDIN>) {
			print $fh2 $_;
		}
		print $fh2 "\n";
		# Skip obsolete section
		while (<$fh>) {
			if (/^%(.*)/) {
				print $fh2 $_;
				last;
			}
		}
		# Copy things after updated section
		while (<$fh>) {
			print $fh2 $_;
		}
		unless (close $fh2) {
			die "$arg.patch: $!\n";
		}

		unlink "$arg~";
		unless (rename $arg, "$arg~") {
			die "Failed to rename $arg to $arg~: $!\n";
		}
		unless (rename "$arg.parse", $arg) {
			die "Failed to rename $arg.parse to $arg: $!\n";
		}
	}
	close $fh;
}