#!/usr/bin/perl
use warnings;
use strict;
use Digest::SHA1 qw(sha1 sha1_hex sha1_base64);
use Fcntl qw(:DEFAULT :flock);
use File::Compare;
use File::Path;
use File::Temp;
use File::stat;
use MIME::Base64;

# Copyright (C) 2010 Zygo Blaxell <dm5@mailtoo.hungrycats.org>

# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.

# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.

# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA

sub digest {
	my ($filename) = (@_);
	die "'$filename' is not a plain file" if (-l $filename) || ! (-f _);
	my $ctx = Digest::SHA1->new;
	sysopen(FILE, $filename, O_RDONLY|O_NONBLOCK) or die "open: $filename: $!";
	binmode(FILE);		# FIXME:  Necessary?  Probably harmless...
	$ctx->addfile(\*FILE);
	close(FILE) or die "close: $filename: $!";
	return $ctx->b64digest;
}

sub usage {
	die <<USAGE;
Usage: $0 link-dir
Hashes a NUL-separated list of files on stdin into link-dir.

Version: 20100513.0
USAGE
}

# Link files
sub link_files {
	my ($from, $to) = (@_);

	print STDERR 'T';
	my $inode_dir = $to;
	my $inode_base = $to;
	$inode_dir =~ s:[^/]*$::o;
	$inode_base =~ s:^.*/::os;
	my $tmp_to = File::Temp::tempnam($inode_dir, ".$inode_base.");
	print STDERR "\bL";
	link($from, $tmp_to) or die "link: $from -> $tmp_to: $!";
	print STDERR "\bR";
	unless (rename($tmp_to, $to)) {
		my $saved_bang = $!;
		print STDERR "\bU";
		unlink($tmp_to) or warn "unlink: $tmp_to: $!";	# Try, possibly in vain, to clean up
		die "rename: $tmp_to -> $from: $saved_bang";
	}
	print STDERR "\b";
}

my $link_dir = shift @ARGV;
usage unless $link_dir;

my $prefix_length = 3;

sub slash_prefix {
	my ($file) = @_;
	$file .= '_' x (length($file) + 1 - $prefix_length) if length($file) + 1 < $prefix_length;
	my $prefix = substr($file, 0, $prefix_length);
	my $suffix = substr($file, $prefix_length);
	$prefix =~ s:(.):$1/:osg;
	chop($prefix);
	return ($prefix, $suffix);
}

sub mkdir_p {
	my ($dir) = @_;
	return if -d $dir;
	$dir =~ s:/+$::os;
	my $parent;
	($parent = $dir) =~ s:[^/]+$::os;
	if ($parent ne $dir) {
		mkdir_p($parent);
		print STDERR 'm';
		mkdir($dir) or die "mkdir: $dir: $!";
	}
	die "mkdir: $dir: $!" unless -d $dir;
}

sub prepare_parents {
	my ($link_dir, $file) = @_;
	my ($prefix, $suffix) = slash_prefix($file);
	my $parent = "$link_dir/$prefix";
	mkdir_p($parent);
	return "$parent/$suffix";
}

sub name_quad {
	my ($int64) = @_;
	my $packed = pack('Q', $int64);
	$packed =~ s/^\0+//os;
	my $base64_packed = encode_base64($packed, '');
	# Don't strip off the trailing padding since it makes the string
	# so short we end up just putting it back on again.
	# $base64_packed =~ s/=+$//os;
	return $base64_packed;
}

sub name_ino {
	my ($ino) = @_;
	return name_quad($ino) . 'I';
}

# ext3 cannot handle more than 32000 links to a file.  Leave some headroom.
# Arguably this should be configurable, but the losses are miniscule and
# the coding for option support is not.
my $link_count_max = 31990;

$/ = "\0";
while (<STDIN>) {
	my $file = $_;
	eval {
		for (1) {
			chomp $file;

			# Get file stat data
			print STDERR '.';
			my $st = lstat($file);
			die "lstat: $file: $!" unless $st;

			# Oops?
			next unless -f _;

			# Skip the file if it has far too many links already
			next if ($st->nlink > $link_count_max);

			# Check link to inode
			my $inode_link = prepare_parents($link_dir, name_ino($st->ino));
			print STDERR 'I';
			my $inode_st = lstat($inode_link);
			my $update_links;
			if ($inode_st) {
				my $inode_dev = $inode_st->dev;
				my $inode_ino = $inode_st->ino;
				my $file_dev = $st->dev;
				my $file_ino = $st->ino;
				if ($inode_ino != $file_ino || $inode_dev != $file_dev) {
					warn "inode link '$inode_link' is wrong (inode $inode_ino should be $file_ino)" if $inode_ino != $file_ino;
					warn "inode link '$inode_link' is wrong (dev $inode_dev should be $file_dev)" if $inode_dev != $file_dev;
					$update_links = 1;
				}
			} else {
				$update_links = 1;
			}
			print STDERR "\b";

			# If neither criteria for updating link is met, leave it as-is
			next unless $update_links;

			# Compute digest
			print STDERR 'd';
			my $digest = digest($file);
			print STDERR "\b";

			# Base64 uses /, we prefer _
			$digest =~ y:/:_:;

			# Check link to digest
			my $digest_link = prepare_parents($link_dir, "${digest}D");
			print STDERR 'D';
			my $digest_st = lstat($digest_link);
			if ($digest_st) {
				my $digest_nlink = $digest_st->nlink;
				if ($digest_nlink > 31990) {
					print STDERR 'u';
					unlink($digest_link) or die "unlink: $digest_link: $!";
					undef $digest_st;
				}
			}
			print STDERR "\b";

			# Which file are we keeping?
			my $keep_ino;

			# If digest link exists, link it to file
			if ($digest_st) {
				print STDERR 'c';
				die "NOT identical!" if compare($digest_link, $file);

				# Old, replace input with old file
				print STDERR '-';
				link_files($digest_link, $file);
				$keep_ino = $digest_st->ino;
			} else {
				# New, add input to digest
				print STDERR '+';
				link_files($file, $digest_link);
				$keep_ino = $st->ino;
			}

			# A link to the inode indicates we are done, so do it last
			$inode_link = prepare_parents($link_dir, name_ino($keep_ino));
			print STDERR ' ';
			link_files($digest_link, $inode_link);

		}
	};
	warn "$file: $@" if $@;
}

# Garbage collection
print STDERR "\nGarbage collection in '$link_dir'...";
chdir($link_dir) || die "chdir: $link_dir: $!";
print STDERR "\nRemoving files with link count < 3...";
system("find . -type f -links -3 -print0 | xargs -0rt rm -f") and die "system: exit status $?";
print STDERR "\nRemoving empty directories...";
system("find . -type d -empty -print0 | xargs -0rt rmdir -p --ignore-fail-on-non-empty") and die "system: exit status $?";
print STDERR "\nDone.\n";

exit(0);

__END__

#################################################################################
#                     GNU GENERAL PUBLIC LICENSE                                #
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# proprietary programs.  If your program is a subroutine library, you may       #
# consider it more useful to permit linking proprietary applications with the   #
# library.  If this is what you want to do, use the GNU Library General         #
# Public License instead of this License.                                       #
#################################################################################