#!/usr/bin/env perl
# Copyright 2005, Ryan Anderson <ryan@michonline.com>
# Distribution permitted under the GPL v2, as distributed
# by the Free Software Foundation.
# Later versions of the GPL at the discretion of Linus Torvalds
#
# Scan two git object-trees, and hardlink any common objects between them.

use 5.006;
use strict;
use warnings;
use Getopt::Long;

sub get_canonical_form($);
sub do_scan_directory($$$);
sub compare_two_files($$);
sub usage();
sub link_two_files($$);

# stats
my $total_linked = 0;
my $total_already = 0;
my ($linked,$already);

my $fail_on_different_sizes = 0;
my $help = 0;
GetOptions("safe" => \$fail_on_different_sizes,
           "help" => \$help);

usage() if $help;

my (@dirs) = @ARGV;

usage() if (!defined $dirs[0] || !defined $dirs[1]);

$_ = get_canonical_form($_) foreach (@dirs);

my $master_dir = pop @dirs;

opendir(D,$master_dir . "objects/")
        or die "Failed to open $master_dir/objects/ : $!";

my @hashdirs = grep !/^\.{1,2}$/, readdir(D);

foreach my $repo (@dirs) {
        $linked = 0;
        $already = 0;
        printf("Searching '%s' and '%s' for common objects and hardlinking them...\n",
                $master_dir,$repo);

        foreach my $hashdir (@hashdirs) {
                do_scan_directory($master_dir, $hashdir, $repo);
        }

        printf("Linked %d files, %d were already linked.\n",$linked, $already);

        $total_linked += $linked;
        $total_already += $already;
}

printf("Totals: Linked %d files, %d were already linked.\n",
        $total_linked, $total_already);


sub do_scan_directory($$$) {
        my ($srcdir, $subdir, $dstdir) = @_;

        my $sfulldir = sprintf("%sobjects/%s/",$srcdir,$subdir);
        my $dfulldir = sprintf("%sobjects/%s/",$dstdir,$subdir);

        opendir(S,$sfulldir)
                or die "Failed to opendir $sfulldir: $!";

        foreach my $file (grep(!/\.{1,2}$/, readdir(S))) {
                my $sfilename = $sfulldir . $file;
                my $dfilename = $dfulldir . $file;

                compare_two_files($sfilename,$dfilename);

        }
        closedir(S);
}

sub compare_two_files($$) {
        my ($sfilename, $dfilename) = @_;

        # Perl's stat returns relevant information as follows:
        # 0 = dev number
        # 1 = inode number
        # 7 = size
        my @sstatinfo = stat($sfilename);
        my @dstatinfo = stat($dfilename);

        if (@sstatinfo == 0 && @dstatinfo == 0) {
                die sprintf("Stat of both %s and %s failed: %s\n",$sfilename, $dfilename, $!);

        } elsif (@dstatinfo == 0) {
                return;
        }

        if ( ($sstatinfo[0] == $dstatinfo[0]) &&
             ($sstatinfo[1] != $dstatinfo[1])) {
                if ($sstatinfo[7] == $dstatinfo[7]) {
                        link_two_files($sfilename, $dfilename);

                } else {
                        my $err = sprintf("ERROR: File sizes are not the same, cannot relink %s to %s.\n",
                                $sfilename, $dfilename);
                        if ($fail_on_different_sizes) {
                                die $err;
                        } else {
                                warn $err;
                        }
                }

        } elsif ( ($sstatinfo[0] == $dstatinfo[0]) &&
             ($sstatinfo[1] == $dstatinfo[1])) {
                $already++;
        }
}

sub get_canonical_form($) {
        my $dir = shift;
        my $original = $dir;

        die "$dir is not a directory." unless -d $dir;

        $dir .= "/" unless $dir =~ m#/$#;
        $dir .= ".git/" unless $dir =~ m#\.git/$#;

        die "$original does not have a .git/ subdirectory.\n" unless -d $dir;

        return $dir;
}

sub link_two_files($$) {
        my ($sfilename, $dfilename) = @_;
        my $tmpdname = sprintf("%s.old",$dfilename);
        rename($dfilename,$tmpdname)
                or die sprintf("Failure renaming %s to %s: %s",
                        $dfilename, $tmpdname, $!);

        if (! link($sfilename,$dfilename)) {
                my $failtxt = "";
                unless (rename($tmpdname,$dfilename)) {
                        $failtxt = sprintf(
                                "Git Repository containing %s is probably corrupted, " .
                                "please copy '%s' to '%s' to fix.\n",
                                $tmpdname, $dfilename);
                }

                die sprintf("Failed to link %s to %s: %s\n%s" .
                        $sfilename, $dfilename,
                        $!, $dfilename, $failtxt);
        }

        unlink($tmpdname)
                or die sprintf("Unlink of %s failed: %s\n",
                        $dfilename, $!);

        $linked++;
}


sub usage() {
        print("Usage: $0 [--safe] <dir> [<dir> ...] <master_dir> \n");
        print("All directories should contain a .git/objects/ subdirectory.\n");
        print("Options\n");
        print("\t--safe\t" .
                "Stops if two objects with the same hash exist but " .
                "have different sizes.  Default is to warn and continue.\n");
        exit(1);
}