#!/usr/bin/perl -w
#

use strict;
use IO::Handle;

my ($passwd,$dashuid,$chown,$phase) = @ARGV;
my $offset = 20000;
my $find = "find -xdev";

warn "strips setuid bits!";

our %undomap;
# construct array mapping
#   new_id -> old_id

my $re = '^(\w[^:]*)\:[^:]+\:(\d+)\:';

sub find_did ($$) {
    my ($xname,$xid) = @_;
    # returns the actual uid that source uid xid was (perhaps mistakenly)
    # mapped to
    open D, "$passwd-dst" or die $!;
    while (<D>) {
	m/$re/o or die "$_ $!";
	my ($dname,$did) = ($1,$2);
	return $did if $dname eq $xname;
    }
    die $! if D->error;
    return $xid;
}

open S, "$passwd-src" or die $!;
while (<S>) {
    m/$re/o or die "$_ $!";
    my ($sname,$sid) = ($1,$2);
    my $did = find_did($sname,$sid);
    push @{ $undomap{$did} }, $sid;
}
die $! if S->error;

sub mkmap ($$) {
    my ($in,$out) = @_;
    printf "$find $dashuid $in -print0 | xargs -0r $chown -- $out\n"
	or die $!;
}

our @ambigs;

foreach my $sid (keys %undomap) {
    my @dids = @{ $undomap{$sid} };
    next if @dids==1 && $dids[0]==$sid;
    if ($phase eq '1') {
	mkmap($sid,$sid+$offset);
    } elsif ($phase eq '2') {
	if (@dids==1) {
	    mkmap($sid+$offset,$dids[0]);
	} else {
	    print "# ambiguous $sid->@dids\n";
	    print "$find $dashuid ".($sid+$offset)." -ls\n"
		or die $!;
	}
    } elsif ($phase eq '0') {
	next if @dids==1;
	push @ambigs, $sid;
    } else {
	die "$phase ?";
    }
}

if ($phase eq '0' && @ambigs) {
    print "$find \\( ".
	(join " -o ", map { "$dashuid $_" } @ambigs).
	" \\) -ls\n"
	or die $!;
}

close STDOUT or die $!;