################################################################################
sub checksum {
        Digest::MD5::md5_hex (Dumper ($_[0]));
}
################################################################################
sub checksum_filter {
        my ($kind, $prefix, $name2def) = @_;
         
        my $hash = $preconf -> {_} -> {checksums} -> {$kind} or return ($name2def, {});
        my $needed_tables = {};
        my $new_checksums = {};
        checksum_lock ($kind);
        foreach my $key (keys %$name2def) {
         
                my $name     = $prefix . $key;
                my $def      = $name2def -> {$key};
                my $checksum;
                 
                if (ref $def) {
                        $checksum = checksum ($def);                    
                        next if ($hash -> {$name} || '') eq $checksum;
                        $needed_tables -> {$key}  = Storable::dclone ($def);
                }
                else {
                        $checksum = $def;
                        next if $hash -> {$name} >= $checksum;
                        $needed_tables -> {$key}  = $def;
                }
                $new_checksums -> {$name} = $checksum;
         
        }
        checksum_unlock ($kind);
         
        return ($needed_tables, $new_checksums);
}
################################################################################
sub checksum_write {
        my ($kind, $name2value) = @_;
         
        my $hash = $preconf -> {_} -> {checksums} -> {$kind} or return;
        checksum_lock ($kind);
        foreach my $key (keys %$name2value) {
                $hash -> {$key} = $name2value -> {$key};
        }
         
        checksum_unlock ($kind);
}
################################################################################
sub checksum_get {
        my ($kind, $name) = @_;
         
        my $hash = $preconf -> {_} -> {checksums} -> {$kind} or return undef;
         
        checksum_lock ($kind);
         
        my $value = $hash -> {$name};
        checksum_unlock ($kind);
         
        return $value;
}
################################################################################
sub checksum_set {
        my ($kind, $name, $value) = @_;
         
        my $hash = $preconf -> {_} -> {checksums} -> {$kind} or return;
        checksum_lock ($kind);
        $hash -> {$name} = $value;
        checksum_unlock ($kind);
}
################################################################################
sub get_last_update {
        my ($kind, $name) = ('last_update', '_');
        checksum_lock ($kind);
        my $value = checksum_get ($kind, $name);
         
        unless ($value) {
         
                my $last_update_table = sql_table_name ($conf->{systables}->{__last_update});
                $value = sql_select_scalar ("SELECT unix_ts FROM $last_update_table");
                 
                my $hash = $preconf -> {_} -> {checksums} -> {$kind};
                 
                $hash -> {$name} = $value if $hash;
         
        }
         
        $value ||= -1;
         
        checksum_unlock ($kind);
        return $value;
}
################################################################################
sub set_last_update {
        my ($value) = @_;
        my ($kind, $name) = ('last_update', '_');
         
        checksum_lock ($kind);
        my $hash = $preconf -> {_} -> {checksums} -> {$kind};
        $hash -> {$name} = $value if $hash;
         
        my $last_update_table = sql_table_name ($conf->{systables}->{__last_update});
        sql_do ("DELETE FROM $last_update_table");
         
        eval {
                sql_do ("INSERT INTO $last_update_table (unix_ts, pid) VALUES (?, ?)", $value, $$);
        };
         
        if ($@) {
                sql_do ("INSERT INTO $last_update_table (unix_ts, pid, id) VALUES (?, ?, 1)", $value, $$);
        }
        checksum_unlock ($kind);
}
################################################################################
BEGIN {
        print STDERR " checksums........................... ";
        my @modules = MP2 ? ('Txt') : ('SDBM');
        foreach (@modules) {
         
                eval "require Eludia::Content::Checksums::$_";
                 
                last if $preconf -> {_} -> {checksums};
         
        }
         
        if ($preconf -> {_} -> {checksums}) {
                print STDERR "  checksum hashes...\n";
                foreach my $kind (qw( 
                 
                        db_model 
                        last_update 
                        model_scripts 
                        updates_scripts
                         
                )) { 
                 
                        checksum_init ($kind)
                         
                }
        }
        else {
         
                "DISABLED. ok.\n";
         
        }
}
1;