--- loncom/interface/lonpreferences.pm	2016/01/27 00:24:09	1.217
+++ loncom/interface/lonpreferences.pm	2016/01/31 21:25:37	1.218
@@ -1,7 +1,7 @@
 # The LearningOnline Network
 # Preferences
 #
-# $Id: lonpreferences.pm,v 1.217 2016/01/27 00:24:09 raeburn Exp $
+# $Id: lonpreferences.pm,v 1.218 2016/01/31 21:25:37 raeburn Exp $
 #
 # Copyright Michigan State University Board of Trustees
 #
@@ -713,16 +713,51 @@ sub verify_and_change_clicker {
     my $r = shift;
     my $user       = $env{'user.name'};
     my $domain     = $env{'user.domain'};
+    my $uhome      = $env{'user.home'};
     my $newclickers  = $env{'form.clickers'};
+    my $message;
     $newclickers=~s/[^\w\:\-]+/\,/gs;
     $newclickers=~tr/a-z/A-Z/;
     $newclickers=~s/[\:\-]+/\-/g;
     $newclickers=~s/\,+/\,/g;
     $newclickers=~s/^\,//;
     $newclickers=~s/\,$//;
-    &Apache::lonnet::put('environment',{'clickers' => $newclickers});
-    &Apache::lonnet::appenv({'environment.clickers' => $newclickers});
-    my $message=&Apache::lonhtmlcommon::confirm_success(&mt('Registering clickers: [_1]',$newclickers));
+    my @oldclickers = split(/,/,$env{'environment.clickers'});
+    my @newclickers = split(/,/,$newclickers);
+    my %newuniq;
+    map { $newuniq{$_} = 1; }  @newclickers;
+    @newclickers = sort(keys(%newuniq));
+    my @differences = &Apache::loncommon::compare_arrays(\@oldclickers,\@newclickers);
+    if (@differences) {
+        my $putres = &Apache::lonnet::put('environment',{'clickers' => $newclickers});
+        if ($putres eq 'ok') {
+            my @adds = ();
+            my @dels = ();
+            foreach my $item (@differences) {
+                if (grep(/^\Q$item\E$/,@newclickers)) {
+                    push(@adds,$item);
+                } else {
+                    push(@dels,$item);
+                }
+            }
+            if (@dels) {
+                 my %delclicker;
+                 map { $delclicker{$_} = $user; } @dels;
+                 my $putresult = &Apache::lonnet::iddel($domain,\%delclicker,$uhome,'clickers');
+            }
+            if (@adds) {
+                 my %addclicker;
+                 map { $addclicker{$_} = $user; } @adds;
+                 my $putresult = &Apache::lonnet::updateclickers($domain,'add',\%addclicker,$uhome,1);
+            }
+            &Apache::lonnet::appenv({'environment.clickers' => $newclickers});
+            $message=&Apache::lonhtmlcommon::confirm_success(&mt('Registering clickers: [_1]',$newclickers));
+        } else {
+            $message=&Apache::lonhtmlcommon::confirm_success(&mt('Error saving clicker ID').1);
+        }
+    } else {
+        $message='<span class="LC_info">'.&mt('Clicker information unchanged').'</span>';
+    }
     $message=&Apache::loncommon::confirmwrapper($message);
     &print_main_menu($r, $message);
 }