[Notifications] Show hint if notifications aren't available or provided by someone else

When Plasma notification service isn't available or provided by someone else, disable the plasmoid.
Do not disturb controls are disabled and the applet stays in the popup crossed out.
Effectively D25097 of plasma-desktop for the applet itself.

Differential Revision: https://phabricator.kde.org/D25917

applets/notifications/package/contents/ui/FullRepresentation.qml

@@ -79,6 +79,7 @@ ColumnLayout{
             RowLayout {
                 id: dndRow
                 spacing: units.smallSpacing
+                enabled: NotificationManager.Server.valid
 
                 PlasmaComponents3.CheckBox {
                     id: dndCheck
@@ -590,7 +591,37 @@ ColumnLayout{
                 level: 3
                 opacity: 0.6
                 text: i18n("No unread notifications.")
-                visible: list.count === 0
+                visible: list.count === 0 && NotificationManager.Server.valid
+            }
+
+            ColumnLayout {
+                id: serverUnavailableColumn
+
+                width: list.width
+                visible: list.count === 0 && !NotificationManager.Server.valid
+
+                PlasmaExtras.Heading {
+                    Layout.fillWidth: true
+                    level: 3
+                    opacity: 0.6
+                    text: i18n("Notification service not available")
+                    wrapMode: Text.WordWrap
+                }
+
+                PlasmaComponents.Label {
+                    // Checking valid to avoid creating ServerInfo object if everything is alright
+                    readonly property NotificationManager.ServerInfo currentOwner: !NotificationManager.Server.valid ? NotificationManager.Server.currentOwner
+                                                                                                                     : null
+
+                    Layout.fillWidth: true
+                    wrapMode: Text.WordWrap
+                    text: currentOwner ? i18nc("Vendor and product name",
+                                         "Notifications are currently provided by '%1 %2'",
+                                         currentOwner.vendor,
+                                         currentOwner.name)
+                                       : ""
+                    visible: currentOwner && currentOwner.vendor && currentOwner.name
+                }
             }
         }
     }

applets/notifications/package/contents/ui/global/Globals.qml

@@ -200,6 +200,10 @@ QtObject {
         globals.inhibited = Qt.binding(function() {
             var inhibited = false;
 
+            if (!NotificationManager.Server.valid) {
+                return false;
+            }
+
             var inhibitedUntil = notificationSettings.notificationsInhibitedUntil;
             if (!isNaN(inhibitedUntil.getTime())) {
                 inhibited |= (new Date().getTime() < inhibitedUntil.getTime());

applets/notifications/package/contents/ui/main.qml

@@ -46,6 +46,9 @@ Item {
             lines.push(i18np("%1 running job", "%1 running jobs", historyModel.activeJobsCount));
         }
 
+        if (!NotificationManager.Server.valid) {
+            lines.push(i18n("Notification service not available"));
+        } else {
             // Any notification that is newer than "lastRead" is "unread"
             // since it doesn't know the popup is on screen which makes the user see it
             var actualUnread = historyModel.unreadNotificationsCount - Globals.popupNotificationsModel.activeNotificationsCount;
@@ -65,6 +68,7 @@ Item {
             } else if (lines.length === 0) {
                 lines.push(i18n("No unread notifications"));
             }
+        }
 
         return lines.join("\n");
     }
@@ -92,7 +96,7 @@ Item {
         jobsCount: historyModel.activeJobsCount
         jobsPercentage: historyModel.jobsPercentage
 
-        inhibited: Globals.inhibited
+        inhibited: Globals.inhibited || !NotificationManager.Server.valid
     }
 
     Plasmoid.fullRepresentation: FullRepresentation {