taskswitcher: implement close all button

Hi, this implements a close all button for the task switcher.

Regarding the double check (`Clear All` -> `Are you sure?`), as far as I know, no system has such a feature for this kind of operation, at the moment, so take it as a proposal.

components/mobileshell/qml/taskswitcher/TaskList.qml

@@ -19,6 +19,17 @@ Item {
     required property var taskSwitcher
     readonly property var taskSwitcherState: taskSwitcher.taskSwitcherState
     
+    // account for system header and footer offset (center the preview image)
+    readonly property real taskY: {
+        let headerHeight = MobileShell.Shell.topMargin;
+        let footerHeight = MobileShell.Shell.bottomMargin;
+        let diff = headerHeight - footerHeight;
+        
+        let baseY = (taskSwitcher.height / 2) - (taskSwitcherState.taskHeight / 2) - (taskSwitcherState.taskHeaderHeight / 2)
+        
+        return baseY + diff / 2 - MobileShell.TopPanelControls.panelHeight;
+    }
+    
     transform: Scale {
         origin.x: root.width / 2
         origin.y: root.height / 2
@@ -26,6 +37,12 @@ Item {
         yScale: taskSwitcherState.currentScale
     }
     
+    function closeAll() {
+        for (var i = 0; i < repeater.count; i++) {
+            repeater.itemAt(i).closeApp();
+        }
+    }
+    
     // taphandler activates even if delegate touched
     TapHandler {
         enabled: !taskSwitcherState.currentlyBeingOpened
@@ -69,16 +86,7 @@ Item {
             // this is the actual displayed x-position on screen
             x: listX + repeater.leftMargin - taskSwitcherState.xPosition
             
-            // account for system header and footer offset (center the preview image)
+            y: root.taskY
-            y: {
-                let headerHeight = MobileShell.Shell.topMargin;
-                let footerHeight = MobileShell.Shell.bottomMargin;
-                let diff = headerHeight - footerHeight;
-                
-                let baseY = (taskSwitcher.height / 2) - (height / 2) - (taskSwitcherState.taskHeaderHeight / 2)
-                
-                return baseY + diff / 2 - MobileShell.TopPanelControls.panelHeight;
-            }
             
             // ensure current task is above others
             z: taskSwitcherState.currentTaskIndex === currentIndex ? 1 : 0

components/mobileshell/qml/taskswitcher/TaskSwitcher.qml

@@ -115,6 +115,7 @@ Item {
     function instantHide() {
         opacity = 0;
         visible = false;
+        closeAllButton.closeRequested = false;
     }
     
     function hide() {
@@ -171,9 +172,11 @@ Item {
         to: 0
         duration: PlasmaCore.Units.shortDuration
         easing.type: Easing.InOutQuad
+                
         onFinished: {
             root.visible = false;
             tasksModel.taskReorderingEnabled = true;
+            closeAllButton.closeRequested = false;
         }
     }
 
@@ -204,11 +207,15 @@ Item {
         
         FlickContainer {
             id: flickable
+            
             anchors.fill: parent
+            
             taskSwitcherState: root.taskSwitcherState
             
             // the item is effectively anchored to the flickable bounds
             TaskList {
+                id: taskList
+                
                 taskSwitcher: root
                 
                 opacity: {
@@ -223,6 +230,41 @@ Item {
                 x: flickable.contentX
                 width: flickable.width
                 height: flickable.height
+                
+                PlasmaComponents.ToolButton {
+                    id: closeAllButton
+                    
+                    property bool closeRequested: false
+                    
+                    anchors {
+                        bottom: parent.bottom
+                        bottomMargin: taskList.taskY / 2
+                        horizontalCenter: parent.horizontalCenter
+                    }
+                    
+                    PlasmaCore.ColorScope.colorGroup: PlasmaCore.Theme.ComplementaryColorGroup
+                    PlasmaCore.ColorScope.inherit: false
+                    
+                    opacity: taskSwitcherState.currentlyBeingOpened || taskSwitcherState.currentlyBeingClosed || !root.visible ? 0.0 : 1.0
+                    
+                    Behavior on opacity {
+                        NumberAnimation {
+                            duration: PlasmaCore.Units.shortDuration
+                        }
+                    }
+                    
+                    icon.name: "edit-clear-history"
+                    
+                    text: closeRequested ? "Confirm Close All" : "Close All"
+                    
+                    onClicked: {
+                        if (closeRequested) {
+                            taskList.closeAll();
+                        } else {
+                            closeRequested = true;
+                        }
+                    }
+                }
             }
         }
     }

components/mobileshell/qml/taskswitcher/TaskSwitcherState.qml

@@ -62,6 +62,9 @@ QtObject {
     // whether we are in a swipe up gesture to open the task switcher
     property bool currentlyBeingOpened: false
     
+    // whether the task switcher is being closed: an animation is running
+    property bool currentlyBeingClosed: false
+    
     // whether we are in a swipe left/right gesture to walk through tasks
     property bool scrollingTasks: false
     
@@ -237,7 +240,10 @@ QtObject {
         duration: MobileShell.MobileShellSettings.animationsEnabled ? 300 : 0
         easing.type: Easing.OutQuint
         
+        onStarted: root.currentlyBeingClosed = true
+        
         onFinished: {
+            root.currentlyBeingClosed = false;
             root.currentlyBeingOpened = false;
             taskSwitcher.setSingleActiveWindow(root.currentTaskIndex);
             taskSwitcher.instantHide();