Can move window

lib/ui/widgets/tablet_mode/calls/call_window_widget.dart

@@ -1,10 +1,13 @@
 import 'package:comunic/ui/screens/call_screen.dart';
+import 'package:comunic/ui/widgets/tablet_mode/calls/calls_area.dart';
 import 'package:flutter/material.dart';
 
 /// Call window widget
 ///
 /// @author Pierre HUBERT
 
+const _WindowSize = Size(500, 200);
+
 class CallWindowWidget extends StatefulWidget {
   final int convID;
 
@@ -19,14 +22,59 @@ class CallWindowWidget extends StatefulWidget {
 }
 
 class _CallWindowWidgetState extends State<CallWindowWidget> {
+  double _left, _top;
+
+  @override
+  void didChangeDependencies() {
+    super.didChangeDependencies();
+
+    // Initialize window coordinates
+    _top = 10;
+    _left = MediaQuery.of(context).size.width - 10 - _WindowSize.width;
+  }
+
   @override
   Widget build(BuildContext context) {
     return Positioned(
-      width: 500,
-      height: 200,
-      right: 10,
-      top: 10,
-      child: Card(child: CallScreen(convID: widget.convID)),
+      width: _WindowSize.width,
+      height: _WindowSize.height,
+      left: _left,
+      top: _top,
+      child: Draggable(
+        child: Card(child: CallScreen(convID: widget.convID)),
+        feedback: Container(
+          width: _WindowSize.width,
+          height: _WindowSize.height,
+          color: Colors.red,
+        ),
+        onDragEnd: _moveEnd,
+      ),
     );
   }
+
+  /// Compute new window position
+  void _moveEnd(DraggableDetails details) {
+    // Determine the limits of containing stack
+    RenderBox renderBox = context
+        .findAncestorStateOfType<CallsAreaState>()
+        .context
+        .findRenderObject();
+    final size = renderBox.size;
+    final offset = renderBox.localToGlobal(Offset.zero);
+
+    // Determine new window position
+    _top = details.offset.dy - offset.dy;
+    _left = details.offset.dx - offset.dx;
+
+    // Force the window to appear completely on the screen
+    if (_top + _WindowSize.height >= size.height)
+      _top = size.height - _WindowSize.height;
+    if (_left + _WindowSize.width >= size.width)
+      _left = size.width - _WindowSize.width;
+
+    if (_top < 0) _top = 0;
+    if (_left < 0) _left = 0;
+
+    setState(() {});
+  }
 }