Fix swapping with two windows visible for two-pane layout (#1241)

Amethyst/Managers/WindowManager.swift

@@ -670,6 +670,10 @@ extension WindowManager: WindowTransitionTarget {
         return windows.isWindowFloating(window)
     }
 
+    func currentLayout() -> Layout<Application.Window>? {
+        return focusedScreenManager()?.currentLayout
+    }
+
     func activeWindows(on screen: Screen) -> [Window] {
         return windows.activeWindows(onScreen: screen).filter { window in
             return window.shouldBeManaged() && !self.windows.isWindowFloating(window)

Amethyst/Managers/WindowTransitionCoordinator.swift

@@ -26,6 +26,7 @@ protocol WindowTransitionTarget: class {
     func executeTransition(_ transition: WindowTransition<Window>)
 
     func isWindowFloating(_ window: Window) -> Bool
+    func currentLayout() -> Layout<Application.Window>?
     func screen(at index: Int) -> Screen?
     func activeWindows(on screen: Screen) -> [Window]
     func nextScreenIndexClockwise(from screen: Screen) -> Int
@@ -49,13 +50,16 @@ class WindowTransitionCoordinator<Target: WindowTransitionTarget> {
             return
         }
 
-        // if there are 2 windows, we can always swap.  Just make sure we don't swap focusedWindow with itself.
-        switch windows.count {
-        case 1:
+        if windows.count == 1 {
             return
-        case 2:
+        } else if windows.count == 2 || target?.currentLayout()?.layoutKey == TwoPaneLayout<Window>.layoutKey {
+            // Swap the two visible windows, keep focus on the main window if it already was there
             target?.executeTransition(.switchWindows(focusedWindow, windows[1 - focusedIndex]))
-        default:
+            if focusedWindow == windows[0] {
+                windows[1 - focusedIndex].focus()
+            }
+        } else {
+            // Swap focused window with main window
             target?.executeTransition(.switchWindows(focusedWindow, windows[0]))
         }
     }