fix: flatten nested container when it only has one child remaining

GlazeWM.Domain/Common/Enums/TilingDirection.cs

@@ -1,8 +1,27 @@
+using System;
+
 namespace GlazeWM.Domain.Common.Enums
 {
   public enum TilingDirection
   {
     Vertical,
     Horizontal,
   }
+
+  public static class TilingDirectionExtensions
+  {
+    /// <summary>
+    /// Get the inverse of a given tiling direction.
+    /// </summary>
+    /// <exception cref="ArgumentOutOfRangeException"></exception>
+    public static TilingDirection Inverse(this TilingDirection tilingDirection)
+    {
+      return tilingDirection switch
+      {
+        TilingDirection.Vertical => TilingDirection.Horizontal,
+        TilingDirection.Horizontal => TilingDirection.Vertical,
+        _ => throw new ArgumentOutOfRangeException(nameof(tilingDirection)),
+      };
+    }
+  }
 }

GlazeWM.Domain/Containers/CommandHandlers/AttachContainerHandler.cs

@@ -1,15 +1,18 @@
 using System;
+using System.Linq;
 using GlazeWM.Domain.Containers.Commands;
 using GlazeWM.Infrastructure.Bussing;
 
 namespace GlazeWM.Domain.Containers.CommandHandlers
 {
   internal sealed class AttachContainerHandler : ICommandHandler<AttachContainerCommand>
   {
+    private readonly Bus _bus;
     private readonly ContainerService _containerService;
 
-    public AttachContainerHandler(ContainerService containerService)
+    public AttachContainerHandler(Bus bus, ContainerService containerService)
     {
+      _bus = bus;
       _containerService = containerService;
     }
 
@@ -22,13 +25,31 @@ public CommandResponse Handle(AttachContainerCommand command)
       if (!childToAdd.IsDetached())
         throw new Exception("Cannot attach an already attached container. This is a bug.");
 
-      childToAdd.Parent = targetParent;
-      targetParent.Children.Insert(targetIndex, childToAdd);
-      targetParent.ChildFocusOrder.Add(childToAdd);
+      targetParent.InsertChild(targetIndex, childToAdd);
+
+      if (childToAdd is IResizable)
+        ResizeAttachedContainer(childToAdd);
 
       _containerService.ContainersToRedraw.Add(targetParent);
 
       return CommandResponse.Ok;
     }
+
+    public void ResizeAttachedContainer(Container attachedContainer)
+    {
+      var resizableSiblings = attachedContainer.SiblingsOfType<IResizable>();
+
+      if (!resizableSiblings.Any())
+      {
+        (attachedContainer as IResizable).SizePercentage = 1;
+        return;
+      }
+
+      var defaultPercent = 1.0 / (resizableSiblings.Count() + 1);
+
+      // Set initial size percentage to 0, and then size up the container to `defaultPercent`.
+      (attachedContainer as IResizable).SizePercentage = 0;
+      _bus.Invoke(new ResizeContainerCommand(attachedContainer, defaultPercent));
+    }
   }
 }

GlazeWM.Domain/Containers/CommandHandlers/ChangeTilingDirectionHandler.cs

@@ -70,10 +70,10 @@ private void ChangeWindowTilingDirection(
       // the split container after the replacement.
       _bus.Invoke(new ReplaceContainerCommand(splitContainer, parent, window.Index));
 
-      // The child window takes up the full size of its parent split container.
+      // Add the window as a child of the split container and ensure it takes up the full size
+      // of its parent split container.
+      splitContainer.InsertChild(0, window);
       (window as IResizable).SizePercentage = 1;
-      _bus.Invoke(new DetachContainerCommand(window));
-      _bus.Invoke(new AttachContainerCommand(window, splitContainer));
     }
 
     private void ChangeWorkspaceTilingDirection(

GlazeWM.Domain/Containers/CommandHandlers/DetachContainerHandler.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Linq;
 using GlazeWM.Domain.Containers.Commands;
 using GlazeWM.Domain.Workspaces;
 using GlazeWM.Infrastructure.Bussing;
@@ -20,26 +21,63 @@ public CommandResponse Handle(DetachContainerCommand command)
     {
       var childToRemove = command.ChildToRemove;
       var parent = childToRemove.Parent;
+      var grandparent = parent.Parent;
+      var siblings = childToRemove.Siblings;
 
       if (parent == null)
         throw new Exception("Cannot detach an already detached container. This is a bug.");
 
-      childToRemove.Parent = null;
-      parent.Children.Remove(childToRemove);
-      parent.ChildFocusOrder.Remove(childToRemove);
+      parent.RemoveChild(childToRemove);
 
-      var isEmptySplitContainer = parent is SplitContainer && !parent.HasChildren()
-        && parent is not Workspace;
+      var parentSiblings = parent.Siblings;
+      var isEmptySplitContainer =
+        !parent.HasChildren() && parent is SplitContainer and not Workspace;
 
-      // If the parent of the removed child is an empty split container, detach the split container
-      // as well.
+      // Get the freed up space after container is detached.
+      var availableSizePercentage = isEmptySplitContainer
+        ? (parent as IResizable).SizePercentage
+        : (childToRemove as IResizable)?.SizePercentage ?? 0;
+
+      // Resize children of grandparent if `childToRemove`'s parent is also to be detached.
+      var containersToResize = isEmptySplitContainer
+        ? grandparent.ChildrenOfType<IResizable>()
+        : parent.ChildrenOfType<IResizable>();
+
+      // If the parent of the removed child is now an empty split container, detach the
+      // split container as well.
+      // TODO: Move out calls to `ContainersToRedraw.Add(...)`, since detaching might not
+      // always require a redraw.
       if (isEmptySplitContainer)
       {
-        _bus.Invoke(new DetachContainerCommand(parent));
-        return CommandResponse.Ok;
+        _containerService.ContainersToRedraw.Add(parent.Parent);
+        grandparent.RemoveChild(parent);
+      }
+      else
+        _containerService.ContainersToRedraw.Add(parent);
+
+      if (availableSizePercentage != 0)
+      {
+        var sizePercentageIncrement = availableSizePercentage / containersToResize.Count();
+
+        // Adjust `SizePercentage` of the siblings of the removed container.
+        foreach (var containerToResize in containersToResize)
+          ((IResizable)containerToResize).SizePercentage += sizePercentageIncrement;
       }
 
-      _containerService.ContainersToRedraw.Add(parent);
+      var detachedSiblings = isEmptySplitContainer ? parentSiblings : siblings;
+      var detachedParent = isEmptySplitContainer ? grandparent : parent;
+
+      // If there is exactly *one* sibling to the detached container, then flatten that
+      // sibling if it's a split container. This is to handle layouts like H[1 V[2 H[3]]],
+      // where container 2 gets detached.
+      if (detachedSiblings.Count() == 1 && detachedSiblings.ElementAt(0) is SplitContainer && childToRemove is not Workspace)
+      {
+        _bus.Invoke(
+          new FlattenSplitContainerCommand(detachedSiblings.ElementAt(0) as SplitContainer)
+        );
+
+        _bus.Invoke(new FlattenSplitContainerCommand(detachedParent as SplitContainer));
+      }
 
       return CommandResponse.Ok;
     }

GlazeWM.Domain/Containers/CommandHandlers/FlattenSplitContainerHandler.cs

@@ -1,4 +1,5 @@
 using System.Linq;
+using GlazeWM.Domain.Common.Enums;
 using GlazeWM.Domain.Containers.Commands;
 using GlazeWM.Infrastructure.Bussing;
 using GlazeWM.Infrastructure.Utils;
@@ -7,45 +8,47 @@ namespace GlazeWM.Domain.Containers.CommandHandlers
 {
   internal sealed class FlattenSplitContainerHandler : ICommandHandler<FlattenSplitContainerCommand>
   {
-    private readonly Bus _bus;
     private readonly ContainerService _containerService;
 
-    public FlattenSplitContainerHandler(Bus bus, ContainerService containerService)
+    public FlattenSplitContainerHandler(ContainerService containerService)
     {
-      _bus = bus;
       _containerService = containerService;
     }
 
     public CommandResponse Handle(FlattenSplitContainerCommand command)
     {
-      var containerToFlatten = command.ContainerToFlatten;
+      var splitContainer = command.ContainerToFlatten;
 
       // Keep references to properties of container to flatten prior to detaching.
-      var originalParent = containerToFlatten.Parent;
-      var originalChildren = containerToFlatten.Children.ToList();
-      var originalFocusIndex = containerToFlatten.FocusIndex;
-      var originalIndex = containerToFlatten.Index;
-      var originalFocusOrder = containerToFlatten.ChildFocusOrder.ToList();
+      var parent = splitContainer.Parent;
+      var index = splitContainer.Index;
+      var focusIndex = splitContainer.FocusIndex;
+      var children = splitContainer.Children.ToList();
+      var focusOrder = splitContainer.ChildFocusOrder.ToList();
 
-      foreach (var (child, index) in originalChildren.WithIndex())
+      foreach (var (child, childIndex) in children.WithIndex())
       {
-        // Insert children of the split container at its original index in the parent. The split
-        // container will automatically detach once its last child is detached.
-        _bus.Invoke(new DetachContainerCommand(child));
-        _bus.Invoke(new AttachContainerCommand(child, originalParent, originalIndex + index));
+        // Insert child at its original index in the parent.
+        splitContainer.RemoveChild(child);
+        parent.Children.Insert(index + childIndex, child);
+        child.Parent = parent;
 
-        (child as IResizable).SizePercentage = (containerToFlatten as IResizable).SizePercentage
-          * (child as IResizable).SizePercentage;
+        if (child is IResizable childResizable)
+          childResizable.SizePercentage = splitContainer.SizePercentage * childResizable.SizePercentage;
+
+        // Inverse the tiling direction of any child split containers.
+        if (child is SplitContainer childSplitContainer)
+          childSplitContainer.TilingDirection = childSplitContainer.TilingDirection.Inverse();
       }
 
+      // Remove the split container from the tree.
+      parent.RemoveChild(splitContainer);
+
       // Correct focus order of the inserted containers.
-      foreach (var child in originalChildren)
-      {
-        var childFocusIndex = originalFocusOrder.IndexOf(child);
-        originalParent.ChildFocusOrder.ShiftToIndex(originalFocusIndex + childFocusIndex, child);
-      }
+      parent.ChildFocusOrder.InsertRange(focusIndex, focusOrder);
 
-      _containerService.ContainersToRedraw.Add(originalParent);
+      // TODO: Remove unnecessary redraws.
+      _containerService.ContainersToRedraw.Add(parent);
 
       return CommandResponse.Ok;
     }