Add Collapse/Flatten context menu items to a directory

CollapseFolder.ps1

<#
powershell -ExecutionPolicy RemoteSigned -NoProfile -File "CollapseFolder.ps1" Install
#>
Add-Type @"
using System;
using System.Collections.Generic;
using System.Runtime.InteropServices;

public class X
{
	[InterfaceType(ComInterfaceType.InterfaceIsIUnknown)] public interface IBindCtx {}
	public enum SIGDN : uint { SIGDN_NORMALDISPLAY = 0x00000000, SIGDN_DESKTOPABSOLUTEPARSING = 0x80028000 }
	[ComImport] [Guid("43826d1e-e718-42ee-bc55-a1e261c37bfe")] [InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
	public interface IShellItem
	{
		[return: MarshalAs(UnmanagedType.Interface)] object BindToHandler(IBindCtx pbc, ref Guid bhid, ref Guid riid);
		IShellItem GetParent();
		[return: MarshalAs(UnmanagedType.LPWStr)] string GetDisplayName(SIGDN sigdnName);
		int GetAttributes(uint sfgaoMask);
		int Compare(IShellItem psi, uint hint);
	}
	public static Guid IID_IShellItem = typeof(IShellItem).GUID;

	[InterfaceType(ComInterfaceType.InterfaceIsIUnknown)] public interface IFileOperationProgressSink {}
	[ComImport] [Guid("947aab5f-0a5c-4c13-b4d6-4bf7836fc9f8")] [InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
	public interface IFileOperation
	{
		uint Advise();
		void Unadvise(uint dwCookie);
		[PreserveSig] int SetOperationFlags(uint dwOperationFlags);
		void SetProgressMessage([MarshalAs(UnmanagedType.LPWStr)] string pszMessage);
		void SetProgressDialog([MarshalAs(UnmanagedType.Interface)] object popd);
		void SetProperties();
		void SetOwnerWindow();
		void ApplyPropertiesToItem();
		void ApplyPropertiesToItems();
		void RenameItem();
		void RenameItems();
		[PreserveSig] int MoveItem(IShellItem psiItem, IShellItem psiDestinationFolder, IntPtr NewName, IntPtr Sink);
		void MoveItems([MarshalAs(UnmanagedType.Interface)] object punkItems, IShellItem psiDestinationFolder);
		void CopyItem(IShellItem psiItem, IShellItem psiDestinationFolder, [MarshalAs(UnmanagedType.LPWStr)] string pszNewName, IFileOperationProgressSink pfopsItem);
		void CopyItems();
		[PreserveSig] int DeleteItem(IShellItem psiItem, IntPtr Sink);
		void DeleteItems();
		int NewItem();
		[PreserveSig] int PerformOperations();
		[return: MarshalAs(UnmanagedType.Bool)] bool GetAnyOperationsAborted();
	}
	[ComImport] [Guid("3AD05575-8857-4850-9277-11B85BDB8E09")] public class FileOperation { } 

	[DllImport("shell32.dll", SetLastError = false, CharSet = CharSet.Unicode)]
	static extern int SHCreateItemFromParsingName(string Path, IntPtr pbc, ref Guid riid, out IShellItem ppv);

	public static int AddMove(ref IFileOperation FO, string Source, string DestinationFolder)
	{
		IShellItem sis, sid;
		int hr = SHCreateItemFromParsingName(Source, IntPtr.Zero, ref IID_IShellItem, out sis);
		if (hr < 0 ) return hr;
		hr = SHCreateItemFromParsingName(DestinationFolder, IntPtr.Zero, ref IID_IShellItem, out sid);
		if (hr < 0 ) return hr;
		return FO.MoveItem(sis, sid, IntPtr.Zero, IntPtr.Zero);
	}

	public static int CollapseDir(ref IFileOperation FOM, ref List<string> DD, string Src, string Dst, bool Recurse)
	{
		int hr = 0, tmphr;
		Func<string, System.Collections.Generic.IEnumerable<string>> enumfunc = System.IO.Directory.EnumerateFileSystemEntries;
		if (Recurse)
		{
			foreach (var d in System.IO.Directory.EnumerateDirectories(Src))
			{
				CollapseDir(ref FOM, ref DD, d, Dst, Recurse);
			}
			enumfunc = System.IO.Directory.EnumerateFiles;
		}
		foreach (var e in enumfunc(Src))
		{
			tmphr = AddMove(ref FOM, e, Dst);
			if (hr >= 0) hr = tmphr;
		}
		DD.Add(Src);
		return hr;
	}

	public static int Collapse(string Dir, bool Recurse)
	{
		List<string> deleteDirs = new List<string>();
		IFileOperation fom = (IFileOperation) new FileOperation();
		fom.SetOperationFlags(0x4240);
		int hr = 0, tmphr;
		var items = System.IO.Directory.EnumerateDirectories(Dir);
		foreach (var d in items)
		{
			tmphr = CollapseDir(ref fom, ref deleteDirs, d, Dir, Recurse);
			if (hr >= 0) hr = tmphr;
		}
		if (deleteDirs.Count > 0) hr = fom.PerformOperations();
		if (hr >= 0) foreach (var d in deleteDirs) System.IO.Directory.Delete(d);
		return hr;
	}
}
"@

$scriptDir = split-path -parent $MyInvocation.MyCommand.Definition
$scriptPath = [System.IO.Path]::GetFullPath($MyInvocation.MyCommand.Definition)
$mode = $false; $recurse = $false;
ForEach ($arg in $args)
{
	$rp = 'HKCU:\Software\Classes\Directory\Shell';
	$cmdbase = '"PowerShell.exe" -ExecutionPolicy RemoteSigned -NonInteractive -NoProfile -WindowStyle Hidden -File "' + $scriptPath + '" ';
	if ($mode)
	{
		[X]::Collapse($arg, $recurse);
	}
	elseif ($arg -eq 'INSTALL')
	{
		New-Item -Path "$rp\\Collapse\\command" -Force | Out-Null
		New-ItemProperty -Path "$rp\\Collapse\\command" -Name '(Default)' -Type 'String' -Force -Value ($cmdbase + 'One "%1"') | Out-Null
		New-Item -Path "$rp\\Flatten\\command" -Force | Out-Null
		New-ItemProperty -Path "$rp\\Flatten\\command" -Name '(Default)' -Type 'String' -Force -Value ($cmdbase + 'All "%1"') | Out-Null
		Break;
	}
	elseif ($arg -eq 'UNINSTALL')
	{
		if (Test-Path("$rp\\Collapse")) { Remove-Item "$rp\\Collapse" -Recurse -Force | Out-Null }
		if (Test-Path("$rp\\Flatten")) { Remove-Item "$rp\\Flatten" -Recurse -Force | Out-Null }
		Break;
	}
	elseif ($arg -eq 'ONE')
	{
		$mode = $true; $recurse = $false;
	}
	elseif ($arg -eq 'ALL')
	{
		$mode = $true; $recurse = $true;
	}
	else
	{
		Write-Host 'Usage: <INSTALL|UNINSTALL|ONE|ALL> ["Path"] [..]';
		Break;
	}
}