Proper C# Borderless Window Maximization v1.2

CompositionTarget WindowCompositionTarget { get; set; }

double CachedMinWidth { get; set; }

double CachedMinHeight { get; set; }

POINT CachedMinTrackSize { get; set; }

IntPtr WindowProc(IntPtr hwnd, int msg, IntPtr wParam, IntPtr lParam, ref bool handled)
{
    switch (msg)
    {
        case 0x0024:
            MINMAXINFO mmi = (MINMAXINFO)Marshal.PtrToStructure(lParam, typeof(MINMAXINFO));
            IntPtr monitor = MonitorFromWindow(hwnd, 0x00000002 /*MONITOR_DEFAULTTONEAREST*/);
            if (monitor != IntPtr.Zero)
            {
                MONITORINFO monitorInfo = new MONITORINFO { };
                GetMonitorInfo(monitor, monitorInfo);
                RECT rcWorkArea = monitorInfo.rcWork;
                RECT rcMonitorArea = monitorInfo.rcMonitor;
                mmi.ptMaxPosition.x = Math.Abs(rcWorkArea.left - rcMonitorArea.left);
                mmi.ptMaxPosition.y = Math.Abs(rcWorkArea.top - rcMonitorArea.top);
                mmi.ptMaxSize.x = Math.Abs(rcWorkArea.right - rcWorkArea.left);
                mmi.ptMaxSize.y = Math.Abs(rcWorkArea.bottom - rcWorkArea.top);
                if (!CachedMinTrackSize.Equals(mmi.ptMinTrackSize) || CachedMinHeight != MinHeight && CachedMinWidth != MinWidth)
                {
                    mmi.ptMinTrackSize.x = (int)((CachedMinWidth = MinWidth) * WindowCompositionTarget.TransformToDevice.M11);
                    mmi.ptMinTrackSize.y = (int)((CachedMinHeight = MinHeight) * WindowCompositionTarget.TransformToDevice.M22);
                    CachedMinTrackSize = mmi.ptMinTrackSize;
                }
            }
            Marshal.StructureToPtr(mmi, lParam, true);
            handled = true;
            break;
    }
    return IntPtr.Zero;
}

[StructLayout(LayoutKind.Sequential)]
public struct POINT
{
    public int x;
    public int y;
}

[StructLayout(LayoutKind.Sequential)]
public struct MINMAXINFO
{
    public POINT ptReserved;
    public POINT ptMaxSize;
    public POINT ptMaxPosition;
    public POINT ptMinTrackSize;
    public POINT ptMaxTrackSize;
};

[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Auto)]
public class MONITORINFO
{
    public int cbSize = Marshal.SizeOf(typeof(MONITORINFO));
    public RECT rcMonitor = new RECT { };
    public RECT rcWork = new RECT { };
    public int dwFlags = 0;
}

[StructLayout(LayoutKind.Sequential, Pack = 0)]
public struct RECT
{
    public int left;
    public int top;
    public int right;
    public int bottom;
}

[DllImport("user32")]
internal static extern bool GetMonitorInfo(IntPtr hMonitor, MONITORINFO lpmi);

[DllImport("User32")]
internal static extern IntPtr MonitorFromWindow(IntPtr handle, int flags);

public MainWindow()
{
    InitializeComponent();
    MinimizeButton.Click += (s, e) => WindowState = WindowState.Minimized;
    MaximizeButton.Click += (s, e) => WindowState = WindowState == WindowState.Maximized ? WindowState.Normal : WindowState.Maximized;
    CloseButton.Click += (s, e) => Close();
    SourceInitialized += (s, e) =>
    {
        WindowCompositionTarget = PresentationSource.FromVisual(this).CompositionTarget;
        HwndSource.FromHwnd(new WindowInteropHelper(this).Handle).AddHook(WindowProc);
    };
}