param(
    [ValidateSet('Query', 'List', 'Apply', 'Restore')][string]$Action = 'Query',
    [ValidateRange(640, 7680)][int]$Width = 2560,
    [ValidateRange(480, 4320)][int]$Height = 1440,
    [ValidateRange(24, 240)][int]$RefreshRate = 60,
    [string]$BackupPath = 'C:\ProgramData\VDI\mouse-optimization\display-before.json'
)
$ErrorActionPreference = 'Stop'
# Run in the logged-in desktop session. Apply is temporary (no registry update).
# Never assumes DISPLAY1, and refuses ambiguous active virtual displays.
Add-Type -TypeDefinition @'
using System;
using System.Collections.Generic;
using System.Runtime.InteropServices;
public static class VdiModeProbe {
    [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]
    public struct Device {
        public int cb;
        [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 32)] public string Name;
        [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 128)] public string Description;
        public int Flags;
        [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 128)] public string Id;
        [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 128)] public string Key;
    }
    [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]
    public struct Mode {
        [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 32)] public string name;
        public short spec, driver, size, extra;
        public int fields, x, y, orientation, fixedOutput;
        public short color, duplex, yres, tt, collate;
        [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 32)] public string form;
        public short logPixels;
        public int bpp, width, height, flags, hz, icmMethod, icmIntent, media, dither,
            reserved1, reserved2, panWidth, panHeight;
    }
    [DllImport("user32.dll", CharSet = CharSet.Unicode)]
    static extern bool EnumDisplayDevices(string name, uint index, ref Device dev, uint flags);
    [DllImport("user32.dll", CharSet = CharSet.Unicode)]
    static extern bool EnumDisplaySettings(string name, int index, ref Mode mode);
    [DllImport("user32.dll", CharSet = CharSet.Unicode)]
    static extern int ChangeDisplaySettingsEx(string name, ref Mode mode, IntPtr window, uint flags, IntPtr param);
    public static string Find() {
        string found = null;
        for (uint i = 0; ; i++) {
            var d = new Device(); d.cb = Marshal.SizeOf(typeof(Device));
            if (!EnumDisplayDevices(null, i, ref d, 0)) return found;
            if ((d.Flags & 1) == 0 || d.Description.IndexOf("Virtual Display Driver", StringComparison.OrdinalIgnoreCase) < 0) continue;
            if (found != null) throw new InvalidOperationException("Multiple active virtual displays; select manually");
            found = d.Name;
        }
    }
    public static Mode Current(string name) {
        var m = new Mode(); m.size = (short)Marshal.SizeOf(typeof(Mode));
        if (!EnumDisplaySettings(name, -1, ref m)) throw new InvalidOperationException("Cannot query mode");
        return m;
    }
    public static Mode[] List(string name) {
        var modes = new List<Mode>();
        for(int i=0; ; ++i) {
            var m = new Mode(); m.size = (short)Marshal.SizeOf(typeof(Mode));
            if (!EnumDisplaySettings(name, i, ref m)) return modes.ToArray();
            modes.Add(m);
        }
    }
    public static void Apply(string name, int w, int h, int hz, int bpp) {
        foreach(var m0 in List(name)) {
            var m = m0;
            if(m.width != w || m.height != h || m.hz != hz || m.bpp != bpp) continue;
            m.fields = 0x80000 | 0x100000 | 0x400000 | 0x40000;
            int result = ChangeDisplaySettingsEx(name, ref m, IntPtr.Zero, 2, IntPtr.Zero);
            if(result != 0) throw new InvalidOperationException("Mode test failed: " + result);
            result = ChangeDisplaySettingsEx(name, ref m, IntPtr.Zero, 0, IntPtr.Zero);
            if(result != 0) throw new InvalidOperationException("Mode apply failed: " + result);
            var actual = Current(name);
            if(actual.width != w || actual.height != h || actual.hz != hz || actual.bpp != bpp)
                throw new InvalidOperationException("Mode read-back mismatch");
            return;
        }
        throw new InvalidOperationException("Requested mode not advertised");
    }
}
'@
$device = [VdiModeProbe]::Find()
if (-not $device) { throw 'No active Virtual Display Driver in this session' }
$current = [VdiModeProbe]::Current($device)
if ($Action -eq 'List') {
    [VdiModeProbe]::List($device) | Where-Object { $_.width -eq $Width -and $_.height -eq $Height } |
        Select-Object width,height,hz,bpp | ConvertTo-Json -Compress
    exit 0
}
if ($Action -eq 'Apply') {
    if (-not (Test-Path -LiteralPath $BackupPath)) {
        New-Item -ItemType Directory -Force (Split-Path $BackupPath) | Out-Null
        @{device=$device; width=$current.width; height=$current.height; hz=$current.hz; bpp=$current.bpp} |
            ConvertTo-Json | Set-Content -LiteralPath $BackupPath
    }
    try {
        [VdiModeProbe]::Apply($device,$Width,$Height,$RefreshRate,$current.bpp)
    } catch {
        [VdiModeProbe]::Apply($device,$current.width,$current.height,$current.hz,$current.bpp)
        throw
    }
}
if ($Action -eq 'Restore') {
    $before = Get-Content -LiteralPath $BackupPath -Raw | ConvertFrom-Json
    if ($before.device -ne $device) { throw 'Display identity changed; inspect before restoring' }
    [VdiModeProbe]::Apply($device,$before.width,$before.height,$before.hz,$before.bpp)
}
$current = [VdiModeProbe]::Current($device)
@{device=$device; width=$current.width; height=$current.height; hz=$current.hz; bpp=$current.bpp; action=$Action} |
    ConvertTo-Json -Compress