<#
  set-appcompat.ps1 - apply the DirectDraw compatibility shim to the MW4 executables
  sitting NEXT TO this script, wherever that copy of the game happens to live.

  WHY THIS EXISTS
    MW4 renders at bitdepth=16. Modern GPUs report ZERO 16-bit display modes, so the
    exclusive-fullscreen path cannot set a mode and fails. The DWM8And16BitMitigation
    AppCompat layer is what makes 8/16-bit fullscreen work under the desktop compositor.

    Without it GameOS reports:
        "Another application is preventing use of full screen mode."
    That message is a catch-all raised after every SetDisplayMode attempt has failed --
    it even scans for NetMeeting -- so it sends you hunting for a conflicting program
    that does not exist. The real cause is the missing shim.

    The layer is keyed on the executable's FULL PATH. Every install needs its own entry,
    and copying or moving an install silently loses it. Hence this script: run it from
    inside any deployment and it fixes that deployment.

  USAGE
    Double-click set-appcompat.bat  (recommended - one click, no execution-policy fuss)
    or:  .\set-appcompat.ps1            apply the shim
         .\set-appcompat.ps1 -Remove    remove the entries this script adds
         .\set-appcompat.ps1 -WhatIfOnly   report current state, change nothing

    Run as Administrator to also write the all-users (HKLM) entry. Without elevation the
    per-user (HKCU) entry is written, which is enough for the account that runs the game.
#>

param(
    [string]$Layer        = "DWM8And16BitMitigation HIGHDPIAWARE",
    [switch]$Remove,
    [switch]$WhatIfOnly
)

$ErrorActionPreference = "Stop"

# --- Locate ourselves -------------------------------------------------------------
# $PSScriptRoot is empty on very old hosts and when dot-sourced, so fall back.
$here = $PSScriptRoot
if ([string]::IsNullOrEmpty($here)) {
    $here = Split-Path -Parent $MyInvocation.MyCommand.Path
}

$hkcuLayers = "HKCU:\Software\Microsoft\Windows NT\CurrentVersion\AppCompatFlags\Layers"
$hklmLayers = "HKLM:\SOFTWARE\Microsoft\Windows NT\CurrentVersion\AppCompatFlags\Layers"

$isAdmin = ([Security.Principal.WindowsPrincipal] `
                [Security.Principal.WindowsIdentity]::GetCurrent()
           ).IsInRole([Security.Principal.WindowsBuiltInRole]::Administrator)

Write-Host ""
Write-Host "MW4 DirectDraw compatibility shim" -ForegroundColor Cyan
Write-Host "---------------------------------" -ForegroundColor Cyan
Write-Host "  folder    : $here"
Write-Host "  elevated  : $(if ($isAdmin) { 'yes (HKCU + HKLM)' } else { 'no (HKCU only)' })"
Write-Host ""

# --- Find the executables that need it --------------------------------------------
# Only the game/editor executables drive DirectDraw. Launcher/autoconfig/mw4print do not.
$wanted  = @("MW4.exe", "MW4pro.exe", "MW4Ed2.exe")
$targets = @()
foreach ($name in $wanted) {
    $p = Join-Path $here $name
    if (Test-Path -LiteralPath $p) { $targets += $p }
}

if ($targets.Count -eq 0) {
    Write-Host "No MW4 executables found next to this script." -ForegroundColor Red
    Write-Host "Expected one of: $($wanted -join ', ')"
    Write-Host "Put this script in the same folder as MW4.exe and run it again."
    exit 1
}

# --- Helpers ----------------------------------------------------------------------
function Get-Layer([string]$root, [string]$exe) {
    if (-not (Test-Path -LiteralPath $root)) { return $null }
    $item = Get-ItemProperty -LiteralPath $root -ErrorAction SilentlyContinue
    if ($null -eq $item) { return $null }
    $prop = $item.PSObject.Properties | Where-Object { $_.Name -eq $exe }
    if ($null -eq $prop) { return $null }
    return $prop.Value
}

function Set-Layer([string]$root, [string]$exe, [string]$value) {
    if (-not (Test-Path -LiteralPath $root)) { New-Item -Path $root -Force | Out-Null }
    Set-ItemProperty -LiteralPath $root -Name $exe -Value $value -Type String
}

$failed = 0

foreach ($exe in $targets) {

    Write-Host $exe -ForegroundColor White

    $before = Get-Layer $hkcuLayers $exe
    if ($null -ne $before) {
        Write-Host "    existing HKCU : $before" -ForegroundColor DarkGray
        # The historical failure mode: a HIGHDPIAWARE-only entry, which suppresses the
        # automatic shim and produces exactly the fullscreen failure this script fixes.
        if (-not $Remove -and $before -notmatch "DWM8And16BitMitigation") {
            Write-Host "    NOTE: entry exists but has no DWM8And16BitMitigation -" -ForegroundColor Yellow
            Write-Host "          this specific state BLOCKS fullscreen. Replacing it." -ForegroundColor Yellow
        }
    }

    if ($WhatIfOnly) {
        $lm = Get-Layer $hklmLayers $exe
        Write-Host "    existing HKLM : $(if ($null -ne $lm) { $lm } else { '(none)' })" -ForegroundColor DarkGray
        Write-Host ""
        continue
    }

    if ($Remove) {
        Remove-ItemProperty -LiteralPath $hkcuLayers -Name $exe -ErrorAction SilentlyContinue
        if ($isAdmin) {
            Remove-ItemProperty -LiteralPath $hklmLayers -Name $exe -ErrorAction SilentlyContinue
        }
        Write-Host "    removed" -ForegroundColor Yellow
        Write-Host ""
        continue
    }

    # Per-user. No admin needed, and applies to the account that actually runs the game.
    Set-Layer $hkcuLayers $exe $Layer

    # All-users, if we can. Note the different value format: the HKLM entries use a
    # leading "$ " marker. Do not copy one format into the other key.
    if ($isAdmin) {
        Set-Layer $hklmLayers $exe ("$ " + ($Layer -replace '\s*HIGHDPIAWARE\s*', ''))
    }

    # Verify by reading back rather than trusting the write.
    $after = Get-Layer $hkcuLayers $exe
    if ($after -eq $Layer) {
        Write-Host "    HKCU set      : $after" -ForegroundColor Green
    } else {
        Write-Host "    HKCU FAILED   : got '$after'" -ForegroundColor Red
        $failed++
    }

    if ($isAdmin) {
        $afterM = Get-Layer $hklmLayers $exe
        if ($null -ne $afterM) {
            Write-Host "    HKLM set      : $afterM" -ForegroundColor Green
        } else {
            Write-Host "    HKLM FAILED" -ForegroundColor Red
            $failed++
        }
    }
    Write-Host ""
}

if ($WhatIfOnly) {
    Write-Host "Report only - nothing was changed." -ForegroundColor Cyan
    exit 0
}

if ($failed -gt 0) {
    Write-Host "$failed registry write(s) failed." -ForegroundColor Red
    exit 1
}

if ($Remove) {
    Write-Host "Shim removed. Fullscreen will fail on modern GPUs until it is re-applied." -ForegroundColor Yellow
} else {
    Write-Host "Done. The shim is read when the process starts -" -ForegroundColor Green
    Write-Host "restart MW4 to pick it up. No reboot needed." -ForegroundColor Green
    if (-not $isAdmin) {
        Write-Host ""
        Write-Host "Applied for the current user only. To cover all accounts on this" -ForegroundColor DarkGray
        Write-Host "machine, run this script again as Administrator." -ForegroundColor DarkGray
    }
}
exit 0