param(
    [Parameter(Mandatory=$true)][ValidatePattern('^[A-Z]$')][string]$DriveLetter,
    [Parameter(Mandatory=$true)][ValidatePattern('^[A-Za-z0-9_.-]+$')][string]$UsbSerial,
    [ValidateRange(1,64)][int]$SizeMiB=1
)
$ErrorActionPreference='Stop'
$disk=@(Get-CimInstance Win32_DiskDrive | Where-Object {
    $_.InterfaceType -eq 'USB' -and $_.PNPDeviceID -like "USBSTOR\*\$UsbSerial&*"
})
if($disk.Count -ne 1){throw 'Expected exactly one approved USB disk'}
$partition=Get-Partition -DriveLetter $DriveLetter
if($partition.DiskNumber -ne $disk[0].Index){throw 'Drive letter does not belong to the approved USB disk'}
$stamp=Get-Date -Format 'yyyyMMdd-HHmmss'
$name="VDI_USB_TEST_$stamp"
$local=Join-Path $env:TEMP $name
$usb=Join-Path "${DriveLetter}:\" $name
if((Test-Path -LiteralPath $local) -or (Test-Path -LiteralPath $usb)){throw 'Test directory already exists'}
New-Item -ItemType Directory -Path $local,$usb | Out-Null
$bytes=New-Object byte[] ($SizeMiB*1MB)
$rng=[Security.Cryptography.RandomNumberGenerator]::Create()
try{$rng.GetBytes($bytes)}finally{$rng.Dispose()}
$source=Join-Path $local 'source.bin'
[IO.File]::WriteAllBytes($source,$bytes)
$target=Join-Path $usb 'from-windows.bin'
$stream=[IO.File]::Open($target,[IO.FileMode]::CreateNew,[IO.FileAccess]::Write,[IO.FileShare]::None)
try{$stream.Write($bytes,0,$bytes.Length);$stream.Flush($true)}finally{$stream.Dispose()}
$copy=Join-Path $local 'readback.bin'
Copy-Item -LiteralPath $target -Destination $copy
$a=(Get-FileHash -LiteralPath $source -Algorithm SHA256).Hash
$b=(Get-FileHash -LiteralPath $target -Algorithm SHA256).Hash
$c=(Get-FileHash -LiteralPath $copy -Algorithm SHA256).Hash
if($a -ne $b -or $a -ne $c){throw 'USB read/write hash mismatch'}
[IO.File]::WriteAllText((Join-Path $usb 'readme.txt'),"VDI USB device POC test. Only this directory was created by the test.`r`n",[Text.Encoding]::UTF8)
[pscustomobject]@{Result='PASS';Model=$disk[0].Model;InterfaceType=$disk[0].InterfaceType;PNPDeviceID=$disk[0].PNPDeviceID;DriveLetter=$DriveLetter;TestDirectory=$usb;LocalDirectory=$local;Bytes=$bytes.Length;SHA256=$a} | ConvertTo-Json