<#
.SYNOPSIS
    Shows which update source a Windows device is actually pointed at, and can reset it.
.DESCRIPTION
    Reads the Windows Update policy keys (WSUS server, scan source, WUfB deferrals, the
    Intune/MDM policy store) plus the Windows Update Agent's default service, and makes a
    best guess at where the device gets its updates: WSUS, Windows Update for Business,
    a mix of the two, or plain unmanaged Windows Update.

    With -ResetPolicy it backs up and deletes the local WindowsUpdate policy key, then
    restarts the Windows Update service. Group Policy or ConfigMgr will put back whatever
    they own at the next refresh, so this is for clearing out leftovers, not for fighting
    an active policy.
.PARAMETER ResetPolicy
    Back up and remove HKLM\SOFTWARE\Policies\Microsoft\Windows\WindowsUpdate. Honors -WhatIf.
.PARAMETER BackupPath
    Folder for the .reg backup taken before a reset.
.EXAMPLE
    .\Get-WindowsUpdateSource.ps1
.EXAMPLE
    .\Get-WindowsUpdateSource.ps1 -ResetPolicy -WhatIf
#>
[CmdletBinding(SupportsShouldProcess)]
param(
    [switch]$ResetPolicy,
    [ValidateNotNullOrEmpty()]
    [string]$BackupPath = (Join-Path $env:ProgramData 'WindowsUpdatePolicyBackup')
)

$policyKey = 'HKLM:\SOFTWARE\Policies\Microsoft\Windows\WindowsUpdate'
$mdmKey    = 'HKLM:\SOFTWARE\Microsoft\PolicyManager\current\device\Update'

function Get-RegValues([string]$Path) {
    $item = Get-ItemProperty -Path $Path -ErrorAction SilentlyContinue
    if ($item) { $item } else { [pscustomobject]@{} }
}

function Get-UpdateSourceReport {
    $wu  = Get-RegValues $policyKey
    $au  = Get-RegValues "$policyKey\AU"
    $mdm = Get-RegValues $mdmKey

    # Windows 10 2004 and later: per-class scan source. 1 = WSUS, 0 = Windows Update.
    $scanSource = [ordered]@{}
    foreach ($class in 'Feature', 'Quality', 'Driver', 'Other') {
        $value = $wu."SetPolicyDrivenUpdateSourceFor${class}Updates"
        $scanSource[$class] = switch ($value) { 1 { 'WSUS' } 0 { 'WindowsUpdate' } default { 'NotSet' } }
    }

    $defaultService = $null
    try {
        $manager = New-Object -ComObject Microsoft.Update.ServiceManager
        $defaultService = @($manager.Services) | Where-Object { $_.IsDefaultAUService } | Select-Object -First 1 -ExpandProperty Name
    }
    catch { Write-Verbose "Couldn't query the Windows Update Agent: $($_.Exception.Message)" }

    $usesWsus    = ($au.UseWUServer -eq 1) -and [bool]$wu.WUServer
    $mdmSettings = @($mdm.PSObject.Properties | Where-Object { $_.Name -notlike 'PS*' -and $_.Name -notlike '*_ProviderSet' -and $_.Name -notlike '*_WinningProvider' })
    $hasWufb     = ($null -ne $wu.DeferQualityUpdatesPeriodInDays) -or ($null -ne $wu.DeferFeatureUpdatesPeriodInDays) -or ($null -ne $wu.TargetReleaseVersionInfo) -or ($mdmSettings.Count -gt 0)

    $source = if ($usesWsus -and ($scanSource.Values -contains 'WindowsUpdate')) { 'Mixed (WSUS + Windows Update)' }
              elseif ($usesWsus) { 'WSUS' }
              elseif ($hasWufb) { 'Windows Update for Business' }
              else { 'Windows Update (unmanaged)' }

    $target = (@($wu.ProductVersion, $wu.TargetReleaseVersionInfo) | Where-Object { $_ }) -join ' '

    [pscustomobject]@{
        ComputerName        = $env:COMPUTERNAME
        LikelySource        = $source
        WUServer            = $wu.WUServer
        WUStatusServer      = $wu.WUStatusServer
        UseWUServer         = $au.UseWUServer
        BlockInternetWU     = $wu.DoNotConnectToWindowsUpdateInternetLocations
        ScanSourceFeature   = $scanSource.Feature
        ScanSourceQuality   = $scanSource.Quality
        ScanSourceDriver    = $scanSource.Driver
        ScanSourceOther     = $scanSource.Other
        DeferQualityDays    = $wu.DeferQualityUpdatesPeriodInDays
        DeferFeatureDays    = $wu.DeferFeatureUpdatesPeriodInDays
        TargetVersion       = if ($target) { $target } else { $null }
        MdmUpdateSettings   = $mdmSettings.Count
        NoAutoUpdate        = $au.NoAutoUpdate
        DefaultAUService    = $defaultService
        ConfigMgrClient     = [bool](Get-Service -Name CcmExec -ErrorAction SilentlyContinue)
    }
}

$report = Get-UpdateSourceReport

if (-not $ResetPolicy) { return $report }

if (-not (Get-Item -Path $policyKey -ErrorAction SilentlyContinue)) {
    Write-Verbose 'No local WindowsUpdate policy key. Nothing to reset.'
    return $report
}

if ($report.ConfigMgrClient) {
    Write-Warning 'This device has a ConfigMgr client. Its software update point will rewrite the WSUS settings at the next policy cycle.'
}

if ($PSCmdlet.ShouldProcess($env:COMPUTERNAME, "Back up and remove $policyKey, then restart wuauserv")) {
    try {
        if (-not (Test-Path -Path $BackupPath)) { New-Item -Path $BackupPath -ItemType Directory -Force | Out-Null }
        $backupFile = Join-Path $BackupPath ("WindowsUpdate-{0:yyyyMMdd-HHmmss}.reg" -f (Get-Date))
        & reg.exe export 'HKLM\SOFTWARE\Policies\Microsoft\Windows\WindowsUpdate' $backupFile /y | Out-Null
        if ($LASTEXITCODE -ne 0) { throw "reg export failed with exit code $LASTEXITCODE. Not removing anything." }
        Write-Verbose "Backed up policy to $backupFile"

        Remove-Item -Path $policyKey -Recurse -Force -ErrorAction Stop
        Restart-Service -Name wuauserv -Force -ErrorAction Stop
        Write-Verbose 'Policy key removed and Windows Update service restarted.'
    }
    catch {
        Write-Error "Reset failed: $($_.Exception.Message)"
        exit 1
    }
    Get-UpdateSourceReport
}
else {
    $report
}