Function Get-PendingReboot {
	<#
.SYNOPSIS
    Gets the pending reboot status on a local or remote computer.

.DESCRIPTION
    This function will query the registry on a local or remote computer and determine if the
    system is pending a reboot, from Microsoft updates, Configuration Manager Client SDK, Pending Computer
    Rename, Domain Join or Pending File Rename Operations. For Windows 2008+ the function will query the
    CBS registry key as another factor in determining pending reboot state.  "PendingFileRenameOperations"
    and "Auto Update\RebootRequired" are observed as being consistant across Windows Server 2003 & 2008.

    CBServicing = Component Based Servicing (Windows 2008+)
    WindowsUpdate = Windows Update / Auto Update (Windows 2003+)
    CCMClientSDK = SCCM 2012 Clients only (DetermineIfRebootPending method) otherwise $null value
    PendComputerRename = Detects either a computer rename or domain join operation (Windows 2003+)
    PendFileRename = PendingFileRenameOperations (Windows 2003+)
    PendFileRenVal = PendingFilerenameOperations registry value; used to filter if need be, some Anti-
                     Virus leverage this key for def/dat removal, giving a false positive PendingReboot

.PARAMETER ComputerName
    A single Computer or an array of computer names.  The default is localhost ($env:COMPUTERNAME).

.PARAMETER ErrorLog
    A single path to send error data to a log file.

.EXAMPLE
    PS C:\> Get-PendingReboot -ComputerName (Get-Content C:\ServerList.txt) | Format-Table -AutoSize

    Computer CBServicing WindowsUpdate CCMClientSDK PendFileRename PendFileRenVal RebootPending
    -------- ----------- ------------- ------------ -------------- -------------- -------------
    DC01           False         False                       False                        False
    DC02           False         False                       False                        False
    FS01           False         False                       False                        False

    This example will capture the contents of C:\ServerList.txt and query the pending reboot
    information from the systems contained in the file and display the output in a table. The
    null values are by design, since these systems do not have the SCCM 2012 client installed,
    nor was the PendingFileRenameOperations value populated.

.EXAMPLE
    PS C:\> Get-PendingReboot

    Computer           : WKS01
    CBServicing        : False
    WindowsUpdate      : True
    CCMClient          : False
    PendComputerRename : False
    PendFileRename     : False
    PendFileRenVal     :
    RebootPending      : True

    This example will query the local machine for pending reboot information.

.EXAMPLE
    PS C:\> $Servers = Get-Content C:\Servers.txt
    PS C:\> Get-PendingReboot -Computer $Servers | Export-Csv C:\PendingRebootReport.csv -NoTypeInformation

    This example will create a report that contains pending reboot information.

.LINK
    Component-Based Servicing:
    http://technet.microsoft.com/en-us/library/cc756291(v=WS.10).aspx

    PendingFileRename/Auto Update:
    http://support.microsoft.com/kb/2723674
    http://technet.microsoft.com/en-us/library/cc960241.aspx
    http://blogs.msdn.com/b/hansr/archive/2006/02/17/patchreboot.aspx

    SCCM 2012/CCM_ClientSDK:
    http://msdn.microsoft.com/en-us/library/jj902723.aspx

.NOTES
    Author:  Brian Wilhite
    Email:   bcwilhite (at) live.com
    Date:    29AUG2012
    PSVer:   2.0/3.0/4.0/5.0
    Updated: 27JUL2015
    UpdNote: Added Domain Join detection to PendComputerRename, does not detect Workgroup Join/Change
             Fixed Bug where a computer rename was not detected in 2008 R2 and above if a domain join occurred at the same time.
             Fixed Bug where the CBServicing wasn't detected on Windows 10 and/or Windows Server Technical Preview (2016)
             Added CCMClient property - Used with SCCM 2012 Clients only
             Added ValueFromPipelineByPropertyName=$true to the ComputerName Parameter
             Removed $Data variable from the PSObject - it is not needed
             Bug with the way CCMClientSDK returned null value if it was false
             Removed unneeded variables
             Added PendFileRenVal - Contents of the PendingFileRenameOperations Reg Entry
             Removed .Net Registry connection, replaced with WMI StdRegProv
             Added ComputerPendingRename
#>

	[CmdletBinding()]
	param(
		[Parameter(Position = 0, ValueFromPipeline = $true, ValueFromPipelineByPropertyName = $true)]
		[Alias("CN", "Computer")]
		[String[]]$ComputerName = "$env:COMPUTERNAME",
		[String]$ErrorLog
	)

	Begin {  }## End Begin Script Block
	Process {
  Foreach ($Computer in $ComputerName) {
			Try {
				## Setting pending values to false to cut down on the number of else statements
				$CompPendRen, $PendFileRename, $Pending, $SCCM = $false, $false, $false, $false

				## Setting CBSRebootPend to null since not all versions of Windows has this value
				$CBSRebootPend = $null

				## Querying WMI for build version
				$WMI_OS = Get-WmiObject -Class Win32_OperatingSystem -Property BuildNumber, CSName -ComputerName $Computer -ErrorAction Stop

				## Making registry connection to the local/remote computer
				$HKLM = [UInt32] "0x80000002"
				$WMI_Reg = [WMIClass] "\\$Computer\root\default:StdRegProv"

				## If Vista/2008 & Above query the CBS Reg Key
				If ([Int32]$WMI_OS.BuildNumber -ge 6001) {
					$RegSubKeysCBS = $WMI_Reg.EnumKey($HKLM, "SOFTWARE\Microsoft\Windows\CurrentVersion\Component Based Servicing\")
					$CBSRebootPend = $RegSubKeysCBS.sNames -contains "RebootPending"
				}

				## Query WUAU from the registry
				$RegWUAURebootReq = $WMI_Reg.EnumKey($HKLM, "SOFTWARE\Microsoft\Windows\CurrentVersion\WindowsUpdate\Auto Update\")
				$WUAURebootReq = $RegWUAURebootReq.sNames -contains "RebootRequired"

				## Query PendingFileRenameOperations from the registry
				$RegSubKeySM = $WMI_Reg.GetMultiStringValue($HKLM, "SYSTEM\CurrentControlSet\Control\Session Manager\", "PendingFileRenameOperations")
				$RegValuePFRO = $RegSubKeySM.sValue

				## Query JoinDomain key from the registry - These keys are present if pending a reboot from a domain join operation
				$Netlogon = $WMI_Reg.EnumKey($HKLM, "SYSTEM\CurrentControlSet\Services\Netlogon").sNames
				$PendDomJoin = ($Netlogon -contains 'JoinDomain') -or ($Netlogon -contains 'AvoidSpnSet')

				## Query ComputerName and ActiveComputerName from the registry
				$ActCompNm = $WMI_Reg.GetStringValue($HKLM, "SYSTEM\CurrentControlSet\Control\ComputerName\ActiveComputerName\", "ComputerName")
				$CompNm = $WMI_Reg.GetStringValue($HKLM, "SYSTEM\CurrentControlSet\Control\ComputerName\ComputerName\", "ComputerName")

				If (($ActCompNm -ne $CompNm) -or $PendDomJoin) {
					$CompPendRen = $true
				}

				## If PendingFileRenameOperations has a value set $RegValuePFRO variable to $true
				If ($RegValuePFRO) {
					$PendFileRename = $true
				}

				## Determine SCCM 2012 Client Reboot Pending Status
				## To avoid nested 'if' statements and unneeded WMI calls to determine if the CCM_ClientUtilities class exist, setting EA = 0
				$CCMClientSDK = $null
				$CCMSplat = @{
					NameSpace    = 'ROOT\ccm\ClientSDK'
					Class        = 'CCM_ClientUtilities'
					Name         = 'DetermineIfRebootPending'
					ComputerName = $Computer
					ErrorAction  = 'Stop'
				}
				## Try CCMClientSDK
				Try {
					$CCMClientSDK = Invoke-WmiMethod @CCMSplat
				}
				Catch [System.UnauthorizedAccessException] {
					$CcmStatus = Get-Service -Name CcmExec -ComputerName $Computer -ErrorAction SilentlyContinue
					If ($CcmStatus.Status -ne 'Running') {
						Write-Warning "$Computer`: Error - CcmExec service is not running."
						$CCMClientSDK = $null
					}
				}
				Catch {
					$CCMClientSDK = $null
				}

				If ($CCMClientSDK) {
					If ($CCMClientSDK.ReturnValue -ne 0) {
						Write-Warning "Error: DetermineIfRebootPending returned error code $($CCMClientSDK.ReturnValue)"
					}
					If ($CCMClientSDK.IsHardRebootPending -or $CCMClientSDK.RebootPending) {
						$SCCM = $true
					}
				}

				Else {
					$SCCM = $null
				}

				## Creating Custom PSObject and Select-Object Splat
				$SelectSplat = @{
					Property = (
						'Computer',
						'CBServicing',
						'WindowsUpdate',
						'CCMClientSDK',
						'PendComputerRename',
						'PendFileRename',
						'PendFileRenVal',
						'RebootPending'
					)
				}
				New-Object -TypeName PSObject -Property @{
					Computer           = $WMI_OS.CSName
					CBServicing        = $CBSRebootPend
					WindowsUpdate      = $WUAURebootReq
					CCMClientSDK       = $SCCM
					PendComputerRename = $CompPendRen
					PendFileRename     = $PendFileRename
					PendFileRenVal     = $RegValuePFRO
					RebootPending      = ($CompPendRen -or $CBSRebootPend -or $WUAURebootReq -or $SCCM -or $PendFileRename)
				} | Select-Object @SelectSplat

			}
			Catch {
				Write-Warning "$Computer`: $_"
				## If $ErrorLog, log the file to a user specified location/path
				If ($ErrorLog) {
					Out-File -InputObject "$Computer`,$_" -FilePath $ErrorLog -Append
				}
			}
  }## End Foreach ($Computer in $ComputerName)
	}## End Process

	End {  }## End End

}## End Function Get-PendingReboot