Set-DrainAndReboot.ps1

Import-Module PSScheduledJob
function Set-DrainAndReboot {
    [cmdletbinding()]
    param(
        [parameter(Mandatory)]
        $ComputerName
    )
    $RebootScriptBlock = @'
        $CitrixSessionCount = (Get-CimInstance -Namespace Root\Citrix\hdx -ClassName Citrix_Sessions ).count
        $CycleCount = 0
        do {
            $CycleCount++
            $LogEntry = '[{0}]{1} Cycle:{4} There are {2} sessions remaining on {3}' -f ([datetime]::Now), "`t", $CitrixSessionCount, $env:COMPUTERNAME, $CycleCount
            $ACParams = @{
                Path  = 'C:\RebootMonitor.txt'
                Value = $LogEntry
            }
            Add-Content @ACParams
            Start-Sleep -Seconds 300
        } until ($CitrixSessionCount -eq 0)

        $LogEntry = '[{0}]{1}Rebooting {2}' -f ([datetime]::Now), "`t", $env:COMPUTERNAME
        Restart-Computer -Force
'@
    $Argument = '-nologo -noprofile -encodedcommand {0}' -f  ([System.Convert]::ToBase64String([System.Text.Encoding]::Unicode.GetBytes($RebootScriptBlock)))

    $TaskParams = @{
        Trigger     = New-ScheduledTaskTrigger -At ([datetime]::Now) -Once
        Principal   = New-ScheduledTaskPrincipal 'NT Authority\System' -LogonType ServiceAccount -RunLevel Highest
        Action      = New-ScheduledTaskAction -Execute 'powershell.exe' -Argument $Argument
        Description = 'Drain_and_Reboot; This script monitors the number of active Citrix Sessions, and when it reaches 0, it reboots the system'
    }
    $thisTask = New-ScheduledTask @TaskParams

    Invoke-command -ComputerName $ComputerName -ScriptBlock {
        $thisTask = Register-ScheduledTask -InputObject $using:thisTask -TaskName 'DrainAndReboot'
        $thisTask.Author = '{0}\{1}' -f $env:USERDOMAIN, $env:USERNAME
        $thisTask | Set-ScheduledTask
    }
    Invoke-command -ComputerName $ComputerName -ScriptBlock { Start-ScheduledTask -TaskName 'DrainAndReboot' }
}