## Only specify a network ID here if it isn't specified in an environment variable (RMM or endpoint) or you need to override that value:
$JoinNetwork = ''

## If $JoinNetwork is not specified at the command line, use Syncro's ZTNetworkID customer custom field if it exists
If ( (-not $JoinNetwork) -and ($ZeroTierNetworkID) ) { $JoinNetwork = $ZeroTierNetworkID }

## Get Windows version
$WinVersion = [double]("{0}.{1}" -f ([System.Environment]::OSVersion.Version).Major,([System.Environment]::OSVersion.Version).Minor)

## Make sure we're running at least Windows 7
If ( $WinVersion -ge 6.1 ) {

    ## Specify the ZeroTier One MSI installer URL
    $URL = 'https://download.zerotier.com/dist/ZeroTier%20One.msi'

    ## Install ZeroTier One
    Start-Process "msiexec.exe" -ArgumentList "/i ${URL} /qn /norestart" -Wait

    ## Make sure there's a network to join before attempting to start the ZeroTierOneService or join a network
    If ( $JoinNetwork ) {

        ## This will be used to determine whether or not the service was successfully started
        $ServiceRunning = $false

        ## Check to make sure the ZeroTierOneService has started
        ## We'll only loop through this for a few seconds before failing
        For ( $i = 1 ; $i -le 5 ; $i++ ) {
            
            ## Check to see if the service is running
            If ( (Get-Service -Name ZeroTierOneService).Status -ne "Running" ) {
                
                ## Attempt to stop/start the service
                Restart-Service -Name ZeroTierOneService -Force

                ## Wait a few seconds before checking again
                Start-Sleep -Seconds 5
            }
            
            ## If the service is running, break the loop
            Else { $ServiceRunning = $true ; break }
        }

        ## Make sure the service is running before attempting to join a network
        If ( $ServiceRunning ) {

            ## Set the path to the ZeroTier installation directory
            If ( Test-Path "${Env:ProgramFiles(x86)}" ) { $ZTPath = (Get-ItemProperty -Path 'HKLM:\SOFTWARE\WOW6432Node\ZeroTier, Inc.\ZeroTier One').Path }
            Else { $ZTPath = (Get-ItemProperty -Path 'HKLM:\SOFTWARE\ZeroTier, Inc.\ZeroTier One').Path }

            ## Make sure the path actually exists
            If ( Test-Path $ZTPath ) {
                
                $ZTcli = "${ZTPath}\zerotier-cli.bat"

                ## Join the network, if $ZTcli exists
                If ( Test-Path $ZTcli ) { Start-Process $ZTcli -ArgumentList "join ${JoinNetwork}" -Wait }

                ## Otherwise write an error message
                Else { Write-Host "Could not find zerotier-cli" }

            } Else { Write-Host "ZeroTier may not be installed correctly" }
        }

        ## If the service still isn't running, just error out
        Else { Write-Host "ZeroTierOneService service could not be started" }

    } Else { Write-Host "A network to join was not specified" }

    ## Remove the ZeroTier One Start Menu shortcut
    $ShortcutPath = "${ProgramData}\Microsoft\Windows\Start Menu\Programs\ZeroTier One.lnk"
    If ( Test-Path $ShortcutPath ) { Remove-Item $ShortcutPath -Force }

} Else { Write-Host "ZeroTier requires at least Windows 7 to function properly" }