Function Write-LogMessage {
	param(
		[Parameter(Mandatory)]
		[ValidateNotNullOrEmpty()]
		[string]$Message,
		[switch]$IsError
	)
	if ($IsError.IsPresent) {
		Write-EventLog -LogName "Application" `
			-Source "RMMWindows10Upgrade" `
			-EntryType Error `
			-EventId 42042 `
			-Message "$(Get-Date -Format 'MM/dd/yyyy HH:mm K') [ERROR] $message"
		Write-Verbose "$(Get-Date -Format 'MM/dd/yyyy HH:mm K') [ERROR] $message"
	}
	else {
		Write-EventLog -LogName "Application" `
			-Source "RMMWindows10Upgrade" `
			-EntryType Information `
			-EventId 42042 `
			-Message "$(Get-Date -Format 'MM/dd/yyyy HH:mm K') [INFO] $message"
		Write-Verbose "$(Get-Date -Format 'MM/dd/yyyy HH:mm K') [INFO] $message"
	}
}
Function New-Windows10EventSource {
	try { 
		New-EventLog -LogName "Application" `
			-Source "RMMWindows10Upgrade" `
			-ErrorAction Stop 
	}
 catch { Write-LogMessage -Message "Summary of Actions - Set Up Windows Event Log Source`r`nEvent Log Source already registered." }
}
Function Remove-BuildNotificationRestrictions {
	$returnVal = $true
	$logEntry = ""
	$basePath = "HKLM:\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Image File Execution Options\"
	$fileNames = (
		"Windows10UpgraderApp.exe",
		"Windows10Upgrader.exe",
		"WindowsUpdateBox.exe",
		"SetupHost.exe",
		"setupprep.exe",
		"EOSNotify.exe",
		"MusNotifyIcon.exe",
		"MusNotification.exe"
	)
	foreach ($file in $fileNames) {
		if (Test-Path "$($basePath)$($file)") {
			$logEntry = $logEntry + "Found $($file) in IFEO, removing.`r`n"
			Remove-Item -Path "$($basePath)$($file)"
			if (Test-Path "$($basePath)$($file)") {
				$returnVal = $false
				Write-LogMessage -Message "Failed to remove existing Registry Key $($basePath)\$file " -IsError
			}
		}
	}
	Write-LogMessage -Message "Summary of Actions - Removing Build Restrictions`r`n$($logEntry)"
	return $returnVal
}
Function Remove-OldUpgrades {
	$logMessage = ""
	$returnVal = $true
	$folders = ("_Windows_FU", "Windows10Upgrade")
	foreach ($folder in $folders) {
		if (Test-Path -Path "$($env:SystemDrive)\$folder") {
			$logMessage = $logMessage + "Found $($env:SystemDrive)\$folder... Removing`r`n"
			Remove-Item -Recurse -Path "$($env:SystemDrive)\$folder" -Force
			if (Test-Path -Path "$($env:SystemDrive)\$folder") {
				Write-LogMessage -Message "Failed to remove existing folder $($env:SystemDrive)\$folder " -IsError
				$returnVal = $false
			}
		}
	}
	Write-LogMessage -Message "Summary of Actions - Removing Old Upgrades`r`n$($logMessage)"
	return $returnVal
}
Function Test-FreeSpace {
	$filter = "DeviceID='$($env:SystemDrive)'"
	If (!((Get-WmiObject Win32_LogicalDisk -Filter $filter | Select-Object -expand freespace) / 1GB -ge 23)) {
		Write-LogMessage -Message "Insufficient Free Space available to perform Upgrade, 23 GB is required" -IsError
		return $false
	}
	return $true
}
Function Test-License {
	#Not a big fan of Doing it this way, but it's a lot easier/faster than the alternatives
	$returnVal = $false
	if ((cscript "$($env:windir)\system32\\slmgr.vbs" /dli) -match "Licensed") { $returnVal = $true }
	return $returnVal
}
Function New-Windows10Install {
	$ErrorActionPreference = "SilentlyContinue"
	$dir = "$($env:SystemDrive)\_Windows_FU\packages"
	New-Item -ItemType directory -Path $dir
	$webClient = New-Object System.Net.WebClient
	$url = 'https://go.microsoft.com/fwlink/?LinkID=799445'
	$file = "$($dir)\Win10Upgrade.exe"
	$webClient.DownloadFile($url, $file)
	$install = Start-Process -FilePath $file -ArgumentList "/quietinstall /skipeula /auto upgrade /copylogs $dir /migratedrivers all" -Wait -PassThru
	$hex = "{0:x}" -f $install.ExitCode
	$exit_code = "0x$hex"

	# Convert hex code to human readable
	$message = Switch ($exit_code) {
		"0xC1900210" { "SUCCESS: No compatibility issues detected"; break }
		"0xC1900101" { "ERROR: Driver compatibility issue detected. https://docs.microsoft.com/en-us/windows/deployment/upgrade/resolution-procedures"; break }
		"0xC1900208" { "ERROR: Compatibility issue detected, unsupported programs:`r`n$incompatible_programs`r`n"; break }
		"0xC1900204" { "ERROR: Migration choice not available." ; break }
		"0xC1900200" { "ERROR: System not compatible with upgrade." ; break }
		"0xC190020E" { "ERROR: Insufficient disk space." ; break }
		"0x80070490" { "ERROR: General Windows Update failure, try the following troubleshooting steps`r`n- Run update troubleshooter`r`n- sfc /scannow`r`n- DISM.exe /Online /Cleanup-image /Restorehealth`r`n - Reset windows update components.`r`n"; break }
		"0xC1800118" { "ERROR: WSUS has downloaded content that it cannot use due to a missing decryption key."; break }
		"0x80090011" { "ERROR: A device driver error occurred during user data migration."; break }
		"0xC7700112" { "ERROR: Failure to complete writing data to the system drive, possibly due to write access failure on the hard disk."; break }
		"0xC1900201" { "ERROR: The system did not pass the minimum requirements to install the update."; break }
		"0x80240017" { "ERROR: The upgrade is unavailable for this edition of Windows."; break }
		"0x80070020" { "ERROR: The existing process cannot access the file because it is being used by another process."; break }
		"0xC1900107" { "ERROR: A cleanup operation from a previous installation attempt is still pending and a system reboot is required in order to continue the upgrade."; break }
		"0x3" { "SUCCESS: The upgrade started, no compatibility issues."; break }
		"0x5" { "ERROR: The compatibility check detected issues that require resolution before the upgrade can continue."; break }
		"0x7" { "ERROR: The installation option (upgrade or data only) was not available."; break }
		"0x0" { "SUCCESS: Upgrade started."; break }
		default { "WARNING: Unknown exit code."; break }
	}
	if ($exit_code -eq "0xC1900210" -or $exit_code -eq "0x3" -or $exit_code -eq "0x0") { Write-LogMessage -Message $message }
	else { Write-LogMessage -Message $message -IsError }
}

#The Magic happens here
New-Windows10EventSource
Remove-BuildNotificationRestrictions | Out-Null
Remove-OldUpgrades | Out-Null
if (!$(Test-FreeSpace) -or !$(Test-License)) { Exit 1 }
New-Windows10Install