Drive Check

param (
    [string]$Path = "C:\MSNICT",                        #file path
    [string]$LogFile = "drivechange.log",               #log file name
    [int]$MaxLogLines = 500,                            #maximum number of lines for the log file
    [bool]$EventLog = $False,                           #log errors to the event log
    [Parameter(Mandatory=$true)][string]$DriveLetter,   #drive letter to check
    [int]$Frequency = 7                                 #number of days before drive swap warnings
)

[int]$DaysSinceSwitch                                   # global variable to hold days since the drive was switched out
[string]$DriveUUID                                      # global variable to hold persistent drive hash
[string]$CurrentDriveUUID                               # global variable to hold current drive hash
$Drive = $DriveLetter+":"                               # drive letter with : added
$UUIDRegex = [regex]"(?<=\{).*?(?=\})"                  # regular expression to pull the uuid out of the volume device id
$LogCanonical = $Path+'\'+$LogFile                      # create full log file with path string
$LogTime = Get-Date -Format "[dd-MM-yyyy hh:mm:ss]"     # get timestamp



# log writing convenience function
function Write-Log {
    param( [string]$Value, [bool]$Force = $False, [bool]$DoEvent = $False, [int]$EventID = 1 )

    if($Force) {
        Add-Content -Path $LogCanonical -Value $LogTime" $Value" -Force
    } else {
        Add-Content -Path $LogCanonical -Value $LogTime" $Value"
    }

    if($EventLog -And $DoEvent) {
        New-EventLog -LogName Application -Source "Backup Drive Monitor"
        Write-EventLog -LogName Application -Source "Backup Drive Monitor" -EntryType Error -EventId $EventID -Message $Value
    }
}

# log file size limiting function - call before any exit
function Log-Trunicate {
    # Limit log file length
    (get-content $LogCanonical -tail $MaxLogLines -readcount 0) | set-content $LogCanonical
}

# check registry keys and values for drive and create if not exist
function Initialize-Registry {
    # check if registry key exists for drive and create if not exist
    $RegistryKey = 'HKLM:\SOFTWARE\MSNICT\DriveChange\'+$DriveLetter
    if( -not (Test-Path $RegistryKey)) {
        New-Item -Path $RegistryKey -Force
        Write-Log -Value $DriveLetter" drive registry key created"
        Write-Host "Created the registry key for drive"$DriveLetter" and logged creation"
    }

    # check if registry values exist for drive and create if not exist
    $TestKey = Get-Item -Path $RegistryKey
    if( $TestKey.GetValue('DaysSinceSwitch') -eq $null) {
        #create value and initialize variable if it doesn't exist
        $DaysSinceSwitch = 0
        New-ItemProperty -Path $RegistryKey -Name 'DaysSinceSwitch' -PropertyType DWord -Value 0
        Write-Host "Created registry value DaysSinceSwitch: "$DaysSinceSwitch
    } else {
        #load value from the registry to variable
        try {
            $Key = Get-ItemProperty -Path $RegistryKey -Name 'DaysSinceSwitch' -ErrorAction Stop
            $DaysSinceSwitch = $Key.DaysSinceSwitch
            Write-Host "Loaded DaysSinceSwitch registry key: "$DaysSinceSwitch
        } catch {
            $DaysSinceSwitch = 0
        }
    }
    if( $TestKey.GetValue('DriveUUID') -eq $null) {
        #create value and initialize variable if it doesn't exist
        $QueryObject = Get-WmiObject -Class Win32_Volume -Filter "DriveLetter = '$Drive'" | Select-Object -ExpandProperty DeviceID | Select -First 1
        $DriveUUID = $UUIDRegex.match($QueryObject)
        New-ItemProperty -Path $RegistryKey -Name 'DriveUUID' -PropertyType String -Value $DriveUUID
        Write-Host "Created registry value DriveUUID: "$DriveUUID
    } else {
        #load value from the registry to variable
        try {
            $Key = Get-ItemProperty -Path $RegistryKey -Name 'DriveUUID' -ErrorAction Stop
            $DriveUUID = $Key.DriveUUID
            Write-Host "Loaded DriveUUID registry key: "$DriveUUID
        } catch {
            $QueryObject = Get-WmiObject -Class Win32_Volume -Filter "DriveLetter = '$Drive'" | Select-Object -ExpandProperty DeviceID | Select -First 1
            $DriveUUID = $UUIDRegex.match($QueryObject)
        }
    }
}



# check file path and create if not exist
if((Test-Path $Path) -eq $False) {
    New-Item -ItemType Directory -Force -Path $Path
}

# check log file and create if not exist
if ((Test-Path $LogCanonical) -eq $False)
{
    Write-Log -Value "Log file created" -Force
    Write-Host "Created new log file and logged creation"
}



# drive letter checking
if(Test-Path $DriveLetter":") {
    Write-Host "Backup Drive Found: $DriveLetter"
    #Load saved UUID and drive change number of days from registry
    Initialize-Registry
    #Load current drive's UUID
    $QueryObject = Get-WmiObject -Class Win32_Volume -Filter "DriveLetter = '$Drive'" | Select-Object -ExpandProperty DeviceID | Select -First 1
    $CurrentDriveUUID = $UUIDRegex.match($QueryObject)
    Write-Host "Current DriveUUID: "$CurrentDriveUUID
} else {
    Write-Log -Value "Backup Drive Not Found: $DriveLetter" -DoEvent $True
    Write-Host "Backup Drive Not Found: $DriveLetter"
    Log-Trunicate
    exit
}