#Requires -Version 5.1
<#
.SYNOPSIS
    Sets the AD computer's "Managed By" to the logged-in user, and stamps the
    computer name into the user's "Notes" field.

.DESCRIPTION
    Designed to run as a GPO User Logon Script. On each login it:
      1. Sets the computer object's "managedBy" attribute to the user's DN
      2. Sets the user object's "info" attribute (Notes / Telephones tab) to the computer name

    Each operation runs independently - if one fails the other still runs.

    PREREQUISITES:
    - AD permissions must be delegated so that Authenticated Users (or Domain Users)
      can WRITE the "managedBy" attribute on Computer objects in the relevant OU(s).
    - Users can write their own "info" attribute by default (Personal Information
      property set). No extra delegation needed for the Notes field.
    - RSAT AD module is optional; the script falls back to ADSI if unavailable.

.NOTES
    Deploy via: GPO > User Configuration > Policies > Windows Settings > Scripts > Logon
    Filename: Set-ComputerManagedBy.ps1
#>

# -- Configuration ------------------------------------------------------------
$LogFile = "$env:TEMP\Set-ComputerManagedBy.log"
$MaxLogSizeKB = 256

# -- Logging helper ------------------------------------------------------------
function Write-Log {
    param([string]$Message, [string]$Level = "INFO")
    $timestamp = Get-Date -Format "yyyy-MM-dd HH:mm:ss"
    $entry = "[$timestamp] [$Level] $Message"
    if ((Test-Path $LogFile) -and ((Get-Item $LogFile).Length / 1KB -gt $MaxLogSizeKB)) {
        Remove-Item $LogFile -Force -ErrorAction SilentlyContinue
    }
    Add-Content -Path $LogFile -Value $entry -ErrorAction SilentlyContinue
}

# -- Gather environment --------------------------------------------------------
$currentUser = $env:USERNAME
$computerName = $env:COMPUTERNAME
$userDomain = $env:USERDOMAIN
$loginTimestamp = Get-Date -Format "yyyy-MM-dd HH:mm"

Write-Log "Script started. User=$userDomain\$currentUser, Computer=$computerName"

# -- Skip if local/non-domain login --------------------------------------------
if ($userDomain -eq $computerName) {
    Write-Log "Local login detected (domain = computername). Skipping." "WARN"
    exit 0
}

# -- Try AD module first, fall back to ADSI ------------------------------------
$useADModule = $false
try {
    Import-Module ActiveDirectory -ErrorAction Stop
    $useADModule = $true
    Write-Log "Using ActiveDirectory PowerShell module."
} catch {
    Write-Log "AD module not available. Falling back to ADSI/DirectorySearcher." "WARN"
}

# -- Build the notes string ----------------------------------------------------
$notesValue = "Last logon: $computerName ($loginTimestamp)"

# -- Resolve user and computer DNs --------------------------------------------
$userDN = $null
$userObj = $null
$computerDN = $null

if ($useADModule) {
    try {
        $userObj = Get-ADUser -Identity $currentUser -Properties info -ErrorAction Stop
        $userDN = $userObj.DistinguishedName
    } catch {
        Write-Log "Could not find user '$currentUser' in AD: $($_.Exception.Message)" "ERROR"
        exit 1
    }
    try {
        $computerObj = Get-ADComputer -Identity $computerName -Properties managedBy -ErrorAction Stop
        $computerDN = $computerObj.DistinguishedName
    } catch {
        Write-Log "Could not find computer '$computerName' in AD: $($_.Exception.Message)" "ERROR"
    }
} else {
    $rootDSE = [ADSI]"LDAP://RootDSE"
    $domainDN = $rootDSE.defaultNamingContext

    $searcher = New-Object DirectoryServices.DirectorySearcher
    $searcher.SearchRoot = [ADSI]"LDAP://$domainDN"

    # Find the user
    $searcher.Filter = "(&(objectCategory=person)(objectClass=user)(sAMAccountName=$currentUser))"
    $searcher.PropertiesToLoad.AddRange(@("distinguishedName", "info"))
    $userResult = $searcher.FindOne()

    if (-not $userResult) {
        Write-Log "Could not find user '$currentUser' in AD." "ERROR"
        exit 1
    }
    $userDN = $userResult.Properties["distinguishedname"][0]

    # Find the computer
    $searcher.Filter = "(&(objectCategory=computer)(sAMAccountName=$computerName$))"
    $searcher.PropertiesToLoad.Clear()
    $searcher.PropertiesToLoad.AddRange(@("distinguishedName", "managedBy"))
    $computerResult = $searcher.FindOne()

    if (-not $computerResult) {
        Write-Log "Could not find computer '$computerName' in AD." "ERROR"
    } else {
        $computerDN = $computerResult.Properties["distinguishedname"][0]
    }
}

# -- Task 1: Set computer ManagedBy (separate try/catch) -----------------------
if ($computerDN -and $userDN) {
    try {
        if ($useADModule) {
            if ($computerObj.managedBy -eq $userDN) {
                Write-Log "ManagedBy already set to $currentUser. No change needed."
            } else {
                Set-ADComputer -Identity $computerName -ManagedBy $userDN -ErrorAction Stop
                Write-Log "SUCCESS: Set ManagedBy on '$computerName' to '$userDN'"
            }
        } else {
            $currentManagedBy = $null
            if ($computerResult.Properties["managedby"].Count -gt 0) {
                $currentManagedBy = $computerResult.Properties["managedby"][0]
            }

            if ($currentManagedBy -eq $userDN) {
                Write-Log "ManagedBy already set to $currentUser. No change needed."
            } else {
                $computerEntry = [ADSI]"LDAP://$computerDN"
                $computerEntry.Put("managedBy", $userDN)
                $computerEntry.SetInfo()
                Write-Log "SUCCESS: Set ManagedBy on '$computerName' to '$userDN'"
            }
        }
    } catch {
        Write-Log "FAILED to set ManagedBy: $($_.Exception.Message)" "ERROR"
    }
} else {
    Write-Log "Skipping ManagedBy - computer object not found." "WARN"
}

# -- Task 2: Set user Notes (separate try/catch) -------------------------------
if ($userDN) {
    try {
        if ($useADModule) {
            if ($userObj.info -eq $notesValue) {
                Write-Log "User notes already current. No change needed."
            } else {
                Set-ADUser -Identity $currentUser -Replace @{info = $notesValue} -ErrorAction Stop
                Write-Log "SUCCESS: Set Notes on '$currentUser' to '$notesValue'"
            }
        } else {
            $currentNotes = $null
            if ($userResult.Properties["info"].Count -gt 0) {
                $currentNotes = $userResult.Properties["info"][0]
            }

            if ($currentNotes -eq $notesValue) {
                Write-Log "User notes already current. No change needed."
            } else {
                $userEntry = [ADSI]"LDAP://$userDN"
                $userEntry.Put("info", $notesValue)
                $userEntry.SetInfo()
                Write-Log "SUCCESS: Set Notes on '$currentUser' to '$notesValue'"
            }
        }
    } catch {
        Write-Log "FAILED to set Notes: $($_.Exception.Message)" "ERROR"
    }
}

Write-Log "Script finished."
exit 0