#Requires -Modules ActiveDirectory
<#
.SYNOPSIS
    Exports a CSV report of users and the last PC they logged into.

.DESCRIPTION
    Queries Domain Controller security event logs for logon events (4624)
    to determine which computer each user last authenticated from.
    Resolves IP addresses to DNS names and looks up user display names.
    
    CSV Report Columns: Date, Username, Display Name, PC Name, DNS, IP

    PERFORMANCE: Uses regex-based XML extraction instead of DOM parsing
    and bulk AD user preloading for significantly faster execution.

.PARAMETER OutputPath
    Path for the output CSV file. Defaults to current directory.

.PARAMETER DaysBack
    Number of days of event logs to search. Default is 7.

.PARAMETER ExcludeNetworkLogons
    Exclude Type 3 (Network) logons. Default includes them.

.PARAMETER SkipIPResolve
    Skip IP to hostname resolution. Faster but less useful.

.EXAMPLE
    .\Get-UserLastLogonComputer.ps1

.EXAMPLE
    .\Get-UserLastLogonComputer.ps1 -OutputPath "C:\Reports" -DaysBack 30

.NOTES
    Must be run on a Domain Controller with appropriate permissions to read Security logs.
    Logon Type 2 = Interactive (console)
    Logon Type 3 = Network (file shares, etc.)
    Logon Type 10 = RemoteInteractive (RDP)
    Logon Type 11 = CachedInteractive
#>

[CmdletBinding()]
param(
    [Parameter()]
    [string]$OutputPath = (Get-Location).Path,

    [Parameter()]
    [int]$DaysBack = 7,

    [Parameter()]
    [switch]$ExcludeNetworkLogons,

    [Parameter()]
    [switch]$SkipIPResolve
)

$ScriptStart = Get-Date

# Validate output path exists
if (-not (Test-Path $OutputPath)) {
    Write-Host "Output path '$OutputPath' does not exist. Creating it..." -ForegroundColor Yellow
    try {
        New-Item -Path $OutputPath -ItemType Directory -Force | Out-Null
    } catch {
        Write-Host "Error: Could not create output directory '$OutputPath'. $($_.Exception.Message)" -ForegroundColor Red
        return
    }
}

# Build logon types lookup (HashSet for fast contains-check)
$LogonTypesAllowed = [System.Collections.Generic.HashSet[string]]::new()
@('2', '10', '11') | ForEach-Object { [void]$LogonTypesAllowed.Add($_) }
if (-not $ExcludeNetworkLogons) {
    [void]$LogonTypesAllowed.Add('3')
}

# System accounts to exclude (HashSet for O(1) lookup)
$ExcludeUsers = [System.Collections.Generic.HashSet[string]]::new(
    [System.StringComparer]::OrdinalIgnoreCase
)
@('SYSTEM', 'LOCAL SERVICE', 'NETWORK SERVICE', 'DWM-1', 'DWM-2', 'DWM-3', 'DWM-4',
  'UMFD-0', 'UMFD-1', 'UMFD-2', 'UMFD-3', 'ANONYMOUS LOGON', '-') | 
    ForEach-Object { [void]$ExcludeUsers.Add($_) }

$ExcludeDomains = [System.Collections.Generic.HashSet[string]]::new(
    [System.StringComparer]::OrdinalIgnoreCase
)
@('Window Manager', 'Font Driver Host', 'NT AUTHORITY') | 
    ForEach-Object { [void]$ExcludeDomains.Add($_) }

$Timestamp = Get-Date -Format "yyyyMMdd_HHmmss"
$CsvFile = Join-Path $OutputPath "UserLastLogonReport_$Timestamp.csv"

Write-Host "`nQuerying security event logs for the last $DaysBack days..." -ForegroundColor Cyan
Write-Host "Looking for logon types: $($LogonTypesAllowed -join ', ')" -ForegroundColor Cyan
Write-Host "CSV will be saved to: $CsvFile" -ForegroundColor Cyan
Write-Host ""

$StartDate = (Get-Date).AddDays(-$DaysBack)

# ==========================================
# PHASE 1: Bulk preload all AD users (one query)
# ==========================================
Write-Host "Pre-loading AD user display names (bulk query)..." -ForegroundColor Yellow
$UserDisplayNames = @{}
try {
    Get-ADUser -Filter * -Properties DisplayName | ForEach-Object {
        if ($_.DisplayName) {
            $UserDisplayNames[$_.SamAccountName] = $_.DisplayName
        }
    }
    Write-Host "  Loaded $($UserDisplayNames.Count) user display names." -ForegroundColor Gray
} catch {
    Write-Host "  Warning: Could not bulk-load AD users. Display names will be empty." -ForegroundColor DarkYellow
}

# Cache for IP to DNS name resolution
$DNSCache = @{}

function Resolve-IPToDNSName {
    param([string]$IP)
    
    if ([string]::IsNullOrWhiteSpace($IP) -or $IP -eq '-' -or $IP -eq '::1' -or $IP -eq '127.0.0.1') {
        return @{ Short = $null; FQDN = $null }
    }
    
    if ($DNSCache.ContainsKey($IP)) {
        return $DNSCache[$IP]
    }
    
    try {
        $fqdn = [System.Net.Dns]::GetHostEntry($IP).HostName
        $shortName = ($fqdn -split '\.')[0].ToUpper()
        $result = @{ Short = $shortName; FQDN = $fqdn.ToLower() }
        $DNSCache[$IP] = $result
        return $result
    } catch {
        try {
            $computer = Get-ADComputer -Filter "IPv4Address -eq '$IP'" -Properties DNSHostName, Name -ErrorAction SilentlyContinue
            if ($computer) {
                $result = @{ Short = $computer.Name; FQDN = if ($computer.DNSHostName) { $computer.DNSHostName.ToLower() } else { '' } }
                $DNSCache[$IP] = $result
                return $result
            }
        } catch {}
        
        $result = @{ Short = $null; FQDN = $null }
        $DNSCache[$IP] = $result
        return $result
    }
}

try {
    # ==========================================
    # PHASE 2: Retrieve events
    # ==========================================
    Write-Host "Retrieving logon events from Security log..." -ForegroundColor Yellow
    
    $FilterHash = @{
        LogName   = 'Security'
        ID        = 4624
        StartTime = $StartDate
    }
    
    $Events = Get-WinEvent -FilterHashtable $FilterHash -ErrorAction Stop
    
    Write-Host "Found $($Events.Count) total 4624 events. Processing..." -ForegroundColor Yellow

    # ==========================================
    # PHASE 3: Process events with regex (FAST)
    # ==========================================
    $UserLogons = @{}
    $ProcessedCount = 0
    $SkippedCount = 0
    $i = 0

    # Pre-compiled regex patterns for extracting fields from raw XML
    $rxLogonType    = [regex]'Name="LogonType">(\d+)<'
    $rxTargetUser   = [regex]'Name="TargetUserName">([^<]+)<'
    $rxTargetDomain = [regex]'Name="TargetDomainName">([^<]+)<'
    $rxWorkstation  = [regex]'Name="WorkstationName">([^<]*)<'
    $rxIPAddress    = [regex]'Name="IpAddress">([^<]*)<'

    foreach ($Event in $Events) {
        $i++
        if ($i % 10000 -eq 0) {
            Write-Host "  Processing event $i of $($Events.Count)... ($ProcessedCount matched, $SkippedCount skipped as already seen)" -ForegroundColor Gray
        }
        
        # Get raw XML string - regex instead of [xml] DOM parsing
        $xmlStr = $Event.ToXml()
        
        # 1. Check logon type FIRST (cheapest filter)
        $m = $rxLogonType.Match($xmlStr)
        if (-not $m.Success) { continue }
        $LogonType = $m.Groups[1].Value
        if (-not $LogonTypesAllowed.Contains($LogonType)) { continue }
        
        # 2. Extract username
        $m = $rxTargetUser.Match($xmlStr)
        if (-not $m.Success) { continue }
        $Username = $m.Groups[1].Value
        
        # 3. Quick filters before extracting more fields
        if ([string]::IsNullOrWhiteSpace($Username)) { continue }
        if ($Username.EndsWith('$')) { continue }
        if ($ExcludeUsers.Contains($Username)) { continue }
        
        $m = $rxTargetDomain.Match($xmlStr)
        $Domain = if ($m.Success) { $m.Groups[1].Value } else { '' }
        if ($ExcludeDomains.Contains($Domain)) { continue }
        
        # 4. Already seen this user? Skip (events are newest-first)
        $UserKey = "$Domain\$Username"
        if ($UserLogons.ContainsKey($UserKey)) { 
            $SkippedCount++
            continue 
        }
        
        # 5. Extract workstation and IP
        $m = $rxWorkstation.Match($xmlStr)
        $Workstation = if ($m.Success) { $m.Groups[1].Value } else { '' }
        
        $m = $rxIPAddress.Match($xmlStr)
        $IPAddress = if ($m.Success) { $m.Groups[1].Value } else { '' }
        
        $LogonTime = $Event.TimeCreated

        # Determine PC name and DNS name
        $PCName = $null
        $DNSName = ''
        
        if (-not $SkipIPResolve -and -not [string]::IsNullOrWhiteSpace($IPAddress) -and $IPAddress -ne '-') {
            $resolved = Resolve-IPToDNSName -IP $IPAddress
            if ($resolved.Short) { $PCName = $resolved.Short }
            if ($resolved.FQDN) { $DNSName = $resolved.FQDN }
        }
        
        # Fall back to WorkstationName if IP didn't resolve
        if ([string]::IsNullOrWhiteSpace($PCName)) {
            if (-not [string]::IsNullOrWhiteSpace($Workstation) -and $Workstation -ne '-') {
                $PCName = $Workstation.ToUpper()
            } else {
                $PCName = 'Unknown'
            }
        }

        # Clean up IP for display
        $IPDisplay = if ($IPAddress -and $IPAddress -ne '-' -and $IPAddress -ne '::1' -and $IPAddress -ne '127.0.0.1') { $IPAddress } else { '' }

        $ProcessedCount++

        # Store result with report column names
        $DisplayName = if ($UserDisplayNames.ContainsKey($Username)) { $UserDisplayNames[$Username] } else { '' }

        $UserLogons[$UserKey] = [PSCustomObject]@{
            'Date'         = $LogonTime.ToString('yyyy-MM-dd HH:mm:ss')
            'Username'     = $Username
            'Display Name' = $DisplayName
            'PC Name'      = $PCName
            'DNS'          = $DNSName
            'IP'           = $IPDisplay
        }
    }

    $ProcessTime = (Get-Date) - $ScriptStart

    Write-Host "Processed $ProcessedCount unique user logons ($SkippedCount duplicate events skipped)." -ForegroundColor Yellow

    # ==========================================
    # PHASE 4: Export CSV
    # ==========================================
    $Results = @($UserLogons.Values | Sort-Object Username)

    if ($Results.Count -eq 0) {
        Write-Host "`nNo user logon events found matching criteria." -ForegroundColor Yellow
        return
    }

    # Write CSV
    try {
        $Results | Export-Csv -Path $CsvFile -NoTypeInformation -Encoding UTF8 -Force
        
        if (Test-Path $CsvFile) {
            $FileSize = (Get-Item $CsvFile).Length
            Write-Host "`n===== Report Saved =====" -ForegroundColor Green
            Write-Host "Total users:  $($Results.Count)"
            Write-Host "File size:    $([math]::Round($FileSize / 1KB, 1)) KB"
            Write-Host "Saved to:     $CsvFile" -ForegroundColor Green
            Write-Host "Completed in: $($ProcessTime.Minutes)m $($ProcessTime.Seconds)s" -ForegroundColor Cyan
        } else {
            Write-Host "`nError: CSV file was not created at '$CsvFile'" -ForegroundColor Red
        }
    } catch {
        Write-Host "`nError saving CSV: $($_.Exception.Message)" -ForegroundColor Red
        Write-Host "Attempting to save to Desktop instead..." -ForegroundColor Yellow
        $FallbackPath = Join-Path ([Environment]::GetFolderPath('Desktop')) "UserLastLogonReport_$Timestamp.csv"
        try {
            $Results | Export-Csv -Path $FallbackPath -NoTypeInformation -Encoding UTF8 -Force
            Write-Host "Saved to fallback location: $FallbackPath" -ForegroundColor Green
        } catch {
            Write-Host "Error: Could not save CSV. $($_.Exception.Message)" -ForegroundColor Red
        }
    }

    Write-Host ""

    # Display summary table in console
    $Results | Format-Table -AutoSize

} catch [System.Exception] {
    if ($_.Exception.Message -match "No events were found") {
        Write-Host "`nNo logon events (Event ID 4624) found in the last $DaysBack days." -ForegroundColor Yellow
    } elseif ($_.Exception.Message -match "Access is denied") {
        Write-Host "`nError: Access denied. Run PowerShell as Administrator." -ForegroundColor Red
    } else {
        Write-Host "`nError: $($_.Exception.Message)" -ForegroundColor Red
    }
}