<#
.SYNOPSIS
    Simple local network scanner using ping.exe.

.DESCRIPTION
    - Detects your primary IPv4 address and subnet.
    - Pings every IP in that subnet using ping.exe.
    - Shows IP, optional hostname, and MAC address (from ARP cache).
    - Default timeout: 250 ms per host (adjustable).

.PARAMETER TimeoutMs
    Ping timeout in milliseconds per host. Default: 250 ms.

.PARAMETER ResolveNames
    If set, try to resolve hostnames via DNS / reverse lookup.

.EXAMPLE
    .\Scan-Network.ps1

.EXAMPLE
    .\Scan-Network.ps1 -TimeoutMs 500 -ResolveNames -Verbose
#>

[CmdletBinding()]
param(
    [int]
    $TimeoutMs = 250,

    [switch]
    $ResolveNames
)

function ConvertTo-UInt32 {
    param(
        [Parameter(Mandatory = $true)]
        [System.Net.IPAddress] $IPAddress
    )
    $bytes = $IPAddress.GetAddressBytes()
    [Array]::Reverse($bytes)
    return [BitConverter]::ToUInt32($bytes, 0)
}

function ConvertFrom-UInt32 {
    param(
        [Parameter(Mandatory = $true)]
        [uint32] $Value
    )
    $bytes = [BitConverter]::GetBytes($Value)
    [Array]::Reverse($bytes)
    return [System.Net.IPAddress]::new($bytes)
}

Write-Host "Detecting local IPv4 configuration..." -ForegroundColor Cyan

# Get a usable IPv4 address (skip loopback / APIPA)
$ipConfig = Get-NetIPAddress -AddressFamily IPv4 |
    Where-Object {
        $_.IPAddress -notlike '169.254*' -and
        $_.IPAddress -notlike '127.*'     -and
        $_.PrefixOrigin -ne 'WellKnown'
    } |
    Sort-Object -Property SkipAsSource, InterfaceMetric |
    Select-Object -First 1

if (-not $ipConfig) {
    Write-Error "No valid IPv4 address found. Are you connected to a network?"
    exit 1
}

$localIp      = [System.Net.IPAddress]::Parse($ipConfig.IPAddress)
$prefixLength = $ipConfig.PrefixLength

Write-Host "Using local IP: $($localIp) /$prefixLength on interface: $($ipConfig.InterfaceAlias)" -ForegroundColor Green

if ($prefixLength -lt 16) {
    Write-Warning "Subnet is large (/16 or bigger). This scan may take a while."
}

# Build subnet mask from prefix length
$maskUint32 = if ($prefixLength -eq 0) {
    0u
} else {
    [uint32]::MaxValue -shl (32 - $prefixLength)
}

$ipUint32        = ConvertTo-UInt32 -IPAddress $localIp
$networkUint32   = $ipUint32 -band $maskUint32
$broadcastUint32 = $networkUint32 -bor (-bnot $maskUint32)

Write-Host "Calculated network range: $(ConvertFrom-UInt32 $networkUint32) - $(ConvertFrom-UInt32 $broadcastUint32)" -ForegroundColor Yellow

# Build list of host IPs (skip network & broadcast)
$start = $networkUint32 + 1
$end   = $broadcastUint32 - 1

if ($end -lt $start) {
    Write-Error "Invalid IP range calculated. Aborting."
    exit 1
}

$ipList = New-Object System.Collections.Generic.List[System.Net.IPAddress]

for ($i = $start; $i -le $end; $i++) {
    $ipList.Add( (ConvertFrom-UInt32 -Value $i) )
}

Write-Host "Scanning $($ipList.Count) addresses with timeout = ${TimeoutMs}ms using ping.exe ..." -ForegroundColor Cyan

$results = @()
$pingCmd = "$env:SystemRoot\System32\ping.exe"

foreach ($ip in $ipList) {
    $ipString = $ip.ToString()
    Write-Verbose "Pinging $ipString ..."
    
    # Call ping.exe with separate arguments
    $null = & $pingCmd -n 1 -w $TimeoutMs $ipString
    $exitCode = $LASTEXITCODE

    if ($exitCode -eq 0) {
        Write-Host "Host up: $ipString" -ForegroundColor DarkGreen

        $hostname = $null

        if ($ResolveNames) {
            try {
                $entry = [System.Net.Dns]::GetHostEntry($ipString)
                $hostname = $entry.HostName
            } catch {
                $hostname = $null
            }
        }

        # Query ARP cache for MAC address
        $mac = $null
        try {
            $arpOutput = arp -a $ipString 2>$null
            if ($arpOutput) {
                $line = $arpOutput -split "`n" |
                    Where-Object { $_ -match $ipString } |
                    Select-Object -First 1

                if ($line -and ($line -match '([0-9a-fA-F]{2}-){5}[0-9a-fA-F]{2}')) {
                    $mac = $Matches[0]
                }
            }
        } catch {
            $mac = $null
        }

        $results += [PSCustomObject]@{
            IPAddress = $ipString
            Hostname  = $hostname
            MAC       = $mac
        }
    } else {
        Write-Verbose "No reply from $ipString (exit code $exitCode)"
    }
}

Write-Host ""
Write-Host "Scan complete. Devices that responded to ping.exe:" -ForegroundColor Green

if ($results.Count -eq 0) {
    Write-Host "No active hosts found (no ping replies)." -ForegroundColor Yellow
} else {
    $results |
        Sort-Object IPAddress |
        Format-Table -AutoSize
}

# Uncomment below line if you want to export to CSV automatically:
# $results | Sort-Object IPAddress | Export-Csv -Path ".\NetworkScan_$(Get-Date -Format 'yyyyMMdd_HHmmss').csv" -NoTypeInformation