param(
    [Parameter(Mandatory=$true)]
    [ValidateNotNullOrEmpty()]
    [string]$BaseUrl,

    [ValidateNotNullOrEmpty()]
    [string]$OutputFile = "sitemap.xml",

    [int]$MaxDepth = 3
)

function Resolve-Url {
    param(
        [string]$Base,
        [string]$Reference
    )
    try {
        $baseUri = [uri]$Base
        $resolved = [uri]::new($baseUri, $Reference)
        return $resolved.AbsoluteUri
    } catch {
        return $null
    }
}

function Get-PageLinks {
    param(
        [string]$Url,
        [string]$Domain
    )
    $links = @()
    try {
        $response = Invoke-WebRequest -Uri $Url -UseBasicParsing -ErrorAction Stop
        foreach ($a in $response.ParsedHtml.getElementsByTagName("a")) {
            $href = $a.href
            if (-not $href) { continue }
            $abs = Resolve-Url -Base $Url -Reference $href
            if (-not $abs) { continue }
            $uri = [uri]$abs
            if ($uri.Host -eq $Domain) {
                $clean = $uri.GetLeftPart("Path")
                $links += $clean
            }
        }
        # Optionally collect URLs from <link>, <script>, etc. For sitemap we care about navigable links.
    } catch {
        # ignore failures (404, etc.)
    }
    return $links | Sort-Object -Unique
}

$baseUri = [uri]$BaseUrl
$domain = $baseUri.Host.ToLower()
$queue = New-Object System.Collections.Generic.Queue[object]
$visited = [System.Collections.Generic.HashSet[string]]::new()
$depthMap = @{}

$queue.Enqueue($BaseUrl)
$depthMap[$BaseUrl] = 0
$visited.Add($BaseUrl) | Out-Null

while ($queue.Count -gt 0) {
    $current = $queue.Dequeue()
    $currentDepth = $depthMap[$current]

    if ($currentDepth -ge $MaxDepth) { continue }

    $childLinks = Get-PageLinks -Url $current -Domain $domain
    foreach ($link in $childLinks) {
        if (-not $visited.Contains($link)) {
            $visited.Add($link) | Out-Null
            $queue.Enqueue($link)
            $depthMap[$link] = $currentDepth + 1
        }
    }
}

# Build XML
$ns = "http://www.sitemaps.org/schemas/sitemap/0.9"
$xmlSettings = New-Object System.Xml.XmlWriterSettings
$xmlSettings.Indent = $true
$xmlSettings.Encoding = [System.Text.Encoding]::UTF8

$writer = [System.Xml.XmlWriter]::Create($OutputFile, $xmlSettings)
$writer.WriteStartDocument()
$writer.WriteStartElement("urlset", $ns)

foreach ($url in $visited) {
    $writer.WriteStartElement("url", $ns)
    $writer.WriteElementString("loc", $ns, $url)
    # Optionally add lastmod, changefreq, priority here if desired.
    $writer.WriteEndElement() # url
}

$writer.WriteEndElement() # urlset
$writer.WriteEndDocument()
$writer.Flush()
$writer.Close()

Write-Host "Sitemap generated at $OutputFile containing $($visited.Count) URLs."