param(
    [Parameter(Mandatory=$true)]
    [string]$BaseUrl,
    [string]$OutputPath = "sitemap.xml",
    [int]$MaxDepth = 3,
    [string[]]$ExcludePatterns = @()
)

function Get-AbsoluteUrl {
    param(
        [string]$Base,
        [string]$Relative
    )
    try {
        $uri = New-Object System.Uri ([System.Uri]$Base), $Relative
        return $uri.AbsoluteUri
    } catch {
        return $null
    }
}

$visited = [System.Collections.Generic.HashSet[string]]::new()
$baseUri = [System.Uri]$BaseUrl
$hostName = $baseUri.Host

function Should-Exclude {
    param([string]$Url)
    foreach ($pattern in $ExcludePatterns) {
        if ($Url -like $pattern) { return $true }
    }
    return $false
}

function Crawl {
    param(
        [string]$Url,
        [int]$Depth
    )
    if ($Depth -gt $MaxDepth) { return }
    if ($visited.Contains($Url)) { return }
    if (Should-Exclude $Url) { return }

    $visited.Add($Url) | Out-Null

    try {
        $response = Invoke-WebRequest -Uri $Url -UseBasicParsing -ErrorAction Stop
    } catch {
        return
    }

    if ($response.Headers["Content-Type"] -notmatch "text/html") { return }

    $links = $response.Links | Where-Object { $_.href } | ForEach-Object { $_.href }
    foreach ($link in $links) {
        $abs = Get-AbsoluteUrl -Base $Url -Relative $link
        if (-not $abs) { continue }
        $linkUri = [System.Uri]$abs
        if ($linkUri.Host -ne $hostName) { continue }
        Crawl -Url $abs -Depth ($Depth + 1)
    }
}

Crawl -Url $BaseUrl -Depth 0

$ns = "http://www.sitemaps.org/schemas/sitemap/0.9"
$xmlDoc = New-Object System.Xml.XmlDocument
$root = $xmlDoc.CreateElement("urlset", $ns)
$xmlDoc.AppendChild($root) | Out-Null

foreach ($url in $visited) {
    $urlElem = $xmlDoc.CreateElement("url", $ns)
    $loc = $xmlDoc.CreateElement("loc", $ns)
    $loc.InnerText = $url
    $urlElem.AppendChild($loc) | Out-Null
    $root.AppendChild($urlElem) | Out-Null
}

$xmlWriterSettings = New-Object System.Xml.XmlWriterSettings
$xmlWriterSettings.Indent = $true
$xmlWriterSettings.Encoding = [System.Text.Encoding]::UTF8
$writer = [System.Xml.XmlWriter]::Create($OutputPath, $xmlWriterSettings)
$xmlDoc.WriteTo($writer)
$writer.Flush()
$writer.Close()

Write-Host "Sitemap generated at '$OutputPath' with $($visited.Count) URLs."