Param(
    [Parameter(Mandatory = $true)]
    [ValidateScript({ Test-Path $_ -PathType Container })]
    [string]$RootPath,

    [Parameter(Mandatory = $true)]
    [ValidatePattern('^https?://')]
    [string]$BaseUrl,

    [string[]]$Extensions = @('.html', '.htm', '.php', '.aspx', '.asp', '.jsp')
)

# Normalize base URL (remove trailing slash)
if ($BaseUrl.EndsWith('/')) {
    $BaseUrl = $BaseUrl.TrimEnd('/')
}

$files = Get-ChildItem -Path $RootPath -Recurse -File |
    Where-Object { $Extensions -contains $_.Extension.ToLower() }

$sitemapPath = Join-Path -Path $RootPath -ChildPath 'sitemap.xml'

$settings = New-Object System.Xml.XmlWriterSettings
$settings.Indent = $true
$settings.IndentChars = "    "
$settings.Encoding = [System.Text.UTF8Encoding]::new($false)

$writer = [System.Xml.XmlWriter]::Create($sitemapPath, $settings)

try {
    $writer.WriteStartDocument()
    $writer.WriteStartElement('urlset', 'http://www.sitemaps.org/schemas/sitemap/0.9')

    foreach ($file in $files) {
        # Compute relative URL
        $relativePath = $file.FullName.Substring($RootPath.Length).TrimStart('\', '/')
        $relativePath = $relativePath -replace '\\', '/'

        $url = "$BaseUrl/$relativePath"

        # Last modification date in UTC ISO 8601 format
        $lastMod = $file.LastWriteTimeUtc.ToString('yyyy-MM-ddTHH:mm:ssZ')

        $writer.WriteStartElement('url')
        $writer.WriteElementString('loc', $url)
        $writer.WriteElementString('lastmod', $lastMod)
        $writer.WriteEndElement() # url
    }

    $writer.WriteEndElement() # urlset
    $writer.WriteEndDocument()
}
finally {
    $writer.Close()
    $writer.Dispose()
}

Write-Host "Sitemap generated at: $sitemapPath" -ForegroundColor Green