Param(
    [Parameter(Mandatory=$false)]
    [string]$RootPath = ".",
    
    [Parameter(Mandatory=$false)]
    [string]$BaseUrl = "https://example.com",
    
    [Parameter(Mandatory=$false)]
    [string]$OutputFile = "sitemap.xml",
    
    [Parameter(Mandatory=$false)]
    [string[]]$Extensions = @(".html", ".htm", ".php", ".asp", ".aspx")
)

# Ensure the root path exists
if (-not (Test-Path -Path $RootPath -PathType Container)) {
    Write-Error "RootPath '$RootPath' does not exist or is not a directory."
    exit 1
}

# Normalize paths
$RootPath = (Resolve-Path -Path $RootPath).Path.TrimEnd('\')
$BaseUrl = $BaseUrl.TrimEnd('/')

# Build a hashset of extensions for fast look‑up
$extSet = [System.Collections.Generic.HashSet[string]]::new([StringComparer]::OrdinalIgnoreCase)
foreach ($e in $Extensions) { $extSet.Add($e.TrimStart('.')) | Out-Null }

# Gather all matching files
$files = Get-ChildItem -Path $RootPath -Recurse -File |
    Where-Object { $extSet.Contains($_.Extension.TrimStart('.')) }

# Prepare XML writer settings
$settings = New-Object System.Xml.XmlWriterSettings
$settings.Indent = $true
$settings.Encoding = [System.Text.Encoding]::UTF8
$settings.NewLineOnAttributes = $false

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

# Start document
$writer.WriteStartDocument()
$writer.WriteStartElement("urlset")
$writer.WriteAttributeString("xmlns", "http://www.sitemaps.org/schemas/sitemap/0.9")

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

    $url = "$BaseUrl/$relativePath"

    # Format last modification date in UTC (W3C Datetime)
    $lastMod = $file.LastWriteTimeUtc.ToString("yyyy-MM-ddTHH:mm:ssZ")

    $writer.WriteStartElement("url")
    $writer.WriteElementString("loc", $url)
    $writer.WriteElementString("lastmod", $lastMod)
    # Optional: changefreq and priority (static defaults; adjust as needed)
    # $writer.WriteElementString("changefreq", "weekly")
    # $writer.WriteElementString("priority", "0.5")
    $writer.WriteEndElement() # </url>
}

# Close root element and document
$writer.WriteEndElement() # </urlset>
$writer.WriteEndDocument()
$writer.Flush()
$writer.Close()

Write-Host "Sitemap generated at: $OutputFile"