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

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

    [string]$OutputFile = "sitemap.xml",

    [ValidateSet('always','hourly','daily','weekly','monthly','yearly','never')]
    [string]$ChangeFreq = 'weekly',

    [ValidateRange(0.0,1.0)]
    [float]$Priority = 0.5
)

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

# Normalize BaseUrl
if ($BaseUrl -notmatch '^https?://') {
    Write-Error "BaseUrl must start with http:// or https://"
    exit 1
}
if ($BaseUrl[-1] -ne '/') { $BaseUrl += '/' }

# Prepare file list
$extensions = '*.html','*.htm','*.php','*.aspx','*.asp','*.jsp'
$files = Get-ChildItem -Path $RootPath -Recurse -File -Include $extensions

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

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

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

foreach ($file in $files) {
    $relativePath = Resolve-Path -LiteralPath $file.FullName -Relative -RelativeBase $RootPath
    # Replace backslashes with forward slashes and URL-encode spaces
    $urlPath = ($relativePath -replace '\\','/').TrimStart('/')
    $escapedPath = [System.Web.HttpUtility]::UrlPathEncode($urlPath).Replace('+','%20')
    $fullUrl = $BaseUrl + $escapedPath

    $lastMod = $file.LastWriteTimeUtc.ToString('yyyy-MM-ddTHH:mm:ssK')

    $writer.WriteStartElement('url')
    $writer.WriteElementString('loc', $fullUrl)
    $writer.WriteElementString('lastmod', $lastMod)
    $writer.WriteElementString('changefreq', $ChangeFreq)
    $writer.WriteElementString('priority', $Priority.ToString('0.0', [System.Globalization.CultureInfo]::InvariantCulture))
    $writer.WriteEndElement() # url
}

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

Write-Host "Sitemap generated at: $(Resolve-Path -LiteralPath $OutputFile)"