param(
    [Parameter(Mandatory=$true,HelpMessage="Base URL of the site (e.g. https://www.example.com)")]
    [ValidateNotNullOrEmpty()]
    [string]$BaseUrl,

    [Parameter(Mandatory=$true,HelpMessage="Root folder of the site on disk")]
    [ValidateScript({Test-Path $_ -PathType 'Container'})]
    [string]$RootPath,

    [Parameter(HelpMessage="Full path to the sitemap file to create")]
    [string]$OutputFile = (Join-Path -Path $RootPath -ChildPath "sitemap.xml"),

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

    [ValidateRange(0,1)]
    [double]$Priority = 0.5
)

# Normalize inputs
$BaseUrl = $BaseUrl.TrimEnd('/')
$RootPath = (Resolve-Path -Path $RootPath).ProviderPath
$OutputFile = (Resolve-Path -Path (Split-Path -Parent $OutputFile) -ErrorAction SilentlyContinue).ProviderPath + "\" + (Split-Path -Leaf $OutputFile)

# Define file extensions to include in the sitemap
$includeExt = @('*.html','*.htm','*.php','*.asp','*.aspx','*.jsp')

# Gather files
$files = Get-ChildItem -Path $RootPath -Recurse -File -Include $includeExt -ErrorAction SilentlyContinue

if (-not $files) {
    Write-Warning "No files matching $($includeExt -join ', ') were found under $RootPath."
    exit 0
}

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

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

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

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

        $writer.WriteStartElement("url")

        $writer.WriteElementString("loc", $url)

        # lastmod in W3C Datetime format (ISO 8601)
        $lastMod = $file.LastWriteTime.ToUniversalTime().ToString("yyyy-MM-ddTHH:mm:ssZ")
        $writer.WriteElementString("lastmod", $lastMod)

        $writer.WriteElementString("changefreq", $ChangeFreq)

        $writer.WriteElementString("priority", $Priority.ToString("0.0", [cultureinfo]::InvariantCulture))

        $writer.WriteEndElement() # </url>
    }

    $writer.WriteEndElement() # </urlset>
    $writer.WriteEndDocument()
}
finally {
    $writer.Close()
}

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