param(
    [Parameter(Mandatory=$true, Position=0)]
    [ValidateNotNullOrEmpty()]
    [string]$SiteRootPath,

    [Parameter(Mandatory=$true, Position=1)]
    [ValidatePattern('^https?://')]
    [string]$BaseUrl,

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

    [ValidateRange(0.0,1.0)]
    [double]$DefaultPriority = 0.5
)

function Get-RelativeWebPath {
    param(
        [string]$FullPath,
        [string]$RootPath
    )
    $relative = Resolve-Path -Path $FullPath -Relative -BasePath $RootPath
    $relative = $relative -replace '\\','/'
    if (-not $relative.StartsWith('/')) { $relative = '/' + $relative }
    return $relative
}

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

# Gather all files considered as web pages
$extensions = '.html', '.htm', '.php', '.aspx', '.asp', '.jsp', '.jspx', '.cfm', '.xml'
$webFiles = Get-ChildItem -Path $SiteRootPath -Recurse -File -Include $extensions |
    Where-Object { $_.Name -notmatch '^sitemap\.xml$' }

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

$sitemapPath = Join-Path -Path $SiteRootPath -ChildPath 'sitemap.xml'
$writer = [System.Xml.XmlWriter]::Create($sitemapPath, $xmlSettings)

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

    foreach ($file in $webFiles) {
        $relativeWebPath = Get-RelativeWebPath -FullPath $file.FullName -RootPath $SiteRootPath
        $url = $BaseUrl.TrimEnd('/') + $relativeWebPath

        $writer.WriteStartElement('url')

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

        $lastMod = $file.LastWriteTimeUtc.ToString('yyyy-MM-ddTHH:mm:sszzz')
        $writer.WriteElementString('lastmod', $lastMod)

        $writer.WriteElementString('changefreq', $DefaultChangeFreq)
        $writer.WriteElementString('priority', ('{0:N1}' -f $DefaultPriority))

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

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

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