param(
    [Parameter(Mandatory = $true, HelpMessage = "Root folder of the website (physical path).")]
    [string]$RootPath,

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

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

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

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

    [string[]]$IncludeExtensions = @('.html', '.htm', '.php')
)

# Ensure paths are resolved
$RootPath = (Resolve-Path -Path $RootPath).ProviderPath
if (-not (Test-Path -Path $RootPath -PathType Container)) {
    Write-Error "RootPath '$RootPath' does not exist or is not a directory."
    exit 1
}

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

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

if ($files.Count -eq 0) {
    Write-Warning "No files with extensions $($IncludeExtensions -join ', ') were found under '$RootPath'."
}

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

$writer = [System.Xml.XmlWriter]::Create($OutputFile, $settings)
try {
    $writer.WriteStartDocument()
    $writer.WriteStartElement('urlset')
    $writer.WriteAttributeString('xmlns', 'http://www.sitemaps.org/schemas/sitemap/0.9')

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

        # Construct full URL
        $url = "$BaseUrl/$relativeUrl"
        $url = $url -replace '//','/'

        # Ensure scheme remains (e.g., https://)
        if ($url -notmatch '^[a-z][a-z0-9+.-]*://') {
            $url = $url -replace ':/','://'
        }

        $writer.WriteStartElement('url')
        $writer.WriteElementString('loc', $url)
        $lastMod = $file.LastWriteTimeUtc.ToString('yyyy-MM-dd')
        $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.Flush()
    $writer.Close()
    $writer.Dispose()
}

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