Param(
    [Parameter(Mandatory=$true)]
    [string]$RootPath,
    
    [Parameter(Mandatory=$true)]
    [ValidatePattern('^https?://')]
    [string]$BaseUrl,
    
    [string]$OutputFile = (Join-Path -Path $RootPath -ChildPath 'sitemap.xml'),
    
    [string[]]$IncludePatterns = @('*.html','*.htm','*.aspx','*.php')
)

function Convert-ToUrlPath {
    param([string]$Path)
    $segments = $Path -split '[\\/]' | ForEach-Object {
        [System.Uri]::EscapeDataString($_)
    }
    return ($segments -join '/')
}

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

# Collect files
$files = Get-ChildItem -Path $RootPath -Recurse -File -Include $IncludePatterns

# Prepare 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) {
    # Relative path from root
    $relativePath = $file.FullName.Substring($RootPath.Length).TrimStart('\','/')
    $urlPath = Convert-ToUrlPath -Path $relativePath
    $loc = "$BaseUrl/$urlPath"

    # lastmod in ISO 8601 (date only)
    $lastMod = $file.LastWriteTimeUtc.ToString('yyyy-MM-dd')

    $writer.WriteStartElement('url')

    $writer.WriteElementString('loc', $loc)
    $writer.WriteElementString('lastmod', $lastMod)
    # Optional elements can be added, e.g., changefreq, priority
    # $writer.WriteElementString('changefreq', 'weekly')
    # $writer.WriteElementString('priority', '0.5')

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

$writer.WriteEndElement() # </urlset>
$writer.WriteEndDocument()
$writer.Flush()
$writer.Close()

Write-Host "Sitemap generated at: $OutputFile"