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

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

    [Parameter(Position=2)]
    [string]$OutputPath = (Join-Path -Path $RootPath -ChildPath 'sitemap.xml')
)

# Ensure trailing slash on BaseUrl
if (-not $BaseUrl.EndsWith('/')) { $BaseUrl = "$BaseUrl/" }

# Resolve the root path
$resolvedRoot = Resolve-Path -Path $RootPath -ErrorAction Stop | Select-Object -ExpandProperty Path
if (-not (Test-Path -LiteralPath $resolvedRoot -PathType Container)) {
    Write-Error "RootPath '$RootPath' does not exist or is not a directory."
    exit 1
}

# Gather files to include in sitemap (common web page extensions)
$extensions = @('.html','.htm','.php','.aspx','.asp')
$files = Get-ChildItem -Path $resolvedRoot -Recurse -File | Where-Object {
    $extensions -contains $_.Extension.ToLower()
}

# Prepare XML document
$ns = 'http://www.sitemaps.org/schemas/sitemap/0.9'
$xml = New-Object System.Xml.XmlDocument
$decl = $xml.CreateXmlDeclaration('1.0','UTF-8',$null)
$xml.AppendChild($decl) | Out-Null

$urlset = $xml.CreateElement('urlset', $ns)
$xml.AppendChild($urlset) | Out-Null

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

    # URL-encode each segment to avoid illegal characters
    $segments = $relativeUrl -split '/'
    $encodedSegments = $segments | ForEach-Object { [uri]::EscapeDataString($_) }
    $encodedPath = ($encodedSegments -join '/')

    $loc = "$BaseUrl$encodedPath"

    $urlElem = $xml.CreateElement('url', $ns)

    $locElem = $xml.CreateElement('loc', $ns)
    $locElem.InnerText = $loc
    $urlElem.AppendChild($locElem) | Out-Null

    # Optional lastmod (UTC ISO 8601)
    $lastModElem = $xml.CreateElement('lastmod', $ns)
    $lastModElem.InnerText = $file.LastWriteTimeUtc.ToString('yyyy-MM-ddTHH:mm:ss+00:00')
    $urlElem.AppendChild($lastModElem) | Out-Null

    $urlset.AppendChild($urlElem) | Out-Null
}

# Ensure output directory exists
$outDir = Split-Path -Parent $OutputPath
if (-not (Test-Path -LiteralPath $outDir)) {
    New-Item -ItemType Directory -Path $outDir -Force | Out-Null
}

# Save the sitemap
$xml.Save($OutputPath)

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