param(
    [Parameter(Mandatory=$true,HelpMessage="Root folder of your website files.")]
    [ValidateScript({Test-Path $_ -PathType Container})]
    [string]$Path,

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

    [Parameter(HelpMessage="Full path for the sitemap output file. Defaults to sitemap.xml in the root folder.")]
    [string]$OutputFile,

    [Parameter(HelpMessage="File extensions to include (case‑insensitive).")]
    [string[]]$IncludeExtensions = @('.html', '.htm', '.php', '.aspx'),

    [Parameter(HelpMessage="File extensions to exclude (case‑insensitive).")]
    [string[]]$ExcludeExtensions = @('.css', '.js', '.json', '.xml', '.txt')
)

# Resolve and normalize paths
$rootPath = (Resolve-Path -Path $Path).ProviderPath
if (-not $OutputFile) {
    $OutputFile = Join-Path -Path $rootPath -ChildPath 'sitemap.xml'
}
$OutputFile = (Resolve-Path -Path $OutputFile -ErrorAction SilentlyContinue).ProviderPath `
               ? (Resolve-Path -Path $OutputFile).ProviderPath `
               : $OutputFile

# Prepare extension hashsets for fast lookup
$includeSet = [System.Collections.Generic.HashSet[string]]::new([StringComparer]::InvariantCultureIgnoreCase)
$IncludeExtensions | ForEach-Object { $includeSet.Add($_) | Out-Null }

$excludeSet = [System.Collections.Generic.HashSet[string]]::new([StringComparer]::InvariantCultureIgnoreCase)
$ExcludeExtensions | ForEach-Object { $excludeSet.Add($_) | Out-Null }

# Gather files
$files = Get-ChildItem -Path $rootPath -Recurse -File -ErrorAction SilentlyContinue |
    Where-Object {
        $ext = $_.Extension
        $includeSet.Contains($ext) -and -not $excludeSet.Contains($ext)
    }

if (-not $files) {
    Write-Warning "No files matching the criteria were found under '$rootPath'."
    exit 0
}

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

try {
    $writer = [System.Xml.XmlWriter]::Create($OutputFile, $xmlSettings)

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

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

        # Ensure URL is properly escaped (encode spaces and other unsafe chars)
        $encodedPath = [System.Web.HttpUtility]::UrlPathEncode($urlPath)

        $loc = ($BaseUrl.TrimEnd('/') + '/' + $encodedPath).TrimEnd('/')

        # Format last modification date in UTC ISO 8601 (e.g., 2024-03-15T12:34:56Z)
        $lastMod = $file.LastWriteTimeUtc.ToString('yyyy-MM-ddTHH:mm:ssZ')

        $writer.WriteStartElement('url')
        $writer.WriteElementString('loc', $loc)
        $writer.WriteElementString('lastmod', $lastMod)
        $writer.WriteEndElement() # </url>
    }

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

Write-Host "Sitemap generated successfully at: $OutputFile"