/// A static file shipped with the website service.
///
/// Each case identifies a file name stored under the static files root (the `Resources/Static`
/// directory) and served by Hummingbird's `FileMiddleware` middleware. A name can be available
/// with more than one extension (see ``fileExtensions``), each resolving to its own file.
enum StaticFile: CaseIterable, Sendable {
    /// The `apple-touch-icon.png` icon.
    case appleTouchIcon
    /// The `css/error.css` stylesheet and `js/error.js` script for the not-found page.
    case error
    /// The `favicon.ico` icon.
    case favicon
    /// The `icon.svg` icon.
    case icon
    /// The `icon-192.png` icon for the web manifest.
    case icon192
    /// The `icon-512.png` icon for the web manifest.
    case icon512
    /// The `css/index.css` stylesheet and `js/index.js` script for the landing page.
    case index
    /// The `robots.txt` crawler directives.
    case robots
    /// The `css/shared.css` stylesheet and `js/shared.js` script shared across pages.
    case shared
    /// The `site.webmanifest` web application manifest.
    case site
    /// The `sitemap.xml` crawler sitemap.
    case sitemap
}

// MARK: - Enumerations

extension StaticFile {
    /// A file extension used by a ``StaticFile``.
    enum Extension: String, Sendable {
        /// A Cascading Style Sheets file.
        case css
        /// A JavaScript file.
        case js
        /// A Portable Network Graphics image.
        case png
        /// A Windows icon image.
        case ico
        /// A Scalable Vector Graphics image.
        case svg
        /// A plain text file.
        case txt
        /// A web application manifest file.
        case webmanifest
        /// An Extensible Markup Language file.
        case xml
    }
}

// MARK: - Extensions

extension StaticFile {

    // MARK: Computed
    
    /// The file extensions the file is available with.
    var fileExtensions: [Extension] {
        switch self {
        case .appleTouchIcon,
             .icon192,
             .icon512: [.png]
        case .error,
             .index,
             .shared: [.css, .js]
        case .favicon: [.ico]
        case .icon: [.svg]
        case .robots: [.txt]
        case .site: [.webmanifest]
        case .sitemap: [.xml]
        }
    }

    /// The file's name, without extension.
    var fileName: String {
        switch self {
        case .appleTouchIcon: "apple-touch-icon"
        case .error: "error"
        case .favicon: "favicon"
        case .icon: "icon"
        case .icon192: "icon-192"
        case .icon512: "icon-512"
        case .index: "index"
        case .robots: "robots"
        case .shared: "shared"
        case .site: "site"
        case .sitemap: "sitemap"
        }
    }

    // MARK: Methods

    /// Resolves the file's path against the given base directory.
    ///
    /// - Parameters:
    ///   - basePath: the directory the static files are served from.
    ///   - fileExtension: the extension of the file to resolve.
    /// - Returns: the path to the file, relative to the `basePath` path.
    func path(
        relativeTo basePath: String,
        for fileExtension: Extension
    ) -> String {
        let relativePath = relativePath(for: fileExtension)

        guard !basePath.isEmpty else {
            return relativePath
        }

        return "\(basePath)/\(relativePath)"
    }
    
    /// Resolves the file's path relative to the static files root (e.g. `"css/shared.css"`).
    ///
    /// This also matches the URL path the file is served at by `FileMiddleware`.
    ///
    /// - Parameter fileExtension: the extension of the file to resolve.
    /// - Returns: the path to the file, relative to the static files root.
    func relativePath(
        for fileExtension: Extension
    ) -> String {
        let file = "\(fileName).\(fileExtension.rawValue)"

        return fileExtension.subdirectory
            .map { "\($0)/\(file)" } ?? file
    }

    /// Resolves the absolute URL path the file is served at (e.g. `"/css/shared.css"`).
    ///
    /// - Parameter fileExtension: the extension of the file to resolve.
    /// - Returns: the path to use in `href` and `src` attributes.
    func urlPath(
        for fileExtension: Extension
    ) -> String {
        "/\(relativePath(for: fileExtension))"
    }

}

extension StaticFile.Extension {
    
    // MARK: Computed

    /// The file's content type.
    var contentType: String {
        switch self {
        case .css: "text/css"
        case .js: "text/javascript"
        case .png: "image/png"
        case .ico: "image/vnd.microsoft.icon"
        case .svg: "image/svg+xml"
        case .txt: "text/plain"
        case .webmanifest: "application/manifest+json"
        case .xml: "application/xml"
        }
    }

    /// The sub-directory within the static root that holds files with this extension, if any.
    var subdirectory: String? {
        switch self {
        case .css: "css"
        case .js: "js"
        default: nil
        }
    }

}