import Foundation

final class NoRedirect: NSObject, URLSessionTaskDelegate {
    func urlSession(_ session: URLSession, task: URLSessionTask,
                    willPerformHTTPRedirection response: HTTPURLResponse,
                    newRequest request: URLRequest,
                    completionHandler: @escaping (URLRequest?) -> Void) {
        completionHandler(nil)
    }
}

enum ServerProbe {
    static func check(_ server: ServerAddress) async throws {
        let configuration = URLSessionConfiguration.ephemeral
        configuration.httpCookieStorage = nil
        configuration.urlCache = nil
        configuration.timeoutIntervalForRequest = 10
        configuration.timeoutIntervalForResource = 20
        let session = URLSession(configuration: configuration, delegate: NoRedirect(), delegateQueue: nil)
        defer { session.invalidateAndCancel() }
        let version = try await json(session, server.url.appendingPathComponent("api/v1/version"))
        guard version["app_name"] is String,
              version["setup_required"] is Bool,
              version["password_reset_enabled"] is Bool else { throw ConnectionError.incompatible }
        let auth = try await json(session, server.url.appendingPathComponent("api/v1/auth/oidc/config"))
        guard auth["enabled"] is Bool, auth["password_login_enabled"] is Bool else {
            throw ConnectionError.incompatible
        }
    }

    private static func json(_ session: URLSession, _ url: URL) async throws -> [String: Any] {
        var request = URLRequest(url: url)
        request.setValue("application/json", forHTTPHeaderField: "Accept")
        let (stream, response) = try await session.bytes(for: request)
        guard (response as? HTTPURLResponse)?.statusCode == 200 else { throw ConnectionError.unavailable }
        var data = Data()
        for try await byte in stream {
            guard data.count < 65_536 else { throw ConnectionError.incompatible }
            data.append(byte)
        }
        guard let result = try JSONSerialization.jsonObject(with: data) as? [String: Any] else {
            throw ConnectionError.incompatible
        }
        return result
    }
}