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"))
        let auth = try await json(session, server.url.appendingPathComponent("api/v1/auth/oidc/config"))
        try ServerMetadata.validate(bootstrap: version, authentication: auth)
    }

    private static func json(_ session: URLSession, _ url: URL) async throws -> Data {
        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)
        }
        return data
    }
}