import NIOCore
import NIOPosix

/// A fake server accepting connections and never answering.
///
/// A client connecting to it completes the TCP handshake and then waits forever for the first protocol byte — the shape of a database that hangs rather
/// than refuses. This is what the probe's deadline test connects to, proving the probe answers within its timeout instead of hanging alongside the server.
final class SilentPostgresServer {

    // MARK: Properties

    /// The port the server listens on, assigned by the system at bind time.
    let port: Int

    /// The listening channel the server accepts connections through.
    private let channel: Channel

    // MARK: Initializers

    private init(
        channel: Channel,
        port: Int
    ) {
        self.channel = channel
        self.port = port
    }

    // MARK: Functions

    /// Starts a server on the loopback interface, on a system-assigned port.
    /// - Returns: the running server, ready to be connected to at ``port``.
    static func start() async throws -> SilentPostgresServer {
        let channel = try await ServerBootstrap(group: MultiThreadedEventLoopGroup.singleton)
            .bind(host: "127.0.0.1", port: 0)
            .get()

        guard let port = channel.localAddress?.port else {
            throw ChannelError.unknownLocalAddress
        }

        return .init(
            channel: channel,
            port: port
        )
    }

    /// Stops the server, closing its listening channel.
    func stop() async throws {
        try await channel
            .close()
            .get()
    }

}