using System;
using System.IO;
using System.Threading;
using System.Threading.Tasks;

namespace EM.LowLevel
{
    /// <summary>
    ///   High-level transport abstraction for device communication. Derives from Stream and
    ///   encapsulates initialization/handshake and frame (header/tail/checksum) handling as needed
    ///   by the device. Implementations may wrap SerialPort, Sockets, USB, etc.
    /// </summary>
    public abstract class PortStream : Stream
    {

        /// <summary>
        ///   Optional bytes available hint if the transport can provide it.
        /// </summary>
        public virtual long? BytesAvailable => null;

        /// <summary>
        ///   Close the underlying transport and release resources.
        /// </summary>
        public abstract override void Close();

        /// <summary>
        ///   Ensure the port is opened and ready. Idempotent. May perform device-specific
        ///   handshakes.
        /// </summary>
        public abstract ValueTask OpenAsync(CancellationToken cancellationToken = default);

        // Concrete transports must implement Stream's abstract members.
        // Seek-related members are typically not supported and should throw NotSupportedException.
    }
}