#nullable enable
using System;
using System.Collections.Generic;
using Cysharp.Threading.Tasks;

namespace ShrinkNetwork
{
    public sealed class ShrinkLoopbackTransport : IShrinkNetworkAsyncTransport, IShrinkNetworkSessionControlTransport
    {
        private readonly HashSet<long> _openedSessions = new();
        private ShrinkLoopbackTransport? _peer;

        public bool IsStarted { get; private set; }

        public event Action<ShrinkNetworkTransportEvent>? OnEvent;

        public void LinkPeer(ShrinkLoopbackTransport peer)
        {
            _peer = peer;
            if (peer._peer != this)
                peer.LinkPeer(this);
        }

        public void Start()
        {
            IsStarted = true;
        }

        public void Stop()
        {
            IsStarted = false;
        }

        public void OpenSession(long sessionId, string remoteAddress = "loopback")
        {
            _openedSessions.Add(sessionId);
            _peer?._openedSessions.Add(sessionId);
            OnEvent?.Invoke(ShrinkNetworkTransportEvent.Connected(sessionId, remoteAddress));
            _peer?.OnEvent?.Invoke(ShrinkNetworkTransportEvent.Connected(sessionId, remoteAddress));
        }

        public void CloseSession(long sessionId, string remoteAddress = "loopback")
        {
            _openedSessions.Remove(sessionId);
            _peer?._openedSessions.Remove(sessionId);
            OnEvent?.Invoke(ShrinkNetworkTransportEvent.Disconnected(sessionId, remoteAddress));
            _peer?.OnEvent?.Invoke(ShrinkNetworkTransportEvent.Disconnected(sessionId, remoteAddress));
        }

        public bool DisconnectSession(long sessionId, string? reason = null)
        {
            if (!_openedSessions.Contains(sessionId))
                return false;

            CloseSession(sessionId);
            return true;
        }

        public void Send(long sessionId, byte[] packetData)
        {
            SendAsync(sessionId, packetData).Forget();
        }

        public UniTask SendAsync(long sessionId, byte[] packetData)
        {
            if (!IsStarted)
                throw new InvalidOperationException("Transport has not been started.");
            if (_peer == null)
                throw new InvalidOperationException("Peer transport is not linked.");
            if (!_openedSessions.Contains(sessionId))
                throw new InvalidOperationException($"Session {sessionId} is not open.");

            _peer.OnEvent?.Invoke(ShrinkNetworkTransportEvent.Packet(sessionId, packetData));
            return UniTask.CompletedTask;
        }
    }
}