using System.Collections.Concurrent;
using System.Net;
using System.Net.Sockets;
using Microsoft.Extensions.Logging;
using NATS.Server.Configuration;

namespace NATS.Server.Routes;

public sealed class RouteManager : IAsyncDisposable
{
    private readonly ClusterOptions _options;
    private readonly ServerStats _stats;
    private readonly string _serverId;
    private readonly ILogger<RouteManager> _logger;
    private readonly ConcurrentDictionary<string, RouteConnection> _routes = new(StringComparer.Ordinal);

    private CancellationTokenSource? _cts;
    private Socket? _listener;
    private Task? _acceptLoopTask;

    public string ListenEndpoint => $"{_options.Host}:{_options.Port}";

    public RouteManager(ClusterOptions options, ServerStats stats, string serverId, ILogger<RouteManager> logger)
    {
        _options = options;
        _stats = stats;
        _serverId = serverId;
        _logger = logger;
    }

    public Task StartAsync(CancellationToken ct)
    {
        _cts = CancellationTokenSource.CreateLinkedTokenSource(ct);
        _listener = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
        _listener.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.ReuseAddress, true);
        _listener.Bind(new IPEndPoint(IPAddress.Parse(_options.Host), _options.Port));
        _listener.Listen(128);

        if (_options.Port == 0)
            _options.Port = ((IPEndPoint)_listener.LocalEndPoint!).Port;

        _acceptLoopTask = Task.Run(() => AcceptLoopAsync(_cts.Token));
        foreach (var route in _options.Routes.Distinct(StringComparer.OrdinalIgnoreCase))
            _ = Task.Run(() => ConnectToRouteWithRetryAsync(route, _cts.Token));

        return Task.CompletedTask;
    }

    public async ValueTask DisposeAsync()
    {
        if (_cts == null)
            return;

        await _cts.CancelAsync();
        _listener?.Dispose();

        if (_acceptLoopTask != null)
            await _acceptLoopTask.ConfigureAwait(ConfigureAwaitOptions.SuppressThrowing);

        foreach (var route in _routes.Values)
            await route.DisposeAsync();

        _routes.Clear();
        Interlocked.Exchange(ref _stats.Routes, 0);
        _cts.Dispose();
        _cts = null;
    }

    private async Task AcceptLoopAsync(CancellationToken ct)
    {
        while (!ct.IsCancellationRequested)
        {
            Socket socket;
            try
            {
                socket = await _listener!.AcceptAsync(ct);
            }
            catch (OperationCanceledException)
            {
                break;
            }
            catch (ObjectDisposedException)
            {
                break;
            }
            catch (Exception ex)
            {
                _logger.LogDebug(ex, "Route accept loop error");
                break;
            }

            _ = Task.Run(() => HandleInboundRouteAsync(socket, ct), ct);
        }
    }

    private async Task HandleInboundRouteAsync(Socket socket, CancellationToken ct)
    {
        var route = new RouteConnection(socket);
        try
        {
            await route.PerformInboundHandshakeAsync(_serverId, ct);
            Register(route);
        }
        catch (Exception ex)
        {
            _logger.LogDebug(ex, "Inbound route handshake failed");
            await route.DisposeAsync();
        }
    }

    private async Task ConnectToRouteWithRetryAsync(string route, CancellationToken ct)
    {
        while (!ct.IsCancellationRequested)
        {
            try
            {
                var endPoint = ParseRouteEndpoint(route);
                var socket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
                await socket.ConnectAsync(endPoint.Address, endPoint.Port, ct);
                var connection = new RouteConnection(socket);
                await connection.PerformOutboundHandshakeAsync(_serverId, ct);
                Register(connection);
                return;
            }
            catch (OperationCanceledException)
            {
                return;
            }
            catch (Exception ex)
            {
                _logger.LogDebug(ex, "Failed to connect route seed {Route}", route);
            }

            try
            {
                await Task.Delay(250, ct);
            }
            catch (OperationCanceledException)
            {
                return;
            }
        }
    }

    private void Register(RouteConnection route)
    {
        var key = $"{route.RemoteServerId}:{route.RemoteEndpoint}";
        if (!_routes.TryAdd(key, route))
        {
            _ = route.DisposeAsync();
            return;
        }

        Interlocked.Increment(ref _stats.Routes);
        _ = Task.Run(() => WatchRouteAsync(key, route, _cts!.Token));
    }

    private async Task WatchRouteAsync(string key, RouteConnection route, CancellationToken ct)
    {
        try
        {
            await route.WaitUntilClosedAsync(ct);
        }
        catch (OperationCanceledException)
        {
            // Shutdown path.
        }
        catch (Exception ex)
        {
            _logger.LogDebug(ex, "Route {RouteKey} closed with error", key);
        }
        finally
        {
            if (_routes.TryRemove(key, out _))
                Interlocked.Decrement(ref _stats.Routes);

            await route.DisposeAsync();
        }
    }

    private static IPEndPoint ParseRouteEndpoint(string route)
    {
        var trimmed = route.Trim();
        var parts = trimmed.Split(':', 2, StringSplitOptions.TrimEntries | StringSplitOptions.RemoveEmptyEntries);
        if (parts.Length != 2)
            throw new FormatException($"Invalid route endpoint: '{route}'");

        return new IPEndPoint(IPAddress.Parse(parts[0]), int.Parse(parts[1]));
    }
}