using System.Net.WebSockets;
using System.Text.Json;

using Myriad.Gateway.Limit;
using Myriad.Gateway.State;
using Myriad.Serialization;
using Myriad.Types;

using Serilog;
using Serilog.Context;

namespace Myriad.Gateway;

public class Shard
{
    private const string LibraryName = "Myriad (for PluralKit)";

    private readonly GatewaySettings _settings;
    private readonly ShardInfo _info;
    private readonly IGatewayRatelimiter _ratelimiter;
    private readonly string _url;
    private readonly ILogger _logger;
    private readonly ShardStateManager _stateManager;
    private readonly JsonSerializerOptions _jsonSerializerOptions;
    private readonly ShardConnection _conn;

    public int ShardId => _info.ShardId;
    public ShardState State => _stateManager.State;
    public TimeSpan? Latency => _stateManager.Latency;
    public User? User => _stateManager.User;
    public ApplicationPartial? Application => _stateManager.Application;

    // TODO: I wanna get rid of these or move them at some point
    public event Func<IGatewayEvent, Task>? OnEventReceived;
    public event Action<TimeSpan>? HeartbeatReceived;
    public event Action? SocketOpened;
    public event Action? Resumed;
    public event Action? Ready;
    public event Action<WebSocketCloseStatus?, string?>? SocketClosed;

    private TimeSpan _reconnectDelay = TimeSpan.Zero;
    private Task? _worker;

    public Shard(GatewaySettings settings, ShardInfo info, IGatewayRatelimiter ratelimiter, string url, ILogger logger)
    {
        _jsonSerializerOptions = new JsonSerializerOptions().ConfigureForMyriad();

        _settings = settings;
        _info = info;
        _ratelimiter = ratelimiter;
        _url = url;
        _logger = logger.ForContext<Shard>().ForContext("ShardId", info.ShardId);
        _stateManager = new ShardStateManager(info, _jsonSerializerOptions, logger)
        {
            HandleEvent = HandleEvent,
            SendHeartbeat = SendHeartbeat,
            SendIdentify = SendIdentify,
            SendResume = SendResume,
            Connect = ConnectInner,
            Reconnect = Reconnect,
        };
        _stateManager.OnHeartbeatReceived += latency =>
        {
            HeartbeatReceived?.Invoke(latency);
        };

        _conn = new ShardConnection(_jsonSerializerOptions, _logger, info.ShardId);
    }

    private async Task ShardLoop()
    {
        // may be superfluous but this adds shard id to ambient context which is nice
        using var _ = LogContext.PushProperty("ShardId", _info.ShardId);

        while (true)
        {
            try
            {
                await ConnectInner();

                await HandleConnectionOpened();

                while (_conn.State == WebSocketState.Open)
                {
                    var packet = await _conn.Read();
                    if (packet == null)
                        break;

                    await _stateManager.HandlePacketReceived(packet);
                }

                await HandleConnectionClosed(_conn.CloseStatus, _conn.CloseStatusDescription);

                _logger.Information("Shard {ShardId}: Reconnecting after delay {ReconnectDelay}",
                    _info.ShardId, _reconnectDelay);

                if (_reconnectDelay > TimeSpan.Zero)
                    await Task.Delay(_reconnectDelay);
                _reconnectDelay = TimeSpan.Zero;
            }
            catch (Exception e)
            {
                _logger.Error(e, "Shard {ShardId}: Error in main shard loop, reconnecting in 5 seconds...", _info.ShardId);

                // todo: exponential backoff here? this should never happen, ideally...
                await Task.Delay(TimeSpan.FromSeconds(5));
            }
        }
    }

    public async Task Start()
    {
        if (_worker == null)
            _worker = ShardLoop();

        // Ideally we'd stagger the startups so we don't smash the websocket but that's difficult with the
        // identify rate limiter so this is the best we can do rn, maybe?
        await Task.Delay(200);
    }

    public async Task UpdateStatus(GatewayStatusUpdate payload)
        => await _conn.Send(new GatewayPacket
        {
            Opcode = GatewayOpcode.PresenceUpdate,
            Payload = payload
        });

    private async Task ConnectInner()
    {
        while (true)
        {
            await _ratelimiter.Identify(_info.ShardId);

            _logger.Information("Shard {ShardId}: Connecting to WebSocket", _info.ShardId);
            try
            {
                await _conn.Connect(_url, default);
                break;
            }
            catch (WebSocketException e)
            {
                _logger.Error(e, "Shard {ShardId}: Error connecting to WebSocket, retrying in 5 seconds...", _info.ShardId);
                await Task.Delay(TimeSpan.FromSeconds(5));
            }
        }
    }

    private Task DisconnectInner(WebSocketCloseStatus closeStatus)
        => _conn.Disconnect(closeStatus, null);

    private async Task SendIdentify()
        => await _conn.Send(new GatewayPacket
        {
            Opcode = GatewayOpcode.Identify,
            Payload = new GatewayIdentify
            {
                Compress = false,
                Intents = _settings.Intents,
                Properties = new GatewayIdentify.ConnectionProperties
                {
                    Browser = LibraryName,
                    Device = LibraryName,
                    Os = Environment.OSVersion.ToString()
                },
                Shard = _info,
                Token = _settings.Token,
                LargeThreshold = 50
            }
        });

    private async Task SendResume((string SessionId, int? LastSeq) arg)
        => await _conn.Send(new GatewayPacket
        {
            Opcode = GatewayOpcode.Resume,
            Payload = new GatewayResume(_settings.Token, arg.SessionId, arg.LastSeq ?? 0)
        });

    private async Task SendHeartbeat(int? lastSeq)
        => await _conn.Send(new GatewayPacket { Opcode = GatewayOpcode.Heartbeat, Payload = lastSeq });

    private async Task Reconnect(WebSocketCloseStatus closeStatus, TimeSpan delay)
    {
        _reconnectDelay = delay;
        await DisconnectInner(closeStatus);
    }

    private async Task HandleEvent(IGatewayEvent arg)
    {
        if (arg is ReadyEvent)
            Ready?.Invoke();
        if (arg is ResumedEvent)
            Resumed?.Invoke();

        await (OnEventReceived?.Invoke(arg) ?? Task.CompletedTask);
    }

    private async Task HandleConnectionOpened()
    {
        _logger.Information("Shard {ShardId}: Connection opened", _info.ShardId);
        await _stateManager.HandleConnectionOpened();
        SocketOpened?.Invoke();
    }

    private async Task HandleConnectionClosed(WebSocketCloseStatus? closeStatus, string? description)
    {
        _logger.Information("Shard {ShardId}: Connection closed ({CloseStatus}/{Description})",
            _info.ShardId, closeStatus, description ?? "<null>");
        await _stateManager.HandleConnectionClosed();
        SocketClosed?.Invoke(closeStatus, description);
    }
}