package network

import (
	"sync"
	"sync/atomic"
	"time"

	"github.com/gorilla/websocket"
	"google.golang.org/protobuf/proto"

	"a301_game_server/pkg/logger"
)

// ConnState represents the lifecycle state of a connection.
type ConnState int32

const (
	ConnStateActive ConnState = iota
	ConnStateClosed
)

// Connection wraps a WebSocket connection with send buffering and lifecycle management.
type Connection struct {
	id       uint64
	ws       *websocket.Conn
	sendCh   chan []byte
	handler  PacketHandler
	state    atomic.Int32
	closeOnce sync.Once

	maxMessageSize    int64
	heartbeatInterval time.Duration
	heartbeatTimeout  time.Duration
}

// PacketHandler processes incoming packets from a connection.
type PacketHandler interface {
	OnPacket(conn *Connection, pkt *Packet)
	OnDisconnect(conn *Connection)
}

// NewConnection creates a new Connection wrapping the given WebSocket.
func NewConnection(id uint64, ws *websocket.Conn, handler PacketHandler, sendChSize int, maxMsgSize int64, hbInterval, hbTimeout time.Duration) *Connection {
	c := &Connection{
		id:                id,
		ws:                ws,
		sendCh:            make(chan []byte, sendChSize),
		handler:           handler,
		maxMessageSize:    maxMsgSize,
		heartbeatInterval: hbInterval,
		heartbeatTimeout:  hbTimeout,
	}
	c.state.Store(int32(ConnStateActive))
	return c
}

// ID returns the connection's unique identifier.
func (c *Connection) ID() uint64 { return c.id }

// Start launches the read and write goroutines.
func (c *Connection) Start() {
	go c.readLoop()
	go c.writeLoop()
}

// Send encodes and queues a message for sending. Non-blocking: drops if buffer is full.
func (c *Connection) Send(msgType uint16, msg proto.Message) {
	if c.IsClosed() {
		return
	}

	data, err := Encode(msgType, msg)
	if err != nil {
		logger.Error("encode failed", "connID", c.id, "msgType", msgType, "error", err)
		return
	}

	select {
	case c.sendCh <- data:
	default:
		logger.Warn("send buffer full, dropping message", "connID", c.id, "msgType", msgType)
	}
}

// SendRaw queues pre-encoded data for sending. Non-blocking.
func (c *Connection) SendRaw(data []byte) {
	if c.IsClosed() {
		return
	}
	select {
	case c.sendCh <- data:
	default:
		logger.Warn("send buffer full, dropping raw message", "connID", c.id)
	}
}

// Close terminates the connection.
func (c *Connection) Close() {
	c.closeOnce.Do(func() {
		c.state.Store(int32(ConnStateClosed))
		close(c.sendCh)
		_ = c.ws.Close()
	})
}

// IsClosed returns true if the connection has been closed.
func (c *Connection) IsClosed() bool {
	return ConnState(c.state.Load()) == ConnStateClosed
}

func (c *Connection) readLoop() {
	defer func() {
		c.handler.OnDisconnect(c)
		c.Close()
	}()

	c.ws.SetReadLimit(c.maxMessageSize)
	_ = c.ws.SetReadDeadline(time.Now().Add(c.heartbeatTimeout))

	c.ws.SetPongHandler(func(string) error {
		_ = c.ws.SetReadDeadline(time.Now().Add(c.heartbeatTimeout))
		return nil
	})

	for {
		msgType, data, err := c.ws.ReadMessage()
		if err != nil {
			if websocket.IsUnexpectedCloseError(err, websocket.CloseGoingAway, websocket.CloseNormalClosure) {
				logger.Debug("read error", "connID", c.id, "error", err)
			}
			return
		}

		if msgType != websocket.BinaryMessage {
			continue
		}

		pkt, err := Decode(data)
		if err != nil {
			logger.Warn("decode error", "connID", c.id, "error", err)
			continue
		}

		c.handler.OnPacket(c, pkt)
	}
}

func (c *Connection) writeLoop() {
	ticker := time.NewTicker(c.heartbeatInterval)
	defer ticker.Stop()

	for {
		select {
		case data, ok := <-c.sendCh:
			if !ok {
				_ = c.ws.WriteMessage(websocket.CloseMessage,
					websocket.FormatCloseMessage(websocket.CloseNormalClosure, ""))
				return
			}

			_ = c.ws.SetWriteDeadline(time.Now().Add(10 * time.Second))
			if err := c.ws.WriteMessage(websocket.BinaryMessage, data); err != nil {
				logger.Debug("write error", "connID", c.id, "error", err)
				return
			}

		case <-ticker.C:
			_ = c.ws.SetWriteDeadline(time.Now().Add(10 * time.Second))
			if err := c.ws.WriteMessage(websocket.PingMessage, nil); err != nil {
				return
			}
		}
	}
}