package server

import (
	"bufio"
	"context"
	"encoding/binary"
	"errors"
	"file-manger-server/util"
	"fmt"
	"io"
	"log"
	"net"
	"os"
	"os/signal"
	"sync"
	"sync/atomic"
	"syscall"
	"time"
)

// ConnPool 改进后的连接池结构
type ConnPool struct {
	connections  sync.Map           // 使用sync.Map替代原生map
	maxConns     int32              // 最大连接数
	currentConns atomic.Int32       // 当前连接数（原子操作）
	ctx          context.Context    // 上下文
	cancel       context.CancelFunc // 用于取消上下文
}

type ConnInfo struct {
	conn         net.Conn      // 原始连接
	lastActive   atomic.Int64  // 最后活跃时间（原子操作）
	heartbeatTTL time.Duration // 心跳TTL
	closed       atomic.Bool   // 关闭状态标记
	bufReader    *bufio.Reader // 带缓冲的读取器
}

const (
	MaxConnections    = 1000             // 最大连接数
	HeartbeatInterval = 30 * time.Second // 心跳间隔
	ReadTimeout       = 2 * time.Minute  // 读取超时时间
)

func NewConnPool(maxConns int) *ConnPool {
	ctx, cancel := context.WithCancel(context.Background())
	return &ConnPool{
		maxConns: int32(maxConns),
		ctx:      ctx,
		cancel:   cancel,
	}
}

// Add 添加连接到池（带数量检查）
func (p *ConnPool) Add(conn net.Conn) error {
	if p.currentConns.Load() >= p.maxConns {
		return errors.New("connection limit reached")
	}

	ci := &ConnInfo{
		conn:         conn,
		heartbeatTTL: HeartbeatInterval * 3,
		bufReader:    bufio.NewReaderSize(conn, 4096),
	}
	ci.lastActive.Store(time.Now().UnixNano())

	p.connections.Store(conn, ci)
	p.currentConns.Add(1)
	return nil
}

// Remove 移除连接
func (p *ConnPool) Remove(conn net.Conn) {
	if ci, loaded := p.connections.LoadAndDelete(conn); loaded {
		ci.(*ConnInfo).Close()
		p.currentConns.Add(-1)
	}
}

// Close 关闭连接
func (ci *ConnInfo) Close() {
	if ci.closed.CompareAndSwap(false, true) {
		ci.conn.Close()
	}
}

// StartCleaner 启动自动清理协程
func (p *ConnPool) StartCleaner() {
	go func() {
		ticker := time.NewTicker(1 * time.Minute)
		defer ticker.Stop()

		for {
			select {
			case <-ticker.C:
				p.cleanup()
			case <-p.ctx.Done():
				return
			}
		}
	}()
}

// 清理失效连接
func (p *ConnPool) cleanup() {
	p.connections.Range(func(key, value any) bool {
		ci := value.(*ConnInfo)
		if time.Since(time.Unix(0, ci.lastActive.Load())) > ci.heartbeatTTL {
			p.Remove(ci.conn)
		}
		return true
	})
}

// Shutdown 优雅关闭
func (p *ConnPool) Shutdown() {
	p.cancel()
	p.connections.Range(func(key, value any) bool {
		ci := value.(*ConnInfo)
		ci.Close()
		p.connections.Delete(key)
		return true
	})
}

func Run() {
	pool := NewConnPool(MaxConnections)
	pool.StartCleaner()

	listener, err := net.Listen("tcp", ":8080")
	if err != nil {
		log.Fatal(err)
	}

	// 信号处理
	sigCh := make(chan os.Signal, 1)
	signal.Notify(sigCh, syscall.SIGINT, syscall.SIGTERM)

	go func() {
		<-sigCh
		log.Println("Shutting down server...")
		listener.Close()
		pool.Shutdown()
	}()

	for {
		conn, err := listener.Accept()
		if err != nil {
			if errors.Is(err, net.ErrClosed) {
				break // 正常关闭
			}
			log.Printf("Accept error: %v", err)
			continue
		}

		if err := pool.Add(conn); err != nil {
			conn.Close()
			log.Printf("Reject connection: %v", err)
			continue
		}

		go handleConnection(pool, conn)
	}
}

func handleConnection(pool *ConnPool, conn net.Conn) {
	defer func() {
		if r := recover(); r != nil {
			log.Printf("Connection panic: %v", r)
		}
		pool.Remove(conn)
	}()

	// 获取连接信息
	ci, ok := pool.connections.Load(conn)
	if !ok {
		return
	}
	connInfo := ci.(*ConnInfo)

	// 心跳检测
	ctx, cancel := context.WithCancel(context.Background())
	defer cancel()
	go heartbeat(ctx, connInfo)

	// 消息处理循环
	for {
		// 设置读取超时
		connInfo.conn.SetReadDeadline(time.Now().Add(ReadTimeout))

		// 使用长度前缀协议处理粘包
		message, err := readMessage(connInfo.bufReader)
		if err != nil {
			if !errors.Is(err, io.EOF) {
				log.Printf("Read error: %v", err)
			}
			return
		}

		// 更新活跃时间
		connInfo.lastActive.Store(time.Now().UnixNano())

		// 处理业务逻辑
		if err := processMessage(connInfo, message); err != nil {
			log.Printf("Process message error: %v", err)
			return
		}
	}
}

// 自定义错误类型
var (
	ErrInvalidStartByte = errors.New("invalid start byte")
	ErrChecksumMismatch = errors.New("checksum mismatch")
	ErrMessageTooLarge  = errors.New("message exceeds size limit")
)

func readMessage(r *bufio.Reader) ([]byte, error) {

	// 读取起始字节 (0x2a)
	startByte, err := r.ReadByte()
	if err != nil {
		return nil, fmt.Errorf("read start byte failed: %w", err)
	}
	if startByte != 0x2a {
		return nil, fmt.Errorf("%w: received 0x%02x", ErrInvalidStartByte, startByte)
	}

	// 读取长度字段 (4字节大端序)
	lengthBuf := make([]byte, 4)
	if _, err := io.ReadFull(r, lengthBuf); err != nil {
		return nil, fmt.Errorf("read length failed: %w", err)
	}
	dataLength := binary.BigEndian.Uint32(lengthBuf)

	// 验证数据长度 (10MB限制)
	if dataLength > 10*1024*1024 {
		return nil, fmt.Errorf("%w: %d bytes", ErrMessageTooLarge, dataLength)
	}

	// 读取数据体
	dataBody := make([]byte, dataLength)
	if _, err := io.ReadFull(r, dataBody); err != nil {
		return nil, fmt.Errorf("read data body failed: %w", err)
	}

	// 读取校验和 (2字节大端序)
	checksumBuf := make([]byte, 2)
	if _, err := io.ReadFull(r, checksumBuf); err != nil {
		return nil, fmt.Errorf("read checksum failed: %w", err)
	}
	receivedChecksum := binary.BigEndian.Uint16(checksumBuf)

	// 计算校验和 (CRC16-CCITT)
	calculatedChecksum := util.Crc16CCITT(dataBody)
	if calculatedChecksum != receivedChecksum {
		return nil, fmt.Errorf("%w: expected %04X, got %04X",
			ErrChecksumMismatch, calculatedChecksum, receivedChecksum)
	}
	return dataBody, nil
}

// 心跳检测
func heartbeat(ctx context.Context, ci *ConnInfo) {
	ticker := time.NewTicker(HeartbeatInterval)
	defer ticker.Stop()

	for {
		select {
		case <-ticker.C:
			if ci.closed.Load() {
				return
			}

			// 发送心跳包
			if _, err := ci.conn.Write([]byte("PING")); err != nil {
				ci.Close()
				return
			}
		case <-ctx.Done():
			return
		}
	}
}

// 示例消息处理
func processMessage(info *ConnInfo, msg []byte) error {
	// 实现业务逻辑
	fmt.Printf("Processing message: %s\n", util.ToHexBytes(msg))
	info.conn.Write(msg)
	return nil
}