package connection

import (
	"errors"
	"fmt"
	"git.noahlan.cn/noahlan/nnet/packet"
	"git.noahlan.cn/noahlan/nnet/session"
	"git.noahlan.cn/noahlan/ntool/ndef"
	"git.noahlan.cn/noahlan/ntool/nlog"
	"github.com/panjf2000/ants/v2"
	"net"
	"sync/atomic"
)

var (
	ErrCloseClosedSession = errors.New("close closed session")
	// ErrBrokenPipe represents the low-level connection has broken.
	ErrBrokenPipe = errors.New("broken low-level pipe")
)

const (
	// StatusStart 开始阶段
	StatusStart int32 = iota + 1
	// StatusPrepare 准备阶段
	StatusPrepare
	// StatusPending 等待工作阶段
	StatusPending
	// StatusWorking 工作阶段
	StatusWorking
	// StatusClosed 连接关闭
	StatusClosed
)

type ConnType int

const (
	ConnTypeTCP    ConnType = iota // TCP connection
	ConnTypeWS                     // Websocket connection
	ConnTypeSerial                 // Websocket connection
)

type (
	Connection struct {
		conf    Config           // 配置
		session *session.Session // Session
		pool    *ants.Pool       // 连接池

		status int32    // 连接状态
		conn   net.Conn // low-level conn fd
		typ    ConnType // 连接类型

		packer     packet.Packer                              // 封包、拆包器
		serializer ndef.Serializer                            // 消息序列化/反序列化器
		pipeline   Pipeline                                   // 连接生命周期管理
		handleFn   func(conn *Connection, pkg packet.IPacket) // 消息处理方法

		lastMid uint64 // 最近一次消息ID

		chDie   chan struct{}       // 停止通道
		chSend  chan PendingMessage // 消息发送通道（结构化消息）
		chWrite chan []byte         // 消息发送通道（二进制消息）
	}

	packetFn func(conn *Connection, pkg packet.IPacket)

	Config struct {
		LogDebug  bool
		LogPrefix string
	}

	PendingMessage struct {
		header  any
		payload any
	}
)

func NewConnection(
	id int64,
	conn net.Conn,
	pool *ants.Pool,
	conf Config,
	packerBuilder packet.PackerBuilder,
	serializer ndef.Serializer,
	pipeline Pipeline,
	handleFn packetFn) *Connection {
	r := &Connection{
		conf:    conf,
		session: session.NewSession(id),
		pool:    pool,

		status: StatusStart,
		conn:   conn,
		typ:    ConnTypeTCP,

		packer:     packerBuilder(),
		serializer: serializer,
		pipeline:   pipeline,
		handleFn:   handleFn,

		lastMid: 0,

		chDie:   make(chan struct{}),
		chSend:  make(chan PendingMessage, 128),
		chWrite: make(chan []byte, 128),
	}
	if _, ok := conn.(*WSConn); ok {
		r.typ = ConnTypeWS
		return r
	}
	if _, ok := conn.(*SerialConn); ok {
		r.typ = ConnTypeSerial
		return r
	}
	return r
}

func (r *Connection) Send(header, payload any) (err error) {
	defer func() {
		if e := recover(); e != nil {
			err = ErrBrokenPipe
		}
	}()
	r.chSend <- PendingMessage{
		header:  header,
		payload: payload,
	}
	return err
}

func (r *Connection) SendBytes(data []byte) (err error) {
	defer func() {
		if e := recover(); e != nil {
			err = ErrBrokenPipe
		}
	}()
	r.chWrite <- data
	return err
}

func (r *Connection) Status() int32 {
	return atomic.LoadInt32(&r.status)
}

func (r *Connection) SetStatus(s int32) {
	atomic.StoreInt32(&r.status, s)
}

func (r *Connection) Conn() (net.Conn, ConnType) {
	return r.conn, r.typ
}

func (r *Connection) ID() int64 {
	return r.session.ID()
}

func (r *Connection) Session() *session.Session {
	return r.session
}

func (r *Connection) LastMID() uint64 {
	return r.lastMid
}

func (r *Connection) SetLastMID(mid uint64) {
	atomic.StoreUint64(&r.lastMid, mid)
}

func (r *Connection) Serve() {
	_ = r.pool.Submit(func() {
		r.write()
	})

	_ = r.pool.Submit(func() {
		r.read()
	})
}

func (r *Connection) write() {
	defer func() {
		close(r.chSend)
		close(r.chWrite)
		_ = r.Close()

		if r.conf.LogDebug {
			nlog.Debugf("%s [writeLoop] connection write goroutine exit, ConnID=%d, SessionUID=%s",
				r.conf.LogPrefix, r.ID(), r.session.UID())
		}
	}()

	for {
		select {
		case data := <-r.chSend:
			// marshal packet body (data)
			if r.serializer == nil {
				if _, ok := data.payload.([]byte); !ok {
					nlog.Errorf("%s serializer is nil, but payload type not []byte", r.conf.LogPrefix)
					break
				}
			} else {
				payload, err := r.serializer.Marshal(data.payload)
				if err != nil {
					nlog.Errorf("%s message body marshal err: %v", r.conf.LogPrefix, err)
					break
				}
				data.payload = payload
			}

			// invoke pipeline
			if pipe := r.pipeline; pipe != nil {
				err := pipe.Outbound().Process(r, data)
				if err != nil {
					nlog.Errorf("%s pipeline err: %s", r.conf.LogPrefix, err.Error())
				}
			}

			// packet pack data
			p, err := r.packer.Pack(data.header, data.payload.([]byte))
			if err != nil {
				nlog.Errorf("%s pack err: %s", r.conf.LogPrefix, err.Error())
				break
			}
			r.chWrite <- p
		case data := <-r.chWrite:
			// 回写数据
			if _, err := r.conn.Write(data); err != nil {
				nlog.Errorf("%s write data err: %s", r.conf.LogPrefix, err.Error())
				break
			}
			//nlog.Debugf("write data %v", data)
		case <-r.chDie: // connection close signal
			return
			// TODO
			//case <-r.ngin.dieChan: // application quit signal
			//	return
		}
	}
}

func (r *Connection) read() {
	defer func() {
		_ = r.Close()
	}()
	buf := make([]byte, 4096)
	for {
		n, err := r.conn.Read(buf)
		//nlog.Debugf("receive data %v", buf[:n])
		if err != nil {
			nlog.Errorf("%s [readLoop] Read message error: %s, session will be closed immediately",
				r.conf.LogPrefix, err.Error())
			return
		}

		if n == 0 {
			nlog.Errorf("%s [readLoop] Read empty message, session will be closed immediately",
				r.conf.LogPrefix)
			return
		}

		if r.packer == nil {
			nlog.Errorf("%s [readLoop] unexpected error: packer is nil", r.conf.LogPrefix)
			return
		}

		// warning: 为性能考虑，复用slice处理数据，buf传入后必须要copy再处理
		packets, err := r.packer.Unpack(buf[:n])
		if err != nil {
			nlog.Errorf("%s unpack err: %s", r.conf.LogPrefix, err.Error())
		}
		// packets 处理
		for _, p := range packets {
			if err := r.processPacket(p); err != nil {
				nlog.Errorf("%s process packet err: %s", r.conf.LogPrefix, err.Error())
				continue
			}
		}
	}
}

func (r *Connection) processPacket(packet packet.IPacket) error {
	if pipe := r.pipeline; pipe != nil {
		err := pipe.Inbound().Process(r, packet)
		if err != nil {
			return errors.New(fmt.Sprintf("pipeline process failed: %v", err.Error()))
		}
	}

	if r.Status() == StatusWorking {
		// 处理包消息
		_ = r.pool.Submit(func() {
			r.handleFn(r, packet)
		})
	}
	return nil
}

func (r *Connection) DieChan() chan struct{} {
	return r.chDie
}

func (r *Connection) Close() error {
	if r.Status() == StatusClosed {
		return ErrCloseClosedSession
	}
	r.SetStatus(StatusClosed)

	if r.conf.LogDebug {
		nlog.Debugf("%s close connection, ID: %d", r.conf.LogPrefix, r.ID())
	}

	select {
	case <-r.chDie:
	default:
		close(r.chDie)
	}

	r.session.Close()
	return r.conn.Close()
}