package net

import (
	"context"
	"fmt"
	"net"
	"sync"
	"sync/atomic"
	"time"

	"git.loafle.net/commons/logging-go"
	"git.loafle.net/commons/server-go"
)

type Server struct {
	ServerHandler ServerHandler

	ctx         server.ServerCtx
	connections sync.Map
	stopChan    chan struct{}
	stopWg      sync.WaitGroup
}

func (s *Server) ListenAndServe() error {
	if s.stopChan != nil {
		return fmt.Errorf(s.serverMessage("already running. Stop it before starting it again"))
	}

	var (
		err      error
		listener net.Listener
	)
	if nil == s.ServerHandler {
		return fmt.Errorf("Server: server handler must be specified")
	}
	if err = s.ServerHandler.Validate(); nil != err {
		return err
	}

	s.ctx = s.ServerHandler.ServerCtx()
	if nil == s.ctx {
		return fmt.Errorf(s.serverMessage("ServerCtx is nil"))
	}

	if err = s.ServerHandler.Init(s.ctx); nil != err {
		return err
	}

	if listener, err = s.ServerHandler.Listener(s.ctx); nil != err {
		return err
	}

	s.stopChan = make(chan struct{})
	s.stopWg.Add(1)
	return s.handleServer(listener)
}

func (s *Server) Shutdown(ctx context.Context) error {
	if s.stopChan == nil {
		return fmt.Errorf(s.serverMessage("server must be started before stopping it"))
	}
	close(s.stopChan)
	s.stopWg.Wait()

	s.ServerHandler.Destroy(s.ctx)

	s.stopChan = nil

	return nil
}

func (s *Server) ConnectionSize() int {
	var sz int
	s.connections.Range(func(k, v interface{}) bool {
		sz++
		return true
	})
	return sz
}

func (s *Server) serverMessage(msg string) string {
	return fmt.Sprintf("Server[%s]: %s", s.ServerHandler.GetName(), msg)
}

func (s *Server) handleServer(listener net.Listener) error {
	var (
		stopping atomic.Value
		netConn  net.Conn
		err      error
	)

	defer func() {
		if nil != listener {
			listener.Close()
		}

		s.ServerHandler.OnStop(s.ctx)

		logging.Logger().Infof(s.serverMessage("Stopped"))

		s.stopWg.Done()
	}()

	if err = s.ServerHandler.OnStart(s.ctx); nil != err {
		return err
	}

	logging.Logger().Infof(s.serverMessage("Started"))

	for {
		acceptChan := make(chan struct{})

		go func() {
			if netConn, err = listener.Accept(); err != nil {
				if nil == stopping.Load() {
					logging.Logger().Errorf(s.serverMessage(fmt.Sprintf("%v", err)))
				}
			}
			close(acceptChan)
		}()

		select {
		case <-s.stopChan:
			stopping.Store(true)
			listener.Close()
			<-acceptChan
			listener = nil
			return nil
		case <-acceptChan:
		}

		if nil != err {
			select {
			case <-s.stopChan:
				return nil
			case <-time.After(time.Second):
			}
			continue
		}

		if 0 < s.ServerHandler.GetConcurrency() {
			sz := s.ConnectionSize()
			if sz >= s.ServerHandler.GetConcurrency() {
				logging.Logger().Warnf(s.serverMessage(fmt.Sprintf("max connections size %d, refuse", sz)))
				netConn.Close()
				continue
			}
		}

		servlet := s.ServerHandler.Servlet()
		if nil == servlet {
			logging.Logger().Errorf(s.serverMessage("Servlet is nil"))
			continue
		}

		servletCtx := servlet.ServletCtx(s.ctx)
		if nil == servletCtx {
			logging.Logger().Errorf(s.serverMessage("ServletCtx is nil"))
			continue
		}

		if err := servlet.Handshake(servletCtx, netConn); nil != err {
			logging.Logger().Infof(s.serverMessage(fmt.Sprintf("Handshaking of Client[%s] has been failed %v", netConn.RemoteAddr(), err)))
			continue
		}

		conn := server.NewConn(netConn, true, s.ServerHandler.GetReadBufferSize(), s.ServerHandler.GetWriteBufferSize())

		s.stopWg.Add(1)
		go s.handleConnection(servlet, servletCtx, conn)
	}
}

func (s *Server) handleConnection(servlet Servlet, servletCtx server.ServletCtx, conn *server.Conn) {
	addr := conn.RemoteAddr()

	defer func() {
		if nil != conn {
			conn.Close()
		}
		logging.Logger().Infof(s.serverMessage(fmt.Sprintf("Client[%s] has been disconnected", addr)))
		s.stopWg.Done()
	}()

	logging.Logger().Infof(s.serverMessage(fmt.Sprintf("Client[%s] has been connected", addr)))

	s.connections.Store(conn, true)
	defer s.connections.Delete(conn)

	servlet.OnConnect(servletCtx, conn)

	stopChan := make(chan struct{})
	servletDoneChan := make(chan struct{})

	readChan := make(chan []byte, 256)
	writeChan := make(chan []byte, 256)

	readerDoneChan := make(chan struct{})
	writerDoneChan := make(chan struct{})

	go servlet.Handle(servletCtx, stopChan, servletDoneChan, readChan, writeChan)
	go handleRead(s, conn, stopChan, readerDoneChan, readChan)
	go handleWrite(s, conn, stopChan, writerDoneChan, writeChan)

	select {
	case <-readerDoneChan:
		close(stopChan)
		conn.Close()
		<-writerDoneChan
		<-servletDoneChan
		conn = nil
	case <-writerDoneChan:
		close(stopChan)
		conn.Close()
		<-readerDoneChan
		<-servletDoneChan
		conn = nil
	case <-servletDoneChan:
		close(stopChan)
		conn.Close()
		<-readerDoneChan
		<-writerDoneChan
		conn = nil
	case <-s.stopChan:
		close(stopChan)
		conn.Close()
		<-readerDoneChan
		<-writerDoneChan
		<-servletDoneChan
		conn = nil
	}
}

func handleRead(s *Server, conn *server.Conn, doneChan chan<- struct{}, stopChan <-chan struct{}, readChan chan []byte) {
	defer func() {
		close(doneChan)
	}()

	conn.SetReadLimit(s.ServerHandler.GetMaxMessageSize())
	conn.SetReadDeadline(time.Now().Add(s.ServerHandler.GetReadTimeout()))
	conn.SetPongHandler(func(string) error {
		conn.SetReadDeadline(time.Now().Add(s.ServerHandler.GetPongTimeout()))
		return nil
	})

	var (
		message []byte
		err     error
	)

	for {
		readMessageChan := make(chan struct{})

		go func() {
			_, message, err = conn.ReadMessage()
			if err != nil {
				if server.IsUnexpectedCloseError(err, server.CloseGoingAway, server.CloseAbnormalClosure) {
					logging.Logger().Debugf(s.serverMessage(fmt.Sprintf("Read error %v", err)))
				}
			}
			close(readMessageChan)
		}()

		select {
		case <-s.stopChan:
			<-readMessageChan
			break
		case <-readMessageChan:
		}

		if nil != err {
			select {
			case <-s.stopChan:
				break
			case <-time.After(time.Second):
			}
			continue
		}

		readChan <- message
	}
}

func handleWrite(s *Server, conn *server.Conn, doneChan chan<- struct{}, stopChan <-chan struct{}, writeChan chan []byte) {
	defer func() {
		close(doneChan)
	}()

	ticker := time.NewTicker(s.ServerHandler.GetPingPeriod())
	defer func() {
		ticker.Stop()
	}()
	for {
		select {
		case message, ok := <-writeChan:
			conn.SetWriteDeadline(time.Now().Add(s.ServerHandler.GetWriteTimeout()))
			if !ok {
				conn.WriteMessage(server.CloseMessage, []byte{})
				return
			}

			w, err := conn.NextWriter(server.TextMessage)
			if err != nil {
				return
			}
			w.Write(message)

			if err := w.Close(); nil != err {
				return
			}
		case <-ticker.C:
			conn.SetWriteDeadline(time.Now().Add(s.ServerHandler.GetPingTimeout()))
			if err := conn.WriteMessage(server.PingMessage, nil); nil != err {
				return
			}
		case <-s.stopChan:
			break
		}
	}
}