package gateway

import (
	"bytes"
	"context"
	"errors"
	"io"
	"net"
	"sync"
	"time"
)

const (
	MinFeatureLength = 3
)

var (
	ErrShortFeature  = errors.New("short feature")
	ErrFeatureExists = errors.New("feature already exists")
)

type (
	listener struct {
		feature []byte
		l       *Listener
	}

	Gateway struct {
		listeners []*listener
		l         net.Listener
		ch        chan net.Conn
	}
)

func (g *Gateway) Attach(feature []byte, l *Listener) (err error) {
	//特征量不够大
	if len(feature) < MinFeatureLength {
		return ErrShortFeature
	}
	//判断重复
	for _, v := range g.listeners {
		if bytes.Equal(v.feature, feature) {
			return ErrFeatureExists
		}
	}
	g.listeners = append(g.listeners, &listener{
		feature: feature,
		l:       l,
	})
	return
}

func (g *Gateway) Attaches(features [][]byte, l *Listener) (err error) {
	for _, b := range features {
		if err = g.Attach(b, l); err != nil {
			break
		}
	}
	return
}

func (g *Gateway) Detach(feature []byte) (err error) {
	for i, l := range g.listeners {
		if bytes.Equal(l.feature, feature) {
			g.listeners = append(g.listeners[:i], g.listeners[i+1:]...)
			break
		}
	}
	return
}

func (g *Gateway) loop(ctx context.Context) {
	var (
		n       int
		ok      bool
		err     error
		conn    net.Conn
		feature = make([]byte, MinFeatureLength)
	)
	for {
		select {
		case conn, ok = <-g.ch:
			if ok {
				//set deadline
				_ = conn.SetReadDeadline(time.Now().Add(time.Millisecond * 800))
				if n, err = io.ReadFull(conn, feature); err != nil {
					_ = conn.Close()
					break
				}
				//reset deadline
				_ = conn.SetReadDeadline(time.Time{})
				for _, l := range g.listeners {
					if bytes.Equal(feature[:n], l.feature[:n]) {
						l.l.Receive(wrapConn(conn, feature[:n]))
						break
					}
				}
			}
		case <-ctx.Done():
			return
		}
	}
}

func (g *Gateway) schedule(ctx context.Context) {
	for {
		conn, err := g.l.Accept()
		if err != nil {
			return
		}
		select {
		case g.ch <- conn:
		case <-ctx.Done():
			return
		}
	}
}

//运行项目
func (g *Gateway) Run(ctx context.Context) {
	var wg sync.WaitGroup
	wg.Add(2)
	go func() {
		g.loop(ctx)
		wg.Done()
	}()
	go func() {
		g.schedule(ctx)
		wg.Done()
	}()
	wg.Wait()
}

func New(l net.Listener) *Gateway {
	return &Gateway{
		l:         l,
		ch:        make(chan net.Conn, 10),
		listeners: make([]*listener, 0),
	}
}