package main

import (
  "fmt"
  "net/http"
)

func main() {
 fmt.Println("Listen localhost:8080")
   // 注册一个用于WebSocket的路由，实际业务中不可能只有一个路由
  http.HandleFunc("/messages", messageHandler)
  // 监听8080端口，没有实现服务异常处理器，因此第二个参数是nil
  http.ListenAndServe("localhost:8080", nil)
}

func messageHandler(response http.ResponseWriter, request *http.Request) {
  // TODO: 实现消息处理
  response.Write([]byte("HelloWorld"))
}

func messageHandler(response http.ResponseWriter, request *http.Request) {
  var upgrader = websocket.Upgrader{
    // 允许跨域
    CheckOrigin: func(resquest *http.Request) bool {
      return true
    },
  }

  // 建立连接
  conn, err := upgrader.Upgrade(response, request, nil)
  if err != nil {
    return
  }

  // 收发消息
  for {
    // 读取消息
    _, bytes, err := conn.ReadMessage()
    if err != nil {
      _ = conn.Close()
    }
    // 写入消息
    err = conn.WriteMessage(websocket.TextMessage, bytes)
    if err != nil {
      _ = conn.Close()
    }
  }
}

// main.go
package main

import (
  "bluemiaomiao.github.io/websocket-go/service"
  "fmt"
  "net/http"

  "github.com/gorilla/websocket"
)

func main() {
  fmt.Println("Listen localhost:8080")
  http.HandleFunc("/messages", messageHandler)
  _ = http.ListenAndServe("localhost:8080", nil)
}

func messageHandler(response http.ResponseWriter, request *http.Request) {
  var upgrader = websocket.Upgrader{
    // 允许跨域
    CheckOrigin: func(resquest *http.Request) bool {
      return true
    },
  }

  // 建立连接
  conn, err := upgrader.Upgrade(response, request, nil)
  wsConn, err := service.Create(conn)
  if err != nil {
    return
  }

  // 收发消息
  for {
    // 读取消息
    msg, err := wsConn.ReadOne()
    if err != nil {
      wsConn.Close()
    }
    // 写入消息
    err = wsConn.WriteOne(msg)
    if err != nil {
      _ = conn.Close()
    }
  }
}

// service/messsage_service.go
package service

import (
  "errors"
  "github.com/gorilla/websocket"
  "sync"
)

// 封装的连接对象
// 
// 由于websocket的Close()方法是可重入的，所以可以多次调用，但是关闭Channel的close()
// 方法不是可重入的，因此通过isClosed进行判断
// isClosed可能发生资源竞争，因此通过互斥锁避免
// 关闭websocket连接后，也要自动关闭输入输出消息流，因此通过signalCloseLoopChan实现
type Connection struct {
  conn                  *websocket.Conn  // 具体的连接对象
  inputStream             chan []byte       // 输入流，使用Channel模拟
  outputStream           chan []byte       // 输出流，使用chaneel模拟
  signalCloseLoopChan     chan byte       // 关闭信号
  isClosed               bool            // 是否调用过close()方法
  lock                   sync.Mutex      // 简单的锁
}

// 用于初始化一个连接对象
func Create(conn *websocket.Conn) (connection *Connection, err error) {
  connection = &Connection{
    conn:              conn,
    inputStream:        make(chan []byte, 1000),
    outputStream:       make(chan []byte, 1000),
    signalCloseLoopChan: make(chan byte, 1),
    isClosed:            false,
  }

  // 启动读写循环
  go connection.readLoop()
  go connection.writeLoop()
  return
}

// 读取一条消息
func (c *Connection) ReadOne() (msg []byte, err error) {
  select {
  case msg = <-(*c).inputStream:
  case <-(*c).signalCloseLoopChan:
    err = errors.New("connection is closed")
  }
  return
}

// 写入一条消息
func (c *Connection) WriteOne(msg []byte) (err error) {
  select {
  case (*c).outputStream <- msg:
  case <-(*c).signalCloseLoopChan:
    err = errors.New("connection is closed")
  }
  return
}

// 关闭连接对象
func (c *Connection) Close() {
  _ = (*c).conn.Close()
  (*c).lock.Lock()
  if !(*c).isClosed {
    close((*c).signalCloseLoopChan)
  }
  (*c).lock.Unlock()

}

// 读取循环
func (c *Connection) readLoop() {
  // 不停的读取长连接中的消息，只要存在消息就将其放到队列中
  for {
    _, bytes, err := (*c).conn.ReadMessage()
    if err != nil {
      (*c).Close()
    }
    select {
    case <-(*c).signalCloseLoopChan:
      (*c).Close()
    case (*c).inputStream <- bytes:
    }
  }
}

// 写入循环
func (c *Connection) writeLoop() {
  // 只要队列中存在消息，就将其写入
  var data []byte
  for {
    select {
    case data = <-(*c).outputStream:
    case <-(*c).signalCloseLoopChan:
      (*c).Close()
    }
    err := (*c).conn.WriteMessage(websocket.TextMessage, data)
    if err != nil {
      _ = (*c).conn.Close()
    }
  }
}