package sse

import (
	"github.com/gin-gonic/gin"
	"io"
	"net/http"
	"sync"
	"sync/atomic"
)

var _ Server = (*event)(nil)

type Server interface {
	HandlerFunc(auth func(c *gin.Context) (string, error)) gin.HandlerFunc
	Push(user, name, msg string) bool
	Broadcast(name, msg string)
}

type clientChan struct {
	User string
	Chan chan msgChan
}

type msgChan struct {
	Name    string
	Message string
}

type event struct {
	SessionList sync.Map
	Count       atomic.Int32

	Register   chan clientChan
	Unregister chan string
}

func NewServer() Server {
	e := &event{
		SessionList: sync.Map{},
		Count:       atomic.Int32{},
		Register:    make(chan clientChan),
		Unregister:  make(chan string),
	}

	go e.listen()

	return e
}

func (stream *event) listen() {
	for {
		select {
		case client := <-stream.Register:
			stream.SessionList.Store(client.User, client.Chan)
			stream.Count.Add(1)
		case user := <-stream.Unregister:
			value, ok := stream.SessionList.Load(user)
			if ok {
				event := value.(chan msgChan)
				close(event)
				stream.SessionList.Delete(user)
				stream.Count.Add(-1)
			}
		}
	}
}

func (stream *event) HandlerFunc(auth func(c *gin.Context) (string, error)) gin.HandlerFunc {
	return func(c *gin.Context) {
		user, err := auth(c)
		if err != nil {
			c.AbortWithStatus(http.StatusBadRequest)
			return
		}

		e := make(chan msgChan)
		client := clientChan{
			User: user,
			Chan: e,
		}
		stream.Register <- client
		defer func() {
			stream.Unregister <- user
		}()

		c.Writer.Header().Set("Content-Type", "text/event-stream")
		c.Writer.Header().Set("Cache-Control", "no-cache")
		c.Writer.Header().Set("Connection", "keep-alive")
		c.Writer.Header().Set("Transfer-Encoding", "chunked")

		c.Stream(func(w io.Writer) bool {
			if msg, ok := <-e; ok {
				c.SSEvent(msg.Name, msg.Message)
				return true
			}
			return false
		})

		c.Next()
	}
}

func (stream *event) Push(user, name, msg string) bool {
	value, ok := stream.SessionList.Load(user)
	if ok {
		val := value.(chan msgChan)
		val <- msgChan{Name: name, Message: msg}
	}
	return false
}

func (stream *event) Broadcast(name, msg string) {
	stream.SessionList.Range(func(user, value any) bool {
		val := value.(chan msgChan)
		val <- msgChan{Name: name, Message: msg}
		return true
	})
}