package serverevents

import (
	"fmt"
	"net/http"
)

type Config struct {
	Connected    func(chan string)
	Disconnected func(chan string)
}

type Handler interface {
	http.Handler
	Broadcast(message string)
}

type handler struct {
	clients map[chan string]bool

	Connected    func(chan string)
	Disconnected func(chan string)
}

func New(config *Config) Handler {
	return &handler{
		make(map[chan string]bool),
		config.Connected,
		config.Disconnected,
	}
}

func (sse *handler) Broadcast(message string) {
	for client := range sse.clients {
		client <- message
	}
}

func (sse *handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	w.Header().Set("Content-Type", "text/event-stream")
	w.Header().Set("Cache-Control", "no-cache")
	w.Header().Set("Connection", "keep-alive")
	w.Header().Set("Access-Control-Allow-Origin", "*")

	client := make(chan string)
	sse.clients[client] = true

	if sse.Connected != nil {
		sse.Connected(client)
	}

	defer func() {
		close(client)
		delete(sse.clients, client)
		if sse.Disconnected != nil {
			sse.Disconnected(client)
		}
	}()

	flusher, _ := w.(http.Flusher)
	for {
		select {
		case message, ok := <-client:
			if !ok {
				return
			}

			fmt.Fprintf(w, "data: %s\n\n", message)
			flusher.Flush()
		case <-r.Context().Done():
			return
		}
	}
}