package rsp

import (
	"errors"
	"fmt"
	"github.com/labstack/echo/v4"
	"net/http"
	"strings"
	"time"
)

type SseOptions struct {
	Id    string
	Event string
	Data  string
	Retry int
}

func Echo(c echo.Context, e <-chan *SseOptions) error {
	w := c.Response().Writer
	f, ok := w.(http.Flusher)
	if !ok {
		return errors.New("unable to get http.Flusher interface; this is probably due " +
			"to nginx buffering the response")
	}
	if want, have := "text/event-stream", c.Request().Header.Get("Accept"); want != have {
		return fmt.Errorf("accept header: want %q, have %q; seems like the browser doesn't "+
			"support server-side events", want, have)
	}
	// Instruct nginx to NOT buffer the response
	w.Header().Set("X-Accel-Buffering", "no")
	w.Header().Set("Content-Type", "text/event-stream")
	w.Header().Set("Cache-Control", "no-cache")
	w.Header().Set("Connection", "keep-alive")
	w.WriteHeader(http.StatusOK)
	// Send heartbeats to ensure the connection stays up
	heartbeat := time.NewTicker(30 * time.Second)
	defer heartbeat.Stop()
	for {
		select {
		case <-c.Request().Context().Done(): // When the browser closes the connection
			f.Flush()
			return nil
		case <-heartbeat.C:
			sendEvent(w, "", "heartbeat", "{}", 2000)
		case opts := <-e:
			sendEvent(w, cleanNewline(opts.Id), cleanNewline(opts.Event), cleanNewline(opts.Data), opts.Retry)
		}
	}
}

func cleanNewline(str string) string {
	return strings.ReplaceAll(str, "\n", "")
}

func sendEvent(w http.ResponseWriter, id, event, data string, retry int) {
	f := w.(http.Flusher)
	if id != "" {
		fmt.Fprintf(w, "id: %s\n", id)
	}
	if event != "" {
		fmt.Fprintf(w, "event: %s\n", event)
	}
	if data != "" {
		fmt.Fprintf(w, "data: %s\n", data)
	}
	if retry > 0 {
		fmt.Fprintf(w, "retry: %d\n", retry)
	}
	fmt.Fprint(w, "\n")
	f.Flush()
}