package sse

import (
	"encoding/json"
	"fmt"
	"net/http"
	"time"

	"github.com/gin-gonic/gin"
)

func Serve(c *gin.Context, sub *Subscription, heartbeat time.Duration) {
	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("X-Accel-Buffering", "no")
	c.Writer.WriteHeader(http.StatusOK)

	flusher, ok := c.Writer.(http.Flusher)
	if !ok {
		c.AbortWithStatus(http.StatusInternalServerError)
		return
	}
	fmt.Fprint(c.Writer, ": connected\n\n")
	flusher.Flush()

	if heartbeat <= 0 {
		heartbeat = 25 * time.Second
	}
	ticker := time.NewTicker(heartbeat)
	defer ticker.Stop()

	ctx := c.Request.Context()
	for {
		select {
		case <-ctx.Done():
			return
		case ev, ok := <-sub.Events():
			if !ok {
				return
			}
			payload, err := json.Marshal(ev.Data)
			if err != nil {
				continue
			}
			fmt.Fprintf(c.Writer, "event: %s\ndata: %s\n\n", ev.Type, payload)
			flusher.Flush()
		case <-ticker.C:
			fmt.Fprint(c.Writer, ": heartbeat\n\n")
			flusher.Flush()
		}
	}
}