package broker

import (
	"fmt"
	"log/slog"
	"net/http"
	"os"
	"time"
)

// the amount of time to wait when pushing a message to
// a slow client or a client that closed after `range clients` started.
// const patience time.Duration = time.Second * 1

type (
	NotificationEvent struct {
		EventName string
		Payload   string
	}
	NotifierChan chan NotificationEvent
	Broker       struct {
		// Events are pushed to this channel by the main events-gathering routine
		Notifier NotifierChan
		log      *slog.Logger
	}
)

func NewBroker() (broker *Broker) {
	// Instantiate a broker
	return &Broker{
		Notifier: make(NotifierChan, 100),
		log: slog.New(slog.NewJSONHandler(os.Stderr, &slog.HandlerOptions{
			Level:     slog.LevelDebug,
			AddSource: true,
		})),
	}
}

var Notifier *Broker

// for use in different packages
func init() {
	Notifier = NewBroker()
}

func (broker *Broker) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	// Headers (keep these as-is)
	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", "*")
	origin := r.Header.Get("Origin")
	if origin == "" {
		origin = "*" // Fallback for non-browser clients
	}
	w.Header().Set("Access-Control-Allow-Origin", origin)
	w.Header().Set("Access-Control-Allow-Credentials", "true")
	ctx := r.Context()
	// browser can close sse on its own; ping every 2s to prevent
	heartbeat := time.NewTicker(2 * time.Second)
	defer heartbeat.Stop()
	for {
		select {
		case <-ctx.Done():
			broker.log.Debug("broker: got ctx done")
			// Client disconnected
			return
		case event := <-broker.Notifier:
			broker.log.Debug("got event", "event", event)
			_, err := fmt.Fprintf(w, "event: %s\ndata: %s\n\n", event.EventName, event.Payload)
			if err != nil {
				broker.log.Error("failed to write event", "error", err)
				// Client disconnected
				return
			}
			w.(http.Flusher).Flush()
		case <-heartbeat.C:
			// Send SSE heartbeat comment
			if _, err := fmt.Fprint(w, ":\n\n"); err != nil {
				broker.log.Error("failed to write heartbeat", "error", err)
				return // Client disconnected
			}
			w.(http.Flusher).Flush()
		}
	}
}