package broker

import (
	"fmt"
	"log/slog"
	"net/http"
	"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
		// New client connections
		newClients chan NotifierChan
		// Closed client connections
		closingClients chan NotifierChan
		// Client connections registry
		clients map[NotifierChan]struct{}
	}
)

func NewBroker() (broker *Broker) {
	// Instantiate a broker
	return &Broker{
		Notifier:       make(NotifierChan, 1),
		newClients:     make(chan NotifierChan),
		closingClients: make(chan NotifierChan),
		clients:        make(map[NotifierChan]struct{}),
	}
}

var Notifier *Broker

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

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", "*")
	messageChan := make(NotifierChan)
	broker.newClients <- messageChan
	defer func() { broker.closingClients <- messageChan }()
	ctx := r.Context()
	for {
		select {
		case <-ctx.Done():
			// Client disconnected
			return
		case event := <-messageChan:
			_, err := fmt.Fprintf(w, "event: %s\ndata: %s\n\n", event.EventName, event.Payload)
			if err != nil {
				fmt.Println(err)
				// Client disconnected
				return
			}
			w.(http.Flusher).Flush()
		}
	}
}

// Listen for new notifications and redistribute them to clients
func (broker *Broker) Listen() {
	for {
		select {
		case s := <-broker.newClients:
			// A new client has connected.
			// Register their message channel
			broker.clients[s] = struct{}{}
			slog.Info("Client added", "clients listening", len(broker.clients))
		case s := <-broker.closingClients:
			// A client has dettached and we want to
			// stop sending them messages.
			delete(broker.clients, s)
			slog.Info("Client removed", "clients listening", len(broker.clients))
		case event := <-broker.Notifier:
			// We got a new event from the outside!
			// Send event to all connected clients
			for clientMessageChan := range broker.clients {
				select {
				case clientMessageChan <- event:
				case <-time.After(patience):
					slog.Info("Client was skipped", "clients listening", len(broker.clients))
				}
			}
		}
	}
}