package api

import (
	"encoding/json"
	"fmt"
	"net/http"
	"sync"
)

// Event is a change notification pushed to SSE clients.
type Event struct {
	Type      string `json:"type"`
	ProjectID string `json:"projectId,omitempty"`
}

type hub struct {
	mu      sync.Mutex
	clients map[chan Event]struct{}
}

func newHub() *hub {
	return &hub{clients: map[chan Event]struct{}{}}
}

func (h *hub) subscribe() chan Event {
	ch := make(chan Event, 16)
	h.mu.Lock()
	h.clients[ch] = struct{}{}
	h.mu.Unlock()
	return ch
}

func (h *hub) unsubscribe(ch chan Event) {
	h.mu.Lock()
	delete(h.clients, ch)
	h.mu.Unlock()
	close(ch)
}

func (h *hub) publish(ev Event) {
	h.mu.Lock()
	defer h.mu.Unlock()
	for ch := range h.clients {
		select {
		case ch <- ev:
		default:
		}
	}
}

func (s *Server) handleEvents(w http.ResponseWriter, r *http.Request) {
	flusher, ok := w.(http.Flusher)
	if !ok {
		http.Error(w, "streaming unsupported", http.StatusInternalServerError)
		return
	}
	w.Header().Set("Content-Type", "text/event-stream")
	w.Header().Set("Cache-Control", "no-cache")
	w.Header().Set("Connection", "keep-alive")

	ch := s.hub.subscribe()
	defer s.hub.unsubscribe(ch)

	fmt.Fprintf(w, ": ok\n\n")
	flusher.Flush()

	ctx := r.Context()
	for {
		select {
		case <-ctx.Done():
			return
		case ev, ok := <-ch:
			if !ok {
				return
			}
			data, _ := json.Marshal(ev)
			fmt.Fprintf(w, "data: %s\n\n", data)
			flusher.Flush()
		}
	}
}