// Package ws implements the single multiplexed live-update WebSocket (§2.2):
// one connection per logged-in session carrying `chat`, `board`, and
// `notifications` channels, with 30 s heartbeats so idle proxies keep the
// connection alive (§12).
package ws

import (
	"context"
	"encoding/json"
	"log/slog"
	"net/http"
	"sync"
	"time"

	"github.com/coder/websocket"
)

// Message is the wire format in both directions.
type Message struct {
	Channel string          `json:"channel"`
	Event   string          `json:"event"`
	Data    json.RawMessage `json:"data,omitempty"`
}

type client struct {
	userID string
	send   chan []byte
}

// Inbound handles client→server messages (e.g. typing indicators).
type Inbound func(userID string, msg Message)

type Hub struct {
	log      *slog.Logger
	originOK func(r *http.Request) bool
	inbound  Inbound
	mu       sync.RWMutex
	clients  map[*client]struct{}
	byUser   map[string]map[*client]struct{}
}

func NewHub(log *slog.Logger, originOK func(*http.Request) bool) *Hub {
	return &Hub{
		log:      log,
		originOK: originOK,
		clients:  map[*client]struct{}{},
		byUser:   map[string]map[*client]struct{}{},
	}
}

// SetInbound installs the client-message handler (chat typing etc.).
func (h *Hub) SetInbound(f Inbound) { h.inbound = f }

// ConnectedUserIDs lists users with at least one live socket.
func (h *Hub) ConnectedUserIDs() []string {
	h.mu.RLock()
	defer h.mu.RUnlock()
	out := make([]string, 0, len(h.byUser))
	for id := range h.byUser {
		out = append(out, id)
	}
	return out
}

func (h *Hub) register(c *client) {
	h.mu.Lock()
	defer h.mu.Unlock()
	h.clients[c] = struct{}{}
	if h.byUser[c.userID] == nil {
		h.byUser[c.userID] = map[*client]struct{}{}
	}
	h.byUser[c.userID][c] = struct{}{}
}

func (h *Hub) unregister(c *client) {
	h.mu.Lock()
	defer h.mu.Unlock()
	delete(h.clients, c)
	if set := h.byUser[c.userID]; set != nil {
		delete(set, c)
		if len(set) == 0 {
			delete(h.byUser, c.userID)
		}
	}
}

func encode(channel, event string, payload any) []byte {
	data, err := json.Marshal(payload)
	if err != nil {
		data = []byte("null")
	}
	b, _ := json.Marshal(Message{Channel: channel, Event: event, Data: data})
	return b
}

// Broadcast sends to every connected client.
func (h *Hub) Broadcast(channel, event string, payload any) {
	b := encode(channel, event, payload)
	h.mu.RLock()
	defer h.mu.RUnlock()
	for c := range h.clients {
		select {
		case c.send <- b:
		default: // slow client: drop rather than block the publisher
		}
	}
}

// SendTo delivers to all sockets of the given users.
func (h *Hub) SendTo(userIDs []string, channel, event string, payload any) {
	b := encode(channel, event, payload)
	h.mu.RLock()
	defer h.mu.RUnlock()
	for _, id := range userIDs {
		for c := range h.byUser[id] {
			select {
			case c.send <- b:
			default:
			}
		}
	}
}

// Handle upgrades the request (the caller has already authenticated userID).
func (h *Hub) Handle(w http.ResponseWriter, r *http.Request, userID string) {
	if h.originOK != nil && !h.originOK(r) {
		http.Error(w, "origin not allowed", http.StatusForbidden)
		return
	}
	conn, err := websocket.Accept(w, r, &websocket.AcceptOptions{
		// Origin verified above against APP_BASE_URL (§12).
		InsecureSkipVerify: true,
	})
	if err != nil {
		h.log.Warn("ws accept", "err", err)
		return
	}
	c := &client{userID: userID, send: make(chan []byte, 64)}
	h.register(c)
	defer h.unregister(c)

	ctx, cancel := context.WithCancel(r.Context())
	defer cancel()
	go h.writeLoop(ctx, cancel, conn, c)
	h.readLoop(ctx, conn, c)
	conn.Close(websocket.StatusNormalClosure, "bye")
}

func (h *Hub) writeLoop(ctx context.Context, cancel func(), conn *websocket.Conn, c *client) {
	defer cancel()
	heartbeat := time.NewTicker(30 * time.Second)
	defer heartbeat.Stop()
	for {
		select {
		case <-ctx.Done():
			return
		case msg := <-c.send:
			wctx, wcancel := context.WithTimeout(ctx, 10*time.Second)
			err := conn.Write(wctx, websocket.MessageText, msg)
			wcancel()
			if err != nil {
				return
			}
		case <-heartbeat.C:
			pctx, pcancel := context.WithTimeout(ctx, 10*time.Second)
			err := conn.Ping(pctx)
			pcancel()
			if err != nil {
				return
			}
		}
	}
}

func (h *Hub) readLoop(ctx context.Context, conn *websocket.Conn, c *client) {
	for {
		_, data, err := conn.Read(ctx)
		if err != nil {
			return
		}
		if h.inbound == nil {
			continue
		}
		var msg Message
		if err := json.Unmarshal(data, &msg); err != nil {
			continue
		}
		h.inbound(c.userID, msg)
	}
}