package gateway

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

	"github.com/gorilla/websocket"
)

const (
	writeWait      = 10 * time.Second
	pongWait       = 60 * time.Second
	pingPeriod     = (pongWait * 9) / 10
	maxMessageSize = 4096
)

var upgrader = websocket.Upgrader{
	ReadBufferSize:  1024,
	WriteBufferSize: 1024,
	CheckOrigin:     func(r *http.Request) bool { return true },
}

// Client is a middleman between the websocket connection and the hub.
type Client struct {
	Hub    *Hub
	Conn   *websocket.Conn
	UserID string
	send   chan []byte
}

// readPump pumps messages from the websocket connection to the hub.
func (c *Client) readPump() {
	defer func() {
		c.Hub.Unregister(c)
		c.Conn.Close()
	}()

	c.Conn.SetReadLimit(maxMessageSize)
	c.Conn.SetReadDeadline(time.Now().Add(pongWait))
	c.Conn.SetPongHandler(func(string) error {
		c.Conn.SetReadDeadline(time.Now().Add(pongWait))
		return nil
	})

	for {
		_, raw, err := c.Conn.ReadMessage()
		if err != nil {
			if websocket.IsUnexpectedCloseError(err, websocket.CloseGoingAway, websocket.CloseNormalClosure) {
				c.Hub.logger.Warn("websocket read error", "error", err, "user_id", c.UserID)
			}
			break
		}

		var event Event
		if err := json.Unmarshal(raw, &event); err != nil {
			c.Hub.logger.Warn("invalid event JSON", "error", err, "user_id", c.UserID)
			continue
		}

		// Record activity for idle detection.
		c.Hub.RecordActivity(c.UserID)

		// Handle client-sent events (e.g. TYPING_START, PRESENCE_UPDATE)
		// For now, broadcast them to all clients
		switch event.Type {
		case EventTypingStart, EventPresenceUpdate:
			c.Hub.BroadcastEvent(event)
		default:
			c.Hub.logger.Info("received event from client", "type", event.Type, "user_id", c.UserID)
		}
	}
}

// writePump pumps messages from the hub to the websocket connection.
func (c *Client) writePump() {
	ticker := time.NewTicker(pingPeriod)
	defer func() {
		ticker.Stop()
		c.Conn.Close()
	}()

	for {
		select {
		case message, ok := <-c.send:
			c.Conn.SetWriteDeadline(time.Now().Add(writeWait))
			if !ok {
				c.Conn.WriteMessage(websocket.CloseMessage, []byte{})
				return
			}

			w, err := c.Conn.NextWriter(websocket.TextMessage)
			if err != nil {
				return
			}
			w.Write(message)

			// Drain queued messages into the current write
			n := len(c.send)
			for i := 0; i < n; i++ {
				w.Write([]byte{'\n'})
				w.Write(<-c.send)
			}

			if err := w.Close(); err != nil {
				return
			}

		case <-ticker.C:
			c.Conn.SetWriteDeadline(time.Now().Add(writeWait))
			if err := c.Conn.WriteMessage(websocket.PingMessage, nil); err != nil {
				return
			}
		}
	}
}

// ServeWS handles websocket requests from the peer. It authenticates the
// client via a session token passed as the "token" query parameter.
func ServeWS(db *sql.DB, hub *Hub, logger *slog.Logger, w http.ResponseWriter, r *http.Request) {
	token := r.URL.Query().Get("token")
	if token == "" {
		http.Error(w, `{"error":"missing token"}`, http.StatusUnauthorized)
		return
	}

	var userID string
	err := db.QueryRowContext(context.Background(),
		`SELECT user_id FROM sessions WHERE token = $1 AND expires_at > NOW()`,
		token,
	).Scan(&userID)
	if err != nil {
		http.Error(w, `{"error":"invalid or expired session"}`, http.StatusUnauthorized)
		return
	}

	conn, err := upgrader.Upgrade(w, r, nil)
	if err != nil {
		logger.Error("websocket upgrade failed", "error", err)
		return
	}

	client := &Client{
		Hub:    hub,
		Conn:   conn,
		UserID: userID,
		send:   make(chan []byte, 256),
	}

	hub.Register(client)

	go client.writePump()
	go client.readPump()
}