package ws

import (
	"log"
	"net/http"
	"sync"
	"time"

	"github.com/gorilla/websocket"

	"git.saqut.com/saqut/mwse/internal/protocol"
)

// Heartbeat and transport defaults used by DefaultOptions and NewClient. The
// PingPeriod matches the original server's 10s interval; the ping payload is the
// magic string the SDK's pong echoes.
const (
	defaultWriteWait      = 10 * time.Second
	defaultPongWait       = 60 * time.Second
	defaultPingPeriod     = 10 * time.Second
	defaultMaxMessageSize = 16 << 20 // 16 MiB; supports large tunneled payloads (#30)

	pingPayload = "saQut"
)

// Options tunes the transport for scale. Zero fields fall back to defaults.
type Options struct {
	OutboundBuffer  int           // per-connection send queue depth
	MaxMessageSize  int64         // max inbound frame size
	ReadBufferSize  int           // gorilla per-connection read buffer
	WriteBufferSize int           // gorilla write buffer size (pooled)
	PingInterval    time.Duration // heartbeat period
	PongWait        time.Duration // max wait for a pong before dropping
	WriteWait       time.Duration // per-write socket deadline
}

// DefaultOptions returns the built-in tuning.
func DefaultOptions() Options {
	return Options{
		OutboundBuffer:  defaultOutboundBuffer,
		MaxMessageSize:  defaultMaxMessageSize,
		ReadBufferSize:  4096,
		WriteBufferSize: 4096,
		PingInterval:    defaultPingPeriod,
		PongWait:        defaultPongWait,
		WriteWait:       defaultWriteWait,
	}
}

func (o Options) withDefaults() Options {
	d := DefaultOptions()
	if o.OutboundBuffer <= 0 {
		o.OutboundBuffer = d.OutboundBuffer
	}
	if o.MaxMessageSize <= 0 {
		o.MaxMessageSize = d.MaxMessageSize
	}
	if o.ReadBufferSize <= 0 {
		o.ReadBufferSize = d.ReadBufferSize
	}
	if o.WriteBufferSize <= 0 {
		o.WriteBufferSize = d.WriteBufferSize
	}
	if o.PingInterval <= 0 {
		o.PingInterval = d.PingInterval
	}
	if o.PongWait <= 0 {
		o.PongWait = d.PongWait
	}
	if o.WriteWait <= 0 {
		o.WriteWait = d.WriteWait
	}
	return o
}

// Server upgrades HTTP requests to WebSocket connections and runs each one's
// lifecycle. It holds no per-connection state itself; everything lives on the Hub.
type Server struct {
	hub      *Hub
	upgrader websocket.Upgrader
	opts     Options
}

// NewServer returns a Server bound to hub. An optional Options tunes the
// transport; omit it for defaults.
//
// The upgrader uses a shared WriteBufferPool so write scratch buffers are reused
// across connections instead of allocated per connection — a large memory saving
// at high connection counts. CheckOrigin always returns true to preserve the
// original autoAcceptConnections behaviour (origin policy belongs in front of the
// engine).
func NewServer(hub *Hub, opts ...Options) *Server {
	o := DefaultOptions()
	if len(opts) > 0 {
		o = opts[0].withDefaults()
	}
	return &Server{
		hub:  hub,
		opts: o,
		upgrader: websocket.Upgrader{
			ReadBufferSize:  o.ReadBufferSize,
			WriteBufferSize: o.WriteBufferSize,
			WriteBufferPool: &sync.Pool{},
			CheckOrigin:     func(*http.Request) bool { return true },
		},
	}
}

// ServeHTTP implements http.Handler: it upgrades the request and hands the
// connection to the lifecycle. It is the WebSocket endpoint.
func (s *Server) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	conn, err := s.upgrader.Upgrade(w, r, nil)
	if err != nil {
		log.Printf("ws: upgrade failed: %v", err)
		return
	}
	s.handle(conn)
}

// handle drives one connection from accept to disconnect. It is generic over the
// Conn interface so tests can feed it a scripted in-memory connection.
func (s *Server) handle(conn Conn) {
	client := newClient(conn, newUUID(), s.opts.OutboundBuffer, s.opts.WriteWait)

	// Connect: register, start the writer, fire connect listeners (id, private
	// room, session defaults). Must happen before the read loop so the client can
	// already receive server-initiated messages.
	s.hub.Connect(client)

	// Heartbeat lives in its own goroutine; it stops when the client closes.
	go s.pingLoop(client)

	// Read loop blocks here until the socket errors or closes.
	s.readLoop(client)

	// Disconnect runs exactly once, here, when the read loop ends.
	s.hub.Disconnect(client)
}

// readLoop consumes inbound frames. Pongs that do not echo the magic payload drop
// the connection (matching the original); a valid pong extends the read deadline.
func (s *Server) readLoop(c *Client) {
	c.conn.SetReadLimit(s.opts.MaxMessageSize)
	_ = c.conn.SetReadDeadline(time.Now().Add(s.opts.PongWait))
	c.conn.SetPongHandler(func(appData string) error {
		if appData != pingPayload {
			return errBadPong
		}
		return c.conn.SetReadDeadline(time.Now().Add(s.opts.PongWait))
	})

	for {
		msgType, data, err := c.conn.ReadMessage()
		if err != nil {
			return
		}
		if msgType != websocket.TextMessage {
			continue // the protocol is JSON text; ignore binary frames
		}
		s.dispatch(c, data)
	}
}

// errBadPong is returned by the pong handler to force a disconnect.
var errBadPong = &pongError{}

type pongError struct{}

func (*pongError) Error() string { return "ws: pong validation failed" }

// dispatch decodes one frame and routes it, then replies according to the WSTS
// rules. A frame that fails to decode is logged as a message error (the Node
// server emitted a 'messageError' event here).
func (s *Server) dispatch(c *Client, data []byte) {
	env, err := protocol.Decode(data)
	if err != nil {
		log.Printf("ws: message error from %s: %v", c.ID, err)
		return
	}

	result := s.hub.Handle(c, env.Message)

	// Reply only when the handler actually produced a result. A nil result marks a
	// handler that is either fire-and-forget (a WOM relay such as pack/to without a
	// handshake) or one that will be answered out-of-band later: request/to is
	// answered by the peer's response/to frame carrying the *same* request id.
	//
	// Sending a premature [null, id, "E"] in those cases would resolve and then
	// delete the SDK's pending request before the real answer arrived — exactly the
	// #33 "promise hangs / gets clobbered" bug. Returning nil from a handler is the
	// engine's explicit "no reply from me" signal. See decisions.md.
	if flag, ok := env.WantsReply(); ok && result != nil {
		c.Send(protocol.Reply(result, env.ID, flag))
		return
	}

	// "No id" branch: the original inspected the result for a broadcast directive.
	// No service currently emits one, but the hook is preserved for parity.
	if env.IsBroadcast() {
		if m, ok := result.(map[string]any); ok {
			if _, has := m["broadcast"]; has {
				log.Printf("ws: broadcast directive from %s (no listener registered)", c.ID)
			}
		}
	}
}

// pingLoop sends a ping with the magic payload every ping period until the client
// closes.
func (s *Server) pingLoop(c *Client) {
	ticker := time.NewTicker(s.opts.PingInterval)
	defer ticker.Stop()
	for {
		select {
		case <-ticker.C:
			err := c.conn.WriteControl(
				websocket.PingMessage,
				[]byte(pingPayload),
				time.Now().Add(s.opts.WriteWait),
			)
			if err != nil {
				c.Close()
				return
			}
		case <-c.Done():
			return
		}
	}
}

// ---- lifecycle helpers (shared by the server and by tests) ---------------

// Connect registers a client, starts its writer goroutine, and fires the connect
// listeners. Exposed so tests and tools can drive the same path the server uses.
func (h *Hub) Connect(c *Client) {
	h.addClient(c)
	go c.writePump()
	h.emitConnect(c)
}

// Disconnect fires the disconnect listeners, unregisters the client, and tears
// its transport down. Safe to call once per client.
func (h *Hub) Disconnect(c *Client) {
	h.emitDisconnect(c)
	h.removeClient(c.ID)
	c.Close()
}

// CloseAll closes every connected client. Used during graceful shutdown so peers
// receive a clean close frame before the process exits.
func (h *Hub) CloseAll() {
	for _, c := range h.Clients() {
		c.Close()
	}
}