package main

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

	"github.com/gorilla/websocket"
	"powerpod/gotool/pb"
)

const (
	defaultAccelStreamInterval = 16 * time.Millisecond
	minAPIStreamInterval       = 1 * time.Millisecond
	maxAPIStreamInterval       = 10 * time.Second
)

// AccelClientSample is one slave's cached accel on the master.
type AccelClientSample struct {
	ClientID uint32 `json:"client_id"`
	Valid    bool   `json:"valid"`
	X        int32  `json:"x,omitempty"`
	Y        int32  `json:"y,omitempty"`
	Z        int32  `json:"z,omitempty"`
	AgeMs    uint32 `json:"age_ms,omitempty"`
}

// AccelStreamMessage is sent to external WebSocket clients.
type AccelStreamMessage struct {
	Type       string   `json:"type"` // "hello" | "accel"
	Serial     string   `json:"serial_port,omitempty"`
	IntervalMs int      `json:"interval_ms,omitempty"`
	Commands   []string `json:"commands,omitempty"`

	T       int64               `json:"t,omitempty"` // Unix nanoseconds
	Success bool                `json:"success,omitempty"`
	Clients []AccelClientSample `json:"clients,omitempty"`
	Error   string              `json:"error,omitempty"`
}

// StreamStatusMessage is the reply to set_stream / get_stream (this connection).
type StreamStatusMessage struct {
	Type         string `json:"type"` // "stream_status"
	ReceiveAccel bool   `json:"receive_accel"`
	IntervalMs   int    `json:"interval_ms"`
	Success      bool   `json:"success"`
	Error        string `json:"error,omitempty"`
}

// AccelStreamStatusMessage is the reply to set_accel_stream / get_accel_stream (slave).
type AccelStreamStatusMessage struct {
	Type          string `json:"type"` // "accel_stream_status"
	ClientID      uint32 `json:"client_id"`
	Enabled       bool   `json:"enabled"`
	Success       bool   `json:"success"`
	SlavesUpdated uint32 `json:"slaves_updated,omitempty"`
	Error         string `json:"error,omitempty"`
}

type accelWSCommand struct {
	Type       string `json:"type"`
	ClientID   uint32 `json:"client_id"`
	Enable     *bool  `json:"enable"`
	IntervalMs *int   `json:"interval_ms"`
}

type APIInfoResponse struct {
	Name             string `json:"name"`
	Version          string `json:"version"`
	SerialPort       string `json:"serial_port"`
	WebSocket        string `json:"websocket"`
	DefaultIntervalMs int    `json:"default_interval_ms"`
	MinIntervalMs    int    `json:"min_interval_ms"`
	MaxIntervalMs    int    `json:"max_interval_ms"`
	Description      string `json:"description"`
}

type wsSubscriber struct {
	conn         *websocket.Conn
	receiveAccel bool
	interval     time.Duration
	lastSent     time.Time
}

type accelStreamHub struct {
	mu            sync.RWMutex
	clients       map[*websocket.Conn]*wsSubscriber
	defaultInterval time.Duration
	configChanged chan struct{}
}

func newAccelStreamHub(defaultInterval time.Duration) *accelStreamHub {
	return &accelStreamHub{
		clients:         make(map[*websocket.Conn]*wsSubscriber),
		defaultInterval: defaultInterval,
		configChanged:   make(chan struct{}, 1),
	}
}

func (h *accelStreamHub) notifyConfigChanged() {
	select {
	case h.configChanged <- struct{}{}:
	default:
	}
}

func clampAPIInterval(d time.Duration) time.Duration {
	if d < minAPIStreamInterval {
		return minAPIStreamInterval
	}
	if d > maxAPIStreamInterval {
		return maxAPIStreamInterval
	}
	return d
}

func (h *accelStreamHub) register(conn *websocket.Conn, portName string) *wsSubscriber {
	sub := &wsSubscriber{
		conn:         conn,
		receiveAccel: false,
		interval:     h.defaultInterval,
	}
	h.mu.Lock()
	h.clients[conn] = sub
	h.mu.Unlock()

	hello := AccelStreamMessage{
		Type:       "hello",
		Serial:     portName,
		IntervalMs: int(h.defaultInterval / time.Millisecond),
		Commands:   []string{"set_stream", "get_stream", "set_accel_stream", "get_accel_stream"},
	}
	if data, err := json.Marshal(hello); err == nil {
		_ = conn.WriteMessage(websocket.TextMessage, data)
	}
	return sub
}

func (h *accelStreamHub) unregister(conn *websocket.Conn) {
	h.mu.Lock()
	delete(h.clients, conn)
	h.mu.Unlock()
	h.notifyConfigChanged()
}

func (h *accelStreamHub) anyWantsAccel() bool {
	h.mu.RLock()
	defer h.mu.RUnlock()
	for _, sub := range h.clients {
		if sub.receiveAccel {
			return true
		}
	}
	return false
}

func (h *accelStreamHub) minWantedInterval() time.Duration {
	h.mu.RLock()
	defer h.mu.RUnlock()
	var min time.Duration
	for _, sub := range h.clients {
		if !sub.receiveAccel {
			continue
		}
		if min == 0 || sub.interval < min {
			min = sub.interval
		}
	}
	if min == 0 {
		return h.defaultInterval
	}
	return min
}

func (h *accelStreamHub) setStream(sub *wsSubscriber, enable bool, intervalMs *int) StreamStatusMessage {
	h.mu.Lock()
	sub.receiveAccel = enable
	if intervalMs != nil {
		sub.interval = clampAPIInterval(time.Duration(*intervalMs) * time.Millisecond)
	}
	ms := int(sub.interval / time.Millisecond)
	h.mu.Unlock()
	h.notifyConfigChanged()

	return StreamStatusMessage{
		Type:         "stream_status",
		ReceiveAccel: enable,
		IntervalMs:   ms,
		Success:      true,
	}
}

func (h *accelStreamHub) getStream(sub *wsSubscriber) StreamStatusMessage {
	h.mu.RLock()
	defer h.mu.RUnlock()
	return StreamStatusMessage{
		Type:         "stream_status",
		ReceiveAccel: sub.receiveAccel,
		IntervalMs:   int(sub.interval / time.Millisecond),
		Success:      true,
	}
}

func (h *accelStreamHub) deliver(msg AccelStreamMessage) {
	data, err := json.Marshal(msg)
	if err != nil {
		return
	}

	now := time.Now()
	h.mu.Lock()
	defer h.mu.Unlock()
	for conn, sub := range h.clients {
		if !sub.receiveAccel {
			continue
		}
		if !sub.lastSent.IsZero() && now.Sub(sub.lastSent) < sub.interval {
			continue
		}
		sub.lastSent = now
		if err := conn.WriteMessage(websocket.TextMessage, data); err != nil {
			delete(h.clients, conn)
			_ = conn.Close()
		}
	}
}

func runAccelStreamer(link *managedSerial, hub *accelStreamHub, dash *wsHub, ctl *accelStreamCtl, stop <-chan struct{}) {
	var ticker *time.Ticker
	var tick <-chan time.Time

	resetTicker := func() {
		if ticker != nil {
			ticker.Stop()
		}
		interval := hub.minWantedInterval()
		ticker = time.NewTicker(interval)
		tick = ticker.C
	}
	resetTicker()
	defer func() {
		if ticker != nil {
			ticker.Stop()
		}
	}()

	for {
		select {
		case <-stop:
			return
		case <-hub.configChanged:
			resetTicker()
		case <-tick:
			if !hub.anyWantsAccel() {
				continue
			}
			if !accelStreamPollingActive(dash, ctl) {
				continue
			}
			now := time.Now().UnixNano()
			resp, err := link.readAccelSnapshotPoll(0)
			if errors.Is(err, errUARTBusy) {
				hub.deliver(AccelStreamMessage{
					Type:    "accel",
					T:       now,
					Success: false,
					Error:   "uart busy",
				})
				continue
			}
			if err != nil {
				hub.deliver(AccelStreamMessage{
					Type:    "accel",
					T:       now,
					Success: false,
					Error:   err.Error(),
				})
				continue
			}
			clients := make([]AccelClientSample, 0, len(resp.GetSamples()))
			for _, s := range resp.GetSamples() {
				clients = append(clients, AccelClientSample{
					ClientID: s.GetClientId(),
					Valid:    s.GetValid(),
					X:        s.GetX(),
					Y:        s.GetY(),
					Z:        s.GetZ(),
					AgeMs:    s.GetAgeMs(),
				})
			}
			hub.deliver(AccelStreamMessage{
				Type:    "accel",
				T:       now,
				Success: true,
				Clients: clients,
			})
		}
	}
}

func accelStreamPollingActive(dash *wsHub, ctl *accelStreamCtl) bool {
	if ctl != nil && ctl.Any() {
		return true
	}
	return dash != nil && dash.anyAccelStreamEnabled()
}

func writeStreamStatus(conn *websocket.Conn, msg StreamStatusMessage) {
	data, err := json.Marshal(msg)
	if err != nil {
		return
	}
	_ = conn.WriteMessage(websocket.TextMessage, data)
}

func writeAccelStreamStatus(conn *websocket.Conn, out accelStreamAPIResponse) {
	msg := AccelStreamStatusMessage{
		Type:          "accel_stream_status",
		ClientID:      out.ClientID,
		Enabled:       out.Enabled,
		Success:       out.Success,
		SlavesUpdated: out.SlavesUpdated,
		Error:         out.Error,
	}
	data, err := json.Marshal(msg)
	if err != nil {
		return
	}
	_ = conn.WriteMessage(websocket.TextMessage, data)
}

func handleAccelWSCommand(conn *websocket.Conn, sub *wsSubscriber, data []byte, link *managedSerial, dash *wsHub, ctl *accelStreamCtl, hub *accelStreamHub) {
	var cmd accelWSCommand
	if err := json.Unmarshal(data, &cmd); err != nil {
		writeStreamStatus(conn, StreamStatusMessage{Type: "stream_status", Error: "invalid JSON"})
		return
	}

	switch cmd.Type {
	case "set_stream":
		if cmd.Enable == nil {
			writeStreamStatus(conn, StreamStatusMessage{
				Type:  "stream_status",
				Error: "enable required",
			})
			return
		}
		writeStreamStatus(conn, hub.setStream(sub, *cmd.Enable, cmd.IntervalMs))

	case "get_stream":
		writeStreamStatus(conn, hub.getStream(sub))

	case "set_accel_stream":
		if cmd.ClientID == 0 {
			writeAccelStreamStatus(conn, accelStreamAPIResponse{Error: "client_id required"})
			return
		}
		if cmd.Enable == nil {
			writeAccelStreamStatus(conn, accelStreamAPIResponse{
				ClientID: cmd.ClientID,
				Error:    "enable required",
			})
			return
		}
		writeAccelStreamStatus(conn, applyAccelStreamClient(link, dash, ctl, cmd.ClientID, *cmd.Enable))

	case "get_accel_stream":
		if cmd.ClientID == 0 {
			writeAccelStreamStatus(conn, accelStreamAPIResponse{Error: "client_id required"})
			return
		}
		resp, err := link.AccelStreamPoll(&pb.AccelStreamRequest{
			Write:    false,
			ClientId: cmd.ClientID,
		})
		if err != nil {
			writeAccelStreamStatus(conn, accelStreamAPIResponse{
				ClientID: cmd.ClientID,
				Error:    err.Error(),
			})
			return
		}
		if ctl != nil {
			ctl.Set(cmd.ClientID, resp.GetEnabled())
		}
		writeAccelStreamStatus(conn, accelStreamAPIResponse{
			Enabled:  resp.GetEnabled(),
			ClientID: resp.GetClientId(),
			Success:  resp.GetSuccess(),
		})

	default:
		writeStreamStatus(conn, StreamStatusMessage{
			Type:  "stream_status",
			Error: "unknown type (set_stream, get_stream, set_accel_stream, get_accel_stream)",
		})
	}
}

func serveExternalWS(conn *websocket.Conn, link *managedSerial, dash *wsHub, ctl *accelStreamCtl, portName string, hub *accelStreamHub) {
	sub := hub.register(conn, portName)
	defer hub.unregister(conn)
	defer conn.Close()

	for {
		_, data, err := conn.ReadMessage()
		if err != nil {
			return
		}
		handleAccelWSCommand(conn, sub, data, link, dash, ctl, hub)
	}
}

func mountExternalAPI(mux *http.ServeMux, portName string, defaultInterval time.Duration, hub *accelStreamHub, link *managedSerial, dash *wsHub, ctl *accelStreamCtl) {
	defMs := int(defaultInterval / time.Millisecond)
	mux.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
		if r.URL.Path != "/" && r.URL.Path != "/api/v1" && r.URL.Path != "/api/v1/" {
			http.NotFound(w, r)
			return
		}
		if r.Method != http.MethodGet {
			http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
			return
		}
		writeJSON(w, http.StatusOK, APIInfoResponse{
			Name:              "powerpod-external-api",
			Version:           "1",
			SerialPort:        portName,
			WebSocket:         "/ws",
			DefaultIntervalMs: defMs,
			MinIntervalMs:     int(minAPIStreamInterval / time.Millisecond),
			MaxIntervalMs:     int(maxAPIStreamInterval / time.Millisecond),
			Description:       "WebSocket: per-connection accel receive + interval; slave stream via set_accel_stream",
		})
	})

	mux.HandleFunc("/ws", func(w http.ResponseWriter, r *http.Request) {
		conn, err := wsUpgrader.Upgrade(w, r, nil)
		if err != nil {
			log.Printf("api websocket upgrade: %v", err)
			return
		}
		serveExternalWS(conn, link, dash, ctl, portName, hub)
	})
}

func runAPIServer(portName string, link *managedSerial, addr string, defaultInterval time.Duration, dash *wsHub, ctl *accelStreamCtl, stop <-chan struct{}) *http.Server {
	hub := newAccelStreamHub(defaultInterval)
	go runAccelStreamer(link, hub, dash, ctl, stop)

	mux := http.NewServeMux()
	mountExternalAPI(mux, portName, defaultInterval, hub, link, dash, ctl)

	srv := &http.Server{Addr: addr, Handler: mux}
	go func() {
		log.Printf("external API http://localhost%s  WebSocket ws://localhost%s/ws  (default accel interval %s, per-client via set_stream)",
			addr, addr, defaultInterval.String())
		if err := srv.ListenAndServe(); err != nil && !errors.Is(err, http.ErrServerClosed) {
			log.Printf("external API server: %v", err)
		}
	}()
	return srv
}

func shutdownAPIServer(srv *http.Server) {
	if srv == nil {
		return
	}
	ctx, cancel := context.WithTimeout(context.Background(), 2*time.Second)
	defer cancel()
	_ = srv.Shutdown(ctx)
}