package weblive

import (
	"sync"

	"github.com/gorilla/websocket"
	"github.com/pion/rtp"
	"github.com/pion/webrtc/v3"
)

// trackForwarder 从主播轨读 RTP，复制到所有观众本地轨
type trackForwarder struct {
	remote *webrtc.TrackRemote
	mu     sync.Mutex
	locals map[string]*webrtc.TrackLocalStaticRTP
	stopCh chan struct{}
}

func newTrackForwarder(track *webrtc.TrackRemote) *trackForwarder {
	return &trackForwarder{
		remote: track,
		locals: make(map[string]*webrtc.TrackLocalStaticRTP),
		stopCh: make(chan struct{}),
	}
}

func (tf *trackForwarder) addViewer(id string, t *webrtc.TrackLocalStaticRTP) {
	tf.mu.Lock()
	defer tf.mu.Unlock()
	tf.locals[id] = t
}

func (tf *trackForwarder) removeViewer(id string) {
	tf.mu.Lock()
	defer tf.mu.Unlock()
	delete(tf.locals, id)
}

func (tf *trackForwarder) close() {
	select {
	case <-tf.stopCh:
	default:
		close(tf.stopCh)
	}
}

func (tf *trackForwarder) runReadLoop() {
	buf := make([]byte, 1500)
	for {
		select {
		case <-tf.stopCh:
			return
		default:
		}
		n, _, err := tf.remote.Read(buf)
		if err != nil {
			return
		}
		tf.mu.Lock()
		for _, lt := range tf.locals {
			cp := &rtp.Packet{}
			if err := cp.Unmarshal(buf[:n]); err != nil {
				continue
			}
			_ = lt.WriteRTP(cp)
		}
		tf.mu.Unlock()
	}
}

// Hub 单房间：一名主播、多名观众（进程内内存态，重启清空）
type Hub struct {
	mu sync.RWMutex

	api *webrtc.API
	cfg webrtc.Configuration

	publishConn *websocket.Conn
	pubPC       *webrtc.PeerConnection
	forwarders  []*trackForwarder

	viewers map[string]*viewerSession
}

type viewerSession struct {
	id       string
	ws       *websocket.Conn
	pc       *webrtc.PeerConnection
	pending  []webrtc.ICECandidateInit
	answered bool
}

func newHub(api *webrtc.API) *Hub {
	return &Hub{
		api:     api,
		cfg:     webrtc.Configuration{ICEServers: iceServersFromEnv()},
		viewers: make(map[string]*viewerSession),
	}
}

var (
	defaultHub *Hub
	hubOnce    sync.Once
	hubInitErr error
)

func getHub() (*Hub, error) {
	hubOnce.Do(func() {
		var api *webrtc.API
		api, hubInitErr = buildAPI()
		if hubInitErr != nil {
			return
		}
		defaultHub = newHub(api)
	})
	return defaultHub, hubInitErr
}

func (h *Hub) clearPublisher() {
	h.mu.Lock()
	defer h.mu.Unlock()
	for _, tf := range h.forwarders {
		tf.close()
	}
	h.forwarders = nil
	if h.pubPC != nil {
		_ = h.pubPC.Close()
		h.pubPC = nil
	}
	h.publishConn = nil
}

func (h *Hub) removeViewer(id string) {
	h.mu.Lock()
	vs, ok := h.viewers[id]
	if ok {
		delete(h.viewers, id)
	}
	for _, tf := range h.forwarders {
		tf.removeViewer(id)
	}
	h.mu.Unlock()
	if ok && vs != nil && vs.pc != nil {
		_ = vs.pc.Close()
	}
}

func (h *Hub) onPublisherTrack(track *webrtc.TrackRemote) {
	// 仅转发视频轨，降低协商复杂度
	if track.Kind() != webrtc.RTPCodecTypeVideo {
		return
	}
	tf := newTrackForwarder(track)
	h.mu.Lock()
	h.forwarders = append(h.forwarders, tf)
	h.mu.Unlock()
	go tf.runReadLoop()
	// 观众仅在「已开播」后拉流：首次协商时 attachForwardersToViewerPC 会带上当前全部轨，无需在此重协商
}

func (h *Hub) attachForwardersToViewerPC(v *viewerSession) {
	h.mu.RLock()
	fwd := append([]*trackForwarder(nil), h.forwarders...)
	h.mu.RUnlock()
	for _, tf := range fwd {
		cap := tf.remote.Codec().RTPCodecCapability
		lt, err := webrtc.NewTrackLocalStaticRTP(cap, tf.remote.ID()+"_"+v.id, tf.remote.StreamID())
		if err != nil {
			continue
		}
		if _, err := v.pc.AddTrack(lt); err != nil {
			continue
		}
		tf.addViewer(v.id, lt)
	}
}