package stream

import (
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"sync"
	"time"

	"oc-discovery/daemons/node/common"

	oclib "cloud.o-forge.io/core/oc-lib"
	"cloud.o-forge.io/core/oc-lib/dbs"
	"cloud.o-forge.io/core/oc-lib/models/peer"
	"cloud.o-forge.io/core/oc-lib/tools"
	"github.com/libp2p/go-libp2p/core/network"
	pp "github.com/libp2p/go-libp2p/core/peer"
)

// ProtocolObserve is the libp2p protocol for peer connectivity observation.
// The requesting oc-discovery opens a stream to the remote oc-discovery and
// sends an ObserveRequest. The remote side keeps the stream open and writes
// ObserveHeartbeat events back every observeHBInterval seconds.
const ProtocolObserve = "/opencloud/peer/observe/1.0"

// observeHBEventType is used as the common.Event.Type for heartbeat responses.
const observeHBEventType = "/opencloud/peer/observe/heartbeat"

const observeHBInterval = 30 * time.Second
const observeDrainDuration = 30 * time.Second

// observeBatchWindow is the accumulation window before a heartbeat batch is
// flushed to NATS. All peer heartbeats received within this window are grouped
// into a single PEER_OBSERVE_RESPONSE_EVENT, reducing NATS traffic.
const observeBatchWindow = 2 * time.Second

// ObserveRequest is the first (and only) message sent by the observing side
// when opening a ProtocolObserve stream.
type ObserveRequest struct {
	// Close, when true, asks the remote side to stop the heartbeat goroutine
	// and remove the observer from its cache. Used for graceful teardown.
	Close bool `json:"close,omitempty"`
}

// ObserveHeartbeat is sent by the observed side every observeHBInterval.
type ObserveHeartbeat struct {
	State string `json:"state"` // always "online" when actively emitted
}

// ShallowPeer is the minimal peer representation sent by oc-peer in a
// PEER_OBSERVE_EVENT. StreamAddress lets oc-discovery connect without a DB
// lookup; Address carries the NATSAddress (unused here, forwarded as-is).
type ShallowPeer struct {
	ID            string `json:"id"`
	PeerID        string `json:"peer_id"`
	Address       string `json:"address"`
	StreamAddress string `json:"stream_address"`
}

// ObserveCommand is the payload carried by a PEER_OBSERVE_EVENT NATS message
// (from oc-peer).
//
//	Observe  → User + Peers populated
//	Close    → User + PeerIDs + Close=true
//	CloseAll → CloseAll=true (User optional)
type ObserveCommand struct {
	User     string        `json:"user"`
	Peers    []ShallowPeer `json:"peers,omitempty"`
	PeerIDs  []string      `json:"peer_ids,omitempty"`
	Close    bool          `json:"close,omitempty"`
	CloseAll bool          `json:"close_all,omitempty"`
}

// ── observe cache (observed side) ────────────────────────────────────────────

// observeCache tracks running heartbeat goroutines keyed by the observing
// peer's libp2p PeerID string. It is used exclusively on the OBSERVED side.
type observeCache struct {
	mu      sync.Mutex
	cancels map[string]context.CancelFunc
}

func newObserveCache() *observeCache {
	return &observeCache{cancels: map[string]context.CancelFunc{}}
}

func (c *observeCache) set(pid string, cancel context.CancelFunc) {
	c.mu.Lock()
	defer c.mu.Unlock()
	if old, ok := c.cancels[pid]; ok {
		old() // cancel previous goroutine if any
	}
	c.cancels[pid] = cancel
}

func (c *observeCache) cancel(pid string) {
	c.mu.Lock()
	defer c.mu.Unlock()
	if fn, ok := c.cancels[pid]; ok {
		fn()
		delete(c.cancels, pid)
	}
}

func (c *observeCache) cancelAll() {
	c.mu.Lock()
	defer c.mu.Unlock()
	for _, fn := range c.cancels {
		fn()
	}
	c.cancels = map[string]context.CancelFunc{}
}

func (c *observeCache) delete(pid string) {
	c.mu.Lock()
	defer c.mu.Unlock()
	delete(c.cancels, pid)
}

// ── heartbeat batcher (observing side) ───────────────────────────────────────

// heartbeatBatcher accumulates peer_ids from incoming heartbeats over
// observeBatchWindow, then flushes them in a single NATS call.
// Using a map as the backing store deduplicates multiple heartbeats from the
// same peer within the same window (should not happen, but is harmless).
type heartbeatBatcher struct {
	mu    sync.Mutex
	ids   map[string]struct{}
	timer *time.Timer
	flush func(peerIDs []string)
}

func newHeartbeatBatcher(flush func([]string)) *heartbeatBatcher {
	return &heartbeatBatcher{
		ids:   make(map[string]struct{}),
		flush: flush,
	}
}

// add records peerID in the current batch and arms the flush timer if needed.
func (b *heartbeatBatcher) add(peerID string) {
	b.mu.Lock()
	defer b.mu.Unlock()
	b.ids[peerID] = struct{}{}
	if b.timer == nil {
		b.timer = time.AfterFunc(observeBatchWindow, b.fire)
	}
}

// fire is called by the timer; it drains the batch and invokes flush.
func (b *heartbeatBatcher) fire() {
	b.mu.Lock()
	ids := make([]string, 0, len(b.ids))
	for id := range b.ids {
		ids = append(ids, id)
	}
	b.ids = make(map[string]struct{})
	b.timer = nil
	b.mu.Unlock()
	if len(ids) > 0 {
		b.flush(ids)
	}
}

// flushObserveBatch is the flush function wired into the heartbeatBatcher.
// It emits two NATS messages:
//   - PEER_OBSERVE_RESPONSE_EVENT  → consumed by oc-peer (direct channel)
//   - PROPALGATION_EVENT / PB_PROPAGATE → consumed by other oc-discovery nodes
func flushObserveBatch(peerIDs []string) {
	payload, err := json.Marshal(map[string]interface{}{
		"peer_ids": peerIDs,
		"state":    "online",
	})
	if err != nil {
		return
	}

	// Direct notification to oc-peer.
	tools.NewNATSCaller().SetNATSPub(tools.PEER_OBSERVE_RESPONSE_EVENT, tools.NATSResponse{
		FromApp:  "oc-discovery",
		Datatype: tools.PEER,
		Method:   int(tools.PEER_OBSERVE_RESPONSE_EVENT),
		Payload:  payload,
	})

	// Broadcast to other oc-discovery nodes so they can forward to their
	// local oc-peer if needed.
	propPayload, err := json.Marshal(tools.PropalgationMessage{
		DataType: int(tools.PEER),
		Action:   tools.PB_PROPAGATE,
		Payload:  payload,
	})
	if err != nil {
		return
	}
	tools.NewNATSCaller().SetNATSPub(tools.PROPALGATION_EVENT, tools.NATSResponse{
		FromApp:  "oc-discovery",
		Datatype: tools.PEER,
		Method:   int(tools.PROPALGATION_EVENT),
		Payload:  propPayload,
	})
}

// ── incoming observe handler (observed side) ──────────────────────────────────

// handleIncomingObserve is registered as the ProtocolObserve stream handler.
// It is called when a remote peer opens an observe stream to us.
// The function reads the request, validates it, then starts (or stops) the
// heartbeat goroutine and returns immediately — the goroutine owns the stream.
func (s *StreamService) handleIncomingObserve(rawStream network.Stream) error {
	remotePeerID := rawStream.Conn().RemotePeer().String()
	addr := rawStream.Conn().RemoteMultiaddr().String()
	ad, err := pp.AddrInfoFromString(addr + "/p2p/" + remotePeerID)
	if err != nil {
		fmt.Println("qndlqnl EERR", addr, err)
		return err
	}
	log := oclib.GetLogger()

	// Drain mode: reject any new observations for 30 s after a close-all.
	s.drainMu.RLock()
	draining := !s.drainUntil.IsZero() && time.Now().Before(s.drainUntil)
	s.drainMu.RUnlock()
	if draining {
		rawStream.Close()
		fmt.Println("Draining")
		return errors.New("Draining")
	}
	// Read the observe request (with a generous deadline to avoid hangs).
	// Guard: the requesting peer must not be blacklisted or be ourself.
	did := ""
	access := oclib.NewRequestAdmin(oclib.LibDataEnum(oclib.PEER), nil)
	res := access.Search(&dbs.Filters{
		And: map[string][]dbs.Filter{
			"peer_id": {{Operator: dbs.EQUAL.String(), Value: remotePeerID}},
		},
	}, "", false, 0, 1)
	if len(res.Data) > 0 {
		p := res.Data[0].(*peer.Peer)
		did = p.GetID()
		if p.Relation == peer.BLACKLIST { // || p.Relation == peer.SELF
			rawStream.Close()
			fmt.Println("CLOSE blacklist or self")
			return errors.New("can't exploit blacklist or self")
		}
	}

	// Replace any existing heartbeat goroutine for this observer.
	ctx, cancel := context.WithCancel(context.Background())
	s.observeCache.set(remotePeerID, cancel)
	fmt.Println("LOOP OBSERVE")
	go func() {
		defer rawStream.Close()
		defer cancel()
		defer s.observeCache.delete(remotePeerID)

		ticker := time.NewTicker(observeHBInterval)
		defer ticker.Stop()

		hbPayload, _ := json.Marshal(ObserveHeartbeat{State: "online"})
		evt := common.NewEvent(observeHBEventType, s.Host.ID().String(), nil, "", hbPayload)
		if evt == nil {
			return
		}
		if s.Streams, err = common.TempStream(s.Host, *ad, ProtocolObserve, did, s.Streams, protocols, &s.Mu); err == nil {
			stream := s.Streams[ProtocolObserve][ad.ID]
			if err := json.NewEncoder(stream.Stream).Encode(evt); err != nil {
				// Moderate connectivity event: the observer is unreachable.
				// The deferred calls above purge this observer from the cache.
				fmt.Println("LOOP EVT ERR", err)
				log.Info().
					Str("observer", remotePeerID).
					Err(err).
					Msg("[observe] heartbeat write failed — moderate connectivity event, purging observer from cache")
				return
			}
		}
		for {
			select {
			case <-ctx.Done():
				return
			case <-ticker.C:

				rawStream.SetWriteDeadline(time.Now().Add(5 * time.Second))
				fmt.Println("LOOP EVT", evt)
				var err error
				if s.Streams, err = common.TempStream(s.Host, *ad, ProtocolObserve, did, s.Streams, protocols, &s.Mu); err == nil {
					stream := s.Streams[ProtocolObserve][ad.ID]
					if err := json.NewEncoder(stream.Stream).Encode(evt); err != nil {
						// Moderate connectivity event: the observer is unreachable.
						// The deferred calls above purge this observer from the cache.
						fmt.Println("LOOP EVT ERR", err)
						log.Info().
							Str("observer", remotePeerID).
							Err(err).
							Msg("[observe] heartbeat write failed — moderate connectivity event, purging observer from cache")
						return
					}
				}
				rawStream.SetWriteDeadline(time.Time{})
			}
		}
	}()
	return nil
}

// ── heartbeat receiver (observing side) ───────────────────────────────────────

// handleObserveHeartbeat is called by readLoop when a heartbeat event arrives
// on an outgoing ProtocolObserve stream. It queues the peer_id in the batch
// accumulator; the batcher flushes to NATS after observeBatchWindow.
func (ps *StreamService) handleObserveHeartbeat(evt *common.Event) error {
	// ps.hbBatcher.add(evt.From)
	flushObserveBatch([]string{evt.From})
	return nil
}

// ── user→peer index (ref-counted observe management) ─────────────────────────

// userPeerIndex tracks which users are observing which peers.
// A libp2p observe stream is kept open as long as at least one user watches
// the peer; it is closed only when the last user stops.
type userPeerIndex struct {
	mu    sync.Mutex
	index map[string]map[string]struct{} // user → set of peer_id strings
}

func newUserPeerIndex() *userPeerIndex {
	return &userPeerIndex{index: map[string]map[string]struct{}{}}
}

// add registers user as an observer of peerID.
// Returns true if peerID was not yet observed by any user (first observer).
func (u *userPeerIndex) add(user, peerID string) (isFirst bool) {
	u.mu.Lock()
	defer u.mu.Unlock()
	// Count total observers for peerID across all users before adding.
	total := 0
	for _, peers := range u.index {
		if _, ok := peers[peerID]; ok {
			total++
		}
	}
	if u.index[user] == nil {
		u.index[user] = map[string]struct{}{}
	}
	u.index[user][peerID] = struct{}{}
	return total == 0
}

// remove unregisters user from peerID.
// Returns true if no user is observing peerID anymore (last observer removed).
func (u *userPeerIndex) remove(user, peerID string) (isLast bool) {
	u.mu.Lock()
	defer u.mu.Unlock()
	delete(u.index[user], peerID)
	if len(u.index[user]) == 0 {
		delete(u.index, user)
	}
	for _, peers := range u.index {
		if _, ok := peers[peerID]; ok {
			return false
		}
	}
	return true
}

// removeUser removes all entries for user and returns the peer_ids that now
// have no remaining observers (i.e., those whose streams should be closed).
func (u *userPeerIndex) removeUser(user string) []string {
	u.mu.Lock()
	defer u.mu.Unlock()
	watched := u.index[user]
	delete(u.index, user)
	var orphans []string
	for peerID := range watched {
		found := false
		for _, peers := range u.index {
			if _, ok := peers[peerID]; ok {
				found = true
				break
			}
		}
		if !found {
			orphans = append(orphans, peerID)
		}
	}
	return orphans
}

// ── NATS command handler (observing side) ─────────────────────────────────────

// HandleObserveNATSCommand processes a PEER_OBSERVE_EVENT received from oc-peer.
func (ps *StreamService) HandleObserveNATSCommand(resp tools.NATSResponse) {
	log := oclib.GetLogger()
	var cmd ObserveCommand
	if err := json.Unmarshal(resp.Payload, &cmd); err != nil {
		log.Warn().Err(err).Msg("[observe] failed to unmarshal ObserveCommand")
		return
	}
	if cmd.CloseAll {
		log.Info().Msg("[observe] close-all received via NATS")
		ps.CloseAllObserves()
		return
	}
	if cmd.Close {
		for _, peerID := range cmd.PeerIDs {
			if isLast := ps.observeUsers.remove(cmd.User, peerID); isLast {
				if err := ps.closeObserveStream(peerID); err != nil {
					log.Warn().Str("peer", peerID).Err(err).Msg("[observe] closeObserveStream failed")
				}
			}
		}
		return
	}
	// Observe: open streams for any new peer, using the address from the payload.
	for _, p := range cmd.Peers {
		if isFirst := ps.observeUsers.add(cmd.User, p.PeerID); isFirst {
			if err := ps.openObserveStream(p); err != nil {
				// Roll back the index entry so the next NATS command can retry.
				ps.observeUsers.remove(cmd.User, p.PeerID)
				log.Warn().Str("peer", p.PeerID).Err(err).Msg("[observe] openObserveStream failed")
			}
		}
	}
}

// ── outgoing observe management (observing side) ──────────────────────────────

// OpenObserveStream is the exported variant for inter-discovery propagation
// (no user context available). It bypasses the user index and opens the stream
// directly if not already open.
func (ps *StreamService) OpenObserveStream(p ShallowPeer) error {
	return ps.openObserveStream(p)
}

// CloseObserveStream is the exported variant for inter-discovery propagation.
func (ps *StreamService) CloseObserveStream(toPeerID string) error {
	return ps.closeObserveStream(toPeerID)
}

// openObserveStream opens a ProtocolObserve stream to p.
// Uses p.StreamAddress directly; falls back to DB then DHT lookup if empty.
func (ps *StreamService) openObserveStream(p ShallowPeer) error {
	streamAddr := p.StreamAddress
	fmt.Println("STREAM OBS", streamAddr)
	access := oclib.NewRequestAdmin(oclib.LibDataEnum(oclib.PEER), nil)
	res := access.Search(&dbs.Filters{
		And: map[string][]dbs.Filter{
			"peer_id": {{Operator: dbs.EQUAL.String(), Value: p.PeerID}},
		},
	}, "", false, 0, 1)
	if streamAddr == "" {
		// Fallback: DB then DHT.
		if len(res.Data) > 0 {
			streamAddr = res.Data[0].(*peer.Peer).StreamAddress
		} else if peers, err := ps.Node.GetPeerRecord(context.Background(), p.PeerID); err == nil && len(peers) > 0 {
			streamAddr = peers[0].StreamAddress
		}
	}
	if len(res.Data) > 0 && res.Data[0].(*peer.Peer).Relation == peer.SELF {
		return errors.New("Can't send to self")
	}
	fmt.Println("STREAM OBS SSS", streamAddr)

	if streamAddr == "" {
		return nil // can't resolve address — silently skip
	}

	decodedID, err := pp.Decode(p.PeerID)
	if err != nil {
		return err
	}

	// If a stream already exists, reuse it.
	ps.Mu.RLock()
	_, alreadyOpen := ps.Streams[ProtocolObserve][decodedID]
	ps.Mu.RUnlock()
	if alreadyOpen {
		return nil
	}
	ad, err := pp.AddrInfoFromString(streamAddr)
	if err != nil {
		return err
	}
	fmt.Println("TempStream OBSERVE", ad)
	if ps.Streams, err = common.TempStream(ps.Host, *ad, ProtocolObserve, p.ID, ps.Streams, protocols, &ps.Mu); err == nil {
		rawStream := ps.Streams[ProtocolObserve][ad.ID]
		if hbPayload, err := json.Marshal(ObserveRequest{Close: false}); err == nil {
			if err := json.NewEncoder(rawStream.Stream).Encode(common.NewEvent(ProtocolObserve, ps.Host.ID().String(), nil, "", hbPayload)); err != nil {
				fmt.Println("ERR")
				rawStream.Stream.Close()
				return err
			}
			s := &common.Stream{
				Stream: rawStream.Stream,
				Expiry: time.Now().Add(365 * 24 * time.Hour),
			}
			ps.Mu.Lock()
			if ps.Streams[ProtocolObserve] == nil {
				ps.Streams[ProtocolObserve] = map[pp.ID]*common.Stream{}
			}
			ps.Streams[ProtocolObserve][ad.ID] = s
			ps.Mu.Unlock()

			go ps.readLoop(s, ad.ID, ProtocolObserve, &common.ProtocolInfo{PersistantStream: true})
		}

	} else {
		return err
	}
	return nil
}

// closeObserveStream closes the ProtocolObserve stream to toPeerID and notifies
// the remote side.
func (ps *StreamService) closeObserveStream(toPeerID string) error {
	decodedID, err := pp.Decode(toPeerID)
	if err != nil {
		return err
	}
	ps.Mu.Lock()
	if ps.Streams[ProtocolObserve] != nil {
		if s, ok := ps.Streams[ProtocolObserve][decodedID]; ok {
			_ = json.NewEncoder(s.Stream).Encode(ObserveRequest{Close: true})
			s.Stream.Close()
			delete(ps.Streams[ProtocolObserve], decodedID)
		}
	}
	ps.Mu.Unlock()
	return nil
}

// CloseAllObserves closes every outgoing ProtocolObserve stream, clears the
// user index, and enters drain mode for observeDrainDuration.
func (ps *StreamService) CloseAllObserves() {
	ps.Mu.Lock()
	for _, s := range ps.Streams[ProtocolObserve] {
		_ = json.NewEncoder(s.Stream).Encode(ObserveRequest{Close: true})
		s.Stream.Close()
	}
	delete(ps.Streams, ProtocolObserve)
	ps.Mu.Unlock()

	// Reset user index so stale ref-counts don't block future opens.
	ps.observeUsers = newUserPeerIndex()

	ps.drainMu.Lock()
	ps.drainUntil = time.Now().Add(observeDrainDuration)
	ps.drainMu.Unlock()
}