package common

import (
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"math/rand"
	"oc-discovery/conf"
	"strings"
	"sync"
	"time"

	oclib "cloud.o-forge.io/core/oc-lib"
	"github.com/libp2p/go-libp2p/core/crypto"
	"github.com/libp2p/go-libp2p/core/host"
	pp "github.com/libp2p/go-libp2p/core/peer"
	"github.com/libp2p/go-libp2p/core/protocol"
)

const (
	ProtocolNativeSubscription  = "/opencloud/native/subscribe/1.0"
	ProtocolNativeUnsubscribe   = "/opencloud/native/unsubscribe/1.0"
	ProtocolNativeGetIndexers   = "/opencloud/native/indexers/1.0"
	// ProtocolNativeConsensus is used by nodes/indexers to cross-validate an indexer
	// pool against all configured native peers.
	ProtocolNativeConsensus      = "/opencloud/native/consensus/1.0"
	RecommendedHeartbeatInterval = 60 * time.Second

	// TopicIndexerRegistry is the PubSub topic used by native indexers to gossip
	// newly registered indexer PeerIDs to neighbouring natives.
	TopicIndexerRegistry = "oc-indexer-registry"

	// consensusQueryTimeout is the per-native timeout for a consensus query.
	consensusQueryTimeout = 3 * time.Second
	// consensusCollectTimeout is the total wait for all native responses.
	consensusCollectTimeout = 4 * time.Second
)

// ConsensusRequest is sent by a node/indexer to a native to validate a candidate
// indexer list. The native replies with what it trusts and what it suggests instead.
type ConsensusRequest struct {
	Candidates []string `json:"candidates"`
}

// ConsensusResponse is returned by a native during a consensus challenge.
// Trusted = candidates the native considers alive.
// Suggestions = extras the native knows and trusts but that were not in the candidate list.
type ConsensusResponse struct {
	Trusted     []string `json:"trusted"`
	Suggestions []string `json:"suggestions,omitempty"`
}

// IndexerRegistration is sent by an indexer to a native to signal its alive state.
// Only Addr is required; PeerID is derived from it if omitted.
// Timestamp + PubKey + Signature allow the native and DHT to verify that the
// registration was produced by the peer that owns the declared PeerID.
type IndexerRegistration struct {
	PeerID    string `json:"peer_id,omitempty"`
	Addr      string `json:"addr"`
	Timestamp int64  `json:"ts,omitempty"`          // Unix nanoseconds (anti-replay)
	PubKey    []byte `json:"pub_key,omitempty"`     // marshaled libp2p public key
	Signature []byte `json:"sig,omitempty"`         // Sign(signaturePayload())
}

// SignaturePayload returns the canonical byte slice that is signed/verified.
// Format: "<PeerID>|<Addr>|<Timestamp>"
func (r *IndexerRegistration) SignaturePayload() []byte {
	return []byte(fmt.Sprintf("%s|%s|%d", r.PeerID, r.Addr, r.Timestamp))
}

// Sign fills PubKey and Signature using the host's own private key.
func (r *IndexerRegistration) Sign(h host.Host) {
	priv := h.Peerstore().PrivKey(h.ID())
	if priv == nil {
		return
	}
	if pub, err := crypto.MarshalPublicKey(priv.GetPublic()); err == nil {
		r.PubKey = pub
	}
	r.Signature, _ = priv.Sign(r.SignaturePayload())
}

// Verify returns true when the registration carries a valid self-signature.
// Returns true (not an error) when no signature is present, to remain backward-
// compatible with older nodes that do not sign their registrations.
func (r *IndexerRegistration) Verify() (bool, error) {
	if len(r.Signature) == 0 || len(r.PubKey) == 0 {
		return true, nil // unsigned — accepted but untrusted
	}
	pub, err := crypto.UnmarshalPublicKey(r.PubKey)
	if err != nil {
		return false, fmt.Errorf("unmarshal pub key: %w", err)
	}
	ok, err := pub.Verify(r.SignaturePayload(), r.Signature)
	if err != nil {
		return false, err
	}
	return ok, nil
}

// GetIndexersRequest asks a native for a pool of live indexers.
type GetIndexersRequest struct {
	Count int    `json:"count"`
	From  string `json:"from"`
}

// GetIndexersResponse is returned by the native with live indexer multiaddrs.
type GetIndexersResponse struct {
	Indexers       []string `json:"indexers"`
	IsSelfFallback bool     `json:"is_self_fallback,omitempty"`
}

var StaticNatives = map[string]*pp.AddrInfo{}
var StreamNativeMu sync.RWMutex
var StreamNatives ProtocolStream = ProtocolStream{}

// nativeHeartbeatOnce ensures we start exactly one long-lived heartbeat goroutine
// toward the native mesh, even when ConnectToNatives is called from recovery paths.
var nativeHeartbeatOnce sync.Once

// nativeMeshHeartbeatOnce guards the native-to-native heartbeat goroutine started
// by EnsureNativePeers so only one goroutine covers the whole StaticNatives map.
var nativeMeshHeartbeatOnce sync.Once

// ConnectToNatives is the initial setup for nodes/indexers in native mode:
//  1. Parses native addresses → StaticNatives.
//  2. Starts a single long-lived heartbeat goroutine toward the native mesh.
//  3. Fetches an initial indexer pool from the first responsive native.
//  4. Runs consensus when real (non-fallback) indexers are returned.
//  5. Replaces StaticIndexers with the confirmed pool.
func ConnectToNatives(h host.Host, minIndexer int, maxIndexer int, myPID pp.ID) error {
	logger := oclib.GetLogger()
	logger.Info().Msg("[native] step 1 — parsing native addresses")

	// Parse native addresses — safe to call multiple times.
	StreamNativeMu.Lock()
	orderedAddrs := []string{}
	for _, addr := range strings.Split(conf.GetConfig().NativeIndexerAddresses, ",") {
		addr = strings.TrimSpace(addr)
		if addr == "" {
			continue
		}
		ad, err := pp.AddrInfoFromString(addr)
		if err != nil {
			logger.Err(err).Msg("[native] step 1 — invalid native addr")
			continue
		}
		StaticNatives[addr] = ad
		orderedAddrs = append(orderedAddrs, addr)
		logger.Info().Str("addr", addr).Msg("[native] step 1 — native registered")
	}
	if len(StaticNatives) == 0 {
		StreamNativeMu.Unlock()
		return errors.New("no valid native addresses configured")
	}
	StreamNativeMu.Unlock()
	logger.Info().Int("count", len(orderedAddrs)).Msg("[native] step 1 — natives parsed")

	// Step 1: one long-lived heartbeat to each native.
	nativeHeartbeatOnce.Do(func() {
		logger.Info().Msg("[native] step 1 — starting long-lived heartbeat to native mesh")
		SendHeartbeat(context.Background(), ProtocolHeartbeat,
			conf.GetConfig().Name, h, StreamNatives, StaticNatives, &StreamNativeMu, 20*time.Second)
	})

	// Fetch initial pool from the first responsive native.
	logger.Info().Int("want", maxIndexer).Msg("[native] step 1 — fetching indexer pool from native")
	candidates, isFallback := fetchIndexersFromNative(h, orderedAddrs, maxIndexer)
	if len(candidates) == 0 {
		logger.Warn().Msg("[native] step 1 — no candidates returned by any native")
		if minIndexer > 0 {
			return errors.New("ConnectToNatives: no indexers available from any native")
		}
		return nil
	}
	logger.Info().Int("candidates", len(candidates)).Bool("fallback", isFallback).Msg("[native] step 1 — pool received")

	// Step 2: populate StaticIndexers — consensus for real indexers, direct for fallback.
	pool := resolvePool(h, candidates, isFallback, maxIndexer)
	replaceStaticIndexers(pool)

	StreamMuIndexes.RLock()
	indexerCount := len(StaticIndexers)
	StreamMuIndexes.RUnlock()
	logger.Info().Int("pool_size", indexerCount).Msg("[native] step 2 — StaticIndexers replaced")

	if minIndexer > 0 && indexerCount < minIndexer {
		return errors.New("not enough majority-confirmed indexers available")
	}
	return nil
}

// replenishIndexersFromNative is called when an indexer heartbeat fails (step 3→4).
// It asks the native for exactly `need` replacement indexers, runs consensus when
// real indexers are returned, and adds the results to StaticIndexers without
// clearing the existing pool.
func replenishIndexersFromNative(h host.Host, need int) {
	if need <= 0 {
		return
	}
	logger := oclib.GetLogger()
	logger.Info().Int("need", need).Msg("[native] step 4 — replenishing indexer pool from native")

	StreamNativeMu.RLock()
	addrs := make([]string, 0, len(StaticNatives))
	for addr := range StaticNatives {
		addrs = append(addrs, addr)
	}
	StreamNativeMu.RUnlock()

	candidates, isFallback := fetchIndexersFromNative(h, addrs, need)
	if len(candidates) == 0 {
		logger.Warn().Msg("[native] step 4 — no candidates returned by any native")
		return
	}
	logger.Info().Int("candidates", len(candidates)).Bool("fallback", isFallback).Msg("[native] step 4 — candidates received")

	pool := resolvePool(h, candidates, isFallback, need)
	if len(pool) == 0 {
		logger.Warn().Msg("[native] step 4 — consensus yielded no confirmed indexers")
		return
	}

	// Add new indexers to the pool — do NOT clear existing ones.
	StreamMuIndexes.Lock()
	for addr, ad := range pool {
		StaticIndexers[addr] = ad
	}
	total := len(StaticIndexers)

	StreamMuIndexes.Unlock()
	logger.Info().Int("added", len(pool)).Int("total", total).Msg("[native] step 4 — pool replenished")

	// Nudge the heartbeat goroutine to connect immediately instead of waiting
	// for the next 20s tick.
	NudgeIndexerHeartbeat()
	logger.Info().Msg("[native] step 4 — heartbeat goroutine nudged")
}

// fetchIndexersFromNative queries ALL configured natives in parallel and merges
// their indexer lists. Non-fallback responses are preferred; if only fallbacks
// respond the fallback list is returned. Results are deduplicated and capped at count.
func fetchIndexersFromNative(h host.Host, nativeAddrs []string, count int) (candidates []string, isFallback bool) {
	logger := oclib.GetLogger()
	if len(nativeAddrs) == 0 {
		return nil, false
	}

	type fetchResult struct {
		indexers   []string
		isFallback bool
	}
	ch := make(chan fetchResult, len(nativeAddrs))

	for _, addr := range nativeAddrs {
		go func(addr string) {
			ad, err := pp.AddrInfoFromString(addr)
			if err != nil {
				ch <- fetchResult{}
				return
			}
			ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
			defer cancel()
			if err := h.Connect(ctx, *ad); err != nil {
				logger.Warn().Str("addr", addr).Err(err).Msg("[native] fetch — connect failed")
				ch <- fetchResult{}
				return
			}
			s, err := h.NewStream(ctx, ad.ID, ProtocolNativeGetIndexers)
			if err != nil {
				logger.Warn().Str("addr", addr).Err(err).Msg("[native] fetch — stream open failed")
				ch <- fetchResult{}
				return
			}
			s.SetDeadline(time.Now().Add(4 * time.Second))
			defer s.Close()
			req := GetIndexersRequest{Count: count, From: h.ID().String()}
			if encErr := json.NewEncoder(s).Encode(req); encErr != nil {
				logger.Warn().Str("addr", addr).Err(encErr).Msg("[native] fetch — encode failed")
				ch <- fetchResult{}
				return
			}
			var resp GetIndexersResponse
			if decErr := json.NewDecoder(s).Decode(&resp); decErr != nil {
				logger.Warn().Str("addr", addr).Err(decErr).Msg("[native] fetch — decode failed")
				ch <- fetchResult{}
				return
			}
			logger.Info().Str("native", addr).Int("indexers", len(resp.Indexers)).Bool("fallback", resp.IsSelfFallback).Msg("[native] fetch — response received")
			ch <- fetchResult{indexers: resp.Indexers, isFallback: resp.IsSelfFallback}
		}(addr)
	}

	timer := time.NewTimer(6 * time.Second)
	defer timer.Stop()

	seen := map[string]struct{}{}
	var realList, fallbackList []string
	collected := 0

collect:
	for collected < len(nativeAddrs) {
		select {
		case r := <-ch:
			collected++
			for _, ix := range r.indexers {
				if _, ok := seen[ix]; ok {
					continue
				}
				seen[ix] = struct{}{}
				if r.isFallback {
					fallbackList = append(fallbackList, ix)
				} else {
					realList = append(realList, ix)
				}
			}
		case <-timer.C:
			break collect
		}
	}

	if len(realList) > 0 {
		if len(realList) > count {
			realList = realList[:count]
		}
		logger.Info().Int("count", len(realList)).Msg("[native] fetch — merged real indexers from all natives")
		return realList, false
	}
	if len(fallbackList) > count {
		fallbackList = fallbackList[:count]
	}
	logger.Info().Int("count", len(fallbackList)).Bool("fallback", true).Msg("[native] fetch — using fallback indexers")
	return fallbackList, len(fallbackList) > 0
}

// resolvePool converts a candidate list to a validated addr→AddrInfo map.
// When isFallback is true the native itself is the indexer — no consensus needed.
// When isFallback is false, consensus is run before accepting the candidates.
func resolvePool(h host.Host, candidates []string, isFallback bool, maxIndexer int) map[string]*pp.AddrInfo {
	logger := oclib.GetLogger()
	if isFallback {
		logger.Info().Strs("addrs", candidates).Msg("[native] resolve — fallback mode, skipping consensus")
		pool := make(map[string]*pp.AddrInfo, len(candidates))
		for _, addr := range candidates {
			ad, err := pp.AddrInfoFromString(addr)
			if err != nil {
				continue
			}
			pool[addr] = ad
		}
		return pool
	}

	// Round 1.
	logger.Info().Int("candidates", len(candidates)).Msg("[native] resolve — consensus round 1")
	confirmed, suggestions := clientSideConsensus(h, candidates)
	logger.Info().Int("confirmed", len(confirmed)).Int("suggestions", len(suggestions)).Msg("[native] resolve — consensus round 1 done")

	// Round 2: fill gaps from suggestions if below target.
	if len(confirmed) < maxIndexer && len(suggestions) > 0 {
		rand.Shuffle(len(suggestions), func(i, j int) { suggestions[i], suggestions[j] = suggestions[j], suggestions[i] })
		gap := maxIndexer - len(confirmed)
		if gap > len(suggestions) {
			gap = len(suggestions)
		}
		logger.Info().Int("gap", gap).Msg("[native] resolve — consensus round 2 (filling gaps)")
		confirmed2, _ := clientSideConsensus(h, append(confirmed, suggestions[:gap]...))
		if len(confirmed2) > 0 {
			confirmed = confirmed2
		}
		logger.Info().Int("confirmed", len(confirmed)).Msg("[native] resolve — consensus round 2 done")
	}

	pool := make(map[string]*pp.AddrInfo, len(confirmed))
	for _, addr := range confirmed {
		ad, err := pp.AddrInfoFromString(addr)
		if err != nil {
			continue
		}
		pool[addr] = ad
	}
	logger.Info().Int("pool_size", len(pool)).Msg("[native] resolve — pool ready")
	return pool
}

// replaceStaticIndexers atomically replaces the active indexer pool.
// Peers no longer in next have their heartbeat streams closed so the SendHeartbeat
// goroutine stops sending to them on the next tick.
func replaceStaticIndexers(next map[string]*pp.AddrInfo) {
	StreamMuIndexes.Lock()
	defer StreamMuIndexes.Unlock()
	for addr, ad := range next {
		StaticIndexers[addr] = ad
	}
}

// clientSideConsensus challenges a candidate list to ALL configured native peers
// in parallel. Each native replies with the candidates it trusts plus extras it
// recommends. An indexer is confirmed when strictly more than 50% of responding
// natives trust it.
func clientSideConsensus(h host.Host, candidates []string) (confirmed []string, suggestions []string) {
	if len(candidates) == 0 {
		return nil, nil
	}

	StreamNativeMu.RLock()
	peers := make([]*pp.AddrInfo, 0, len(StaticNatives))
	for _, ad := range StaticNatives {
		peers = append(peers, ad)
	}
	StreamNativeMu.RUnlock()

	if len(peers) == 0 {
		return candidates, nil
	}

	type nativeResult struct {
		trusted     []string
		suggestions []string
		responded   bool
	}
	ch := make(chan nativeResult, len(peers))

	for _, ad := range peers {
		go func(ad *pp.AddrInfo) {
			ctx, cancel := context.WithTimeout(context.Background(), consensusQueryTimeout)
			defer cancel()
			if err := h.Connect(ctx, *ad); err != nil {
				ch <- nativeResult{}
				return
			}
			s, err := h.NewStream(ctx, ad.ID, ProtocolNativeConsensus)
			if err != nil {
				ch <- nativeResult{}
				return
			}
			// Set an absolute deadline on the stream so Encode/Decode cannot
			// block past the per-query budget, even if the remote native stalls.
			s.SetDeadline(time.Now().Add(consensusQueryTimeout))
			defer s.Close()
			if err := json.NewEncoder(s).Encode(ConsensusRequest{Candidates: candidates}); err != nil {
				ch <- nativeResult{}
				return
			}
			var resp ConsensusResponse
			if err := json.NewDecoder(s).Decode(&resp); err != nil {
				ch <- nativeResult{}
				return
			}
			ch <- nativeResult{trusted: resp.Trusted, suggestions: resp.Suggestions, responded: true}
		}(ad)
	}

	timer := time.NewTimer(consensusCollectTimeout)
	defer timer.Stop()

	trustedCounts := map[string]int{}
	suggestionPool := map[string]struct{}{}
	total := 0
	collected := 0

collect:
	for collected < len(peers) {
		select {
		case r := <-ch:
			collected++
			if !r.responded {
				continue
			}
			total++
			seen := map[string]struct{}{}
			for _, addr := range r.trusted {
				if _, already := seen[addr]; !already {
					trustedCounts[addr]++
					seen[addr] = struct{}{}
				}
			}
			for _, addr := range r.suggestions {
				suggestionPool[addr] = struct{}{}
			}
		case <-timer.C:
			break collect
		}
	}

	if total == 0 {
		return candidates, nil
	}

	quorum := conf.GetConfig().ConsensusQuorum
	if quorum <= 0 {
		quorum = 0.5
	}
	confirmedSet := map[string]struct{}{}
	for addr, count := range trustedCounts {
		if float64(count) > float64(total)*quorum {
			confirmed = append(confirmed, addr)
			confirmedSet[addr] = struct{}{}
		}
	}
	for addr := range suggestionPool {
		if _, ok := confirmedSet[addr]; !ok {
			suggestions = append(suggestions, addr)
		}
	}
	return
}

// RegisterWithNative sends a one-shot registration to each configured native indexer.
// Should be called periodically every RecommendedHeartbeatInterval.
func RegisterWithNative(h host.Host, nativeAddressesStr string) {
	logger := oclib.GetLogger()
	myAddr := ""
	if !strings.Contains(h.Addrs()[len(h.Addrs())-1].String(), "127.0.0.1") {
		myAddr = h.Addrs()[len(h.Addrs())-1].String() + "/p2p/" + h.ID().String()
	}
	if myAddr == "" {
		logger.Warn().Msg("RegisterWithNative: no routable address yet, skipping")
		return
	}
	reg := IndexerRegistration{
		PeerID:    h.ID().String(),
		Addr:      myAddr,
		Timestamp: time.Now().UnixNano(),
	}
	reg.Sign(h)
	for _, addr := range strings.Split(nativeAddressesStr, ",") {
		addr = strings.TrimSpace(addr)
		if addr == "" {
			continue
		}
		ad, err := pp.AddrInfoFromString(addr)
		if err != nil {
			logger.Err(err).Msg("RegisterWithNative: invalid addr")
			continue
		}
		ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
		if err := h.Connect(ctx, *ad); err != nil {
			cancel()
			continue
		}
		s, err := h.NewStream(ctx, ad.ID, ProtocolNativeSubscription)
		cancel()
		if err != nil {
			logger.Err(err).Msg("RegisterWithNative: stream open failed")
			continue
		}
		if err := json.NewEncoder(s).Encode(reg); err != nil {
			logger.Err(err).Msg("RegisterWithNative: encode failed")
		}
		s.Close()
	}
}

// UnregisterFromNative sends an explicit deregistration message to each configured
// native so it can evict this indexer immediately without waiting for TTL expiry.
// Should be called during graceful shutdown.
func UnregisterFromNative(h host.Host, nativeAddressesStr string) {
	logger := oclib.GetLogger()
	reg := IndexerRegistration{PeerID: h.ID().String()}
	for _, addr := range strings.Split(nativeAddressesStr, ",") {
		addr = strings.TrimSpace(addr)
		if addr == "" {
			continue
		}
		ad, err := pp.AddrInfoFromString(addr)
		if err != nil {
			continue
		}
		ctx, cancel := context.WithTimeout(context.Background(), 3*time.Second)
		if err := h.Connect(ctx, *ad); err != nil {
			cancel()
			logger.Warn().Str("addr", addr).Msg("UnregisterFromNative: connect failed")
			continue
		}
		s, err := h.NewStream(ctx, ad.ID, ProtocolNativeUnsubscribe)
		cancel()
		if err != nil {
			logger.Warn().Str("addr", addr).Msg("UnregisterFromNative: stream open failed")
			continue
		}
		if err := json.NewEncoder(s).Encode(reg); err != nil {
			logger.Warn().Str("addr", addr).Msg("UnregisterFromNative: encode failed")
		}
		s.Close()
	}
}

// EnsureNativePeers populates StaticNatives from config and starts a single
// heartbeat goroutine toward the native mesh. Safe to call multiple times;
// the heartbeat goroutine is started at most once (nativeMeshHeartbeatOnce).
func EnsureNativePeers(h host.Host) {
	logger := oclib.GetLogger()
	nativeAddrs := conf.GetConfig().NativeIndexerAddresses
	if nativeAddrs == "" {
		return
	}
	StreamNativeMu.Lock()
	for _, addr := range strings.Split(nativeAddrs, ",") {
		addr = strings.TrimSpace(addr)
		if addr == "" {
			continue
		}
		ad, err := pp.AddrInfoFromString(addr)
		if err != nil {
			continue
		}
		StaticNatives[addr] = ad
		logger.Info().Str("addr", addr).Msg("native: registered peer in native mesh")
	}
	StreamNativeMu.Unlock()
	// One heartbeat goroutine iterates over all of StaticNatives on each tick;
	// starting one per address would multiply heartbeats by the native count.
	nativeMeshHeartbeatOnce.Do(func() {
		logger.Info().Msg("native: starting mesh heartbeat goroutine")
		SendHeartbeat(context.Background(), ProtocolHeartbeat,
			conf.GetConfig().Name, h, StreamNatives, StaticNatives, &StreamNativeMu, 20*time.Second)
	})
}

func StartNativeRegistration(h host.Host, nativeAddressesStr string) {
	go func() {
		// Poll until a routable (non-loopback) address is available before the first
		// registration attempt. libp2p may not have discovered external addresses yet
		// at startup. Cap at 12 retries (~1 minute) so we don't spin indefinitely.
		for i := 0; i < 12; i++ {
			hasRoutable := false
			if !strings.Contains(h.Addrs()[len(h.Addrs())-1].String(), "127.0.0.1") {
				hasRoutable = true
				break
			}

			if hasRoutable {
				break
			}
			time.Sleep(5 * time.Second)
		}
		RegisterWithNative(h, nativeAddressesStr)
		t := time.NewTicker(RecommendedHeartbeatInterval)
		defer t.Stop()
		for range t.C {
			RegisterWithNative(h, nativeAddressesStr)
		}
	}()
}

// ── Lost-native replacement ───────────────────────────────────────────────────

const (
	// ProtocolNativeGetPeers lets a node/indexer ask a native for a random
	// selection of that native's own native contacts (to replace a dead native).
	ProtocolNativeGetPeers = "/opencloud/native/peers/1.0"
	// ProtocolIndexerGetNatives lets nodes/indexers ask a connected indexer for
	// its configured native addresses (fallback when no alive native responds).
	ProtocolIndexerGetNatives = "/opencloud/indexer/natives/1.0"
	// retryNativeInterval is how often retryLostNative polls a dead native.
	retryNativeInterval = 30 * time.Second
)

// GetNativePeersRequest is sent to a native to ask for its known native contacts.
type GetNativePeersRequest struct {
	Exclude []string `json:"exclude"`
	Count   int      `json:"count"`
}

// GetNativePeersResponse carries native addresses returned by a native's peer list.
type GetNativePeersResponse struct {
	Peers []string `json:"peers"`
}

// GetIndexerNativesRequest is sent to an indexer to ask for its configured native addresses.
type GetIndexerNativesRequest struct {
	Exclude []string `json:"exclude"`
}

// GetIndexerNativesResponse carries native addresses returned by an indexer.
type GetIndexerNativesResponse struct {
	Natives []string `json:"natives"`
}

// nativeHeartbeatNudge allows replenishNativesFromPeers to trigger an immediate
// native heartbeat tick after adding a replacement native to the pool.
var nativeHeartbeatNudge = make(chan struct{}, 1)

// NudgeNativeHeartbeat signals the native heartbeat goroutine to fire immediately.
func NudgeNativeHeartbeat() {
	select {
	case nativeHeartbeatNudge <- struct{}{}:
	default: // nudge already pending, skip
	}
}

// replenishIndexersIfNeeded checks if the indexer pool is below the configured
// minimum (or empty) and, if so, asks the native mesh for replacements.
// Called whenever a native is recovered so the indexer pool is restored.
func replenishIndexersIfNeeded(h host.Host) {
	logger := oclib.GetLogger()
	minIdx := conf.GetConfig().MinIndexer
	if minIdx < 1 {
		minIdx = 1
	}
	StreamMuIndexes.RLock()
	indexerCount := len(StaticIndexers)
	StreamMuIndexes.RUnlock()
	if indexerCount < minIdx {
		need := minIdx - indexerCount
		logger.Info().Int("need", need).Int("current", indexerCount).Msg("[native] native recovered — replenishing indexer pool")
		go replenishIndexersFromNative(h, need)
	}
}

// replenishNativesFromPeers is called when the heartbeat to a native fails.
// Flow:
//  1. Ask other alive natives for one of their native contacts (ProtocolNativeGetPeers).
//  2. If none respond or return a new address, ask connected indexers (ProtocolIndexerGetNatives).
//  3. If no replacement found:
//     - remaining > 1 → ignore (enough natives remain).
//     - remaining ≤ 1 → start periodic retry (retryLostNative).
func replenishNativesFromPeers(h host.Host, lostAddr string, proto protocol.ID) {
	if lostAddr == "" {
		return
	}
	logger := oclib.GetLogger()
	logger.Info().Str("lost", lostAddr).Msg("[native] replenish natives — start")

	// Build exclude list: the lost addr + all currently alive natives.
	// lostAddr has already been removed from StaticNatives by doTick.
	StreamNativeMu.RLock()
	remaining := len(StaticNatives)
	exclude := make([]string, 0, remaining+1)
	exclude = append(exclude, lostAddr)
	for addr := range StaticNatives {
		exclude = append(exclude, addr)
	}
	StreamNativeMu.RUnlock()

	logger.Info().Int("remaining", remaining).Msg("[native] replenish natives — step 1: ask alive natives for a peer")

	// Step 1: ask other alive natives for a replacement.
	newAddr := fetchNativeFromNatives(h, exclude)

	// Step 2: fallback — ask connected indexers for their native addresses.
	if newAddr == "" {
		logger.Info().Msg("[native] replenish natives — step 2: ask indexers for their native addresses")
		newAddr = fetchNativeFromIndexers(h, exclude)
	}

	if newAddr != "" {
		ad, err := pp.AddrInfoFromString(newAddr)
		if err == nil {
			StreamNativeMu.Lock()
			StaticNatives[newAddr] = ad
			StreamNativeMu.Unlock()
			logger.Info().Str("new", newAddr).Msg("[native] replenish natives — replacement added, nudging heartbeat")
			NudgeNativeHeartbeat()
			replenishIndexersIfNeeded(h)
			return
		}
	}

	// Step 3: no replacement found.
	logger.Warn().Int("remaining", remaining).Msg("[native] replenish natives — no replacement found")
	if remaining > 1 {
		logger.Info().Msg("[native] replenish natives — enough natives remain, ignoring loss")
		return
	}
	// Last (or only) native — retry periodically.
	logger.Info().Str("addr", lostAddr).Msg("[native] replenish natives — last native lost, starting periodic retry")
	go retryLostNative(context.Background(), h, lostAddr, proto)
}

// fetchNativeFromNatives asks each alive native for one of its own native contacts
// not in exclude. Returns the first new address found or "" if none.
func fetchNativeFromNatives(h host.Host, exclude []string) string {
	logger := oclib.GetLogger()
	excludeSet := make(map[string]struct{}, len(exclude))
	for _, e := range exclude {
		excludeSet[e] = struct{}{}
	}

	StreamNativeMu.RLock()
	natives := make([]*pp.AddrInfo, 0, len(StaticNatives))
	for _, ad := range StaticNatives {
		natives = append(natives, ad)
	}
	StreamNativeMu.RUnlock()

	rand.Shuffle(len(natives), func(i, j int) { natives[i], natives[j] = natives[j], natives[i] })

	for _, ad := range natives {
		ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
		if err := h.Connect(ctx, *ad); err != nil {
			cancel()
			logger.Warn().Str("native", ad.ID.String()).Err(err).Msg("[native] fetch native peers — connect failed")
			continue
		}
		s, err := h.NewStream(ctx, ad.ID, ProtocolNativeGetPeers)
		cancel()
		if err != nil {
			logger.Warn().Str("native", ad.ID.String()).Err(err).Msg("[native] fetch native peers — stream failed")
			continue
		}
		req := GetNativePeersRequest{Exclude: exclude, Count: 1}
		if encErr := json.NewEncoder(s).Encode(req); encErr != nil {
			s.Close()
			continue
		}
		var resp GetNativePeersResponse
		if decErr := json.NewDecoder(s).Decode(&resp); decErr != nil {
			s.Close()
			continue
		}
		s.Close()
		for _, peer := range resp.Peers {
			if _, excluded := excludeSet[peer]; !excluded && peer != "" {
				logger.Info().Str("from", ad.ID.String()).Str("new", peer).Msg("[native] fetch native peers — got replacement")
				return peer
			}
		}
		// logger.Debug().Str("native", ad.ID.String()).Msg("[native] fetch native peers — no new native from this peer")
	}
	return ""
}

// fetchNativeFromIndexers asks connected indexers for their configured native addresses,
// returning the first one not in exclude.
func fetchNativeFromIndexers(h host.Host, exclude []string) string {
	logger := oclib.GetLogger()
	excludeSet := make(map[string]struct{}, len(exclude))
	for _, e := range exclude {
		excludeSet[e] = struct{}{}
	}

	StreamMuIndexes.RLock()
	indexers := make([]*pp.AddrInfo, 0, len(StaticIndexers))
	for _, ad := range StaticIndexers {
		indexers = append(indexers, ad)
	}
	StreamMuIndexes.RUnlock()

	rand.Shuffle(len(indexers), func(i, j int) { indexers[i], indexers[j] = indexers[j], indexers[i] })

	for _, ad := range indexers {
		ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
		if err := h.Connect(ctx, *ad); err != nil {
			cancel()
			continue
		}
		s, err := h.NewStream(ctx, ad.ID, ProtocolIndexerGetNatives)
		cancel()
		if err != nil {
			logger.Warn().Str("indexer", ad.ID.String()).Err(err).Msg("[native] fetch indexer natives — stream failed")
			continue
		}
		req := GetIndexerNativesRequest{Exclude: exclude}
		if encErr := json.NewEncoder(s).Encode(req); encErr != nil {
			s.Close()
			continue
		}
		var resp GetIndexerNativesResponse
		if decErr := json.NewDecoder(s).Decode(&resp); decErr != nil {
			s.Close()
			continue
		}
		s.Close()
		for _, nativeAddr := range resp.Natives {
			if _, excluded := excludeSet[nativeAddr]; !excluded && nativeAddr != "" {
				logger.Info().Str("indexer", ad.ID.String()).Str("native", nativeAddr).Msg("[native] fetch indexer natives — got native")
				return nativeAddr
			}
		}
	}
	logger.Warn().Msg("[native] fetch indexer natives — no native found from indexers")
	return ""
}

// retryLostNative periodically retries connecting to a lost native address until
// it becomes reachable again, was already restored by another path, or ctx is cancelled.
func retryLostNative(ctx context.Context, h host.Host, addr string, nativeProto protocol.ID) {
	logger := oclib.GetLogger()
	logger.Info().Str("addr", addr).Msg("[native] retry — periodic retry for lost native started")
	t := time.NewTicker(retryNativeInterval)
	defer t.Stop()
	for {
		select {
		case <-ctx.Done():
			logger.Info().Str("addr", addr).Msg("[native] retry — context cancelled, stopping retry")
			return
		case <-t.C:
		}
		StreamNativeMu.RLock()
		_, alreadyRestored := StaticNatives[addr]
		StreamNativeMu.RUnlock()
		if alreadyRestored {
			logger.Info().Str("addr", addr).Msg("[native] retry — native already restored, stopping retry")
			return
		}

		ad, err := pp.AddrInfoFromString(addr)
		if err != nil {
			logger.Warn().Str("addr", addr).Msg("[native] retry — invalid addr, stopping retry")
			return
		}
		ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
		err = h.Connect(ctx, *ad)
		cancel()
		if err != nil {
			logger.Warn().Str("addr", addr).Msg("[native] retry — still unreachable")
			continue
		}
		// Reachable again — add back to pool.
		StreamNativeMu.Lock()
		StaticNatives[addr] = ad
		StreamNativeMu.Unlock()
		logger.Info().Str("addr", addr).Msg("[native] retry — native reconnected and added back to pool")
		NudgeNativeHeartbeat()
		replenishIndexersIfNeeded(h)
		if nativeProto == ProtocolNativeGetIndexers {
			StartNativeRegistration(h, addr) // register back
		}
		return
	}
}