package indexer

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

	oclib "cloud.o-forge.io/core/oc-lib"
	dht "github.com/libp2p/go-libp2p-kad-dht"
	pubsub "github.com/libp2p/go-libp2p-pubsub"
	record "github.com/libp2p/go-libp2p-record"
	"github.com/libp2p/go-libp2p/core/host"
	pp "github.com/libp2p/go-libp2p/core/peer"
)

// dhtCacheEntry holds one indexer discovered via DHT for use in suggestion responses.
type dhtCacheEntry struct {
	AI       pp.AddrInfo
	LastSeen time.Time
}

// offloadState tracks which nodes we've already proposed migration to.
// When an indexer is overloaded (fill rate > offloadThreshold) it only sends
// SuggestMigrate to a small batch at a time; peers that don't migrate within
// offloadGracePeriod are moved to alreadyTried so a new batch can be picked.
type offloadState struct {
	inBatch     map[pp.ID]time.Time  // peer → time added to current batch
	alreadyTried map[pp.ID]struct{}  // peers proposed to that didn't migrate
	mu          sync.Mutex
}

const (
	offloadThreshold   = 0.80 // fill rate above which to start offloading
	offloadBatchSize   = 5    // max concurrent "please migrate" proposals
	offloadGracePeriod = 3 * common.RecommendedHeartbeatInterval
)

// IndexerService manages the indexer node's state: stream records, DHT, pubsub.
type IndexerService struct {
	*common.LongLivedStreamRecordedService[PeerRecord]
	PS               *pubsub.PubSub
	DHT              *dht.IpfsDHT
	isStrictIndexer  bool
	mu               sync.RWMutex
	dhtProvideCancel context.CancelFunc
	bornAt           time.Time
	// Passive DHT cache: refreshed every 2 min in background, used for suggestions.
	dhtCache   []dhtCacheEntry
	dhtCacheMu sync.RWMutex
	// Offload state for overloaded-indexer migration proposals.
	offload offloadState
	// referencedNodes holds nodes that have designated this indexer as their
	// search referent (Heartbeat.Referent=true). Used for distributed search.
	referencedNodes   map[pp.ID]PeerRecord
	referencedNodesMu sync.RWMutex
	// pendingSearches maps queryID → result channel for in-flight searches.
	pendingSearches   map[string]chan []common.SearchHit
	pendingSearchesMu sync.Mutex
	// behavior tracks per-node compliance (heartbeat rate, publish/get volume,
	// identity consistency, signature failures).
	behavior  *NodeBehaviorTracker
	// connGuard limits new-connection bursts to protect public indexers.
	connGuard *ConnectionRateGuard
}

// NewIndexerService creates an IndexerService.
// If ps is nil, this is a strict indexer (no pre-existing gossip sub from a node).
func NewIndexerService(h host.Host, ps *pubsub.PubSub, maxNode int) *IndexerService {
	logger := oclib.GetLogger()
	logger.Info().Msg("open indexer mode...")
	var err error
	ix := &IndexerService{
		LongLivedStreamRecordedService: common.NewStreamRecordedService[PeerRecord](h, maxNode),
		isStrictIndexer:                ps == nil,
		referencedNodes:                map[pp.ID]PeerRecord{},
		pendingSearches:                map[string]chan []common.SearchHit{},
		behavior:                       newNodeBehaviorTracker(),
		connGuard:                      newConnectionRateGuard(),
	}
	if ps == nil {
		ps, err = pubsub.NewGossipSub(context.Background(), ix.Host)
		if err != nil {
			panic(err) // can't run your indexer without a propagation pubsub
		}
	}
	ix.PS = ps

	if ix.isStrictIndexer {
		logger.Info().Msg("connect to indexers as strict indexer...")
		common.ConnectToIndexers(h, conf.GetConfig().MinIndexer, conf.GetConfig().MaxIndexer*2)
		logger.Info().Msg("subscribe to decentralized search flow as strict indexer...")
		go ix.SubscribeToSearch(ix.PS, nil)
	}

	ix.LongLivedStreamRecordedService.AfterDelete = func(pid pp.ID, name, did string) {
		// Remove behavior state for peers that are no longer connected and
		// have no active ban — keeps memory bounded to the live node set.
		ix.behavior.Cleanup(pid)
	}

	// AllowInbound: fired once per stream open, before any heartbeat is decoded.
	// 1. Reject peers that are currently banned (behavioral strikes).
	// 2. For genuinely new connections, apply the burst guard.
	ix.AllowInbound = func(remotePeer pp.ID, isNew bool) error {
		if ix.behavior.IsBanned(remotePeer) {
			return errors.New("peer is banned")
		}
		if isNew && !ix.connGuard.Allow() {
			return errors.New("connection rate limit exceeded, retry later")
		}
		return nil
	}

	// ValidateHeartbeat: fired on every heartbeat tick for an established stream.
	// Checks heartbeat cadence — rejects if the node is sending too fast.
	ix.ValidateHeartbeat = func(remotePeer pp.ID) error {
		return ix.behavior.RecordHeartbeat(remotePeer)
	}

	// Parse bootstrap peers from configured indexer addresses so the DHT can
	// find its routing table entries even in a fresh deployment.
	var bootstrapPeers []pp.AddrInfo
	for _, addrStr := range strings.Split(conf.GetConfig().IndexerAddresses, ",") {
		addrStr = strings.TrimSpace(addrStr)
		if addrStr == "" {
			continue
		}
		if ad, err := pp.AddrInfoFromString(addrStr); err == nil {
			bootstrapPeers = append(bootstrapPeers, *ad)
		}
	}
	dhtOpts := []dht.Option{
		dht.Mode(dht.ModeServer),
		dht.ProtocolPrefix("oc"),
		dht.Validator(record.NamespacedValidator{
			"node": PeerRecordValidator{},
			"name": DefaultValidator{},
			"pid":  DefaultValidator{},
		}),
	}
	if len(bootstrapPeers) > 0 {
		dhtOpts = append(dhtOpts, dht.BootstrapPeers(bootstrapPeers...))
	}
	if ix.DHT, err = dht.New(context.Background(), ix.Host, dhtOpts...); err != nil {
		logger.Info().Msg(err.Error())
		return nil
	}

	// Make the DHT available for replenishment from other packages.
	common.SetDiscoveryDHT(ix.DHT)

	ix.bornAt = time.Now().UTC()
	ix.offload.inBatch = make(map[pp.ID]time.Time)
	ix.offload.alreadyTried = make(map[pp.ID]struct{})
	ix.initNodeHandler()

	// Build and send a HeartbeatResponse after each received node heartbeat.
	// Raw metrics only — no pre-cooked score. Node computes the score itself.
	ix.BuildHeartbeatResponse = func(remotePeer pp.ID, need int, challenges []string, challengeDID string, referent bool, rawRecord json.RawMessage) *common.HeartbeatResponse {
		ix.StreamMU.RLock()
		peerCount := len(ix.StreamRecords[common.ProtocolHeartbeat])
		// Collect lastSeen per active peer for challenge responses.
		type peerMeta struct {
			found    bool
			lastSeen time.Time
		}
		peerLookup := make(map[string]peerMeta, peerCount)
		var remotePeerRecord PeerRecord
		for pid, rec := range ix.StreamRecords[common.ProtocolHeartbeat] {
			var ls time.Time
			if rec.HeartbeatStream != nil && rec.HeartbeatStream.UptimeTracker != nil {
				ls = rec.HeartbeatStream.UptimeTracker.LastSeen
			}
			peerLookup[pid.String()] = peerMeta{found: true, lastSeen: ls}
			if pid == remotePeer {
				remotePeerRecord = rec.Record
			}
		}
		ix.StreamMU.RUnlock()

		// AfterHeartbeat updates srec.Record asynchronously — it may not have run yet.
		// Use rawRecord (the fresh signed PeerRecord embedded in the heartbeat) directly
		// so referencedNodes always gets the current Name/DID regardless of timing.
		if remotePeerRecord.Name == "" && len(rawRecord) > 0 {
			var fresh PeerRecord
			if json.Unmarshal(rawRecord, &fresh) == nil {
				remotePeerRecord = fresh
			}
		}

		// Update referent designation: node marks its best-scored indexer with Referent=true.
		ix.updateReferent(remotePeer, remotePeerRecord, referent)

		maxN := ix.MaxNodesConn()
		fillRate := 0.0
		if maxN > 0 {
			fillRate = float64(peerCount) / float64(maxN)
			if fillRate > 1 {
				fillRate = 1
			}
		}

		resp := &common.HeartbeatResponse{
			FillRate:  fillRate,
			PeerCount: peerCount,
			MaxNodes:  maxN,
			BornAt:    ix.bornAt,
		}

		// Answer each challenged PeerID with raw found + lastSeen.
		for _, pidStr := range challenges {
			meta := peerLookup[pidStr] // zero value if not found
			entry := common.ChallengeEntry{
				PeerID:   pidStr,
				Found:    meta.found,
				LastSeen: meta.lastSeen,
			}
			resp.Challenges = append(resp.Challenges, entry)
		}

		// DHT challenge: retrieve the node's own DID to prove DHT is functional.
		if challengeDID != "" {
			ctx3, cancel3 := context.WithTimeout(context.Background(), 3*time.Second)
			val, err := ix.DHT.GetValue(ctx3, "/node/"+challengeDID)
			cancel3()
			resp.DHTFound = err == nil
			if err == nil {
				resp.DHTPayload = json.RawMessage(val)
			}
		}

		// Random sample of connected nodes as witnesses (up to 3).
		// Never include the requesting peer itself — asking a node to witness
		// itself is circular and meaningless.
		ix.StreamMU.RLock()
		for pidStr := range peerLookup {
			if len(resp.Witnesses) >= 3 {
				break
			}
			pid, err := pp.Decode(pidStr)
			if err != nil || pid == remotePeer || pid == ix.Host.ID() {
				continue
			}
			addrs := ix.Host.Peerstore().Addrs(pid)
			ai := common.FilterLoopbackAddrs(pp.AddrInfo{ID: pid, Addrs: addrs})
			if len(ai.Addrs) > 0 {
				resp.Witnesses = append(resp.Witnesses, ai)
			}
		}
		ix.StreamMU.RUnlock()

		// Attach suggestions: exactly `need` entries from the DHT cache.
		// If the indexer is overloaded (SuggestMigrate will be set below), always
		// provide at least 1 suggestion even when need == 0, so the node has
		// somewhere to go.
		suggestionsNeeded := need
		if fillRate > offloadThreshold && suggestionsNeeded < 1 {
			suggestionsNeeded = 1
		}
		if suggestionsNeeded > 0 {
			ix.dhtCacheMu.RLock()
			// When offloading, pick from a random offset within the top N of the
			// cache so concurrent migrations spread across multiple targets rather
			// than all rushing to the same least-loaded indexer (thundering herd).
			// For normal need-based suggestions the full sorted order is fine.
			cache := ix.dhtCache
			if fillRate > offloadThreshold && len(cache) > suggestionsNeeded {
				const spreadWindow = 5 // sample from the top-5 least-loaded
				window := spreadWindow
				if window > len(cache) {
					window = len(cache)
				}
				start := rand.Intn(window)
				cache = cache[start:]
			}
			for _, e := range cache {
				if len(resp.Suggestions) >= suggestionsNeeded {
					break
				}
				// Never suggest the requesting peer itself or this indexer.
				if e.AI.ID == remotePeer || e.AI.ID == h.ID() {
					continue
				}
				resp.Suggestions = append(resp.Suggestions, e.AI)
			}
			ix.dhtCacheMu.RUnlock()
		}

		// Offload logic: when fill rate is too high, selectively ask nodes to migrate.
		if fillRate > offloadThreshold && len(resp.Suggestions) > 0 {
			now := time.Now()
			ix.offload.mu.Lock()
			// Expire stale batch entries -> move to alreadyTried.
			for pid, addedAt := range ix.offload.inBatch {
				if now.Sub(addedAt) > offloadGracePeriod {
					ix.offload.alreadyTried[pid] = struct{}{}
					delete(ix.offload.inBatch, pid)
				}
			}
			// Reset alreadyTried if we've exhausted the whole pool.
			if len(ix.offload.alreadyTried) >= peerCount {
				ix.offload.alreadyTried = make(map[pp.ID]struct{})
			}
			_, tried := ix.offload.alreadyTried[remotePeer]
			_, inBatch := ix.offload.inBatch[remotePeer]
			if !tried {
				if inBatch {
					resp.SuggestMigrate = true
				} else if len(ix.offload.inBatch) < offloadBatchSize {
					ix.offload.inBatch[remotePeer] = now
					resp.SuggestMigrate = true
				}
			}
			ix.offload.mu.Unlock()
		} else if fillRate <= offloadThreshold {
			// Fill rate back to normal: reset offload state.
			ix.offload.mu.Lock()
			if len(ix.offload.inBatch) > 0 || len(ix.offload.alreadyTried) > 0 {
				ix.offload.inBatch = make(map[pp.ID]time.Time)
				ix.offload.alreadyTried = make(map[pp.ID]struct{})
			}
			ix.offload.mu.Unlock()
		}

		// Bootstrap: if this indexer has no indexers of its own, probe the
		// connecting peer to check it supports ProtocolHeartbeat (i.e. it is
		// itself an indexer). Plain nodes do not register the handler and the
		// negotiation fails instantly — no wasted heartbeat cycle.
		// Run in a goroutine: the probe is a short blocking stream open.
		if len(common.Indexers.GetAddrs()) == 0 && remotePeer != h.ID() {
			pid := remotePeer
			go func() {
				if !common.SupportsHeartbeat(h, pid) {
					logger.Debug().Str("peer", pid.String()).
						Msg("[bootstrap] inbound peer has no heartbeat handler — not an indexer, skipping")
					return
				}
				addrs := h.Peerstore().Addrs(pid)
				ai := common.FilterLoopbackAddrs(pp.AddrInfo{ID: pid, Addrs: addrs})
				if len(ai.Addrs) == 0 {
					return
				}
				key := pid.String()
				if !common.Indexers.ExistsAddr(key) {
					adCopy := ai
					common.Indexers.SetAddr(key, &adCopy)
					common.Indexers.NudgeIt()
					logger.Info().Str("peer", key).Msg("[bootstrap] no indexers — added inbound indexer peer as candidate")
				}
			}()
		}

		return resp
	}

	// Advertise this indexer in the DHT so nodes can discover it.
	fillRateFn := func() float64 {
		ix.StreamMU.RLock()
		n := len(ix.StreamRecords[common.ProtocolHeartbeat])
		ix.StreamMU.RUnlock()
		maxN := ix.MaxNodesConn()
		if maxN <= 0 {
			return 0
		}
		rate := float64(n) / float64(maxN)
		if rate > 1 {
			rate = 1
		}
		return rate
	}
	ix.startDHTCacheRefresh()
	ix.startDHTProvide(fillRateFn)

	return ix
}

// startDHTCacheRefresh periodically queries the DHT for peer indexers and
// refreshes ix.dhtCache. This passive cache is used by BuildHeartbeatResponse
// to suggest better indexers to connected nodes without any per-request cost.
func (ix *IndexerService) startDHTCacheRefresh() {
	ctx, cancel := context.WithCancel(context.Background())
	// Store cancel alongside the provide cancel so Close() stops both.
	prevCancel := ix.dhtProvideCancel
	ix.dhtProvideCancel = func() {
		if prevCancel != nil {
			prevCancel()
		}
		cancel()
	}
	go func() {
		logger := oclib.GetLogger()
		refresh := func() {
			if ix.DHT == nil {
				return
			}
			// Fetch more than needed so SelectByFillRate can filter for diversity.
			raw := common.DiscoverIndexersFromDHT(ix.Host, ix.DHT, 30)
			if len(raw) == 0 {
				return
			}
			// Remove self before selection.
			filtered := raw[:0]
			for _, ai := range raw {
				if ai.ID != ix.Host.ID() {
					filtered = append(filtered, ai)
				}
			}
			// SelectByFillRate applies /24 subnet diversity and fill-rate weighting.
			// Fill rates are unknown at this stage (nil map) so all peers get
			// the neutral prior f=0.5 — diversity filtering still applies.
			selected := common.SelectByFillRate(filtered, nil, 10)
			now := time.Now()
			ix.dhtCacheMu.Lock()
			ix.dhtCache = ix.dhtCache[:0]
			for _, ai := range selected {
				ix.dhtCache = append(ix.dhtCache, dhtCacheEntry{AI: ai, LastSeen: now})
			}
			ix.dhtCacheMu.Unlock()
			logger.Info().Int("cached", len(selected)).Msg("[dht] indexer suggestion cache refreshed")
		}
		// Initial delay: let the DHT routing table warm up first.
		select {
		case <-time.After(30 * time.Second):
		case <-ctx.Done():
			return
		}
		refresh()
		t := time.NewTicker(2 * time.Minute)
		defer t.Stop()
		for {
			select {
			case <-t.C:
				refresh()
			case <-ctx.Done():
				return
			}
		}
	}()
}

// startDHTProvide bootstraps the DHT and starts a goroutine that periodically
// advertises this indexer under the well-known provider key.
func (ix *IndexerService) startDHTProvide(fillRateFn func() float64) {
	ctx, cancel := context.WithCancel(context.Background())
	ix.dhtProvideCancel = cancel
	go func() {
		logger := oclib.GetLogger()
		// Wait until a routable (non-loopback) address is available.
		for i := 0; i < 12; i++ {
			addrs := ix.Host.Addrs()
			if len(addrs) > 0 && !strings.Contains(addrs[len(addrs)-1].String(), "127.0.0.1") {
				break
			}
			select {
			case <-ctx.Done():
				return
			case <-time.After(5 * time.Second):
			}
		}
		if err := ix.DHT.Bootstrap(ctx); err != nil {
			logger.Warn().Err(err).Msg("[dht] bootstrap failed")
		}
		provide := func() {
			pCtx, pCancel := context.WithTimeout(ctx, 30*time.Second)
			defer pCancel()
			if err := ix.DHT.Provide(pCtx, common.IndexerCID(), true); err != nil {
				logger.Warn().Err(err).Msg("[dht] Provide failed")
			} else {
				logger.Info().Float64("fill_rate", fillRateFn()).Msg("[dht] indexer advertised in DHT")
			}
		}
		provide()
		t := time.NewTicker(common.RecommendedHeartbeatInterval)
		defer t.Stop()
		for {
			select {
			case <-t.C:
				provide()
			case <-ctx.Done():
				return
			}
		}
	}()
}

func (ix *IndexerService) Close() {
	if ix.dhtProvideCancel != nil {
		ix.dhtProvideCancel()
	}
	ix.DHT.Close()
	ix.PS.UnregisterTopicValidator(common.TopicPubSubSearch)
	for _, s := range ix.StreamRecords {
		for _, ss := range s {
			ss.HeartbeatStream.Stream.Close()
		}
	}
}