package indexer

import (
	"context"
	"encoding/json"
	"strings"
	"sync"
	"time"

	"oc-discovery/daemons/node/common"

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

// TopicNameIndex is the GossipSub topic shared by regular indexers to exchange
// add/delete events for the distributed name→peerID mapping.
const TopicNameIndex = "oc-name-index"

// nameIndexDedupWindow suppresses re-emission of the same (action, name, peerID)
// tuple within this window, reducing duplicate events when a node is registered
// with multiple indexers simultaneously.
const nameIndexDedupWindow = 30 * time.Second

// NameIndexAction indicates whether a name mapping is being added or removed.
type NameIndexAction string

const (
	NameIndexAdd    NameIndexAction = "add"
	NameIndexDelete NameIndexAction = "delete"
)

// NameIndexEvent is published on TopicNameIndex by each indexer when a node
// registers (add) or is evicted by the GC (delete).
type NameIndexEvent struct {
	Action NameIndexAction `json:"action"`
	Name   string          `json:"name"`
	PeerID string          `json:"peer_id"`
	DID    string          `json:"did"`
}

// nameIndexState holds the local in-memory name index and the sender-side
// deduplication tracker.
type nameIndexState struct {
	// index: name → peerID → DID, built from events received from all indexers.
	index   map[string]map[string]string
	indexMu sync.RWMutex

	// emitted tracks the last emission time for each (action, name, peerID) key
	// to suppress duplicates within nameIndexDedupWindow.
	emitted   map[string]time.Time
	emittedMu sync.Mutex
}

// shouldEmit returns true if the (action, name, peerID) tuple has not been
// emitted within nameIndexDedupWindow, updating the tracker if so.
func (s *nameIndexState) shouldEmit(action NameIndexAction, name, peerID string) bool {
	key := string(action) + ":" + name + ":" + peerID
	s.emittedMu.Lock()
	defer s.emittedMu.Unlock()
	if t, ok := s.emitted[key]; ok && time.Since(t) < nameIndexDedupWindow {
		return false
	}
	s.emitted[key] = time.Now()
	return true
}

// onEvent applies a received NameIndexEvent to the local index.
// "add" inserts/updates the mapping; "delete" removes it.
// Operations are idempotent — duplicate events from multiple indexers are harmless.
func (s *nameIndexState) onEvent(evt NameIndexEvent) {
	if evt.Name == "" || evt.PeerID == "" {
		return
	}
	s.indexMu.Lock()
	defer s.indexMu.Unlock()
	switch evt.Action {
	case NameIndexAdd:
		if s.index[evt.Name] == nil {
			s.index[evt.Name] = map[string]string{}
		}
		s.index[evt.Name][evt.PeerID] = evt.DID
	case NameIndexDelete:
		if s.index[evt.Name] != nil {
			delete(s.index[evt.Name], evt.PeerID)
			if len(s.index[evt.Name]) == 0 {
				delete(s.index, evt.Name)
			}
		}
	}
}

// initNameIndex joins TopicNameIndex and starts consuming events.
// Must be called after ix.PS is ready.
func (ix *IndexerService) initNameIndex(ps *pubsub.PubSub) {
	logger := oclib.GetLogger()
	ix.nameIndex = &nameIndexState{
		index:   map[string]map[string]string{},
		emitted: map[string]time.Time{},
	}

	ps.RegisterTopicValidator(TopicNameIndex, func(_ context.Context, _ pp.ID, _ *pubsub.Message) bool {
		return true
	})
	topic, err := ps.Join(TopicNameIndex)
	if err != nil {
		logger.Err(err).Msg("name index: failed to join topic")
		return
	}
	ix.LongLivedStreamRecordedService.LongLivedPubSubService.PubsubMu.Lock()
	ix.LongLivedStreamRecordedService.LongLivedPubSubService.LongLivedPubSubs[TopicNameIndex] = topic
	ix.LongLivedStreamRecordedService.LongLivedPubSubService.PubsubMu.Unlock()

	common.SubscribeEvents(
		ix.LongLivedStreamRecordedService.LongLivedPubSubService,
		context.Background(),
		TopicNameIndex,
		-1,
		func(_ context.Context, evt NameIndexEvent, _ string) {
			ix.nameIndex.onEvent(evt)
		},
	)
}

// publishNameEvent emits a NameIndexEvent on TopicNameIndex, subject to the
// sender-side deduplication window.
func (ix *IndexerService) publishNameEvent(action NameIndexAction, name, peerID, did string) {
	if ix.nameIndex == nil || name == "" || peerID == "" {
		return
	}
	if !ix.nameIndex.shouldEmit(action, name, peerID) {
		return
	}
	ix.LongLivedStreamRecordedService.LongLivedPubSubService.PubsubMu.RLock()
	topic := ix.LongLivedStreamRecordedService.LongLivedPubSubService.LongLivedPubSubs[TopicNameIndex]
	ix.LongLivedStreamRecordedService.LongLivedPubSubService.PubsubMu.RUnlock()
	if topic == nil {
		return
	}
	evt := NameIndexEvent{Action: action, Name: name, PeerID: peerID, DID: did}
	b, err := json.Marshal(evt)
	if err != nil {
		return
	}
	_ = topic.Publish(context.Background(), b)
}

// LookupNameIndex searches the distributed name index for peers whose name
// contains needle (case-insensitive). Returns peerID → DID for matched peers.
// Returns nil if the name index is not initialised (e.g. native indexers).
func (ix *IndexerService) LookupNameIndex(needle string) map[string]string {
	if ix.nameIndex == nil {
		return nil
	}
	result := map[string]string{}
	needleLow := strings.ToLower(needle)
	ix.nameIndex.indexMu.RLock()
	defer ix.nameIndex.indexMu.RUnlock()
	for name, peers := range ix.nameIndex.index {
		if strings.Contains(strings.ToLower(name), needleLow) {
			for peerID, did := range peers {
				result[peerID] = did
			}
		}
	}
	return result
}