package missing

// test

import (
	"context"
	"encoding/hex"
	"errors"
	"sync"
	"time"

	"github.com/libp2p/go-libp2p/core/peer"
	"github.com/waku-org/go-waku/logging"
	"github.com/waku-org/go-waku/waku/v2/protocol"
	"github.com/waku-org/go-waku/waku/v2/protocol/pb"
	"github.com/waku-org/go-waku/waku/v2/protocol/store"
	"github.com/waku-org/go-waku/waku/v2/timesource"
	"go.uber.org/zap"
	"google.golang.org/protobuf/proto"
)

const maxContentTopicsPerRequest = 10

// MessageTracker should keep track of messages it has seen before and
// provide a way to determine whether a message exists or not. This
// is application specific
type MessageTracker interface {
	MessageExists(pb.MessageHash) (bool, error)
}

// MissingMessageVerifier is used to periodically retrieve missing messages from store nodes that have some specific criteria
type MissingMessageVerifier struct {
	ctx    context.Context
	params missingMessageVerifierParams

	messageTracker MessageTracker

	criteriaInterest   map[string]criteriaInterest // Track message verification requests and when was the last time a pubsub topic was verified for missing messages
	criteriaInterestMu sync.Mutex

	C <-chan *protocol.Envelope

	store      *store.WakuStore
	timesource timesource.Timesource
	logger     *zap.Logger
}

// NewMissingMessageVerifier creates an instance of a MissingMessageVerifier
func NewMissingMessageVerifier(store *store.WakuStore, messageTracker MessageTracker, timesource timesource.Timesource, logger *zap.Logger, options ...MissingMessageVerifierOption) *MissingMessageVerifier {
	options = append(defaultMissingMessagesVerifierOptions, options...)
	params := missingMessageVerifierParams{}
	for _, opt := range options {
		opt(&params)
	}

	return &MissingMessageVerifier{
		store:          store,
		timesource:     timesource,
		messageTracker: messageTracker,
		logger:         logger.Named("missing-msg-verifier"),
		params:         params,
	}
}

func (m *MissingMessageVerifier) SetCriteriaInterest(peerID peer.ID, contentFilter protocol.ContentFilter) {
	m.criteriaInterestMu.Lock()
	defer m.criteriaInterestMu.Unlock()

	ctx, cancel := context.WithCancel(m.ctx)
	criteriaInterest := criteriaInterest{
		peerID:        peerID,
		contentFilter: contentFilter,
		lastChecked:   m.timesource.Now().Add(-m.params.delay),
		ctx:           ctx,
		cancel:        cancel,
	}

	currMessageVerificationRequest, ok := m.criteriaInterest[contentFilter.PubsubTopic]

	if ok && currMessageVerificationRequest.equals(criteriaInterest) {
		return
	}

	if ok {
		// If there is an ongoing request, we cancel it before replacing it
		// by the new list. This can be probably optimized further by tracking
		// the last time a content topic was synced, but might not be necessary
		// since cancelling an ongoing request would mean cancelling just a single
		// page of results
		currMessageVerificationRequest.cancel()
	}

	m.criteriaInterest[contentFilter.PubsubTopic] = criteriaInterest
}

func (m *MissingMessageVerifier) Start(ctx context.Context) {
	m.ctx = ctx
	m.criteriaInterest = make(map[string]criteriaInterest)

	c := make(chan *protocol.Envelope, 1000)
	m.C = c

	go func() {
		t := time.NewTicker(m.params.interval)
		defer t.Stop()

		var semaphore = make(chan struct{}, 5)
		for {
			select {
			case <-t.C:
				m.logger.Debug("checking for missing messages...")
				m.criteriaInterestMu.Lock()
				for _, interest := range m.criteriaInterest {
					select {
					case <-ctx.Done():
						return
					default:
						semaphore <- struct{}{}
						go func(interest criteriaInterest) {
							m.fetchHistory(c, interest)
							<-semaphore
						}(interest)
					}
				}
				m.criteriaInterestMu.Unlock()

			case <-ctx.Done():
				return
			}
		}
	}()
}

func (m *MissingMessageVerifier) fetchHistory(c chan<- *protocol.Envelope, interest criteriaInterest) {
	contentTopics := interest.contentFilter.ContentTopics.ToList()
	for i := 0; i < len(contentTopics); i += maxContentTopicsPerRequest {
		j := i + maxContentTopicsPerRequest
		if j > len(contentTopics) {
			j = len(contentTopics)
		}

		now := m.timesource.Now()
		err := m.fetchMessagesBatch(c, interest, i, j, now)
		if err != nil {
			if errors.Is(err, context.Canceled) {
				return
			}

			m.logger.Error("could not fetch history",
				zap.Stringer("peerID", interest.peerID),
				zap.String("pubsubTopic", interest.contentFilter.PubsubTopic),
				zap.Strings("contentTopics", contentTopics))
			continue
		}

		m.criteriaInterestMu.Lock()
		c := m.criteriaInterest[interest.contentFilter.PubsubTopic]
		if c.equals(interest) {
			c.lastChecked = now
			m.criteriaInterest[interest.contentFilter.PubsubTopic] = c
		}
		m.criteriaInterestMu.Unlock()
	}
}

func (m *MissingMessageVerifier) storeQueryWithRetry(ctx context.Context, queryFunc func(ctx context.Context) (*store.Result, error), logger *zap.Logger, logMsg string) (*store.Result, error) {
	retry := true
	count := 1
	for retry && count <= m.params.maxAttemptsToRetrieveHistory {
		logger.Debug(logMsg, zap.Int("attempt", count))
		tCtx, cancel := context.WithTimeout(ctx, 20*time.Second)
		result, err := queryFunc(tCtx)
		cancel()
		if err != nil {
			logger.Error("could not query storenode", zap.Error(err), zap.Int("attempt", count))
			select {
			case <-m.ctx.Done():
				return nil, m.ctx.Err()
			case <-time.After(2 * time.Second):
			}
		} else {
			return result, nil
		}
	}

	return nil, errors.New("storenode not available")
}

func (m *MissingMessageVerifier) fetchMessagesBatch(c chan<- *protocol.Envelope, interest criteriaInterest, batchFrom int, batchTo int, now time.Time) error {
	contentTopics := interest.contentFilter.ContentTopics.ToList()

	logger := m.logger.With(
		zap.Stringer("peerID", interest.peerID),
		zap.Strings("contentTopics", contentTopics[batchFrom:batchTo]),
		zap.String("pubsubTopic", interest.contentFilter.PubsubTopic),
		logging.Epoch("from", interest.lastChecked),
		logging.Epoch("to", now),
	)

	result, err := m.storeQueryWithRetry(interest.ctx, func(ctx context.Context) (*store.Result, error) {
		return m.store.Query(ctx, store.FilterCriteria{
			ContentFilter: protocol.NewContentFilter(interest.contentFilter.PubsubTopic, contentTopics[batchFrom:batchTo]...),
			TimeStart:     proto.Int64(interest.lastChecked.Add(-m.params.delay).UnixNano()),
			TimeEnd:       proto.Int64(now.Add(-m.params.delay).UnixNano()),
		}, store.WithPeer(interest.peerID), store.WithPaging(false, 100), store.IncludeData(false))
	}, logger, "retrieving history to check for missing messages")
	if err != nil {
		if !errors.Is(err, context.Canceled) {
			logger.Error("storenode not available", zap.Error(err))
		}
		return err
	}

	var missingHashes []pb.MessageHash

	for !result.IsComplete() {
		for _, mkv := range result.Messages() {
			hash := pb.ToMessageHash(mkv.MessageHash)
			exists, err := m.messageTracker.MessageExists(hash)
			if err != nil {
				return err
			}

			if exists {
				continue
			}

			missingHashes = append(missingHashes, hash)
		}

		result, err = m.storeQueryWithRetry(interest.ctx, func(ctx context.Context) (*store.Result, error) {
			if err = result.Next(ctx); err != nil {
				return nil, err
			}
			return result, nil
		}, logger.With(zap.String("cursor", hex.EncodeToString(result.Cursor()))), "retrieving next page")
		if err != nil {
			if !errors.Is(err, context.Canceled) {
				logger.Error("storenode not available", zap.Error(err))
			}
			return err
		}
	}

	if len(missingHashes) == 0 {
		// Nothing to do here
		return nil
	}

	result, err = m.storeQueryWithRetry(interest.ctx, func(ctx context.Context) (*store.Result, error) {
		return m.store.QueryByHash(ctx, missingHashes, store.WithPeer(interest.peerID), store.WithPaging(false, 100))
	}, logger, "retrieving missing messages")
	if err != nil {
		if !errors.Is(err, context.Canceled) {
			logger.Error("storenode not available", zap.Error(err))
		}
		return err
	}

	for !result.IsComplete() {
		for _, mkv := range result.Messages() {
			select {
			case c <- protocol.NewEnvelope(mkv.Message, mkv.Message.GetTimestamp(), mkv.GetPubsubTopic()):
			default:
				m.logger.Warn("subscriber is too slow!")
			}
		}

		result, err = m.storeQueryWithRetry(interest.ctx, func(ctx context.Context) (*store.Result, error) {
			if err = result.Next(ctx); err != nil {
				return nil, err
			}
			return result, nil
		}, logger.With(zap.String("cursor", hex.EncodeToString(result.Cursor()))), "retrieving next page")
		if err != nil {
			if !errors.Is(err, context.Canceled) {
				logger.Error("storenode not available", zap.Error(err))
			}
			return err
		}
	}

	return nil
}