import { TypedEventEmitter, StrictSign, StrictNoSign, TopicValidatorResult, serviceCapabilities, serviceDependencies } from '@libp2p/interface'
import { peerIdFromMultihash, peerIdFromString } from '@libp2p/peer-id'
import { encode } from 'it-length-prefixed'
import { pipe } from 'it-pipe'
import { pushable } from 'it-pushable'
import * as Digest from 'multiformats/hashes/digest'
import * as constants from './constants.js'
import {
  ACCEPT_FROM_WHITELIST_DURATION_MS,
  ACCEPT_FROM_WHITELIST_MAX_MESSAGES,
  ACCEPT_FROM_WHITELIST_THRESHOLD_SCORE,
  BACKOFF_SLACK
} from './constants.js'
import { type DecodeRPCLimits, defaultDecodeRpcLimits } from './message/decodeRpc.js'
import { RPC } from './message/rpc.js'
import { MessageCache, type MessageCacheRecord } from './message-cache.js'
import {
  ChurnReason,
  getMetrics,
  IHaveIgnoreReason,
  InclusionReason,
  type Metrics,
  type MetricsRegister,
  ScorePenalty,
  type TopicStrToLabel,
  type ToSendGroupCount
} from './metrics.js'
import {
  PeerScore,
  type PeerScoreParams,
  type PeerScoreThresholds,
  createPeerScoreParams,
  createPeerScoreThresholds,
  type PeerScoreStatsDump
} from './score/index.js'
import { computeAllPeersScoreWeights } from './score/scoreMetrics.js'
import { InboundStream, OutboundStream } from './stream.js'
import { IWantTracer } from './tracer.js'
import {
  type MsgIdFn,
  type PublishConfig,
  type TopicStr,
  type MsgIdStr,
  ValidateError,
  type PeerIdStr,
  MessageStatus,
  RejectReason,
  type RejectReasonObj,
  type FastMsgIdFn,
  type AddrInfo,
  type DataTransform,
  rejectReasonFromAcceptance,
  type MsgIdToStrFn,
  type MessageId,
  type PublishOpts
} from './types.js'
import { buildRawMessage, validateToRawMessage } from './utils/buildRawMessage.js'
import { createGossipRpc, ensureControl } from './utils/create-gossip-rpc.js'
import { shuffle, messageIdToString } from './utils/index.js'
import { msgIdFnStrictNoSign, msgIdFnStrictSign } from './utils/msgIdFn.js'
import { multiaddrToIPStr } from './utils/multiaddr.js'
import { getPublishConfigFromPeerId } from './utils/publishConfig.js'
import { removeFirstNItemsFromSet, removeItemsFromSet } from './utils/set.js'
import { SimpleTimeCache } from './utils/time-cache.js'
import type { GossipsubOptsSpec } from './config.js'
import type {
  Connection, Direction, Stream, PeerId, Peer, PeerStore,
  Message,
  PublishResult,
  PubSub,
  PubSubEvents,
  PubSubInit,
  SubscriptionChangeData,
  TopicValidatorFn,
  Logger,
  ComponentLogger,
  Topology,
  PrivateKey
} from '@libp2p/interface'
import type { ConnectionManager, IncomingStreamData, Registrar } from '@libp2p/interface-internal'
import type { Multiaddr } from '@multiformats/multiaddr'
import type { Uint8ArrayList } from 'uint8arraylist'

type ConnectionDirection = 'inbound' | 'outbound'

type ReceivedMessageResult =
  | { code: MessageStatus.duplicate, msgIdStr: MsgIdStr }
  | ({ code: MessageStatus.invalid, msgIdStr?: MsgIdStr } & RejectReasonObj)
  | { code: MessageStatus.valid, messageId: MessageId, msg: Message }

export const multicodec: string = constants.GossipsubIDv12

export interface GossipsubOpts extends GossipsubOptsSpec, PubSubInit {
  /** if dial should fallback to floodsub */
  fallbackToFloodsub: boolean
  /** if self-published messages should be sent to all peers */
  floodPublish: boolean
  /** serialize message once and send to all peers without control messages */
  batchPublish: boolean
  /** whether PX is enabled; this should be enabled in bootstrappers and other well connected/trusted nodes. */
  doPX: boolean
  /** peers with which we will maintain direct connections */
  directPeers: AddrInfo[]
  /**
   * If true will not forward messages to mesh peers until reportMessageValidationResult() is called.
   * Messages will be cached in mcache for some time after which they are evicted. Calling
   * reportMessageValidationResult() after the message is dropped from mcache won't forward the message.
   */
  asyncValidation: boolean
  /**
   * Do not throw `PublishError.NoPeersSubscribedToTopic` error if there are no
   * peers listening on the topic.
   *
   * N.B. if you sent this option to true, and you publish a message on a topic
   * with no peers listening on that topic, no other network node will ever
   * receive the message.
   */
  allowPublishToZeroTopicPeers: boolean
  /** Do not throw `PublishError.Duplicate` if publishing duplicate messages */
  ignoreDuplicatePublishError: boolean
  /** For a single stream, await processing each RPC before processing the next */
  awaitRpcHandler: boolean
  /** For a single RPC, await processing each message before processing the next */
  awaitRpcMessageHandler: boolean

  /** message id function */
  msgIdFn: MsgIdFn
  /** fast message id function */
  fastMsgIdFn: FastMsgIdFn
  /** Uint8Array message id to string function */
  msgIdToStrFn: MsgIdToStrFn
  /** override the default MessageCache */
  messageCache: MessageCache
  /** peer score parameters */
  scoreParams: Partial<PeerScoreParams>
  /** peer score thresholds */
  scoreThresholds: Partial<PeerScoreThresholds>
  /** customize GossipsubIWantFollowupTime in order not to apply IWANT penalties */
  gossipsubIWantFollowupMs: number

  /** override constants for fine tuning */
  prunePeers?: number
  pruneBackoff?: number
  unsubcribeBackoff?: number
  graftFloodThreshold?: number
  opportunisticGraftPeers?: number
  opportunisticGraftTicks?: number
  directConnectTicks?: number

  dataTransform?: DataTransform
  metricsRegister?: MetricsRegister | null
  metricsTopicStrToLabel?: TopicStrToLabel

  // Debug
  /** Prefix tag for debug logs */
  debugName?: string

  /**
   * Specify the maximum number of inbound gossipsub protocol
   * streams that are allowed to be open concurrently
   */
  maxInboundStreams?: number

  /**
   * Specify the maximum number of outbound gossipsub protocol
   * streams that are allowed to be open concurrently
   */
  maxOutboundStreams?: number

  /**
   * Pass true to run on limited connections - data or time-limited
   * connections that may be closed at any time such as circuit relay
   * connections.
   *
   * @default false
   */
  runOnLimitedConnection?: boolean

  /**
   * Specify max buffer size in bytes for OutboundStream.
   * If full it will throw and reject sending any more data.
   */
  maxOutboundBufferSize?: number

  /**
   * Specify max size to skip decoding messages whose data
   * section exceeds this size.
   *
   */
  maxInboundDataLength?: number

  /**
   * If provided, only allow topics in this list
   */
  allowedTopics?: string[] | Set<string>

  /**
   * Limits to bound protobuf decoding
   */
  decodeRpcLimits?: DecodeRPCLimits

  /**
   * If true, will utilize the libp2p connection manager tagging system to prune/graft connections to peers, defaults to true
   */
  tagMeshPeers: boolean

  /**
   * Specify what percent of peers to send gossip to. If the percent results in
   * a number smaller than `Dlazy`, `Dlazy` will be used instead.
   *
   * It should be a number between 0 and 1, with a reasonable default of 0.25
   */
  gossipFactor: number

  /**
   * The minimum message size in bytes to be considered for sending IDONTWANT messages
   *
   * @default 512
   */
  idontwantMinDataSize?: number

  /**
   * The maximum number of IDONTWANT messages per heartbeat per peer
   *
   * @default 512
   */
  idontwantMaxMessages?: number
}

export interface GossipsubMessage {
  propagationSource: PeerId
  msgId: MsgIdStr
  msg: Message
}

export interface MeshPeer {
  peerId: string
  topic: string
  direction: Direction
}

export interface GossipsubEvents extends PubSubEvents {
  'gossipsub:heartbeat': CustomEvent
  'gossipsub:message': CustomEvent<GossipsubMessage>
  'gossipsub:graft': CustomEvent<MeshPeer>
  'gossipsub:prune': CustomEvent<MeshPeer>
}

enum GossipStatusCode {
  started,
  stopped
}

type GossipStatus =
  | {
    code: GossipStatusCode.started
    registrarTopologyIds: string[]
    heartbeatTimeout: ReturnType<typeof setTimeout>
    hearbeatStartMs: number
  }
  | {
    code: GossipStatusCode.stopped
  }

interface GossipOptions extends GossipsubOpts {
  scoreParams: PeerScoreParams
  scoreThresholds: PeerScoreThresholds
}

interface AcceptFromWhitelistEntry {
  /** number of messages accepted since recomputing the peer's score */
  messagesAccepted: number
  /** have to recompute score after this time */
  acceptUntil: number
}

export interface GossipSubComponents {
  privateKey: PrivateKey
  peerId: PeerId
  peerStore: PeerStore
  registrar: Registrar
  connectionManager: ConnectionManager
  logger: ComponentLogger
}

export class GossipSub extends TypedEventEmitter<GossipsubEvents> implements PubSub<GossipsubEvents> {
  /**
   * The signature policy to follow by default
   */
  public readonly globalSignaturePolicy: typeof StrictSign | typeof StrictNoSign
  public multicodecs: string[] = [constants.GossipsubIDv12, constants.GossipsubIDv11, constants.GossipsubIDv10]

  private publishConfig: PublishConfig | undefined

  private readonly dataTransform: DataTransform | undefined

  // State

  public readonly peers = new Map<PeerIdStr, PeerId>()
  public readonly streamsInbound = new Map<PeerIdStr, InboundStream>()
  public readonly streamsOutbound = new Map<PeerIdStr, OutboundStream>()

  /** Ensures outbound streams are created sequentially */
  private outboundInflightQueue = pushable<{ peerId: PeerId, connection: Connection }>({ objectMode: true })

  /** Direct peers */
  public readonly direct = new Set<PeerIdStr>()

  /** Floodsub peers */
  private readonly floodsubPeers = new Set<PeerIdStr>()

  /** Cache of seen messages */
  private readonly seenCache: SimpleTimeCache<void>

  /**
   * Map of peer id and AcceptRequestWhileListEntry
   */
  private readonly acceptFromWhitelist = new Map<PeerIdStr, AcceptFromWhitelistEntry>()

  /**
   * Map of topics to which peers are subscribed to
   */
  private readonly topics = new Map<TopicStr, Set<PeerIdStr>>()

  /**
   * List of our subscriptions
   */
  private readonly subscriptions = new Set<TopicStr>()

  /**
   * Map of topic meshes
   * topic => peer id set
   */
  public readonly mesh = new Map<TopicStr, Set<PeerIdStr>>()

  /**
   * Map of topics to set of peers. These mesh peers are the ones to which we are publishing without a topic membership
   * topic => peer id set
   */
  public readonly fanout = new Map<TopicStr, Set<PeerIdStr>>()

  /**
   * Map of last publish time for fanout topics
   * topic => last publish time
   */
  private readonly fanoutLastpub = new Map<TopicStr, number>()

  /**
   * Map of pending messages to gossip
   * peer id => control messages
   */
  public readonly gossip = new Map<PeerIdStr, RPC.ControlIHave[]>()

  /**
   * Map of control messages
   * peer id => control message
   */
  public readonly control = new Map<PeerIdStr, RPC.ControlMessage>()

  /**
   * Number of IHAVEs received from peer in the last heartbeat
   */
  private readonly peerhave = new Map<PeerIdStr, number>()

  /** Number of messages we have asked from peer in the last heartbeat */
  private readonly iasked = new Map<PeerIdStr, number>()

  /** Prune backoff map */
  private readonly backoff = new Map<TopicStr, Map<PeerIdStr, number>>()

  /**
   * Connection direction cache, marks peers with outbound connections
   * peer id => direction
   */
  private readonly outbound = new Map<PeerIdStr, boolean>()
  private readonly msgIdFn: MsgIdFn

  /**
   * A fast message id function used for internal message de-duplication
   */
  private readonly fastMsgIdFn: FastMsgIdFn | undefined

  private readonly msgIdToStrFn: MsgIdToStrFn

  /** Maps fast message-id to canonical message-id */
  private readonly fastMsgIdCache: SimpleTimeCache<MsgIdStr> | undefined

  /**
   * Short term cache for published message ids. This is used for penalizing peers sending
   * our own messages back if the messages are anonymous or use a random author.
   */
  private readonly publishedMessageIds: SimpleTimeCache<void>

  /**
   * A message cache that contains the messages for last few heartbeat ticks
   */
  private readonly mcache: MessageCache

  /** Peer score tracking */
  public readonly score: PeerScore

  /**
   * Custom validator function per topic.
   * Must return or resolve quickly (< 100ms) to prevent causing penalties for late messages.
   * If you need to apply validation that may require longer times use `asyncValidation` option and callback the
   * validation result through `Gossipsub.reportValidationResult`
   */
  public readonly topicValidators = new Map<TopicStr, TopicValidatorFn>()

  /**
   * Make this protected so child class may want to redirect to its own log.
   */
  protected readonly log: Logger

  /**
   * Number of heartbeats since the beginning of time
   * This allows us to amortize some resource cleanup -- eg: backoff cleanup
   */
  private heartbeatTicks = 0

  /**
   * Tracks IHAVE/IWANT promises broken by peers
   */
  readonly gossipTracer: IWantTracer

  /**
   * Tracks IDONTWANT messages received by peers in the current heartbeat
   */
  private readonly idontwantCounts = new Map<PeerIdStr, number>()

  /**
   * Tracks IDONTWANT messages received by peers and the heartbeat they were received in
   *
   * idontwants are stored for `mcacheLength` heartbeats before being pruned,
   * so this map is bounded by peerCount * idontwantMaxMessages * mcacheLength
   */
  private readonly idontwants = new Map<PeerIdStr, Map<MsgIdStr, number>>()

  private readonly components: GossipSubComponents

  private directPeerInitial: ReturnType<typeof setTimeout> | null = null

  public static multicodec: string = constants.GossipsubIDv12

  // Options
  readonly opts: Required<GossipOptions>
  private readonly decodeRpcLimits: DecodeRPCLimits

  private readonly metrics: Metrics | null
  private status: GossipStatus = { code: GossipStatusCode.stopped }
  private readonly maxInboundStreams?: number
  private readonly maxOutboundStreams?: number
  private readonly runOnLimitedConnection?: boolean
  private readonly allowedTopics: Set<TopicStr> | null

  private heartbeatTimer: {
    _intervalId: ReturnType<typeof setInterval> | undefined
    runPeriodically(fn: () => void, period: number): void
    cancel(): void
  } | null = null

  constructor (components: GossipSubComponents, options: Partial<GossipsubOpts> = {}) {
    super()

    const opts = {
      fallbackToFloodsub: true,
      floodPublish: true,
      batchPublish: false,
      tagMeshPeers: true,
      doPX: false,
      directPeers: [],
      D: constants.GossipsubD,
      Dlo: constants.GossipsubDlo,
      Dhi: constants.GossipsubDhi,
      Dscore: constants.GossipsubDscore,
      Dout: constants.GossipsubDout,
      Dlazy: constants.GossipsubDlazy,
      heartbeatInterval: constants.GossipsubHeartbeatInterval,
      fanoutTTL: constants.GossipsubFanoutTTL,
      mcacheLength: constants.GossipsubHistoryLength,
      mcacheGossip: constants.GossipsubHistoryGossip,
      seenTTL: constants.GossipsubSeenTTL,
      gossipsubIWantFollowupMs: constants.GossipsubIWantFollowupTime,
      prunePeers: constants.GossipsubPrunePeers,
      pruneBackoff: constants.GossipsubPruneBackoff,
      unsubcribeBackoff: constants.GossipsubUnsubscribeBackoff,
      graftFloodThreshold: constants.GossipsubGraftFloodThreshold,
      opportunisticGraftPeers: constants.GossipsubOpportunisticGraftPeers,
      opportunisticGraftTicks: constants.GossipsubOpportunisticGraftTicks,
      directConnectTicks: constants.GossipsubDirectConnectTicks,
      gossipFactor: constants.GossipsubGossipFactor,
      idontwantMinDataSize: constants.GossipsubIdontwantMinDataSize,
      idontwantMaxMessages: constants.GossipsubIdontwantMaxMessages,
      ...options,
      scoreParams: createPeerScoreParams(options.scoreParams),
      scoreThresholds: createPeerScoreThresholds(options.scoreThresholds)
    }

    this.components = components
    this.decodeRpcLimits = opts.decodeRpcLimits ?? defaultDecodeRpcLimits

    this.globalSignaturePolicy = opts.globalSignaturePolicy ?? StrictSign

    // Also wants to get notified of peers connected using floodsub
    if (opts.fallbackToFloodsub) {
      this.multicodecs.push(constants.FloodsubID)
    }

    // From pubsub
    this.log = components.logger.forComponent(opts.debugName ?? 'libp2p:gossipsub')

    // Gossipsub

    this.opts = opts as Required<GossipOptions>
    this.direct = new Set(opts.directPeers.map((p) => p.id.toString()))
    this.seenCache = new SimpleTimeCache<void>({ validityMs: opts.seenTTL })
    this.publishedMessageIds = new SimpleTimeCache<void>({ validityMs: opts.seenTTL })

    if (options.msgIdFn != null) {
      // Use custom function
      this.msgIdFn = options.msgIdFn
    } else {
      switch (this.globalSignaturePolicy) {
        case StrictSign:
          this.msgIdFn = msgIdFnStrictSign
          break
        case StrictNoSign:
          this.msgIdFn = msgIdFnStrictNoSign
          break
        default:
          throw new Error(`Invalid globalSignaturePolicy: ${this.globalSignaturePolicy}`)
      }
    }

    if (options.fastMsgIdFn != null) {
      this.fastMsgIdFn = options.fastMsgIdFn
      this.fastMsgIdCache = new SimpleTimeCache<MsgIdStr>({ validityMs: opts.seenTTL })
    }

    // By default, gossipsub only provide a browser friendly function to convert Uint8Array message id to string.
    this.msgIdToStrFn = options.msgIdToStrFn ?? messageIdToString

    this.mcache = options.messageCache ?? new MessageCache(opts.mcacheGossip, opts.mcacheLength, this.msgIdToStrFn)

    if (options.dataTransform != null) {
      this.dataTransform = options.dataTransform
    }

    if (options.metricsRegister != null) {
      if (options.metricsTopicStrToLabel == null) {
        throw Error('Must set metricsTopicStrToLabel with metrics')
      }

      // in theory, each topic has its own meshMessageDeliveriesWindow param
      // however in lodestar, we configure it mostly the same so just pick the max of positive ones
      // (some topics have meshMessageDeliveriesWindow as 0)
      const maxMeshMessageDeliveriesWindowMs = Math.max(
        ...Object.values(opts.scoreParams.topics).map((topicParam) => topicParam.meshMessageDeliveriesWindow),
        constants.DEFAULT_METRIC_MESH_MESSAGE_DELIVERIES_WINDOWS
      )

      const metrics = getMetrics(options.metricsRegister, options.metricsTopicStrToLabel, {
        gossipPromiseExpireSec: this.opts.gossipsubIWantFollowupMs / 1000,
        behaviourPenaltyThreshold: opts.scoreParams.behaviourPenaltyThreshold,
        maxMeshMessageDeliveriesWindowSec: maxMeshMessageDeliveriesWindowMs / 1000
      })

      metrics.mcacheSize.addCollect(() => { this.onScrapeMetrics(metrics) })
      for (const protocol of this.multicodecs) {
        metrics.protocolsEnabled.set({ protocol }, 1)
      }

      this.metrics = metrics
    } else {
      this.metrics = null
    }

    this.gossipTracer = new IWantTracer(this.opts.gossipsubIWantFollowupMs, this.msgIdToStrFn, this.metrics)

    /**
     * libp2p
     */
    this.score = new PeerScore(this.opts.scoreParams, this.metrics, this.components.logger, {
      scoreCacheValidityMs: opts.heartbeatInterval
    })

    this.maxInboundStreams = options.maxInboundStreams
    this.maxOutboundStreams = options.maxOutboundStreams
    this.runOnLimitedConnection = options.runOnLimitedConnection

    this.allowedTopics = (opts.allowedTopics != null) ? new Set(opts.allowedTopics) : null
  }

  readonly [Symbol.toStringTag] = '@chainsafe/libp2p-gossipsub'

  readonly [serviceCapabilities]: string[] = [
    '@libp2p/pubsub'
  ]

  readonly [serviceDependencies]: string[] = [
    '@libp2p/identify'
  ]

  getPeers (): PeerId[] {
    return [...this.peers.values()]
  }

  isStarted (): boolean {
    return this.status.code === GossipStatusCode.started
  }

  // LIFECYCLE METHODS

  /**
   * Mounts the gossipsub protocol onto the libp2p node and sends our
   * our subscriptions to every peer connected
   */
  async start (): Promise<void> {
    // From pubsub
    if (this.isStarted()) {
      return
    }

    this.log('starting')

    this.publishConfig = getPublishConfigFromPeerId(this.globalSignaturePolicy, this.components.peerId, this.components.privateKey)

    // Create the outbound inflight queue
    // This ensures that outbound stream creation happens sequentially
    this.outboundInflightQueue = pushable({ objectMode: true })
    pipe(this.outboundInflightQueue, async (source) => {
      for await (const { peerId, connection } of source) {
        await this.createOutboundStream(peerId, connection)
      }
    }).catch((e) => { this.log.error('outbound inflight queue error', e) })

    // set direct peer addresses in the address book
    await Promise.all(
      this.opts.directPeers.map(async (p) => {
        await this.components.peerStore.merge(p.id, {
          multiaddrs: p.addrs
        })
      })
    )

    const registrar = this.components.registrar
    // Incoming streams
    // Called after a peer dials us
    await Promise.all(
      this.multicodecs.map(async (multicodec) =>
        registrar.handle(multicodec, this.onIncomingStream.bind(this), {
          maxInboundStreams: this.maxInboundStreams,
          maxOutboundStreams: this.maxOutboundStreams,
          runOnLimitedConnection: this.runOnLimitedConnection
        })
      )
    )

    // # How does Gossipsub interact with libp2p? Rough guide from Mar 2022
    //
    // ## Setup:
    // Gossipsub requests libp2p to callback, TBD
    //
    // `this.libp2p.handle()` registers a handler for `/meshsub/1.1.0` and other Gossipsub protocols
    // The handler callback is registered in libp2p Upgrader.protocols map.
    //
    // Upgrader receives an inbound connection from some transport and (`Upgrader.upgradeInbound`):
    // - Adds encryption (NOISE in our case)
    // - Multiplex stream
    // - Create a muxer and register that for each new stream call Upgrader.protocols handler
    //
    // ## Topology
    // - new instance of Topology (unlinked to libp2p) with handlers
    // - registar.register(topology)

    // register protocol with topology
    // Topology callbacks called on connection manager changes
    const topology: Topology = {
      onConnect: this.onPeerConnected.bind(this),
      onDisconnect: this.onPeerDisconnected.bind(this),
      notifyOnLimitedConnection: this.runOnLimitedConnection
    }
    const registrarTopologyIds = await Promise.all(
      this.multicodecs.map(async (multicodec) => registrar.register(multicodec, topology))
    )

    // Schedule to start heartbeat after `GossipsubHeartbeatInitialDelay`
    const heartbeatTimeout = setTimeout(this.runHeartbeat, constants.GossipsubHeartbeatInitialDelay)
    // Then, run heartbeat every `heartbeatInterval` offset by `GossipsubHeartbeatInitialDelay`

    this.status = {
      code: GossipStatusCode.started,
      registrarTopologyIds,
      heartbeatTimeout,
      hearbeatStartMs: Date.now() + constants.GossipsubHeartbeatInitialDelay
    }

    this.score.start()
    // connect to direct peers
    this.directPeerInitial = setTimeout(() => {
      Promise.resolve()
        .then(async () => {
          await Promise.all(Array.from(this.direct).map(async (id) => this.connect(id)))
        })
        .catch((err) => {
          this.log(err)
        })
    }, constants.GossipsubDirectConnectInitialDelay)

    if (this.opts.tagMeshPeers) {
      this.addEventListener('gossipsub:graft', this.tagMeshPeer)
      this.addEventListener('gossipsub:prune', this.untagMeshPeer)
    }

    this.log('started')
  }

  /**
   * Unmounts the gossipsub protocol and shuts down every connection
   */
  async stop (): Promise<void> {
    this.log('stopping')
    // From pubsub

    if (this.status.code !== GossipStatusCode.started) {
      return
    }

    const { registrarTopologyIds } = this.status
    this.status = { code: GossipStatusCode.stopped }

    if (this.opts.tagMeshPeers) {
      this.removeEventListener('gossipsub:graft', this.tagMeshPeer)
      this.removeEventListener('gossipsub:prune', this.untagMeshPeer)
    }

    // unregister protocol and handlers
    const registrar = this.components.registrar
    await Promise.all(this.multicodecs.map(async (multicodec) => registrar.unhandle(multicodec)))
    registrarTopologyIds.forEach((id) => { registrar.unregister(id) })

    this.outboundInflightQueue.end()

    const closePromises = []
    for (const outboundStream of this.streamsOutbound.values()) {
      closePromises.push(outboundStream.close())
    }
    this.streamsOutbound.clear()

    for (const inboundStream of this.streamsInbound.values()) {
      closePromises.push(inboundStream.close())
    }
    this.streamsInbound.clear()

    await Promise.all(closePromises)

    this.peers.clear()
    this.subscriptions.clear()

    // Gossipsub

    if (this.heartbeatTimer != null) {
      this.heartbeatTimer.cancel()
      this.heartbeatTimer = null
    }

    this.score.stop()

    this.mesh.clear()
    this.fanout.clear()
    this.fanoutLastpub.clear()
    this.gossip.clear()
    this.control.clear()
    this.peerhave.clear()
    this.iasked.clear()
    this.backoff.clear()
    this.outbound.clear()
    this.gossipTracer.clear()
    this.seenCache.clear()
    if (this.fastMsgIdCache != null) this.fastMsgIdCache.clear()
    if (this.directPeerInitial != null) clearTimeout(this.directPeerInitial)
    this.idontwantCounts.clear()
    this.idontwants.clear()

    this.log('stopped')
  }

  /** FOR DEBUG ONLY - Dump peer stats for all peers. Data is cloned, safe to mutate */
  dumpPeerScoreStats (): PeerScoreStatsDump {
    return this.score.dumpPeerScoreStats()
  }

  /**
   * On an inbound stream opened
   */
  private onIncomingStream ({ stream, connection }: IncomingStreamData): void {
    if (!this.isStarted()) {
      return
    }

    const peerId = connection.remotePeer
    // add peer to router
    this.addPeer(peerId, connection.direction, connection.remoteAddr)
    // create inbound stream
    this.createInboundStream(peerId, stream)
    // attempt to create outbound stream
    this.outboundInflightQueue.push({ peerId, connection })
  }

  /**
   * Registrar notifies an established connection with pubsub protocol
   */
  private onPeerConnected (peerId: PeerId, connection: Connection): void {
    this.metrics?.newConnectionCount.inc({ status: connection.status })
    // libp2p may emit a closed connection and never issue peer:disconnect event
    // see https://github.com/ChainSafe/js-libp2p-gossipsub/issues/398
    if (!this.isStarted() || connection.status !== 'open') {
      return
    }

    this.addPeer(peerId, connection.direction, connection.remoteAddr)
    this.outboundInflightQueue.push({ peerId, connection })
  }

  /**
   * Registrar notifies a closing connection with pubsub protocol
   */
  private onPeerDisconnected (peerId: PeerId): void {
    this.log('connection ended %p', peerId)
    this.removePeer(peerId)
  }

  private async createOutboundStream (peerId: PeerId, connection: Connection): Promise<void> {
    if (!this.isStarted()) {
      return
    }

    const id = peerId.toString()

    if (!this.peers.has(id)) {
      return
    }

    // TODO make this behavior more robust
    // This behavior is different than for inbound streams
    // If an outbound stream already exists, don't create a new stream
    if (this.streamsOutbound.has(id)) {
      return
    }

    try {
      const stream = new OutboundStream(
        await connection.newStream(this.multicodecs, {
          runOnLimitedConnection: this.runOnLimitedConnection
        }),
        (e) => { this.log.error('outbound pipe error', e) },
        { maxBufferSize: this.opts.maxOutboundBufferSize }
      )

      this.log('create outbound stream %p', peerId)

      this.streamsOutbound.set(id, stream)

      const protocol = stream.protocol
      if (protocol === constants.FloodsubID) {
        this.floodsubPeers.add(id)
      }
      this.metrics?.peersPerProtocol.inc({ protocol }, 1)

      // Immediately send own subscriptions via the newly attached stream
      if (this.subscriptions.size > 0) {
        this.log('send subscriptions to', id)
        this.sendSubscriptions(id, Array.from(this.subscriptions), true)
      }
    } catch (e) {
      this.log.error('createOutboundStream error', e)
    }
  }

  private createInboundStream (peerId: PeerId, stream: Stream): void {
    if (!this.isStarted()) {
      return
    }

    const id = peerId.toString()

    if (!this.peers.has(id)) {
      return
    }

    // TODO make this behavior more robust
    // This behavior is different than for outbound streams
    // If a peer initiates a new inbound connection
    // we assume that one is the new canonical inbound stream
    const priorInboundStream = this.streamsInbound.get(id)
    if (priorInboundStream !== undefined) {
      this.log('replacing existing inbound steam %s', id)
      priorInboundStream.close().catch((err) => { this.log.error(err) })
    }

    this.log('create inbound stream %s', id)

    const inboundStream = new InboundStream(stream, { maxDataLength: this.opts.maxInboundDataLength })
    this.streamsInbound.set(id, inboundStream)

    this.pipePeerReadStream(peerId, inboundStream.source).catch((err) => { this.log(err) })
  }

  /**
   * Add a peer to the router
   */
  private addPeer (peerId: PeerId, direction: ConnectionDirection, addr: Multiaddr): void {
    const id = peerId.toString()

    if (!this.peers.has(id)) {
      this.log('new peer %p', peerId)

      this.peers.set(id, peerId)

      // Add to peer scoring
      this.score.addPeer(id)
      const currentIP = multiaddrToIPStr(addr)
      if (currentIP !== null) {
        this.score.addIP(id, currentIP)
      } else {
        this.log('Added peer has no IP in current address %s %s', id, addr.toString())
      }

      // track the connection direction. Don't allow to unset outbound
      if (!this.outbound.has(id)) {
        this.outbound.set(id, direction === 'outbound')
      }
    }
  }

  /**
   * Removes a peer from the router
   */
  private removePeer (peerId: PeerId): void {
    const id = peerId.toString()

    if (!this.peers.has(id)) {
      return
    }

    // delete peer
    this.log('delete peer %p', peerId)
    this.peers.delete(id)

    const outboundStream = this.streamsOutbound.get(id)
    const inboundStream = this.streamsInbound.get(id)

    if (outboundStream != null) {
      this.metrics?.peersPerProtocol.inc({ protocol: outboundStream.protocol }, -1)
    }

    // close streams
    outboundStream?.close().catch((err) => { this.log.error(err) })
    inboundStream?.close().catch((err) => { this.log.error(err) })

    // remove streams
    this.streamsOutbound.delete(id)
    this.streamsInbound.delete(id)

    // remove peer from topics map
    for (const peers of this.topics.values()) {
      peers.delete(id)
    }

    // Remove this peer from the mesh
    for (const [topicStr, peers] of this.mesh) {
      if (peers.delete(id)) {
        this.metrics?.onRemoveFromMesh(topicStr, ChurnReason.Dc, 1)
      }
    }

    // Remove this peer from the fanout
    for (const peers of this.fanout.values()) {
      peers.delete(id)
    }

    // Remove from floodsubPeers
    this.floodsubPeers.delete(id)
    // Remove from gossip mapping
    this.gossip.delete(id)
    // Remove from control mapping
    this.control.delete(id)
    // Remove from backoff mapping
    this.outbound.delete(id)
    // Remove from idontwant tracking
    this.idontwantCounts.delete(id)
    this.idontwants.delete(id)

    // Remove from peer scoring
    this.score.removePeer(id)

    this.acceptFromWhitelist.delete(id)
  }

  // API METHODS

  get started (): boolean {
    return this.status.code === GossipStatusCode.started
  }

  /**
   * Get a the peer-ids in a topic mesh
   */
  getMeshPeers (topic: TopicStr): PeerIdStr[] {
    const peersInTopic = this.mesh.get(topic)
    return (peersInTopic != null) ? Array.from(peersInTopic) : []
  }

  /**
   * Get a list of the peer-ids that are subscribed to one topic.
   */
  getSubscribers (topic: TopicStr): PeerId[] {
    const peersInTopic = this.topics.get(topic)
    return ((peersInTopic != null) ? Array.from(peersInTopic) : []).map((str) => this.peers.get(str) ?? peerIdFromString(str))
  }

  /**
   * Get the list of topics which the peer is subscribed to.
   */
  getTopics (): TopicStr[] {
    return Array.from(this.subscriptions)
  }

  // TODO: Reviewing Pubsub API

  // MESSAGE METHODS

  /**
   * Responsible for processing each RPC message received by other peers.
   */
  private async pipePeerReadStream (peerId: PeerId, stream: AsyncIterable<Uint8ArrayList>): Promise<void> {
    try {
      await pipe(stream, async (source) => {
        for await (const data of source) {
          try {
            // TODO: Check max gossip message size, before decodeRpc()
            const rpcBytes = data.subarray()
            // Note: This function may throw, it must be wrapped in a try {} catch {} to prevent closing the stream.
            // TODO: What should we do if the entire RPC is invalid?
            const rpc = RPC.decode(rpcBytes, {
              limits: {
                subscriptions: this.decodeRpcLimits.maxSubscriptions,
                messages: this.decodeRpcLimits.maxMessages,
                control$: {
                  ihave: this.decodeRpcLimits.maxIhaveMessageIDs,
                  iwant: this.decodeRpcLimits.maxIwantMessageIDs,
                  graft: this.decodeRpcLimits.maxControlMessages,
                  prune: this.decodeRpcLimits.maxControlMessages,
                  prune$: {
                    peers: this.decodeRpcLimits.maxPeerInfos
                  },
                  idontwant: this.decodeRpcLimits.maxControlMessages,
                  idontwant$: {
                    messageIDs: this.decodeRpcLimits.maxIdontwantMessageIDs
                  }
                }
              }
            })

            this.metrics?.onRpcRecv(rpc, rpcBytes.length)

            // Since processRpc may be overridden entirely in unsafe ways,
            // the simplest/safest option here is to wrap in a function and capture all errors
            // to prevent a top-level unhandled exception
            // This processing of rpc messages should happen without awaiting full validation/execution of prior messages
            if (this.opts.awaitRpcHandler) {
              try {
                await this.handleReceivedRpc(peerId, rpc)
              } catch (err) {
                this.metrics?.onRpcRecvError()
                this.log(err)
              }
            } else {
              this.handleReceivedRpc(peerId, rpc).catch((err) => {
                this.metrics?.onRpcRecvError()
                this.log(err)
              })
            }
          } catch (e) {
            this.metrics?.onRpcDataError()
            this.log(e as Error)
          }
        }
      })
    } catch (err) {
      this.metrics?.onPeerReadStreamError()
      this.handlePeerReadStreamError(err as Error, peerId)
    }
  }

  /**
   * Handle error when read stream pipe throws, less of the functional use but more
   * to for testing purposes to spy on the error handling
   * */
  private handlePeerReadStreamError (err: Error, peerId: PeerId): void {
    this.log.error(err)
    this.onPeerDisconnected(peerId)
  }

  /**
   * Handles an rpc request from a peer
   */
  public async handleReceivedRpc (from: PeerId, rpc: RPC): Promise<void> {
    // Check if peer is graylisted in which case we ignore the event
    if (!this.acceptFrom(from.toString())) {
      this.log('received message from unacceptable peer %p', from)
      this.metrics?.rpcRecvNotAccepted.inc()
      return
    }

    const subscriptions = (rpc.subscriptions != null) ? rpc.subscriptions.length : 0
    const messages = (rpc.messages != null) ? rpc.messages.length : 0
    let ihave = 0
    let iwant = 0
    let graft = 0
    let prune = 0
    if (rpc.control != null) {
      if (rpc.control.ihave != null) ihave = rpc.control.ihave.length
      if (rpc.control.iwant != null) iwant = rpc.control.iwant.length
      if (rpc.control.graft != null) graft = rpc.control.graft.length
      if (rpc.control.prune != null) prune = rpc.control.prune.length
    }
    this.log(
      `rpc.from ${from.toString()} subscriptions ${subscriptions} messages ${messages} ihave ${ihave} iwant ${iwant} graft ${graft} prune ${prune}`
    )

    // Handle received subscriptions
    if ((rpc.subscriptions != null) && rpc.subscriptions.length > 0) {
      // update peer subscriptions

      const subscriptions: Array<{ topic: TopicStr, subscribe: boolean }> = []

      rpc.subscriptions.forEach((subOpt) => {
        const topic = subOpt.topic
        const subscribe = subOpt.subscribe === true

        if (topic != null) {
          if ((this.allowedTopics != null) && !this.allowedTopics.has(topic)) {
            // Not allowed: subscription data-structures are not bounded by topic count
            // TODO: Should apply behaviour penalties?
            return
          }

          this.handleReceivedSubscription(from, topic, subscribe)

          subscriptions.push({ topic, subscribe })
        }
      })

      this.safeDispatchEvent<SubscriptionChangeData>('subscription-change', {
        detail: { peerId: from, subscriptions }
      })
    }

    // Handle messages
    // TODO: (up to limit)
    for (const message of rpc.messages) {
      if ((this.allowedTopics != null) && !this.allowedTopics.has(message.topic)) {
        // Not allowed: message cache data-structures are not bounded by topic count
        // TODO: Should apply behaviour penalties?
        continue
      }

      const handleReceivedMessagePromise = this.handleReceivedMessage(from, message)
        // Should never throw, but handle just in case
        .catch((err) => {
          this.metrics?.onMsgRecvError(message.topic)
          this.log(err)
        })

      if (this.opts.awaitRpcMessageHandler) {
        await handleReceivedMessagePromise
      }
    }

    // Handle control messages
    if (rpc.control != null) {
      await this.handleControlMessage(from.toString(), rpc.control)
    }
  }

  /**
   * Handles a subscription change from a peer
   */
  private handleReceivedSubscription (from: PeerId, topic: TopicStr, subscribe: boolean): void {
    this.log('subscription update from %p topic %s', from, topic)

    let topicSet = this.topics.get(topic)
    if (topicSet == null) {
      topicSet = new Set()
      this.topics.set(topic, topicSet)
    }

    if (subscribe) {
      // subscribe peer to new topic
      topicSet.add(from.toString())
    } else {
      // unsubscribe from existing topic
      topicSet.delete(from.toString())
    }

    // TODO: rust-libp2p has A LOT more logic here
  }

  /**
   * Handles a newly received message from an RPC.
   * May forward to all peers in the mesh.
   */
  private async handleReceivedMessage (from: PeerId, rpcMsg: RPC.Message): Promise<void> {
    this.metrics?.onMsgRecvPreValidation(rpcMsg.topic)

    const validationResult = await this.validateReceivedMessage(from, rpcMsg)

    this.metrics?.onPrevalidationResult(rpcMsg.topic, validationResult.code)

    const validationCode = validationResult.code
    switch (validationCode) {
      case MessageStatus.duplicate:
        // Report the duplicate
        this.score.duplicateMessage(from.toString(), validationResult.msgIdStr, rpcMsg.topic)
        // due to the collision of fastMsgIdFn, 2 different messages may end up the same fastMsgId
        // so we need to also mark the duplicate message as delivered or the promise is not resolved
        // and peer gets penalized. See https://github.com/ChainSafe/js-libp2p-gossipsub/pull/385
        this.gossipTracer.deliverMessage(validationResult.msgIdStr, true)
        this.mcache.observeDuplicate(validationResult.msgIdStr, from.toString())
        return

      case MessageStatus.invalid:
        // invalid messages received
        // metrics.register_invalid_message(&raw_message.topic)
        // Tell peer_score about reject
        // Reject the original source, and any duplicates we've seen from other peers.
        if (validationResult.msgIdStr != null) {
          const msgIdStr = validationResult.msgIdStr
          this.score.rejectMessage(from.toString(), msgIdStr, rpcMsg.topic, validationResult.reason)
          this.gossipTracer.rejectMessage(msgIdStr, validationResult.reason)
        } else {
          this.score.rejectInvalidMessage(from.toString(), rpcMsg.topic)
        }

        this.metrics?.onMsgRecvInvalid(rpcMsg.topic, validationResult)
        return

      case MessageStatus.valid:
        // Tells score that message arrived (but is maybe not fully validated yet).
        // Consider the message as delivered for gossip promises.
        this.score.validateMessage(validationResult.messageId.msgIdStr)
        this.gossipTracer.deliverMessage(validationResult.messageId.msgIdStr)

        // Add the message to our memcache
        // if no validation is required, mark the message as validated
        this.mcache.put(validationResult.messageId, rpcMsg, !this.opts.asyncValidation)

        // Dispatch the message to the user if we are subscribed to the topic
        if (this.subscriptions.has(rpcMsg.topic)) {
          const isFromSelf = this.components.peerId.equals(from)

          if (!isFromSelf || this.opts.emitSelf) {
            super.dispatchEvent(
              new CustomEvent<GossipsubMessage>('gossipsub:message', {
                detail: {
                  propagationSource: from,
                  msgId: validationResult.messageId.msgIdStr,
                  msg: validationResult.msg
                }
              })
            )
            // TODO: Add option to switch between emit per topic or all messages in one
            super.dispatchEvent(new CustomEvent<Message>('message', { detail: validationResult.msg }))
          }
        }

        // Forward the message to mesh peers, if no validation is required
        // If asyncValidation is ON, expect the app layer to call reportMessageValidationResult(), then forward
        if (!this.opts.asyncValidation) {
          // TODO: in rust-libp2p
          // .forward_msg(&msg_id, raw_message, Some(propagation_source))
          this.forwardMessage(validationResult.messageId.msgIdStr, rpcMsg, from.toString())
        }
        break
      default:
        throw new Error(`Invalid validation result: ${validationCode}`)
    }
  }

  /**
   * Handles a newly received message from an RPC.
   * May forward to all peers in the mesh.
   */
  private async validateReceivedMessage (
    propagationSource: PeerId,
    rpcMsg: RPC.Message
  ): Promise<ReceivedMessageResult> {
    // Fast message ID stuff
    const fastMsgIdStr = this.fastMsgIdFn?.(rpcMsg)
    const msgIdCached = fastMsgIdStr !== undefined ? this.fastMsgIdCache?.get(fastMsgIdStr) : undefined

    if (msgIdCached != null) {
      // This message has been seen previously. Ignore it
      return { code: MessageStatus.duplicate, msgIdStr: msgIdCached }
    }

    // Perform basic validation on message and convert to RawGossipsubMessage for fastMsgIdFn()
    const validationResult = await validateToRawMessage(this.globalSignaturePolicy, rpcMsg)

    if (!validationResult.valid) {
      return { code: MessageStatus.invalid, reason: RejectReason.Error, error: validationResult.error }
    }

    const msg = validationResult.message

    // Try and perform the data transform to the message. If it fails, consider it invalid.
    try {
      if (this.dataTransform != null) {
        msg.data = this.dataTransform.inboundTransform(rpcMsg.topic, msg.data)
      }
    } catch (e) {
      this.log('Invalid message, transform failed', e)
      return { code: MessageStatus.invalid, reason: RejectReason.Error, error: ValidateError.TransformFailed }
    }

    // TODO: Check if message is from a blacklisted source or propagation origin
    // - Reject any message from a blacklisted peer
    // - Also reject any message that originated from a blacklisted peer
    // - reject messages claiming to be from ourselves but not locally published

    // Calculate the message id on the transformed data.
    const msgId = await this.msgIdFn(msg)
    const msgIdStr = this.msgIdToStrFn(msgId)
    const messageId = { msgId, msgIdStr }

    // Add the message to the duplicate caches
    if (fastMsgIdStr !== undefined && (this.fastMsgIdCache != null)) {
      const collision = this.fastMsgIdCache.put(fastMsgIdStr, msgIdStr)
      if (collision) {
        this.metrics?.fastMsgIdCacheCollision.inc()
      }
    }

    if (this.seenCache.has(msgIdStr)) {
      return { code: MessageStatus.duplicate, msgIdStr }
    } else {
      this.seenCache.put(msgIdStr)
    }

    // possibly send IDONTWANTs to mesh peers
    if ((rpcMsg.data?.length ?? 0) >= this.opts.idontwantMinDataSize) {
      this.sendIDontWants(msgId, rpcMsg.topic, propagationSource.toString())
    }

    // (Optional) Provide custom validation here with dynamic validators per topic
    // NOTE: This custom topicValidator() must resolve fast (< 100ms) to allow scores
    // to not penalize peers for long validation times.
    const topicValidator = this.topicValidators.get(rpcMsg.topic)
    if (topicValidator != null) {
      let acceptance: TopicValidatorResult
      // Use try {} catch {} in case topicValidator() is synchronous
      try {
        acceptance = await topicValidator(propagationSource, msg)
      } catch (e) {
        const errCode = (e as { code: string }).code
        if (errCode === constants.ERR_TOPIC_VALIDATOR_IGNORE) acceptance = TopicValidatorResult.Ignore
        if (errCode === constants.ERR_TOPIC_VALIDATOR_REJECT) acceptance = TopicValidatorResult.Reject
        else acceptance = TopicValidatorResult.Ignore
      }

      if (acceptance !== TopicValidatorResult.Accept) {
        return { code: MessageStatus.invalid, reason: rejectReasonFromAcceptance(acceptance), msgIdStr }
      }
    }

    return { code: MessageStatus.valid, messageId, msg }
  }

  /**
   * Return score of a peer.
   */
  getScore (peerId: PeerIdStr): number {
    return this.score.score(peerId)
  }

  /**
   * Send an rpc object to a peer with subscriptions
   */
  private sendSubscriptions (toPeer: PeerIdStr, topics: string[], subscribe: boolean): void {
    this.sendRpc(toPeer, {
      subscriptions: topics.map((topic) => ({ topic, subscribe })),
      messages: []
    })
  }

  /**
   * Handles an rpc control message from a peer
   */
  private async handleControlMessage (id: PeerIdStr, controlMsg: RPC.ControlMessage): Promise<void> {
    if (controlMsg === undefined) {
      return
    }

    const iwant = (controlMsg.ihave?.length > 0) ? this.handleIHave(id, controlMsg.ihave) : []
    const ihave = (controlMsg.iwant?.length > 0) ? this.handleIWant(id, controlMsg.iwant) : []
    const prune = (controlMsg.graft?.length > 0) ? await this.handleGraft(id, controlMsg.graft) : []
    ;(controlMsg.prune?.length > 0) && (await this.handlePrune(id, controlMsg.prune))
    ;(controlMsg.idontwant?.length > 0) && this.handleIdontwant(id, controlMsg.idontwant)

    if ((iwant.length === 0) && (ihave.length === 0) && (prune.length === 0)) {
      return
    }

    const sent = this.sendRpc(id, createGossipRpc(ihave, { iwant, prune }))
    const iwantMessageIds = iwant[0]?.messageIDs
    if (iwantMessageIds != null) {
      if (sent) {
        this.gossipTracer.addPromise(id, iwantMessageIds)
      } else {
        this.metrics?.iwantPromiseUntracked.inc(1)
      }
    }
  }

  /**
   * Whether to accept a message from a peer
   */
  public acceptFrom (id: PeerIdStr): boolean {
    if (this.direct.has(id)) {
      return true
    }

    const now = Date.now()
    const entry = this.acceptFromWhitelist.get(id)

    if ((entry != null) && entry.messagesAccepted < ACCEPT_FROM_WHITELIST_MAX_MESSAGES && entry.acceptUntil >= now) {
      entry.messagesAccepted += 1
      return true
    }

    const score = this.score.score(id)
    if (score >= ACCEPT_FROM_WHITELIST_THRESHOLD_SCORE) {
      // peer is unlikely to be able to drop its score to `graylistThreshold`
      // after 128 messages or 1s
      this.acceptFromWhitelist.set(id, {
        messagesAccepted: 0,
        acceptUntil: now + ACCEPT_FROM_WHITELIST_DURATION_MS
      })
    } else {
      this.acceptFromWhitelist.delete(id)
    }

    return score >= this.opts.scoreThresholds.graylistThreshold
  }

  /**
   * Handles IHAVE messages
   */
  private handleIHave (id: PeerIdStr, ihave: RPC.ControlIHave[]): RPC.ControlIWant[] {
    if (ihave.length === 0) {
      return []
    }

    // we ignore IHAVE gossip from any peer whose score is below the gossips threshold
    const score = this.score.score(id)
    if (score < this.opts.scoreThresholds.gossipThreshold) {
      this.log('IHAVE: ignoring peer %s with score below threshold [ score = %d ]', id, score)
      this.metrics?.ihaveRcvIgnored.inc({ reason: IHaveIgnoreReason.LowScore })
      return []
    }

    // IHAVE flood protection
    const peerhave = (this.peerhave.get(id) ?? 0) + 1
    this.peerhave.set(id, peerhave)
    if (peerhave > constants.GossipsubMaxIHaveMessages) {
      this.log(
        'IHAVE: peer %s has advertised too many times (%d) within this heartbeat interval; ignoring',
        id,
        peerhave
      )
      this.metrics?.ihaveRcvIgnored.inc({ reason: IHaveIgnoreReason.MaxIhave })
      return []
    }

    const iasked = this.iasked.get(id) ?? 0
    if (iasked >= constants.GossipsubMaxIHaveLength) {
      this.log('IHAVE: peer %s has already advertised too many messages (%d); ignoring', id, iasked)
      this.metrics?.ihaveRcvIgnored.inc({ reason: IHaveIgnoreReason.MaxIasked })
      return []
    }

    // string msgId => msgId
    const iwant = new Map<MsgIdStr, Uint8Array>()

    ihave.forEach(({ topicID, messageIDs }) => {
      if (topicID == null || (messageIDs == null) || !this.mesh.has(topicID)) {
        return
      }

      let idonthave = 0

      messageIDs.forEach((msgId) => {
        const msgIdStr = this.msgIdToStrFn(msgId)
        if (!this.seenCache.has(msgIdStr)) {
          iwant.set(msgIdStr, msgId)
          idonthave++
        }
      })

      this.metrics?.onIhaveRcv(topicID, messageIDs.length, idonthave)
    })

    if (iwant.size === 0) {
      return []
    }

    let iask = iwant.size
    if (iask + iasked > constants.GossipsubMaxIHaveLength) {
      iask = constants.GossipsubMaxIHaveLength - iasked
    }

    this.log('IHAVE: Asking for %d out of %d messages from %s', iask, iwant.size, id)

    let iwantList = Array.from(iwant.values())
    // ask in random order
    shuffle(iwantList)

    // truncate to the messages we are actually asking for and update the iasked counter
    iwantList = iwantList.slice(0, iask)
    this.iasked.set(id, iasked + iask)

    // do not add gossipTracer promise here until a successful sendRpc()

    return [
      {
        messageIDs: iwantList
      }
    ]
  }

  /**
   * Handles IWANT messages
   * Returns messages to send back to peer
   */
  private handleIWant (id: PeerIdStr, iwant: RPC.ControlIWant[]): RPC.Message[] {
    if (iwant.length === 0) {
      return []
    }

    // we don't respond to IWANT requests from any per whose score is below the gossip threshold
    const score = this.score.score(id)
    if (score < this.opts.scoreThresholds.gossipThreshold) {
      this.log('IWANT: ignoring peer %s with score below threshold [score = %d]', id, score)
      return []
    }

    const ihave = new Map<MsgIdStr, RPC.Message>()
    const iwantByTopic = new Map<TopicStr, number>()
    let iwantDonthave = 0

    iwant.forEach(({ messageIDs }) => {
      messageIDs?.forEach((msgId) => {
        const msgIdStr = this.msgIdToStrFn(msgId)
        const entry = this.mcache.getWithIWantCount(msgIdStr, id)
        if (entry == null) {
          iwantDonthave++
          return
        }

        iwantByTopic.set(entry.msg.topic, 1 + (iwantByTopic.get(entry.msg.topic) ?? 0))

        if (entry.count > constants.GossipsubGossipRetransmission) {
          this.log('IWANT: Peer %s has asked for message %s too many times: ignoring request', id, msgId)
          return
        }

        ihave.set(msgIdStr, entry.msg)
      })
    })

    this.metrics?.onIwantRcv(iwantByTopic, iwantDonthave)

    if (ihave.size === 0) {
      this.log('IWANT: Could not provide any wanted messages to %s', id)
      return []
    }

    this.log('IWANT: Sending %d messages to %s', ihave.size, id)

    return Array.from(ihave.values())
  }

  /**
   * Handles Graft messages
   */
  private async handleGraft (id: PeerIdStr, graft: RPC.ControlGraft[]): Promise<RPC.ControlPrune[]> {
    const prune: TopicStr[] = []
    const score = this.score.score(id)
    const now = Date.now()
    let doPX = this.opts.doPX

    graft.forEach(({ topicID }) => {
      if (topicID == null) {
        return
      }

      const peersInMesh = this.mesh.get(topicID)
      if (peersInMesh == null) {
        // don't do PX when there is an unknown topic to avoid leaking our peers
        doPX = false
        // spam hardening: ignore GRAFTs for unknown topics
        return
      }

      // check if peer is already in the mesh; if so do nothing
      if (peersInMesh.has(id)) {
        return
      }

      const backoffExpiry = this.backoff.get(topicID)?.get(id)

      // This if/else chain contains the various cases of valid (and semi-valid) GRAFTs
      // Most of these cases result in a PRUNE immediately being sent in response

      // we don't GRAFT to/from direct peers; complain loudly if this happens
      if (this.direct.has(id)) {
        this.log('GRAFT: ignoring request from direct peer %s', id)
        // this is possibly a bug from a non-reciprical configuration; send a PRUNE
        prune.push(topicID)
        // but don't px
        doPX = false

        // make sure we are not backing off that peer
      } else if (typeof backoffExpiry === 'number' && now < backoffExpiry) {
        this.log('GRAFT: ignoring backed off peer %s', id)
        // add behavioral penalty
        this.score.addPenalty(id, 1, ScorePenalty.GraftBackoff)
        // no PX
        doPX = false
        // check the flood cutoff -- is the GRAFT coming too fast?
        const floodCutoff = backoffExpiry + this.opts.graftFloodThreshold - this.opts.pruneBackoff
        if (now < floodCutoff) {
          // extra penalty
          this.score.addPenalty(id, 1, ScorePenalty.GraftBackoff)
        }
        // refresh the backoff
        this.addBackoff(id, topicID)
        prune.push(topicID)

        // check the score
      } else if (score < 0) {
        // we don't GRAFT peers with negative score
        this.log('GRAFT: ignoring peer %s with negative score: score=%d, topic=%s', id, score, topicID)
        // we do send them PRUNE however, because it's a matter of protocol correctness
        prune.push(topicID)
        // but we won't PX to them
        doPX = false
        // add/refresh backoff so that we don't reGRAFT too early even if the score decays
        this.addBackoff(id, topicID)

        // check the number of mesh peers; if it is at (or over) Dhi, we only accept grafts
        // from peers with outbound connections; this is a defensive check to restrict potential
        // mesh takeover attacks combined with love bombing
      } else if (peersInMesh.size >= this.opts.Dhi && !(this.outbound.get(id) ?? false)) {
        prune.push(topicID)
        this.addBackoff(id, topicID)

        // valid graft
      } else {
        this.log('GRAFT: Add mesh link from %s in %s', id, topicID)
        this.score.graft(id, topicID)
        peersInMesh.add(id)

        this.metrics?.onAddToMesh(topicID, InclusionReason.Subscribed, 1)
      }

      this.safeDispatchEvent<MeshPeer>('gossipsub:graft', { detail: { peerId: id, topic: topicID, direction: 'inbound' } })
    })

    if (prune.length === 0) {
      return []
    }

    const onUnsubscribe = false
    return Promise.all(prune.map(async (topic) => this.makePrune(id, topic, doPX, onUnsubscribe)))
  }

  /**
   * Handles Prune messages
   */
  private async handlePrune (id: PeerIdStr, prune: RPC.ControlPrune[]): Promise<void> {
    const score = this.score.score(id)

    for (const { topicID, backoff, peers } of prune) {
      if (topicID == null) {
        continue
      }

      const peersInMesh = this.mesh.get(topicID)
      if (peersInMesh == null) {
        return
      }

      this.log('PRUNE: Remove mesh link to %s in %s', id, topicID)
      this.score.prune(id, topicID)
      if (peersInMesh.has(id)) {
        peersInMesh.delete(id)
        this.metrics?.onRemoveFromMesh(topicID, ChurnReason.Prune, 1)
      }

      // is there a backoff specified by the peer? if so obey it
      if (typeof backoff === 'number' && backoff > 0) {
        this.doAddBackoff(id, topicID, backoff * 1000)
      } else {
        this.addBackoff(id, topicID)
      }

      // PX
      if ((peers != null) && (peers.length > 0)) {
        // we ignore PX from peers with insufficient scores
        if (score < this.opts.scoreThresholds.acceptPXThreshold) {
          this.log(
            'PRUNE: ignoring PX from peer %s with insufficient score [score = %d, topic = %s]',
            id,
            score,
            topicID
          )
        } else {
          await this.pxConnect(peers)
        }
      }

      this.safeDispatchEvent<MeshPeer>('gossipsub:prune', { detail: { peerId: id, topic: topicID, direction: 'inbound' } })
    }
  }

  private handleIdontwant (id: PeerIdStr, idontwant: RPC.ControlIDontWant[]): void {
    let idontwantCount = this.idontwantCounts.get(id) ?? 0
    // return early if we have already received too many IDONTWANT messages from the peer
    if (idontwantCount >= this.opts.idontwantMaxMessages) {
      return
    }
    const startIdontwantCount = idontwantCount

    let idontwants = this.idontwants.get(id)
    if (idontwants == null) {
      idontwants = new Map()
      this.idontwants.set(id, idontwants)
    }
    let idonthave = 0
    // eslint-disable-next-line no-labels
    out: for (const { messageIDs } of idontwant) {
      for (const msgId of messageIDs) {
        if (idontwantCount >= this.opts.idontwantMaxMessages) {
          // eslint-disable-next-line no-labels
          break out
        }
        idontwantCount++

        const msgIdStr = this.msgIdToStrFn(msgId)
        idontwants.set(msgIdStr, this.heartbeatTicks)
        if (!this.mcache.msgs.has(msgIdStr)) idonthave++
      }
    }
    this.idontwantCounts.set(id, idontwantCount)
    const total = idontwantCount - startIdontwantCount
    this.metrics?.onIdontwantRcv(total, idonthave)
  }

  /**
   * Add standard backoff log for a peer in a topic
   */
  private addBackoff (id: PeerIdStr, topic: TopicStr): void {
    this.doAddBackoff(id, topic, this.opts.pruneBackoff)
  }

  /**
   * Add backoff expiry interval for a peer in a topic
   *
   * @param id
   * @param topic
   * @param intervalMs - backoff duration in milliseconds
   */
  private doAddBackoff (id: PeerIdStr, topic: TopicStr, intervalMs: number): void {
    let backoff = this.backoff.get(topic)
    if (backoff == null) {
      backoff = new Map()
      this.backoff.set(topic, backoff)
    }
    const expire = Date.now() + intervalMs
    const existingExpire = backoff.get(id) ?? 0
    if (existingExpire < expire) {
      backoff.set(id, expire)
    }
  }

  /**
   * Apply penalties from broken IHAVE/IWANT promises
   */
  private applyIwantPenalties (): void {
    this.gossipTracer.getBrokenPromises().forEach((count, p) => {
      this.log("peer %s didn't follow up in %d IWANT requests; adding penalty", p, count)
      this.score.addPenalty(p, count, ScorePenalty.BrokenPromise)
    })
  }

  /**
   * Clear expired backoff expiries
   */
  private clearBackoff (): void {
    // we only clear once every GossipsubPruneBackoffTicks ticks to avoid iterating over the maps too much
    if (this.heartbeatTicks % constants.GossipsubPruneBackoffTicks !== 0) {
      return
    }

    const now = Date.now()
    this.backoff.forEach((backoff, topic) => {
      backoff.forEach((expire, id) => {
        // add some slack time to the expiration, see https://github.com/libp2p/specs/pull/289
        if (expire + BACKOFF_SLACK * this.opts.heartbeatInterval < now) {
          backoff.delete(id)
        }
      })
      if (backoff.size === 0) {
        this.backoff.delete(topic)
      }
    })
  }

  /**
   * Maybe reconnect to direct peers
   */
  private async directConnect (): Promise<void> {
    const toconnect: string[] = []
    this.direct.forEach((id) => {
      if (!this.streamsOutbound.has(id)) {
        toconnect.push(id)
      }
    })

    await Promise.all(toconnect.map(async (id) => this.connect(id)))
  }

  /**
   * Maybe attempt connection given signed peer records
   */
  private async pxConnect (peers: RPC.PeerInfo[]): Promise<void> {
    if (peers.length > this.opts.prunePeers) {
      shuffle(peers)
      peers = peers.slice(0, this.opts.prunePeers)
    }
    const toconnect: string[] = []

    await Promise.all(
      peers.map(async (pi) => {
        if (pi.peerID == null) {
          return
        }

        const peer = peerIdFromMultihash(Digest.decode(pi.peerID))
        const p = peer.toString()

        if (this.peers.has(p)) {
          return
        }

        if (pi.signedPeerRecord == null) {
          toconnect.push(p)
          return
        }

        // The peer sent us a signed record
        // This is not a record from the peer who sent the record, but another peer who is connected with it
        // Ensure that it is valid
        try {
          if (!(await this.components.peerStore.consumePeerRecord(pi.signedPeerRecord, peer))) {
            this.log('bogus peer record obtained through px: could not add peer record to address book')
            return
          }
          toconnect.push(p)
        } catch (e) {
          this.log('bogus peer record obtained through px: invalid signature or not a peer record')
        }
      })
    )

    if (toconnect.length === 0) {
      return
    }

    await Promise.all(toconnect.map(async (id) => this.connect(id)))
  }

  /**
   * Connect to a peer using the gossipsub protocol
   */
  private async connect (id: PeerIdStr): Promise<void> {
    this.log('Initiating connection with %s', id)
    const peerId = peerIdFromString(id)
    const connection = await this.components.connectionManager.openConnection(peerId)
    for (const multicodec of this.multicodecs) {
      for (const topology of this.components.registrar.getTopologies(multicodec)) {
        topology.onConnect?.(peerId, connection)
      }
    }
  }

  /**
   * Subscribes to a topic
   */
  subscribe (topic: TopicStr): void {
    if (this.status.code !== GossipStatusCode.started) {
      throw new Error('Pubsub has not started')
    }

    if (!this.subscriptions.has(topic)) {
      this.subscriptions.add(topic)

      for (const peerId of this.peers.keys()) {
        this.sendSubscriptions(peerId, [topic], true)
      }
    }

    this.join(topic)
  }

  /**
   * Unsubscribe to a topic
   */
  unsubscribe (topic: TopicStr): void {
    if (this.status.code !== GossipStatusCode.started) {
      throw new Error('Pubsub is not started')
    }

    const wasSubscribed = this.subscriptions.delete(topic)

    this.log('unsubscribe from %s - am subscribed %s', topic, wasSubscribed)

    if (wasSubscribed) {
      for (const peerId of this.peers.keys()) {
        this.sendSubscriptions(peerId, [topic], false)
      }
    }

    this.leave(topic)
  }

  /**
   * Join topic
   */
  private join (topic: TopicStr): void {
    if (this.status.code !== GossipStatusCode.started) {
      throw new Error('Gossipsub has not started')
    }

    // if we are already in the mesh, return
    if (this.mesh.has(topic)) {
      return
    }

    this.log('JOIN %s', topic)
    this.metrics?.onJoin(topic)

    const toAdd = new Set<PeerIdStr>()
    const backoff = this.backoff.get(topic)

    // check if we have mesh_n peers in fanout[topic] and add them to the mesh if we do,
    // removing the fanout entry.
    const fanoutPeers = this.fanout.get(topic)
    if (fanoutPeers != null) {
      // Remove fanout entry and the last published time
      this.fanout.delete(topic)
      this.fanoutLastpub.delete(topic)

      // remove explicit peers, peers with negative scores, and backoffed peers
      fanoutPeers.forEach((id) => {
        if (!this.direct.has(id) && this.score.score(id) >= 0 && backoff?.has(id) !== true) {
          toAdd.add(id)
        }
      })

      this.metrics?.onAddToMesh(topic, InclusionReason.Fanout, toAdd.size)
    }

    // check if we need to get more peers, which we randomly select
    if (toAdd.size < this.opts.D) {
      const fanoutCount = toAdd.size
      const newPeers = this.getRandomGossipPeers(
        topic,
        this.opts.D,
        (id: PeerIdStr): boolean =>
          // filter direct peers and peers with negative score
          !toAdd.has(id) && !this.direct.has(id) && this.score.score(id) >= 0 && backoff?.has(id) !== true
      )

      newPeers.forEach((peer) => {
        toAdd.add(peer)
      })

      this.metrics?.onAddToMesh(topic, InclusionReason.Random, toAdd.size - fanoutCount)
    }

    this.mesh.set(topic, toAdd)

    toAdd.forEach((id) => {
      this.log('JOIN: Add mesh link to %s in %s', id, topic)
      this.sendGraft(id, topic)

      // rust-libp2p
      // - peer_score.graft()
      // - Self::control_pool_add()
      // - peer_added_to_mesh()
    })
  }

  /**
   * Leave topic
   */
  private leave (topic: TopicStr): void {
    if (this.status.code !== GossipStatusCode.started) {
      throw new Error('Gossipsub has not started')
    }

    this.log('LEAVE %s', topic)
    this.metrics?.onLeave(topic)

    // Send PRUNE to mesh peers
    const meshPeers = this.mesh.get(topic)
    if (meshPeers != null) {
      Promise.all(
        Array.from(meshPeers).map(async (id) => {
          this.log('LEAVE: Remove mesh link to %s in %s', id, topic)
          await this.sendPrune(id, topic)
        })
      ).catch((err) => {
        this.log('Error sending prunes to mesh peers', err)
      })
      this.mesh.delete(topic)
    }
  }

  private selectPeersToForward (topic: TopicStr, propagationSource?: PeerIdStr, excludePeers?: Set<PeerIdStr>): Set<string> {
    const tosend = new Set<PeerIdStr>()

    // Add explicit peers
    const peersInTopic = this.topics.get(topic)
    if (peersInTopic != null) {
      this.direct.forEach((peer) => {
        if (peersInTopic.has(peer) && propagationSource !== peer && !(excludePeers?.has(peer) ?? false)) {
          tosend.add(peer)
        }
      })

      // As of Mar 2022, spec + golang-libp2p include this while rust-libp2p does not
      // rust-libp2p: https://github.com/libp2p/rust-libp2p/blob/6cc3b4ec52c922bfcf562a29b5805c3150e37c75/protocols/gossipsub/src/behaviour.rs#L2693
      // spec: https://github.com/libp2p/specs/blob/10712c55ab309086a52eec7d25f294df4fa96528/pubsub/gossipsub/gossipsub-v1.0.md?plain=1#L361
      this.floodsubPeers.forEach((peer) => {
        if (
          peersInTopic.has(peer) &&
          propagationSource !== peer &&
          !(excludePeers?.has(peer) ?? false) &&
          this.score.score(peer) >= this.opts.scoreThresholds.publishThreshold
        ) {
          tosend.add(peer)
        }
      })
    }

    // add mesh peers
    const meshPeers = this.mesh.get(topic)
    if ((meshPeers != null) && meshPeers.size > 0) {
      meshPeers.forEach((peer) => {
        if (propagationSource !== peer && !(excludePeers?.has(peer) ?? false)) {
          tosend.add(peer)
        }
      })
    }

    return tosend
  }

  private selectPeersToPublish (topic: TopicStr): {
    tosend: Set<PeerIdStr>
    tosendCount: ToSendGroupCount
  } {
    const tosend = new Set<PeerIdStr>()
    const tosendCount: ToSendGroupCount = {
      direct: 0,
      floodsub: 0,
      mesh: 0,
      fanout: 0
    }

    const peersInTopic = this.topics.get(topic)
    if (peersInTopic != null) {
      // flood-publish behavior
      // send to direct peers and _all_ peers meeting the publishThreshold
      if (this.opts.floodPublish) {
        peersInTopic.forEach((id) => {
          if (this.direct.has(id)) {
            tosend.add(id)
            tosendCount.direct++
          } else if (this.score.score(id) >= this.opts.scoreThresholds.publishThreshold) {
            tosend.add(id)
            tosendCount.floodsub++
          }
        })
      } else {
        // non-flood-publish behavior
        // send to direct peers, subscribed floodsub peers
        // and some mesh peers above publishThreshold

        // direct peers (if subscribed)
        this.direct.forEach((id) => {
          if (peersInTopic.has(id)) {
            tosend.add(id)
            tosendCount.direct++
          }
        })

        // floodsub peers
        // Note: if there are no floodsub peers, we save a loop through peersInTopic Map
        this.floodsubPeers.forEach((id) => {
          if (peersInTopic.has(id) && this.score.score(id) >= this.opts.scoreThresholds.publishThreshold) {
            tosend.add(id)
            tosendCount.floodsub++
          }
        })

        // Gossipsub peers handling
        const meshPeers = this.mesh.get(topic)
        if ((meshPeers != null) && meshPeers.size > 0) {
          meshPeers.forEach((peer) => {
            tosend.add(peer)
            tosendCount.mesh++
          })

          // We want to publish to at least `D` peers.
          // If there are insufficient peers in the mesh, publish to other topic peers
          if (meshPeers.size < this.opts.D) {
            // pick additional topic peers above the publishThreshold
            const topicPeers = this.getRandomGossipPeers(topic, this.opts.D - meshPeers.size, (id) => {
              return !meshPeers.has(id) && !this.direct.has(id) && !this.floodsubPeers.has(id) && this.score.score(id) >= this.opts.scoreThresholds.publishThreshold
            })

            topicPeers.forEach((peer) => {
              tosend.add(peer)
              tosendCount.mesh++
            })
          }
        // eslint-disable-next-line @typescript-eslint/brace-style
        }

        // We are not in the mesh for topic, use fanout peers
        else {
          const fanoutPeers = this.fanout.get(topic)
          if ((fanoutPeers != null) && fanoutPeers.size > 0) {
            fanoutPeers.forEach((peer) => {
              tosend.add(peer)
              tosendCount.fanout++
            })
          // eslint-disable-next-line @typescript-eslint/brace-style
          }

          // We have no fanout peers, select mesh_n of them and add them to the fanout
          else {
            // If we are not in the fanout, then pick peers in topic above the publishThreshold
            const newFanoutPeers = this.getRandomGossipPeers(topic, this.opts.D, (id) => {
              return this.score.score(id) >= this.opts.scoreThresholds.publishThreshold
            })

            // eslint-disable-next-line max-depth
            if (newFanoutPeers.size > 0) {
              this.fanout.set(topic, newFanoutPeers)

              newFanoutPeers.forEach((peer) => {
                tosend.add(peer)
                tosendCount.fanout++
              })
            }
          }

          // We are publishing to fanout peers - update the time we published
          this.fanoutLastpub.set(topic, Date.now())
        }
      }
    }

    return { tosend, tosendCount }
  }

  /**
   * Forwards a message from our peers.
   *
   * For messages published by us (the app layer), this class uses `publish`
   */
  private forwardMessage (
    msgIdStr: string,
    rawMsg: RPC.Message,
    propagationSource?: PeerIdStr,
    excludePeers?: Set<PeerIdStr>
  ): void {
    // message is fully validated inform peer_score
    if (propagationSource != null) {
      this.score.deliverMessage(propagationSource, msgIdStr, rawMsg.topic)
    }

    const tosend = this.selectPeersToForward(rawMsg.topic, propagationSource, excludePeers)

    // Note: Don't throw if tosend is empty, we can have a mesh with a single peer

    // forward the message to peers
    tosend.forEach((id) => {
      // sendRpc may mutate RPC message on piggyback, create a new message for each peer
      this.sendRpc(id, createGossipRpc([rawMsg]))
    })

    this.metrics?.onForwardMsg(rawMsg.topic, tosend.size)
  }

  /**
   * App layer publishes a message to peers, return number of peers this message is published to
   * Note: `async` due to crypto only if `StrictSign`, otherwise it's a sync fn.
   *
   * For messages not from us, this class uses `forwardMessage`.
   */
  async publish (topic: TopicStr, data: Uint8Array, opts?: PublishOpts): Promise<PublishResult> {
    const startMs = Date.now()
    const transformedData = (this.dataTransform != null) ? this.dataTransform.outboundTransform(topic, data) : data

    if (this.publishConfig == null) {
      throw Error('PublishError.Uninitialized')
    }

    // Prepare raw message with user's publishConfig
    const { raw: rawMsg, msg } = await buildRawMessage(this.publishConfig, topic, data, transformedData)

    // calculate the message id from the un-transformed data
    const msgId = await this.msgIdFn(msg)
    const msgIdStr = this.msgIdToStrFn(msgId)

    // Current publish opt takes precedence global opts, while preserving false value
    const ignoreDuplicatePublishError = opts?.ignoreDuplicatePublishError ?? this.opts.ignoreDuplicatePublishError

    if (this.seenCache.has(msgIdStr)) {
      // This message has already been seen. We don't re-publish messages that have already
      // been published on the network.
      if (ignoreDuplicatePublishError) {
        this.metrics?.onPublishDuplicateMsg(topic)
        return { recipients: [] }
      }
      throw Error('PublishError.Duplicate')
    }

    const { tosend, tosendCount } = this.selectPeersToPublish(topic)
    const willSendToSelf = this.opts.emitSelf && this.subscriptions.has(topic)

    // Current publish opt takes precedence global opts, while preserving false value
    const allowPublishToZeroTopicPeers = opts?.allowPublishToZeroTopicPeers ?? this.opts.allowPublishToZeroTopicPeers

    if (tosend.size === 0 && !allowPublishToZeroTopicPeers && !willSendToSelf) {
      throw Error('PublishError.NoPeersSubscribedToTopic')
    }

    // If the message isn't a duplicate and we have sent it to some peers add it to the
    // duplicate cache and memcache.
    this.seenCache.put(msgIdStr)
    // all published messages are valid
    this.mcache.put({ msgId, msgIdStr }, rawMsg, true)

    // If the message is anonymous or has a random author add it to the published message ids cache.
    this.publishedMessageIds.put(msgIdStr)

    const batchPublish = opts?.batchPublish ?? this.opts.batchPublish
    const rpc = createGossipRpc([rawMsg])
    if (batchPublish) {
      this.sendRpcInBatch(tosend, rpc)
    } else {
      // Send to set of peers aggregated from direct, mesh, fanout
      for (const id of tosend) {
        // sendRpc may mutate RPC message on piggyback, create a new message for each peer
        const sent = this.sendRpc(id, rpc)

        // did not actually send the message
        if (!sent) {
          tosend.delete(id)
        }
      }
    }

    const durationMs = Date.now() - startMs
    this.metrics?.onPublishMsg(
      topic,
      tosendCount,
      tosend.size,
      rawMsg.data != null ? rawMsg.data.length : 0,
      durationMs
    )

    // Dispatch the message to the user if we are subscribed to the topic
    if (willSendToSelf) {
      tosend.add(this.components.peerId.toString())

      super.dispatchEvent(
        new CustomEvent<GossipsubMessage>('gossipsub:message', {
          detail: {
            propagationSource: this.components.peerId,
            msgId: msgIdStr,
            msg
          }
        })
      )
      // TODO: Add option to switch between emit per topic or all messages in one
      super.dispatchEvent(new CustomEvent<Message>('message', { detail: msg }))
    }

    return {
      recipients: Array.from(tosend.values()).map((str) => this.peers.get(str) ?? peerIdFromString(str))
    }
  }

  /**
   * Send the same data in batch to tosend list without considering cached control messages
   * This is not only faster but also avoid allocating memory for each peer
   * see https://github.com/ChainSafe/js-libp2p-gossipsub/issues/344
   */
  private sendRpcInBatch (tosend: Set<PeerIdStr>, rpc: RPC): void {
    const rpcBytes = RPC.encode(rpc)
    const prefixedData = encode.single(rpcBytes)
    for (const id of tosend) {
      const outboundStream = this.streamsOutbound.get(id)
      if (outboundStream == null) {
        this.log(`Cannot send RPC to ${id} as there is no open stream to it available`)
        tosend.delete(id)
        continue
      }
      try {
        outboundStream.pushPrefixed(prefixedData)
      } catch (e) {
        tosend.delete(id)
        this.log.error(`Cannot send rpc to ${id}`, e)
      }

      this.metrics?.onRpcSent(rpc, rpcBytes.length)
    }
  }

  /**
   * This function should be called when `asyncValidation` is `true` after
   * the message got validated by the caller. Messages are stored in the `mcache` and
   * validation is expected to be fast enough that the messages should still exist in the cache.
   * There are three possible validation outcomes and the outcome is given in acceptance.
   *
   * If acceptance = `MessageAcceptance.Accept` the message will get propagated to the
   * network. The `propagation_source` parameter indicates who the message was received by and
   * will not be forwarded back to that peer.
   *
   * If acceptance = `MessageAcceptance.Reject` the message will be deleted from the memcache
   * and the P₄ penalty will be applied to the `propagationSource`.
   *
   * If acceptance = `MessageAcceptance.Ignore` the message will be deleted from the memcache
   * but no P₄ penalty will be applied.
   *
   * This function will return true if the message was found in the cache and false if was not
   * in the cache anymore.
   *
   * This should only be called once per message.
   */
  reportMessageValidationResult (msgId: MsgIdStr, propagationSource: PeerIdStr, acceptance: TopicValidatorResult): void {
    let cacheEntry: MessageCacheRecord | null

    if (acceptance === TopicValidatorResult.Accept) {
      cacheEntry = this.mcache.validate(msgId)

      if (cacheEntry != null) {
        const { message: rawMsg, originatingPeers } = cacheEntry
        // message is fully validated inform peer_score
        this.score.deliverMessage(propagationSource, msgId, rawMsg.topic)

        this.forwardMessage(msgId, cacheEntry.message, propagationSource, originatingPeers)
      }
      // else, Message not in cache. Ignoring forwarding
    // eslint-disable-next-line @typescript-eslint/brace-style
    }

    // Not valid
    else {
      cacheEntry = this.mcache.remove(msgId)

      if (cacheEntry != null) {
        const rejectReason = rejectReasonFromAcceptance(acceptance)
        const { message: rawMsg, originatingPeers } = cacheEntry

        // Tell peer_score about reject
        // Reject the original source, and any duplicates we've seen from other peers.
        this.score.rejectMessage(propagationSource, msgId, rawMsg.topic, rejectReason)
        for (const peer of originatingPeers) {
          this.score.rejectMessage(peer, msgId, rawMsg.topic, rejectReason)
        }
      }
      // else, Message not in cache. Ignoring forwarding
    }

    const firstSeenTimestampMs = this.score.messageFirstSeenTimestampMs(msgId)
    this.metrics?.onReportValidation(cacheEntry, acceptance, firstSeenTimestampMs)
  }

  /**
   * Sends a GRAFT message to a peer
   */
  private sendGraft (id: PeerIdStr, topic: string): void {
    const graft = [
      {
        topicID: topic
      }
    ]
    const out = createGossipRpc([], { graft })
    this.sendRpc(id, out)
  }

  /**
   * Sends a PRUNE message to a peer
   */
  private async sendPrune (id: PeerIdStr, topic: string): Promise<void> {
    // this is only called from leave() function
    const onUnsubscribe = true
    const prune = [await this.makePrune(id, topic, this.opts.doPX, onUnsubscribe)]
    const out = createGossipRpc([], { prune })
    this.sendRpc(id, out)
  }

  private sendIDontWants (msgId: Uint8Array, topic: string, source: PeerIdStr): void {
    const ids = this.mesh.get(topic)
    if (ids == null) {
      return
    }

    // don't send IDONTWANT to:
    // - the source
    // - peers that don't support v1.2
    const tosend = new Set(ids)
    tosend.delete(source)
    for (const id of tosend) {
      if (this.streamsOutbound.get(id)?.protocol !== constants.GossipsubIDv12) {
        tosend.delete(id)
      }
    }

    const idontwantRpc = createGossipRpc([], { idontwant: [{ messageIDs: [msgId] }] })
    this.sendRpcInBatch(tosend, idontwantRpc)
  }

  /**
   * Send an rpc object to a peer
   */
  private sendRpc (id: PeerIdStr, rpc: RPC): boolean {
    const outboundStream = this.streamsOutbound.get(id)
    if (outboundStream == null) {
      this.log(`Cannot send RPC to ${id} as there is no open stream to it available`)
      return false
    }

    // piggyback control message retries
    const ctrl = this.control.get(id)
    if (ctrl != null) {
      this.piggybackControl(id, rpc, ctrl)
      this.control.delete(id)
    }

    // piggyback gossip
    const ihave = this.gossip.get(id)
    if (ihave != null) {
      this.piggybackGossip(id, rpc, ihave)
      this.gossip.delete(id)
    }

    const rpcBytes = RPC.encode(rpc)
    try {
      outboundStream.push(rpcBytes)
    } catch (e) {
      this.log.error(`Cannot send rpc to ${id}`, e)

      // if the peer had control messages or gossip, re-attach
      if (ctrl != null) {
        this.control.set(id, ctrl)
      }
      if (ihave != null) {
        this.gossip.set(id, ihave)
      }

      return false
    }

    this.metrics?.onRpcSent(rpc, rpcBytes.length)

    if (rpc.control?.graft != null) {
      for (const topic of rpc.control?.graft) {
        if (topic.topicID != null) {
          this.safeDispatchEvent<MeshPeer>('gossipsub:graft', { detail: { peerId: id, topic: topic.topicID, direction: 'outbound' } })
        }
      }
    }
    if (rpc.control?.prune != null) {
      for (const topic of rpc.control?.prune) {
        if (topic.topicID != null) {
          this.safeDispatchEvent<MeshPeer>('gossipsub:prune', { detail: { peerId: id, topic: topic.topicID, direction: 'outbound' } })
        }
      }
    }

    return true
  }

  /** Mutates `outRpc` adding graft and prune control messages */
  public piggybackControl (id: PeerIdStr, outRpc: RPC, ctrl: RPC.ControlMessage): void {
    const rpc = ensureControl(outRpc)
    for (const graft of ctrl.graft) {
      if (graft.topicID != null && (this.mesh.get(graft.topicID)?.has(id) ?? false)) {
        rpc.control.graft.push(graft)
      }
    }

    for (const prune of ctrl.prune) {
      if (prune.topicID != null && !(this.mesh.get(prune.topicID)?.has(id) ?? false)) {
        rpc.control.prune.push(prune)
      }
    }
  }

  /** Mutates `outRpc` adding ihave control messages */
  private piggybackGossip (id: PeerIdStr, outRpc: RPC, ihave: RPC.ControlIHave[]): void {
    const rpc = ensureControl(outRpc)
    rpc.control.ihave = ihave
  }

  /**
   * Send graft and prune messages
   *
   * @param tograft - peer id => topic[]
   * @param toprune - peer id => topic[]
   */
  private async sendGraftPrune (
    tograft: Map<string, string[]>,
    toprune: Map<string, string[]>,
    noPX: Map<string, boolean>
  ): Promise<void> {
    const doPX = this.opts.doPX
    const onUnsubscribe = false
    for (const [id, topics] of tograft) {
      const graft = topics.map((topicID) => ({ topicID }))
      let prune: RPC.ControlPrune[] = []
      // If a peer also has prunes, process them now
      const pruning = toprune.get(id)
      if (pruning != null) {
        prune = await Promise.all(
          pruning.map(
            async (topicID) => this.makePrune(id, topicID, doPX && !(noPX.get(id) ?? false), onUnsubscribe)
          )
        )
        toprune.delete(id)
      }

      this.sendRpc(id, createGossipRpc([], { graft, prune }))
    }
    for (const [id, topics] of toprune) {
      const prune = await Promise.all(
        topics.map(
          async (topicID) => this.makePrune(id, topicID, doPX && !(noPX.get(id) ?? false), onUnsubscribe)
        )
      )
      this.sendRpc(id, createGossipRpc([], { prune }))
    }
  }

  /**
   * Emits gossip - Send IHAVE messages to a random set of gossip peers
   */
  private emitGossip (peersToGossipByTopic: Map<string, Set<PeerIdStr>>): void {
    const gossipIDsByTopic = this.mcache.getGossipIDs(new Set(peersToGossipByTopic.keys()))
    for (const [topic, peersToGossip] of peersToGossipByTopic) {
      this.doEmitGossip(topic, peersToGossip, gossipIDsByTopic.get(topic) ?? [])
    }
  }

  /**
   * Send gossip messages to GossipFactor peers above threshold with a minimum of D_lazy
   * Peers are randomly selected from the heartbeat which exclude mesh + fanout peers
   * We also exclude direct peers, as there is no reason to emit gossip to them
   *
   * @param topic
   * @param candidateToGossip - peers to gossip
   * @param messageIDs - message ids to gossip
   */
  private doEmitGossip (topic: string, candidateToGossip: Set<PeerIdStr>, messageIDs: Uint8Array[]): void {
    if (messageIDs.length === 0) {
      return
    }

    // shuffle to emit in random order
    shuffle(messageIDs)

    // if we are emitting more than GossipsubMaxIHaveLength ids, truncate the list
    if (messageIDs.length > constants.GossipsubMaxIHaveLength) {
      // we do the truncation (with shuffling) per peer below
      this.log('too many messages for gossip; will truncate IHAVE list (%d messages)', messageIDs.length)
    }

    if (candidateToGossip.size === 0) return
    let target = this.opts.Dlazy
    const gossipFactor = this.opts.gossipFactor
    const factor = gossipFactor * candidateToGossip.size
    let peersToGossip: Set<PeerIdStr> | PeerIdStr[] = candidateToGossip
    if (factor > target) {
      target = factor
    }
    if (target > peersToGossip.size) {
      target = peersToGossip.size
    } else {
      // only shuffle if needed
      peersToGossip = shuffle(Array.from(peersToGossip)).slice(0, target)
    }

    // Emit the IHAVE gossip to the selected peers up to the target
    peersToGossip.forEach((id) => {
      let peerMessageIDs = messageIDs
      if (messageIDs.length > constants.GossipsubMaxIHaveLength) {
        // shuffle and slice message IDs per peer so that we emit a different set for each peer
        // we have enough reduncancy in the system that this will significantly increase the message
        // coverage when we do truncate
        peerMessageIDs = shuffle(peerMessageIDs.slice()).slice(0, constants.GossipsubMaxIHaveLength)
      }
      this.pushGossip(id, {
        topicID: topic,
        messageIDs: peerMessageIDs
      })
    })
  }

  /**
   * Flush gossip and control messages
   */
  private flush (): void {
    // send gossip first, which will also piggyback control
    for (const [peer, ihave] of this.gossip.entries()) {
      this.gossip.delete(peer)
      this.sendRpc(peer, createGossipRpc([], { ihave }))
    }
    // send the remaining control messages
    for (const [peer, control] of this.control.entries()) {
      this.control.delete(peer)
      const out = createGossipRpc([], { graft: control.graft, prune: control.prune })
      this.sendRpc(peer, out)
    }
  }

  /**
   * Adds new IHAVE messages to pending gossip
   */
  private pushGossip (id: PeerIdStr, controlIHaveMsgs: RPC.ControlIHave): void {
    this.log('Add gossip to %s', id)
    const gossip = this.gossip.get(id) ?? []
    this.gossip.set(id, gossip.concat(controlIHaveMsgs))
  }

  /**
   * Make a PRUNE control message for a peer in a topic
   */
  private async makePrune (
    id: PeerIdStr,
    topic: string,
    doPX: boolean,
    onUnsubscribe: boolean
  ): Promise<RPC.ControlPrune> {
    this.score.prune(id, topic)
    if (this.streamsOutbound.get(id)?.protocol === constants.GossipsubIDv10) {
      // Gossipsub v1.0 -- no backoff, the peer won't be able to parse it anyway
      return {
        topicID: topic,
        peers: []
      }
    }
    // backoff is measured in seconds
    // GossipsubPruneBackoff and GossipsubUnsubscribeBackoff are measured in milliseconds
    // The protobuf has it as a uint64
    const backoffMs = onUnsubscribe ? this.opts.unsubcribeBackoff : this.opts.pruneBackoff
    const backoff = backoffMs / 1000
    this.doAddBackoff(id, topic, backoffMs)

    if (!doPX) {
      return {
        topicID: topic,
        peers: [],
        backoff
      }
    }

    // select peers for Peer eXchange
    const peers = this.getRandomGossipPeers(topic, this.opts.prunePeers, (xid) => {
      return xid !== id && this.score.score(xid) >= 0
    })
    const px = await Promise.all(
      Array.from(peers).map(async (peerId) => {
        // see if we have a signed record to send back; if we don't, just send
        // the peer ID and let the pruned peer find them in the DHT -- we can't trust
        // unsigned address records through PX anyways
        // Finding signed records in the DHT is not supported at the time of writing in js-libp2p
        const id = this.peers.get(peerId) ?? peerIdFromString(peerId)
        let peerInfo: Peer | undefined

        try {
          peerInfo = await this.components.peerStore.get(id)
        } catch (err: any) {
          if (err.name !== 'NotFoundError') {
            throw err
          }
        }

        return {
          peerID: id.toMultihash().bytes,
          signedPeerRecord: peerInfo?.peerRecordEnvelope
        }
      })
    )
    return {
      topicID: topic,
      peers: px,
      backoff
    }
  }

  private readonly runHeartbeat = (): void => {
    const timer = this.metrics?.heartbeatDuration.startTimer()

    this.heartbeat()
      .catch((err) => {
        this.log('Error running heartbeat', err)
      })
      .finally(() => {
        if (timer != null) {
          timer()
        }

        // Schedule the next run if still in started status
        if (this.status.code === GossipStatusCode.started) {
          // Clear previous timeout before overwriting `status.heartbeatTimeout`, it should be completed tho.
          clearTimeout(this.status.heartbeatTimeout)

          // NodeJS setInterval function is innexact, calls drift by a few miliseconds on each call.
          // To run the heartbeat precisely setTimeout() must be used recomputing the delay on every loop.
          let msToNextHeartbeat =
            this.opts.heartbeatInterval - ((Date.now() - this.status.hearbeatStartMs) % this.opts.heartbeatInterval)

          // If too close to next heartbeat, skip one
          if (msToNextHeartbeat < this.opts.heartbeatInterval * 0.25) {
            msToNextHeartbeat += this.opts.heartbeatInterval
            this.metrics?.heartbeatSkipped.inc()
          }

          this.status.heartbeatTimeout = setTimeout(this.runHeartbeat, msToNextHeartbeat)
        }
      })
  }

  /**
   * Maintains the mesh and fanout maps in gossipsub.
   */
  public async heartbeat (): Promise<void> {
    const { D, Dlo, Dhi, Dscore, Dout, fanoutTTL } = this.opts

    this.heartbeatTicks++

    // cache scores throught the heartbeat
    const scores = new Map<string, number>()
    const getScore = (id: string): number => {
      let s = scores.get(id)
      if (s === undefined) {
        s = this.score.score(id)
        scores.set(id, s)
      }
      return s
    }

    // peer id => topic[]
    const tograft = new Map<string, string[]>()
    // peer id => topic[]
    const toprune = new Map<string, string[]>()
    // peer id => don't px
    const noPX = new Map<string, boolean>()

    // clean up expired backoffs
    this.clearBackoff()

    // clean up peerhave/iasked counters
    this.peerhave.clear()
    this.metrics?.cacheSize.set({ cache: 'iasked' }, this.iasked.size)
    this.iasked.clear()

    // apply IWANT request penalties
    this.applyIwantPenalties()

    // clean up IDONTWANT counters
    this.idontwantCounts.clear()

    // clean up old tracked IDONTWANTs
    for (const idontwants of this.idontwants.values()) {
      for (const [msgId, heartbeatTick] of idontwants) {
        if (this.heartbeatTicks - heartbeatTick >= this.opts.mcacheLength) {
          idontwants.delete(msgId)
        }
      }
    }

    // ensure direct peers are connected
    if (this.heartbeatTicks % this.opts.directConnectTicks === 0) {
      // we only do this every few ticks to allow pending connections to complete and account for restarts/downtime
      await this.directConnect()
    }

    // EXTRA: Prune caches
    this.fastMsgIdCache?.prune()
    this.seenCache.prune()
    this.gossipTracer.prune()
    this.publishedMessageIds.prune()

    /**
     * Instead of calling getRandomGossipPeers multiple times to:
     * + get more mesh peers
     * + more outbound peers
     * + oppportunistic grafting
     * + emitGossip
     *
     * We want to loop through the topic peers only a single time and prepare gossip peers for all topics to improve the performance
     */

    const peersToGossipByTopic = new Map<string, Set<PeerIdStr>>()
    // maintain the mesh for topics we have joined
    // eslint-disable-next-line complexity
    this.mesh.forEach((peers, topic) => {
      const peersInTopic = this.topics.get(topic)
      const candidateMeshPeers = new Set<PeerIdStr>()
      const peersToGossip = new Set<PeerIdStr>()
      peersToGossipByTopic.set(topic, peersToGossip)

      if (peersInTopic != null) {
        const shuffledPeers = shuffle(Array.from(peersInTopic))
        const backoff = this.backoff.get(topic)
        for (const id of shuffledPeers) {
          const peerStreams = this.streamsOutbound.get(id)
          if (
            (peerStreams != null) &&
            this.multicodecs.includes(peerStreams.protocol) &&
            !peers.has(id) &&
            !this.direct.has(id)
          ) {
            const score = getScore(id)
            if (backoff?.has(id) !== true && score >= 0) candidateMeshPeers.add(id)
            // instead of having to find gossip peers after heartbeat which require another loop
            // we prepare peers to gossip in a topic within heartbeat to improve performance
            if (score >= this.opts.scoreThresholds.gossipThreshold) peersToGossip.add(id)
          }
        }
      }

      // prune/graft helper functions (defined per topic)
      const prunePeer = (id: PeerIdStr, reason: ChurnReason): void => {
        this.log('HEARTBEAT: Remove mesh link to %s in %s', id, topic)
        // no need to update peer score here as we do it in makePrune
        // add prune backoff record
        this.addBackoff(id, topic)
        // remove peer from mesh
        peers.delete(id)
        // after pruning a peer from mesh, we want to gossip topic to it if its score meet the gossip threshold
        if (getScore(id) >= this.opts.scoreThresholds.gossipThreshold) peersToGossip.add(id)
        this.metrics?.onRemoveFromMesh(topic, reason, 1)
        // add to toprune
        const topics = toprune.get(id)
        if (topics == null) {
          toprune.set(id, [topic])
        } else {
          topics.push(topic)
        }
      }

      const graftPeer = (id: PeerIdStr, reason: InclusionReason): void => {
        this.log('HEARTBEAT: Add mesh link to %s in %s', id, topic)
        // update peer score
        this.score.graft(id, topic)
        // add peer to mesh
        peers.add(id)
        // when we add a new mesh peer, we don't want to gossip messages to it
        peersToGossip.delete(id)
        this.metrics?.onAddToMesh(topic, reason, 1)
        // add to tograft
        const topics = tograft.get(id)
        if (topics == null) {
          tograft.set(id, [topic])
        } else {
          topics.push(topic)
        }
      }

      // drop all peers with negative score, without PX
      peers.forEach((id) => {
        const score = getScore(id)

        // Record the score

        if (score < 0) {
          this.log('HEARTBEAT: Prune peer %s with negative score: score=%d, topic=%s', id, score, topic)
          prunePeer(id, ChurnReason.BadScore)
          noPX.set(id, true)
        }
      })

      // do we have enough peers?
      if (peers.size < Dlo) {
        const ineed = D - peers.size
        // slice up to first `ineed` items and remove them from candidateMeshPeers
        // same to `const newMeshPeers = candidateMeshPeers.slice(0, ineed)`
        const newMeshPeers = removeFirstNItemsFromSet(candidateMeshPeers, ineed)

        newMeshPeers.forEach((p) => {
          graftPeer(p, InclusionReason.NotEnough)
        })
      }

      // do we have to many peers?
      if (peers.size > Dhi) {
        let peersArray = Array.from(peers)
        // sort by score
        peersArray.sort((a, b) => getScore(b) - getScore(a))
        // We keep the first D_score peers by score and the remaining up to D randomly
        // under the constraint that we keep D_out peers in the mesh (if we have that many)
        peersArray = peersArray.slice(0, Dscore).concat(shuffle(peersArray.slice(Dscore)))

        // count the outbound peers we are keeping
        let outbound = 0
        peersArray.slice(0, D).forEach((p) => {
          if (this.outbound.get(p) ?? false) {
            outbound++
          }
        })

        // if it's less than D_out, bubble up some outbound peers from the random selection
        if (outbound < Dout) {
          const rotate = (i: number): void => {
            // rotate the peersArray to the right and put the ith peer in the front
            const p = peersArray[i]
            for (let j = i; j > 0; j--) {
              peersArray[j] = peersArray[j - 1]
            }
            peersArray[0] = p
          }

          // first bubble up all outbound peers already in the selection to the front
          if (outbound > 0) {
            let ihave = outbound
            for (let i = 1; i < D && ihave > 0; i++) {
              // eslint-disable-next-line max-depth
              if (this.outbound.get(peersArray[i]) ?? false) {
                rotate(i)
                ihave--
              }
            }
          }

          // now bubble up enough outbound peers outside the selection to the front
          let ineed = D - outbound
          for (let i = D; i < peersArray.length && ineed > 0; i++) {
            if (this.outbound.get(peersArray[i]) ?? false) {
              rotate(i)
              ineed--
            }
          }
        }

        // prune the excess peers
        peersArray.slice(D).forEach((p) => {
          prunePeer(p, ChurnReason.Excess)
        })
      }

      // do we have enough outbound peers?
      if (peers.size >= Dlo) {
        // count the outbound peers we have
        let outbound = 0
        peers.forEach((p) => {
          if (this.outbound.get(p) ?? false) {
            outbound++
          }
        })

        // if it's less than D_out, select some peers with outbound connections and graft them
        if (outbound < Dout) {
          const ineed = Dout - outbound
          const newMeshPeers = removeItemsFromSet(candidateMeshPeers, ineed, (id) => this.outbound.get(id) === true)

          newMeshPeers.forEach((p) => {
            graftPeer(p, InclusionReason.Outbound)
          })
        }
      }

      // should we try to improve the mesh with opportunistic grafting?
      if (this.heartbeatTicks % this.opts.opportunisticGraftTicks === 0 && peers.size > 1) {
        // Opportunistic grafting works as follows: we check the median score of peers in the
        // mesh; if this score is below the opportunisticGraftThreshold, we select a few peers at
        // random with score over the median.
        // The intention is to (slowly) improve an underperforming mesh by introducing good
        // scoring peers that may have been gossiping at us. This allows us to get out of sticky
        // situations where we are stuck with poor peers and also recover from churn of good peers.

        // now compute the median peer score in the mesh
        const peersList = Array.from(peers).sort((a, b) => getScore(a) - getScore(b))
        const medianIndex = Math.floor(peers.size / 2)
        const medianScore = getScore(peersList[medianIndex])

        // if the median score is below the threshold, select a better peer (if any) and GRAFT
        if (medianScore < this.opts.scoreThresholds.opportunisticGraftThreshold) {
          const ineed = this.opts.opportunisticGraftPeers
          const newMeshPeers = removeItemsFromSet(candidateMeshPeers, ineed, (id) => getScore(id) > medianScore)
          for (const id of newMeshPeers) {
            this.log('HEARTBEAT: Opportunistically graft peer %s on topic %s', id, topic)
            graftPeer(id, InclusionReason.Opportunistic)
          }
        }
      }
    })

    // expire fanout for topics we haven't published to in a while
    const now = Date.now()
    this.fanoutLastpub.forEach((lastpb, topic) => {
      if (lastpb + fanoutTTL < now) {
        this.fanout.delete(topic)
        this.fanoutLastpub.delete(topic)
      }
    })

    // maintain our fanout for topics we are publishing but we have not joined
    this.fanout.forEach((fanoutPeers, topic) => {
      // checks whether our peers are still in the topic and have a score above the publish threshold
      const topicPeers = this.topics.get(topic)
      fanoutPeers.forEach((id) => {
        if (!(topicPeers?.has(id) ?? false) || getScore(id) < this.opts.scoreThresholds.publishThreshold) {
          fanoutPeers.delete(id)
        }
      })

      const peersInTopic = this.topics.get(topic)
      const candidateFanoutPeers = []
      // the fanout map contains topics to which we are not subscribed.
      const peersToGossip = new Set<PeerIdStr>()
      peersToGossipByTopic.set(topic, peersToGossip)

      if (peersInTopic != null) {
        const shuffledPeers = shuffle(Array.from(peersInTopic))
        for (const id of shuffledPeers) {
          const peerStreams = this.streamsOutbound.get(id)
          if (
            (peerStreams != null) &&
            this.multicodecs.includes(peerStreams.protocol) &&
            !fanoutPeers.has(id) &&
            !this.direct.has(id)
          ) {
            const score = getScore(id)
            if (score >= this.opts.scoreThresholds.publishThreshold) candidateFanoutPeers.push(id)
            // instead of having to find gossip peers after heartbeat which require another loop
            // we prepare peers to gossip in a topic within heartbeat to improve performance
            if (score >= this.opts.scoreThresholds.gossipThreshold) peersToGossip.add(id)
          }
        }
      }

      // do we need more peers?
      if (fanoutPeers.size < D) {
        const ineed = D - fanoutPeers.size
        candidateFanoutPeers.slice(0, ineed).forEach((id) => {
          fanoutPeers.add(id)
          peersToGossip?.delete(id)
        })
      }
    })

    this.emitGossip(peersToGossipByTopic)

    // send coalesced GRAFT/PRUNE messages (will piggyback gossip)
    await this.sendGraftPrune(tograft, toprune, noPX)

    // flush pending gossip that wasn't piggybacked above
    this.flush()

    // advance the message history window
    this.mcache.shift()

    this.dispatchEvent(new CustomEvent('gossipsub:heartbeat'))
  }

  /**
   * Given a topic, returns up to count peers subscribed to that topic
   * that pass an optional filter function
   *
   * @param topic
   * @param count
   * @param filter - a function to filter acceptable peers
   */
  private getRandomGossipPeers (
    topic: string,
    count: number,
    filter: (id: string) => boolean = () => true
  ): Set<string> {
    const peersInTopic = this.topics.get(topic)

    if (peersInTopic == null) {
      return new Set()
    }

    // Adds all peers using our protocol
    // that also pass the filter function
    let peers: string[] = []
    peersInTopic.forEach((id) => {
      const peerStreams = this.streamsOutbound.get(id)
      if (peerStreams == null) {
        return
      }
      if (this.multicodecs.includes(peerStreams.protocol) && filter(id)) {
        peers.push(id)
      }
    })

    // Pseudo-randomly shuffles peers
    peers = shuffle(peers)
    if (count > 0 && peers.length > count) {
      peers = peers.slice(0, count)
    }

    return new Set(peers)
  }

  private onScrapeMetrics (metrics: Metrics): void {
    /* Data structure sizes */
    metrics.mcacheSize.set(this.mcache.size)
    metrics.mcacheNotValidatedCount.set(this.mcache.notValidatedCount)
    // Arbitrary size
    metrics.cacheSize.set({ cache: 'direct' }, this.direct.size)
    metrics.cacheSize.set({ cache: 'seenCache' }, this.seenCache.size)
    metrics.cacheSize.set({ cache: 'fastMsgIdCache' }, this.fastMsgIdCache?.size ?? 0)
    metrics.cacheSize.set({ cache: 'publishedMessageIds' }, this.publishedMessageIds.size)
    metrics.cacheSize.set({ cache: 'mcache' }, this.mcache.size)
    metrics.cacheSize.set({ cache: 'score' }, this.score.size)
    metrics.cacheSize.set({ cache: 'gossipTracer.promises' }, this.gossipTracer.size)
    metrics.cacheSize.set({ cache: 'gossipTracer.requests' }, this.gossipTracer.requestMsByMsgSize)
    // Bounded by topic
    metrics.cacheSize.set({ cache: 'topics' }, this.topics.size)
    metrics.cacheSize.set({ cache: 'subscriptions' }, this.subscriptions.size)
    metrics.cacheSize.set({ cache: 'mesh' }, this.mesh.size)
    metrics.cacheSize.set({ cache: 'fanout' }, this.fanout.size)
    // Bounded by peer
    metrics.cacheSize.set({ cache: 'peers' }, this.peers.size)
    metrics.cacheSize.set({ cache: 'streamsOutbound' }, this.streamsOutbound.size)
    metrics.cacheSize.set({ cache: 'streamsInbound' }, this.streamsInbound.size)
    metrics.cacheSize.set({ cache: 'acceptFromWhitelist' }, this.acceptFromWhitelist.size)
    metrics.cacheSize.set({ cache: 'gossip' }, this.gossip.size)
    metrics.cacheSize.set({ cache: 'control' }, this.control.size)
    metrics.cacheSize.set({ cache: 'peerhave' }, this.peerhave.size)
    metrics.cacheSize.set({ cache: 'outbound' }, this.outbound.size)

    // 2D nested data structure
    let backoffSize = 0
    const now = Date.now()
    metrics.connectedPeersBackoffSec.reset()
    for (const backoff of this.backoff.values()) {
      backoffSize += backoff.size
      for (const [peer, expiredMs] of backoff.entries()) {
        if (this.peers.has(peer)) {
          metrics.connectedPeersBackoffSec.observe(Math.max(0, expiredMs - now) / 1000)
        }
      }
    }
    metrics.cacheSize.set({ cache: 'backoff' }, backoffSize)

    let idontwantsCount = 0
    for (const idontwant of this.idontwants.values()) {
      idontwantsCount += idontwant.size
    }
    metrics.cacheSize.set({ cache: 'idontwants' }, idontwantsCount)

    // Peer counts

    for (const [topicStr, peers] of this.topics) {
      metrics.topicPeersCount.set({ topicStr }, peers.size)
    }

    for (const [topicStr, peers] of this.mesh) {
      metrics.meshPeerCounts.set({ topicStr }, peers.size)
    }

    // Peer scores

    const scores: number[] = []
    const scoreByPeer = new Map<PeerIdStr, number>()
    metrics.behaviourPenalty.reset()

    for (const peerIdStr of this.peers.keys()) {
      const score = this.score.score(peerIdStr)
      scores.push(score)
      scoreByPeer.set(peerIdStr, score)
      metrics.behaviourPenalty.observe(this.score.peerStats.get(peerIdStr)?.behaviourPenalty ?? 0)
    }

    metrics.registerScores(scores, this.opts.scoreThresholds)

    // Breakdown score per mesh topicLabel

    metrics.registerScorePerMesh(this.mesh, scoreByPeer)

    // Breakdown on each score weight

    const sw = computeAllPeersScoreWeights(
      this.peers.keys(),
      this.score.peerStats,
      this.score.params,
      this.score.peerIPs,
      metrics.topicStrToLabel
    )

    metrics.registerScoreWeights(sw)
  }

  private readonly tagMeshPeer = (evt: CustomEvent<MeshPeer>): void => {
    const { peerId, topic } = evt.detail
    this.components.peerStore.merge(this.peers.get(peerId) ?? peerIdFromString(peerId), {
      tags: {
        [topic]: {
          value: 100
        }
      }
    }).catch((err) => { this.log.error('Error tagging peer %s with topic %s', peerId, topic, err) })
  }

  private readonly untagMeshPeer = (evt: CustomEvent<MeshPeer>): void => {
    const { peerId, topic } = evt.detail
    this.components.peerStore.merge(this.peers.get(peerId) ?? peerIdFromString(peerId), {
      tags: {
        [topic]: undefined
      }
    }).catch((err) => { this.log.error('Error untagging peer %s with topic %s', peerId, topic, err) })
  }
}

export function gossipsub (
  init: Partial<GossipsubOpts> = {}
): (components: GossipSubComponents) => PubSub<GossipsubEvents> {
  return (components: GossipSubComponents) => new GossipSub(components, init)
}