import { HashByteOrder, OutPoint } from '@node-dlc/bitcoin';
import { ShortChannelId } from '@node-dlc/common';
import { ILogger } from '@node-dlc/logger';
import { EventEmitter } from 'events';

import { ChannelAnnouncementMessage } from '../messages/ChannelAnnouncementMessage';
import { ExtendedChannelAnnouncementMessage } from '../messages/ExtendedChannelAnnouncementMessage';
import { IWireMessage } from '../messages/IWireMessage';
import { MessageType } from '../MessageType';
import { Peer } from '../Peer';
import { PeerState } from '../PeerState';
import { WireError, WireErrorCode } from '../WireError';
import { GossipFilter } from './GossipFilter';
import { GossipPeer } from './GossipPeer';
import { GossipRelay, IGossipRelay } from './GossipRelay';
import { IGossipStore } from './GossipStore';
import { IGossipFilterChainClient } from './IGossipFilterChainClient';

export enum SyncState {
  Unsynced,
  Syncing,
  Synced,
}

// tslint:disable-next-line: interface-name
export declare interface GossipManager {
  on(event: 'message', fn: (msg: IWireMessage) => void): this;
  on(event: 'error', fn: (err: Error) => void): this;
  on(event: 'flushed', fn: () => void): this;
  off(event: 'restored', fn: (block: number) => void): this;
  off(event: 'message', fn: (msg: IWireMessage) => void): this;
  off(event: 'error', fn: (err: Error) => void): this;
  off(event: 'flushed', fn: () => void): this;
}

/**
 * GossipManager provides is a facade for many parts of gossip. It
 * orchestrates for validating, storing, and emitting
 * routing gossip traffic obtained by peers.
 */
export class GossipManager extends EventEmitter {
  public blockHeight: number;
  public started: boolean;
  public syncState: SyncState;
  public isSynchronizing: boolean;
  public gossipRelay: IGossipRelay;
  public readonly peers: Set<GossipPeer>;
  public readonly logger: ILogger;

  constructor(
    logger: ILogger,
    readonly gossipStore: IGossipStore,
    readonly pendingStore: IGossipStore,
    readonly chainClient?: IGossipFilterChainClient,
  ) {
    super();
    this.logger = logger.sub('gspmgr');
    this.peers = new Set<GossipPeer>();
    this.syncState = SyncState.Unsynced;
    this.gossipRelay = new GossipRelay(logger.sub('gsprel'), 60000, 2000);
  }

  /**
   * The number of peers managed by the PeerManager
   */
  public get peerCount(): number {
    return this.peers.size;
  }

  /**
   * Starts the gossip manager. This method will load information
   * from the gossip store, determine when the last information
   * was obtained, validate the existing messages (to see if any
   * channels have closed), and finally emit all messages that
   * exist in the system.
   */
  public async start(): Promise<void> {
    this.logger.info('starting gossip manager');

    // wait for chain sync to complete
    if (this.chainClient) {
      this.logger.info('waiting for chain sync');
      await this.chainClient.waitForSync();
      this.logger.info('chain sync complete');
    }

    await this._restoreState();

    // emit all restored messages
    for await (const msg of this.allMessages()) {
      this.emit('message', msg);
    }

    // start the gossip relay manager
    this.gossipRelay.start();

    // flag that the manager has now started
    this.started = true;
  }

  /**
   * Adds a new peer to the GossipManager and subscribes to events that will
   * allow it to iteract with other sub-systems managed by the GossipManager.
   */
  public addPeer(peer: Peer): void {
    if (!this.started)
      throw new WireError(WireErrorCode.gossipManagerNotStarted);

    peer.on('ready', () => this._onPeerReady(peer));

    if (peer.state === PeerState.Ready) {
      this._onPeerReady(peer);
    }
  }

  /**
   * Removes the channel from storage by the gossip manager. This
   * will likely be called by a chain-monitoring service.
   */
  public async removeChannel(scid: ShortChannelId): Promise<void> {
    this.logger.debug('removing channel %s', scid.toString());
    await this.gossipStore.deleteChannelAnnouncement(scid);
  }

  /**
   * Removes the channel from storage by the gossip manager. This will
   * likely be called by a chain-monitoring service.
   * @param outpoint
   */
  public async removeChannelByOutpoint(outpoint: OutPoint): Promise<void> {
    const chanAnn = await this.gossipStore.findChannelAnnouncementByOutpoint(
      outpoint,
    );
    if (!chanAnn) return;
    await this.removeChannel(chanAnn.shortChannelId);
  }

  /**
   * Retrieves the valid chan_ann, chan_update, node_ann messages
   * while making sure to not send duplicate node_ann messages.
   *
   * @remarks
   * For now we are going to buffer messages into memory. We could
   * return a stream and yield messages as they are streamed from
   * the gossip_store.
   */
  public async *allMessages(): AsyncGenerator<IWireMessage, void, unknown> {
    this.logger.debug('fetching all messages');

    // maintain a set of node ids that we have already seen so that
    // we do no rebroadcast node announcements. This set stores the
    // nodeid pubkey as a hex string, which through testing is the
    // fastest way to perfrom set operations.
    const seenNodeIds: Set<string> = new Set();

    // obtain full list of channel announcements
    const chanAnns = await this.gossipStore.findChannelAnnouncemnts();
    for (const chanAnn of chanAnns) {
      yield chanAnn;

      // load and add the node1 channel_update
      const update1 = await this.gossipStore.findChannelUpdate(
        chanAnn.shortChannelId,
        0,
      );
      if (update1) yield update1;

      // load and add the nod2 channel_update
      const update2 = await this.gossipStore.findChannelUpdate(
        chanAnn.shortChannelId,
        1,
      );
      if (update2) yield update2;

      // optionally load node1 announcement
      const nodeId1 = chanAnn.nodeId1.toString('hex');
      if (!seenNodeIds.has(nodeId1)) {
        seenNodeIds.add(nodeId1);
        const nodeAnn = await this.gossipStore.findNodeAnnouncement(
          chanAnn.nodeId1,
        );
        if (nodeAnn) yield nodeAnn;
      }

      // optionally load node2 announcement
      const nodeId2 = chanAnn.nodeId2.toString('hex');
      if (!seenNodeIds.has(nodeId2)) {
        seenNodeIds.add(nodeId2);
        const nodeAnn = await this.gossipStore.findNodeAnnouncement(
          chanAnn.nodeId2,
        );
        if (nodeAnn) yield nodeAnn;
      }
    }

    // Broadcast unattached node announcements. These may have been orphaned
    // from previously closed channels, or if the node allows node_ann messages
    // without channels.
    const nodeAnns = await this.gossipStore.findNodeAnnouncements();
    for (const nodeAnn of nodeAnns) {
      if (!seenNodeIds.has(nodeAnn.nodeId.toString('hex'))) yield nodeAnn;
    }
  }

  /**
   * Handles when a peer has been added to the manager and it is finally
   * ready and has negotiated the gossip technique.
   * @param peer
   */
  private _onPeerReady(peer: Peer) {
    // Construct a gossip filter for use by the specific GossipPeer. This
    // filter will be internally used by the GossipPeer to validate and
    // capture gossip messages
    const filter = new GossipFilter(
      this.gossipStore,
      this.pendingStore,
      this.chainClient,
    );

    // Construct the gossip Peer and add it to the collection of Peers
    // that are currently being managed by the GossipPeer
    const gossipPeer = new GossipPeer(peer, filter, this.logger);

    // Attach events from the gossipPeer
    gossipPeer.on('readable', this._onPeerReadable.bind(this, gossipPeer));
    gossipPeer.on('gossip_error', this._onGossipError.bind(this));

    // Add peer to the list of peers
    this.peers.add(gossipPeer);

    // Add event handler for a beer closing
    peer.on('close', this._onPeerClose.bind(this, gossipPeer));

    // Add the peer to the relay manager
    this.gossipRelay.addPeer(gossipPeer);

    // If we have not yet performed a full synchronization then we can
    // perform the full gossip state restore from this node
    if (this.syncState === SyncState.Unsynced) {
      // eslint-disable-next-line @typescript-eslint/no-floating-promises
      this._syncPeer(gossipPeer);
    }

    // If we've already synced, simply enable gossip receiving for the peer
    else {
      gossipPeer.enableGossip();
    }
  }

  /**
   * Handles when a peer closes
   * @param gossipPeer
   */
  private _onPeerClose(gossipPeer: GossipPeer) {
    if (this.gossipRelay) {
      this.gossipRelay.removePeer(gossipPeer);
    }
    this.peers.delete(gossipPeer);
  }

  /**
   * Handles when a peer becomes readable
   * @param peer
   */
  private _onPeerReadable(peer: GossipPeer) {
    // eslint-disable-next-line no-constant-condition
    while (true) {
      const msg = peer.read() as IWireMessage;
      if (msg) this._onGossipMessage(msg);
      else return;
    }
  }

  /**
   * Handles receieved gossip messages
   * @param msg
   */
  private _onGossipMessage(msg: IWireMessage) {
    if (msg.type === MessageType.ChannelAnnouncement) {
      this.blockHeight = Math.max(
        this.blockHeight,
        (msg as ChannelAnnouncementMessage).shortChannelId.block,
      );
    }

    // enqueue the message into the relayer
    this.gossipRelay.enqueue(msg);

    // emit the message generally
    this.emit('message', msg);
  }

  /**
   * Handles Gossip Errors
   */
  private _onGossipError(err: Error) {
    this.emit('error', err);
  }

  /**
   * Synchronize the peer using the peer's synchronization mechanism.
   * @param peer
   */
  private async _syncPeer(peer: GossipPeer) {
    // Disable gossip relay
    this.gossipRelay.stop();

    this.logger.trace("sync status now 'syncing'");
    this.syncState = SyncState.Syncing;

    try {
      // perform synchronization
      await peer.syncRange();

      // finally transition to sync complete status
      this.logger.trace("sync status now 'synced'");
      this.syncState = SyncState.Synced;

      // enable gossip for all the peers
      this.logger.trace('enabling gossip for all peers');
      for (const gossipPeer of this.peers) {
        gossipPeer.enableGossip();
      }
    } catch (ex) {
      // TODO select next peer
      this.syncState = SyncState.Unsynced;
    }

    // Enable gossip relay now that sync is complete
    this.gossipRelay.start();
  }

  private async _restoreState() {
    this.logger.info('retrieving gossip state from store');
    this.blockHeight = 0;
    const chanAnns = await this.gossipStore.findChannelAnnouncemnts();

    // find best block height
    for (const chanAnn of chanAnns) {
      this.blockHeight = Math.max(
        this.blockHeight,
        chanAnn.shortChannelId.block,
      );
    }
    this.logger.info("highest block %d found from %d channels", this.blockHeight, chanAnns.length); // prettier-ignore

    // validate all utxos
    await this._validateUtxos(chanAnns);
  }

  private async _validateUtxos(chanAnns: ChannelAnnouncementMessage[]) {
    if (!this.chainClient) {
      this.logger.info('skipping utxo validation, no chain_client configured');
      return;
    }

    const extChanAnnCount = chanAnns.reduce(
      (acc, msg) =>
        acc + (msg instanceof ExtendedChannelAnnouncementMessage ? 1 : 0),
      0,
    );
    this.logger.info('validating %d utxos', extChanAnnCount);

    if (!extChanAnnCount) return;

    const oct = Math.trunc(extChanAnnCount / 8);
    for (let i = 0; i < chanAnns.length; i++) {
      const chanAnn = chanAnns[i];
      if ((i + 1) % oct === 0) {
        this.logger.info(
          'validating utxos %s% complete',
          (((i + 1) / extChanAnnCount) * 100).toFixed(2),
        );
      }
      if (chanAnn instanceof ExtendedChannelAnnouncementMessage) {
        const utxo = await this.chainClient.getUtxo(
          chanAnn.outpoint.txid.toString(HashByteOrder.RPC),
          chanAnn.outpoint.outputIndex,
        );
        if (!utxo) {
          await this.removeChannel(chanAnn.shortChannelId);
        }
      }
    }
  }
}