import { ShortChannelId } from '@node-dlc/common';
import { ILogger } from '@node-dlc/logger';

import { ChannelUpdateChannelFlags } from '../flags/ChanneUpdateChannelFlags';
import { ChannelAnnouncementMessage } from '../messages/ChannelAnnouncementMessage';
import { ChannelUpdateMessage } from '../messages/ChannelUpdateMessage';
import { IWireMessage } from '../messages/IWireMessage';
import { NodeAnnouncementMessage } from '../messages/NodeAnnouncementMessage';
import { IPeer } from '../Peer';

/**
 * Interface for the sub-system for handling the gossip message relay,
 * also known as rumor mongering.This system is responsible for
 * periodically flushing messages to connected peers and makes a best
 * effort to not send message that have already been sent to a peer.
 *
 * The idea of rumor mongering is that a piece of information is hot. A
 * node attempts to infect connected peers with this information by
 * sending it to them. Once it has been sent, we no longer need to
 * infect them with information.
 */
export interface IGossipRelay {
  /**
   * The current state of gossip relay
   */
  state: GossipRelayState;

  /**
   * Starts gossip relay
   */
  start(): void;

  /**
   * Stops gossip relay
   */
  stop(): void;

  /**
   * Adds a new peer to relay messages to
   * @param peer
   */
  addPeer(peer: IPeer): void;

  /**
   * Removes the peer from relay
   * @param peer
   */
  removePeer(peer: IPeer): void;

  /**
   * Enqueues a message to be broadcast to peers
   * @param msg
   */
  enqueue(msg: IWireMessage): void;
}

/**
 * The state of a IGossipRelay rumor mongerer
 */
export enum GossipRelayState {
  /**
   * Rumor mongering is not active
   */
  Inactive,

  /**
   * Rumor mongering is active
   */
  Active,
}

/**
 * This is a basic implementation of IGossipRelay that enques all
 * messages and maintaining an index of each peer in the queue. When
 * messages are flushed, only messages that haven't been sent to a peer
 * are sent and the index position for that peer is updated. When the
 * queue of messages has reached a maximum length, older messages are
 * pruned and the index positions are updated.
 */
export class GossipRelay {
  private _queue: IWireMessage[];
  private _peers: Map<IPeer, number>;
  private _timer: NodeJS.Timeout;
  private _state: GossipRelayState;

  constructor(
    readonly logger: ILogger,
    readonly relayPeriodMs = 60000,
    readonly maxQueueLen = 10000,
  ) {
    this._peers = new Map() as Map<IPeer, number>;
    this._queue = [];
    this._state = GossipRelayState.Inactive;
  }

  /**
   * Gets the current state of gossip relay
   */
  public get state(): GossipRelayState {
    return this._state;
  }

  /**
   * Starts relay to peers. This enables messages to be enqueued and
   * periodically sent to the peers.
   */
  public start() {
    if (this._state === GossipRelayState.Active) return;
    this.logger.info('starting gossip relay for all peers');
    this._state = GossipRelayState.Active;
    // eslint-disable-next-line @typescript-eslint/no-implied-eval
    this._timer = setInterval(this._onTimer.bind(this), this.relayPeriodMs);
  }

  /**
   * Stops relay to peers.
   */
  public stop() {
    if (this._state === GossipRelayState.Inactive) return;
    this.logger.info('stopping gossip relay for all peers');
    clearTimeout(this._timer);
    this._state = GossipRelayState.Inactive;
  }

  /**
   * Adds a new peer to relay messages to
   * @param peer
   */
  public addPeer(peer: IPeer) {
    this._peers.set(peer, this._queue.length);
  }

  /**
   * Removes the peer from relay
   * @param peer
   */
  public removePeer(peer: IPeer) {
    this._peers.delete(peer);
  }

  /**
   * Enqueues a message to be broadcast to peers.
   * @param msg
   */
  public enqueue(msg: IWireMessage) {
    if (this.state !== GossipRelayState.Active) return;

    // For chan_ann messages there is never an update so we only
    // need to check if the chan_ann exists and add it if it doesn't
    if (msg instanceof ChannelAnnouncementMessage) {
      const existing = this._findChanAnn(msg.shortChannelId);

      // adds to the queue if there is no existing message
      if (!existing) {
        this.logger.trace(
          'adding channel_announcement',
          msg.shortChannelId.toString(),
        );
        this._queue.push(msg);
        return;
      }
    }

    // For chan_update messages we will add messages that don't exist
    // or update an existing update message if one already exists
    if (msg instanceof ChannelUpdateMessage) {
      const existing = this._findChanUpd(
        msg.shortChannelId,
        msg.channelFlags.isSet(ChannelUpdateChannelFlags.direction),
      );

      // Adds to the queue if there is no existing message
      if (!existing) {
        this.logger.trace(
          'adding channel_update',
          msg.shortChannelId.toString(),
          msg.channelFlags.isSet(ChannelUpdateChannelFlags.direction),
        );
        this._queue.push(msg);
        return;
      }

      // Removes the existing message and replaces with a newer
      // message by adding the new message to the back of the queue
      if (existing && existing.timestamp < msg.timestamp) {
        this.logger.trace(
          'updating channel_update',
          msg.shortChannelId.toString(),
          msg.channelFlags.isSet(ChannelUpdateChannelFlags.direction),
        );
        const idx = this._queue.indexOf(existing);
        this._queue.splice(idx, 1);
        this._queue.push(msg);
        return;
      }
    }

    // For node_ann messages we look for the existing messages and
    // abort if the new msg is older than the current node_ann we
    // have in the message queue.
    if (msg instanceof NodeAnnouncementMessage) {
      const existing = this._findNodeAnn(msg.nodeId);

      // Adds to the queue if there is no existing message
      if (!existing) {
        this.logger.trace(
          'adding node_announcement',
          msg.nodeId.toString('hex'),
        );
        this._queue.push(msg);
        return;
      }

      // Removes the existing message and replaces with a newer
      // message by adding the new message to the back of the queue
      if (existing && existing.timestamp < msg.timestamp) {
        this.logger.trace(
          'updating node_announcement',
          msg.nodeId.toString('hex'),
        );
        const idx = this._queue.indexOf(existing);
        this._queue.splice(idx, 1);
        this._queue.push(msg);
        return;
      }
    }
  }

  /**
   * Finds a channel_announcement message based on the short_channel_id
   * @param scid
   */
  private _findChanAnn(scid: ShortChannelId): ChannelAnnouncementMessage {
    return this._queue.find(
      (p) =>
        p instanceof ChannelAnnouncementMessage &&
        p.shortChannelId.toNumber() === scid.toNumber(),
    ) as ChannelAnnouncementMessage;
  }

  /**
   * Finds a channel_update message based on the short_channel_id and
   * direction. The found message can then be compared to an inbound
   * message to determine if the new message is newer.
   * @param scid
   * @param direction
   */
  private _findChanUpd(
    scid: ShortChannelId,
    direction: boolean,
  ): ChannelUpdateMessage {
    return this._queue.find(
      (p) =>
        p instanceof ChannelUpdateMessage &&
        p.shortChannelId.toNumber() === scid.toNumber() &&
        p.channelFlags.isSet(ChannelUpdateChannelFlags.direction) === direction,
    ) as ChannelUpdateMessage;
  }

  /**
   * Finds a node_announcement message based on the node_id. The
   * returned message can be compared to newer messages using the
   * timestamp.
   * @param nodeId
   */
  private _findNodeAnn(nodeId: Buffer): NodeAnnouncementMessage {
    return this._queue.find(
      (p) => p instanceof NodeAnnouncementMessage && p.nodeId.equals(nodeId),
    ) as NodeAnnouncementMessage;
  }

  /**
   * Fires when the timer ticks and will flush messages to peers and
   * prune the queue
   */
  private _onTimer() {
    this.logger.debug(`periodic flush, ${this._peers.size} peers, ${this._queue.length} hot messages`); // prettier-ignore
    for (const peer of this._peers.keys()) {
      this._flushToPeer(peer);
    }

    this._pruneQueue();
  }

  /**
   * Flushes message to a peer based on the index of messages that
   * the peer has received.
   * @param peer
   */
  private _flushToPeer(peer: IPeer) {
    for (let i = this._peers.get(peer); i < this._queue.length; i++) {
      const message = this._queue[i];
      peer.sendMessage(message);
      this._peers.set(peer, this._queue.length);
    }
  }

  /**
   * Prunes excess message
   */
  private _pruneQueue() {
    // calculate the delete count based on the current queue length
    // and the max allowed queue length
    const deleteCount = Math.max(0, this._queue.length - this.maxQueueLen);

    // do nothing if we don't need to prune any items
    if (deleteCount === 0) return;

    // pruning the excess items from the start of the queue
    this._queue.splice(0, deleteCount);

    // adjust all of the peers by reducing their index position by
    // the delete count
    for (const [peer, index] of this._peers.entries()) {
      this._peers.set(peer, index - deleteCount);
    }

    this.logger.debug(`pruned ${deleteCount} old messages`);
  }
}