import * as utils from '../utils.js'
import { compare as uint8ArrayCompare } from 'uint8arrays/compare'
import { xor as uint8ArrayXor } from 'uint8arrays/xor'
import type { PeerId } from '@libp2p/interface-peer-id'

interface PeerDistance {
  peerId: PeerId
  distance: Uint8Array
}

/**
 * Maintains a list of peerIds sorted by distance from a DHT key.
 */
export class PeerDistanceList {
  /**
   * The DHT key from which distance is calculated
   */
  private readonly originDhtKey: Uint8Array

  /**
   * The maximum size of the list
   */
  private readonly capacity: number

  private peerDistances: PeerDistance[]

  constructor (originDhtKey: Uint8Array, capacity: number) {
    this.originDhtKey = originDhtKey
    this.capacity = capacity
    this.peerDistances = []
  }

  /**
   * The length of the list
   */
  get length () {
    return this.peerDistances.length
  }

  /**
   * The peerIds in the list, in order of distance from the origin key
   */
  get peers () {
    return this.peerDistances.map(pd => pd.peerId)
  }

  /**
   * Add a peerId to the list.
   */
  async add (peerId: PeerId) {
    if (this.peerDistances.find(pd => pd.peerId.equals(peerId)) != null) {
      return
    }

    const dhtKey = await utils.convertPeerId(peerId)
    const el = {
      peerId,
      distance: uint8ArrayXor(this.originDhtKey, dhtKey)
    }

    this.peerDistances.push(el)
    this.peerDistances.sort((a, b) => uint8ArrayCompare(a.distance, b.distance))
    this.peerDistances = this.peerDistances.slice(0, this.capacity)
  }

  /**
   * Indicates whether any of the peerIds passed as a parameter are closer
   * to the origin key than the furthest peerId in the PeerDistanceList.
   */
  async anyCloser (peerIds: PeerId[]) {
    if (peerIds.length === 0) {
      return false
    }

    if (this.length === 0) {
      return true
    }

    const dhtKeys = await Promise.all(peerIds.map(utils.convertPeerId))
    const furthestDistance = this.peerDistances[this.peerDistances.length - 1].distance

    for (const dhtKey of dhtKeys) {
      const keyDistance = uint8ArrayXor(this.originDhtKey, dhtKey)

      if (uint8ArrayCompare(keyDistance, furthestDistance) < 0) {
        return true
      }
    }

    return false
  }
}