lib/partialview.js

'use strict'

const EPV = require('./entries/epv.js')

const ExPeerNotFound = require('./exceptions/expeernotfound.js')

/**
 * Structure containing the neighborhood of a peer. Each neigbhor entry
 * comprises a list of ages and a descriptor.  Map of {idPeer => {ages:[age_1,
 * age_2.. age_k], descriptor: {x: exampleX} }} where age_1 <= age_2 <= .. <=
 * age_k.
 */
class PartialView extends Map {
  /**
     * Get the oldest peer in the partial view.
     * @returns {string} The oldest peer in the structure.
     */
  get oldest () {
    if (this.size <= 0) { throw new ExPeerNotFound('getOldest') }
    let oldestPeer = null
    let oldestAge = 0
    this.forEach((epv, peerId) => {
      if (oldestAge <= epv.oldest) {
        oldestPeer = epv.peer
        oldestAge = epv.oldest
      }
    })
    return oldestPeer
  }

  /**
     * Increment the age of the whole partial view
     */
  increment () {
    this.forEach((epv, peerId) => {
      epv.increment()
    })
  }

  /**
     * Add the peer to the partial view with an age of 0.
     * @param {string} peerId The identifier of the peer added to the partial
     * view.
     * @param {object} [descriptor = {}] The descriptor of the peer.
     */
  addNeighbor (peerId, descriptor = {}) {
    if (this.has(peerId)) {
      this.get(peerId).add()
    } else {
      this.set(peerId, new EPV(peerId, descriptor))
    }
  }

  /**
     * Update the peer's descriptor.
     * @param {string} peerId The identifier of the peer to update.
     * @param {object} [descriptor = {}] The new descriptor of peerId.
     */
  updateNeighbor (peerId, descriptor = {}) {
    if (!this.has(peerId)) {
      throw new ExPeerNotFound('updateNeighbor', peerId)
    } else {
      this.get(peerId).update(descriptor)
    }
  }

  /**
     * Remove the newest entry of the peer from the partial view.
     * @param {string} peerId The identifier of the peer to remove from the
     * partial view.
     */
  removeOldest (peerId) {
    if (!this.has(peerId)) {
      throw new ExPeerNotFound('removeNeighbor', peerId)
    } else {
      this.get(peerId).removeOldest() && this.delete(peerId)
    }
  }

  /**
     * Remove all entries of the peer from the partial view.
     * @param {string} peerId The identifier of the peer to remove from the
     * partial view.
     * @returns {number} The number of occurrences of peerId removed.
     */
  removeAllNeighbor (peerId) {
    if (!this.has(peerId)) {
      throw new ExPeerNotFound('removeNeighbor', peerId)
    } else {
      const occ = this.get(peerId).count
      this.delete(peerId)
      return occ
    }
  }

  /**
     * Get the least frequent peer. If multiple peers have the same number of
     * occurrences, it chooses one among them at random.
     * @returns {string} The identifier of a least frequent peer.
     */
  get leastFrequent () {
    if (this.size <= 0) { throw new ExPeerNotFound('getLeastFrequent') }
    let leastFrequent = []
    let frequency = Infinity
    this.forEach((epv, peerId) => {
      if (epv.count < frequency) {
        leastFrequent = []
        frequency = epv.count
      }
      (epv.count === frequency) && leastFrequent.push(peerId)
    })
    return leastFrequent[Math.floor(Math.random() * leastFrequent.length)]
  }

  /**
     * Get the descriptor of the peer in argument.
     * @param {string} peerId The identifier of the peer.
     * @returns {object} The descriptor of the peer.
     */
  getDescriptor (peerId) {
    if (!this.has(peerId)) {
      throw new ExPeerNotFound('getDescriptor', peerId)
    } else {
      return this.get(peerId).descriptor
    }
  }
}

module.exports = PartialView