git ssb

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const Port = require('./port.js')
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const BN = require('bn.js')
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const ENTRY = Symbol('entry')
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// decides which message to go first
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function messageArbiter (pairA, pairB) {
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  const portA = pairA[1]
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  const portB = pairB[1]
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  const a = portA.peek()
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  const b = portB.peek()
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  if (!a) {
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    return pairB
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  } else if (!b) {
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    return pairA
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  }
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  // order by number of ticks if messages have different number of ticks
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  if (portA.ticks !== portB.ticks) {
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    return portA.ticks < portB.ticks ? pairA : pairB
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  } else if (a.priority !== b.priority) {
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    // decide by priority
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    return a.priority > b.priority ? pairA : pairB
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  } else {
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    // insertion order
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    return pairA
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  }
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}
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module.exports = class PortManager {
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  /**
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   * The port manager manages the the ports. This inculdes creation, deletion
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   * fetching and waiting on ports
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   * @param {Object} opts
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   * @param {Object} opts.state
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   * @param {Object} opts.entryPort
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   * @param {Object} opts.parentPort
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   * @param {Object} opts.hypervisor
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   * @param {Object} opts.exoInterface
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   */
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  constructor (opts) {
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    Object.assign(this, opts)
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    this._portMap = new Map()
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    this._unboundPort = new WeakSet()
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  }
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  /**
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   * starts the port manager. This fetchs the ports from the state and maps
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   * them to thier names
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   * @returns {Promise}
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   */
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  async start () {
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    // skip the root, since it doesn't have a parent
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    if (this.parentPort !== undefined) {
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      this._bindRef(this.parentPort, ENTRY)
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    }
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    // map ports to thier id's
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    this.ports = await this.hypervisor.graph.get(this.state, 'ports')
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    Object.keys(this.ports).map(name => {
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      const port = this.ports[name]
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      this._bindRef(port, name)
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    })
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  }
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  _bindRef (portRef, name) {
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    const port = new Port(name)
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    this._portMap.set(portRef, port)
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  }
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  /**
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   * binds a port to a name
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   * @param {Object} port - the port to bind
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   * @param {String} name - the name of the port
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   */
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  bind (port, name) {
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    if (this.isBound(port)) {
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      throw new Error('cannot bind a port that is already bound')
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    }
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    // save the port instance
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    this.ports[name] = port
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    this._bindRef(port, name)
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  }
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  /**
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   * unbinds a port given its name
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   * @param {String} name
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   * @returns {boolean} whether or not the port was deleted
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   */
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  unbind (name) {
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    const port = this.ports[name]
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    delete this.ports[name]
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    this._portMap.delete(port)
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    return port
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  }
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  /**
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   * get the port name given its referance
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   * @return {string}
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   */
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  getBoundName (portRef) {
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    return this._portMap.get(portRef).name
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  }
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  /**
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   * check if a port object is still valid
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   * @param {Object} port
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   * @return {Boolean}
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   */
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  isBound (port) {
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    return this._portMap.has(port)
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  }
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  /**
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   * queues a message on a port
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   * @param {Message} message
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   */
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  queue (message) {
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    this._portMap.get(message.fromPort).queue(message)
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  }
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  /**
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   * gets a port given it's name
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   * @param {String} name
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   * @return {Object}
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   */
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  get (name) {
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    return this.ports[name]
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  }
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  _createPortObject (type, link) {
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    const parentId = this.entryPort ? this.entryPort.id : null
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    let nonce = this.state['/'].nonce
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    const portRef = {
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      'messages': [],
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      'id': {
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        '/': {
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          nonce: nonce,
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          parent: parentId
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        }
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      },
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      'type': type,
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      'link': link
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    }
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    // incerment the nonce
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    nonce = new BN(nonce)
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    nonce.iaddn(1)
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    this.state['/'].nonce = nonce.toArray()
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    this._unboundPort.add(portRef)
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    return portRef
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  }
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  /**
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   * creates a new Port given the container type
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   * @param {String} type
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   * @param {*} data - the data to populate the initail state with
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   * @returns {Object} the newly created port
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   */
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  create (type, data) {
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    const container = this.hypervisor._containerTypes[type]
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    return this._createPortObject(type, {
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      '/': container.Constructor.createState(data)
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    })
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  }
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  /**
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   * creates a copy of a port given a port referance
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   * @param {Object} port - the port to copy
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   */
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  copy (port, type = port.type) {
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    return this._createPortObject(port.type, port.link)
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  }
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  /**
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   * waits till all ports have reached a threshold tick count
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   * @param {Integer} threshold - the number of ticks to wait
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   * @param {Object} fromPort - the port requesting the wait
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   * @param {Array} ports - the ports to wait on
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   * @returns {Promise}
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   */
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  wait (threshold, fromPort = this.entryPort, ports = [...this._portMap]) {
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    // find the ports that have a smaller tick count then the threshold tick count
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    const unkownPorts = ports.filter(([portRef, port]) => {
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      return port.ticks < threshold && fromPort !== portRef
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    })
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    const promises = unkownPorts.map(async([portRef, port]) => {
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      // update the port's tick count
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      port.ticks = await this.hypervisor.wait(portRef, threshold, this.entryPort)
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    })
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    return Promise.all(promises)
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  }
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  /**
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   * gets the next canonical message given the an array of ports to choose from
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   * @param {Array} ports
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   * @returns {Promise}
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   */
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  async getNextMessage (ports = [...this._portMap]) {
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    if (ports.length) {
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      // find the oldest message
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      const ticks = ports.map(([name, port]) => {
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        return port.size ? port.ticks : this.exoInterface.ticks
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      }).reduce((ticksA, ticksB) => {
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        return ticksA < ticksB ? ticksA : ticksB
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      })
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      await this.wait(ticks)
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      const portMap = ports.reduce(messageArbiter)
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      return portMap[1].dequeue()
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    }
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  }
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}
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