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 (a._fromPortTicks !== b._fromPortTicks) {
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    return a._fromPortTicks < b._fromPortTicks ? 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 if (portA.name === ENTRY) {
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    // pairB can never be the entry port since the port map is odered by
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    // insertion order
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    return pairA
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  } else {
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    return portA.name < portB.name ? pairA : pairB
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  }
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}
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module.exports = class PortManager {
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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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  }
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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._mapPort(ENTRY, this.parentPort)
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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._mapPort(name, port)
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    })
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  }
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  _mapPort (name, portRef) {
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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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  queue (message) {
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    this._portMap.get(message.fromPort).queue(message)
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  }
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  get (key) {
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    return this.ports[key]
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  }
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  delete (key) {
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    const port = this.ports[key]
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    delete this.ports[key]
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    this._portMap.delete(port)
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  }
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  isValidPort (port) {
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    return this._portMap.has(port)
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  }
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  create (type, name) {
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    const VM = this.hypervisor._VMs[type]
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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': {
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        '/': VM.createState()
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      }
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    }
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    // save the port instance
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    this.ports[name] = portRef
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    this._mapPort(name, portRef)
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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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    return portRef
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  }
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  // waits till all ports have reached a threshold tick count
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  wait (threshold, fromPort) {
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    // find the ports that have a smaller tick count then the threshold tick count
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    const unkownPorts = [...this._portMap].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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  async getNextMessage () {
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    if (this._portMap.size) {
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      await this.wait(this.kernel.ticks, this.entryPort)
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      const portMap = [...this._portMap].reduce(messageArbiter)
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      return portMap[1].shift()
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    }
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  }
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}
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