const Buffer = require('safe-buffer').Buffer
const crypto = require('crypto')
const Actor = require('./actor.js')
const Scheduler = require('./scheduler.js')
const {ID, decoder} = require('primea-objects')
const cbor = require('borc')

module.exports = class Hypervisor {
  /**
   * The Hypervisor manages the container instances by instantiating them and
   * destorying them when possible. It also facilitates localating Containers
   * @param {Tree} tree - a [radix tree](https://github.com/dfinity/js-dfinity-radix-tree) to store the state
   */
  constructor (tree, containers = [], drivers = [], nonce = 0) {
    tree.dag.decoder = decoder
    this.tree = tree
    this.scheduler = new Scheduler(this)
    this._containerTypes = {}
    this.nonce = nonce
    containers.forEach(container => this.registerContainer(container))
    drivers.forEach(driver => this.registerDriver(driver))
  }

  /**
   * sends a message
   * @param {Object} message - the [message](https://github.com/primea/js-primea-message) to send
   * @returns {Promise} a promise that resolves once the receiving container is loaded
   */
  send (messages) {
    if (!Array.isArray(messages)) {
      messages = [messages]
    }
    this.scheduler.queue(messages)
  }

  /**
   * loads an actor from the tree given its id
   * @param {ID} id
   * @returns {Promise<Actor>}
   */
  async loadActor (id) {
    const state = await this.tree.get(id.id, true)
    const [code, storage] = await Promise.all([
      this.tree.graph.get(state.node, '1'),
      this.tree.graph.get(state.node, '2')
    ])
    const [type, nonce] = state.value
    const Container = this._containerTypes[type]

    // create a new actor instance
    const actor = new Actor({
      hypervisor: this,
      state,
      Container,
      id,
      nonce,
      type,
      code,
      storage,
      tree: this.tree
    })

    await actor.startup()
    return actor
  }

  /**
   * creates an instance of an Actor
   * @param {Integer} type - the type id for the container
   * @param {Object} message - an intial [message](https://github.com/primea/js-primea-message) to send newly created actor
   * @param {Object} id - the id for the actor
   */
  createActor (type, code, id = {nonce: this.nonce++, parent: null}) {
    const Container = this._containerTypes[type]
    const encoded = encodedID(id)
    id = this._hash(encoded)
    id = new ID(id)
    const module = Container.onCreation(code, id, this.tree)
    const metaData = [type, 0]

    // save the container in the state
    this.tree.set(id.id, metaData).then(node => {
      // save the code
      node[1] = {
        '/': code
      }
      // save the storage
      node[2] = {
        '/': []
      }
    })

    return {
      id,
      module
    }
  }

  _hash (buf) {
    const hash = crypto.createHash('sha256')
    hash.update(buf)
    return hash.digest().slice(0, 20)
  }

  /**
   * creates a state root starting from a given container and a given number of
   * ticks
   * @param {Number} ticks the number of ticks at which to create the state root
   * @returns {Promise}
   */
  async createStateRoot () {
    if (this.scheduler._running) {
      await new Promise((resolve, reject) => {
        this.scheduler.once('idle', resolve)
      })
    }
    await this.tree.set(Buffer.from([0]), this.nonce)
    return this.tree.flush()
  }

  /**
   * set the state root
   */
  async setStateRoot (stateRoot) {
    this.tree.root = stateRoot
    const node = await this.tree.get(Buffer.from([0]))
    this.nonce = node.value
  }

  /**
   * regirsters a container with the hypervisor
   * @param {Class} Constructor - a Class for instantiating the container
   * @param {*} args - any args that the contructor takes
   * @param {Integer} typeId - the container's type identification ID
   */
  registerContainer (Constructor) {
    this._containerTypes[Constructor.typeId] = Constructor
  }

  registerDriver (driver) {
    this.scheduler.drivers.set(driver.id.toString(), driver)
  }
}

function encodedID (id) {
  if (id.parent) {
    return cbor.encode([id.nonce, id.parent.id])
  } else {
    return cbor.encode([id.nonce, null])
  }
}