git ssb

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const Graph = require('ipld-graph-builder')
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const Message = require('primea-message')
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const ExoInterface = require('./exoInterface.js')
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const Scheduler = require('./scheduler.js')
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const ROOT_ID = 'zdpuAm6aTdLVMUuiZypxkwtA7sKm7BWERy8MPbaCrFsmiyzxr'
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module.exports = class Hypervisor {
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  /**
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   * The Hypervisor manages the container instances by instantiating them and
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   * destorying them when possible. It also facilitates localating Containers
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   * @param {Graph} dag an instance of [ipfs.dag](https://github.com/ipfs/interface-ipfs-core/tree/master/API/dag#dag-api)
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   */
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  constructor (dag, state = {}) {
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    this.graph = new Graph(dag)
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    this.scheduler = new Scheduler()
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    this.state = state
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    this._containerTypes = {}
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    this._nodesToCheck = new Set()
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  }
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  /**
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   * add a potaintail node in the state graph to check for garbage collection
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   * @param {string} id
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   */
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  addNodeToCheck (id) {
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    this._nodesToCheck.add(id)
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  }
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  /**
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   * removes a potaintail node in the state graph to check for garbage collection
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   * @param {string} id
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   */
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  removeNodeToCheck (id) {
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    this._nodesToCheck.delete(id)
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  }
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  /**
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   * given a port, this finds the corridsponeding endpoint port of the channel
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   * @param {object} port
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   * @returns {Promise}
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   */
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  getDestPort (port) {
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    if (port.destPort) {
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      return port.destPort
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    } else {
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      return this.graph.get(this.state, `${port.destId}/ports/${port.destName}`)
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    }
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  }
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  // loads an instance of a container from the state
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  async _loadInstance (id, lock) {
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    const state = await this.graph.get(this.state, id)
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    const container = this._containerTypes[state.type]
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    // create a new kernel instance
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    const exoInterface = new ExoInterface({
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      hypervisor: this,
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      state: state,
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      container: container,
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      id: id
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    })
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    // save the newly created instance
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    this.scheduler.update(exoInterface)
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    this.scheduler.releaseLock(lock)
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    return exoInterface
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  }
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  /**
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   * gets an existsing container instances
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   * @param {string} id - the containers ID
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   * @returns {Promise}
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   */
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  async getInstance (id) {
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    let instance = this.scheduler.getInstance(id)
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    if (instance) {
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      return instance
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    } else {
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      const lock = this.scheduler.getLock()
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      instance = await this._loadInstance(id, lock)
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      return instance
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    }
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  }
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  /**
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   * creates an new container instances and save it in the state
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   * @param {string} type - the type of container to create
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   * @param {*} code
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   * @param {array} entryPorts
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   * @param {object} id
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   * @param {object} id.nonce
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   * @param {object} id.parent
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   * @returns {Promise}
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   */
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  async createInstance (type, code, entryPorts = [], id = {nonce: 0, parent: null}) {
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    // create a lock to prevent the scheduler from reloving waits before the
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    // new container is loaded
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    const lock = this.scheduler.getLock()
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    id = await this.getHashFromObj(id)
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    const state = {
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      nonce: [0],
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      ports: {},
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      type: type,
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      code: code
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    }
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    // save the container in the state
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    await this.graph.set(this.state, id, state)
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    // create the container instance
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    const exoInterface = await this._loadInstance(id, lock)
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    // send the intialization message
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    exoInterface.queue(null, new Message({
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      ports: entryPorts
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    }))
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    return exoInterface
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  }
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  /**
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   * deletes container from the state
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   * @param {string} id
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   */
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  deleteInstance (id) {
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    if (id !== ROOT_ID) {
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      this._nodesToCheck.delete(id)
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      delete this.state[id]
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    }
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  }
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  /**
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   * creates a state root starting from a given container and a given number of
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   * ticks
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   * @param {Number} ticks the number of ticks at which to create the state root
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   * @returns {Promise}
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   */
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  async createStateRoot (ticks) {
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    await this.scheduler.wait(ticks)
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    const unlinked = await DFSchecker(this.graph, this.state, ROOT_ID, this._nodesToCheck)
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    unlinked.forEach(id => {
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      delete this.state[id]
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    })
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    return this.graph.flush(this.state)
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  }
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  /**
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   * regirsters a container with the hypervisor
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   * @param {String} type - the name of the type
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   * @param {Class} Constructor - a Class for instantiating the container
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   * @param {*} args - any args that the contructor takes
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   */
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  registerContainer (type, Constructor, args) {
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    this._containerTypes[type] = {
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      Constructor: Constructor,
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      args: args
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    }
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  }
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  /**
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   * get a hash from a POJO
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   * @param {object} obj
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   * @return {Promise}
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   */
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  async getHashFromObj (obj) {
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    return (await this.graph.flush(obj))['/']
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  }
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}
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// Implements a parrilizable DFS check for graph connictivity given a set of nodes
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// and a root node. Stating for the set of node to check this does a DFS and
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// will return a set a nodes if any that is not connected to the root node.
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async function DFSchecker (graph, state, root, nodes) {
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  const checkedNodesSet = new Set()
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  let hasRootSet = new Set()
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  const promises = []
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  for (const id of nodes) {
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    // create a set for each of the starting nodes to track the nodes the DFS has
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    // has traversed
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    const checkedNodes = new Set()
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    checkedNodesSet.add(checkedNodes)
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    promises.push(check(id, checkedNodes))
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  }
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  // wait for all the search to complete
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  await Promise.all(promises)
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  // remove the set of nodes that are connected to the root
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  checkedNodesSet.delete(hasRootSet)
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  let unLinkedNodesArray = []
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  // combine the unconnected sets into a single array
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  for (const set of checkedNodesSet) {
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    unLinkedNodesArray = unLinkedNodesArray.concat([...set])
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  }
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  return unLinkedNodesArray
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  // does the DFS starting with a single node ID
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  async function check (id, checkedNodes) {
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    if (!checkedNodesSet.has(checkedNodes) || // check if this DFS is still searching
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        checkedNodes.has(id) ||  // check if this DFS has alread seen the node
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        hasRootSet === checkedNodes) { // check that this DFS has alread found the root node
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      return
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    }
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    // check if any of the the other DFSs have seen this node and if so merge
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    // the sets and stop searching
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    for (const set of checkedNodesSet) {
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      if (set.has(id)) {
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        checkedNodes.forEach(id => set.add(id))
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        checkedNodesSet.delete(checkedNodes)
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        return
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      }
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    }
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    // mark the node 'checked'
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    checkedNodes.add(id)
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    // check to see if we are at the root
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    if (id === root) {
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      hasRootSet = checkedNodes
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      return
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    }
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    const node = state[id]['/']
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    const promises = []
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    // iterate through the nodes ports and recursivly check them
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    for (const name in node.ports) {
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      const port = node.ports[name]
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      promises.push(check(port.destId, checkedNodes))
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    }
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    return Promise.all(promises)
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  }
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}
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