git ssb

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const binarySearchInsert = require('binary-search-insert')
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const SortedMap = require('sortedmap')
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const LockMap = require('lockmap')
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module.exports = class Scheduler {
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  /**
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   * The Scheduler manages the run cycle of the containers and figures out which
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   * order they should run in
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   */
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  constructor () {
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    this._waits = []
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    this._running = new Set()
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    this._loadingInstances = new LockMap()
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    this.instances = new SortedMap(comparator)
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    this.systemServices = new Map()
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    function comparator (a, b) {
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      return a.ticks - b.ticks
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    }
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  }
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  /**
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   * locks the scheduler from clearing waits untill the lock is resolved
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   * @param {string} id
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   * @return {function} the resolve function to call once it to unlock
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   */
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  lock (id) {
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    return this._loadingInstances.lock(id)
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  }
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  /**
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   * updates an instance with a new tick count
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   * @param {Object} instance - a container instance
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   */
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  update (instance) {
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    this._waits = this._waits.filter(wait => wait.id !== instance.id)
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    this._update(instance)
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    this._running.add(instance.id)
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    this._checkWaits()
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  }
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  _update (instance) {
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    this.instances.delete(instance.id)
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    this.instances.set(instance.id, instance)
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  }
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  /**
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   * returns a container
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   * @param {String} id
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   * @return {Object}
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   */
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  getInstance (id) {
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    return this.instances.get(id) || this._loadingInstances.get(id) || this.systemServices.get(id)
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  }
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  /**
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   * deletes an instance from the scheduler
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   * @param {string} id - the containers id
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   */
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  done (id) {
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    this._running.delete(id)
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    this.instances.delete(id)
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    this._checkWaits()
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  }
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  /**
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   * returns a promise that resolves once all containers have reached the given
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   * number of ticks
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   * @param {interger} ticks - the number of ticks to wait
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   * @param {string} id - optional id of the container that is waiting
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   * @return {Promise}
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   */
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  wait (ticks, id) {
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    this._running.delete(id)
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    return new Promise((resolve, reject) => {
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      binarySearchInsert(this._waits, comparator, {
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        ticks: ticks,
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        resolve: resolve,
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        id: id
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      })
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      this._checkWaits()
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    })
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    function comparator (a, b) {
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      return a.ticks - b.ticks
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    }
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  }
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  /**
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   * returns the oldest container's ticks
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   * @return {integer}
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   */
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  syncLeastNumberOfTicks (exculde) {
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    let ticks = 0
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    for (const instance of this.instances) {
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      ticks = instance[1].ticks
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      if (instance[1].id !== exculde) {
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        return ticks
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      }
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    }
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    return ticks
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  }
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  // checks outstanding waits to see if they can be resolved
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  async _checkWaits () {
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    if (this._checkingWaits) {
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      return
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    } else {
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      this._checkingWaits = true
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      await [...this._loadingInstances.values()]
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    }
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    // if there are no running containers
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    if (!this.instances.size) {
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      // clear any remanding waits
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      this._waits.forEach(wait => wait.resolve())
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      this._waits = []
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      this._checkingWaits = false
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    } else {
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      // find the old container and see if to can resolve any of the waits
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      while (this._waits[0]) {
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        const wait = this._waits[0]
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        const least = this.syncLeastNumberOfTicks(wait.id)
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        if (wait.ticks <= least) {
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          this._waits.shift()
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          wait.resolve()
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          this._running.add(wait.id)
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        } else {
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          break
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        }
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      }
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      if (!this._running.size && this._waits.length) {
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        // if there are no containers running find the oldest wait and update
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        // the oldest containers to it ticks
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        const oldest = this._waits[0].ticks
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        for (let instance of this.instances) {
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          instance = instance[1]
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          if (instance.ticks > oldest) {
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            break
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          } else {
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            instance.ticks = oldest
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            this._update(instance)
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          }
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        }
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        this._checkingWaits = false
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        return this._checkWaits()
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      } else {
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        this._checkingWaits = false
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      }
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    }
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  }
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}
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