/**
 * @module RESTControllerVersioned
 */
import * as debugStuff from 'debug'
const debug = debugStuff.debug('dbApiRESTCtrlVer')
import RESTController from './RESTController'

const MAX_RESULTS = 100

/**
 * REST controller for MongoDB backend.
 */
class RESTControllerVersioned extends RESTController {
  constructor (model, key = '_id', subDocuments = {}) {
    super(model, key, subDocuments)
    this.filterOptions = { limit: MAX_RESULTS, skip: 0 }
    this.filterCriteria = { '_history.head': true }
    debug('created RESTControllerVersioned', this.modelName)
  }

  /**
   * Override create function to support versioning.
   *
   * This function generates a history object to allow revision control
   * of the data elements.
   *
   * @param  {object} data object
   * @return {Promise}
   */
  create (data) {
    debug('create data item', data)
    const { author, version, comment, ...newData } = data
    const history = {
      author,
      created: new Date(),
      version,
      comment,
      head: true,
      reference: []
    }
    newData._history = history
    const p = this.model
      .create(newData)
      .then(instance => {
        debug('created instance', instance)
        return instance
      })
    // debug('create return value', p)
    return p
  }

  /**
   * Override read to search by default for head version of given tag.
   *
   * @param  {[type]}
   * @return {[type]}
   */
  read (tag) {
    if (typeof tag === 'string') {
      tag = { tag: tag }
    }
    debug('reading data item', tag)
    const filter = { ...this.filterCriteria, ...tag }

    const p = this.model
      .findOne(filter)
      .then(instance => {
        debug('read instance', instance)
        return instance
      })
    // debug('read return value', p)
    return p
  }

  /**
   * Get a list of all DB items.
   *
   * @return {Promise}
   */
  list (filter = this.filterCriteria) {
    debug('reading data list')
    const p = this.model
      .find(filter)
      .limit(MAX_RESULTS)
      .then(instance => {
        debug('read list instance', instance)
        return instance
      })
    // debug('read return value', p)
    return p
  }

  /**
   * Override update to support versioning.
   *
   * @param  {String} id
   * @param  {String} data
   * @return {Promise}
   */
  update (tag, data) {
    if (typeof tag === 'string') {
      tag = { tag: tag }
    }
    debug('update data item', tag, data)
    const filter = { ...this.filterCriteria, ...tag }

    const p = this.model
      .findOne(filter)
      .then(instance => {
        debug('found data instance', instance)
        instance._history.head = false
        return instance.save()
      })
      .then(instance => {
        const { _id, __v, _history, ...oldData } = instance._doc
        debug('creating new data instance', oldData)
        const { author, version, comment, ...newItems } = data
        const newData = { ...oldData, ...newItems }
        newData._history = {
          author,
          created: new Date(),
          version,
          comment,
          head: true,
          reference: [ _id, ..._history.reference ]
        }
        return this.model
          .create(newData)
          .then(instance => {
            debug('created instance', instance)
            return instance
          })
      })
    // debug('read return value', p)
    return p
  }

  /**
   * Override delete. We don't delete. Just not our thing...
   *
   * @param  {String} id
   * @return {Promise}
   */
  delete (tag) {
    if (typeof tag === 'string') {
      tag = { tag: tag }
    }
    debug('delete data item', tag)
    const filter = { ...this.filterCriteria, ...tag }

    const p = this.model
      .findOne(filter)
      .then(instance => {
        instance._history.head = false
        return instance.save()
      })
    // debug('read return value', p)
    return p
  }
}

export default RESTControllerVersioned