DemocracyOS/app

import bus from 'bus'
import debug from 'debug'
import encode from 'mout/queryString/encode'
import findIndex from 'mout/array/findIndex'
import user from 'lib/site/user/user'
import request from '../../request/request'
import MemoryCache from './memory-cache'

export default class Store {
  constructor () {
    this._fetches = new MemoryCache()
    this._fetchRequests = new MemoryCache()
    this._destroys = new MemoryCache()
    this.item = new MemoryCache()

    this._findAllCache = {
      url: null,
      items: []
    }

    this.log = debug(`democracyos:${this.name()}-store`)
    bus.on('login', this.clear.bind(this))
    bus.on('logout', this.clear.bind(this))
    user.onChange(this.clear.bind(this))
  }

  busEmit (scope, ...args) {
    bus.emit(`${this.name()}-store:${scope}`, ...args)
  }

  /**
   * Name of the scope, to be used as a namespace for events, logs, etc.
   *
   * @return {String} name
   * @api public
   */
  name () {
    throw new Error('Store must implement name():string')
  }

  /**
   * Commmon Prefix for the API url
   *
   * @return {String} name
   * @api public
   */
  prefix () {
    return '/api/'
  }

  /**
   * Returns url where to fetch models, must implement GET, POST, DELETE.
   *
   * @param {String} id
   * @return {String} url
   * @api public
   */
  url (id, params = {}) {
    if (typeof id === 'object') {
      params = id
      id = ''
    }

    id = id ? '/' + id : ''

    return this.prefix() + this.name() + id + encode(params)
  }

  /**
   * Method to implement the parsing of the returned Model on ._fetch().
   * Could be used to add template properties/methods on the received object.
   *
   * @param {Object} item
   * @return {Promise} item
   * @api protected
   */
  parse (item) {
    return Promise.resolve(item)
  }

  /**
   * Save item to the cache.
   *
   * @param {String} id
   * @param {Object} item to save
   * @api public
   */
  set (id, item) {
    this.item.set(id, item)

    this.busEmit('update', item)
    this.busEmit(`update:${id}`, item)

    const findAllCacheIndex = findIndex(this._findAllCache.items, (i) => {
      return item.id === i.id
    })

    if (findAllCacheIndex !== -1) {
      this._findAllCache.items[findAllCacheIndex] = item
      this.busEmit('update:all', this._findAllCache.items)
    }

    return this
  }

  /**
   * Cleans the cache of a previously getted model. Once unloaded will be
   * fetched to the server again when .get() is called.
   *
   * @param {String} id
   * @api public
   */
  unset (id) {
    const item = this.item.remove(id)

    if (!item) return this

    this._fetchAbort(this.url(id))

    this.busEmit('remove', item)
    this.busEmit(`remove:${id}`, item)

    const findAllCacheIndex = findIndex(this._findAllCache.items, (i) => {
      return id === i.id
    })

    if (findAllCacheIndex !== -1) {
      this._findAllCache.items.splice(findAllCacheIndex, 1)
      this.busEmit('update:all', this._findAllCache.items)
    }

    return this
  }

  /**
   * Clears the cache of a all previously getted model.
   *
   * @api public
   */
  clear () {
    const items = this.item.items

    this.item.clear()

    Object.keys(items).forEach((id) => {
      this._fetchAbort(this.url(id))
      this.busEmit('remove', items[id])
      this.busEmit(`remove:${id}`, items[id])
    })

    if (this._findAllCache.url) {
      this._findAllCache.url = null
      this._findAllCache.items = []
      this.busEmit('update:all', this._findAllCache.items)
    }

    return this
  }

  /**
   * Method to get a Model from the Database.
   *
   * @param {String} id
   * @return {Promise} fetch
   * @api public
   */
  findOne (id) {
    if (this.item.get(id)) return Promise.resolve(this.item.get(id))

    let url = this.url(id)

    if (this._fetches.get(url)) return this._fetches.get(url)

    let fetch = this._fetch(url)

    fetch.then((item) => {
      this.item.set(id, item)
    }).catch((err) => {
      this.log('Found error', err)
    })

    return fetch
  }

  /**
   * Sends to the server a PUT call to .url(id)
   *
   * @param {String} id
   * @param {Object} data - Data to set on `id`
   * @return {Promise} fetch
   * @api public
   */
  update (id, data) {
    let promise = new Promise((resolve, reject) => {
      request
        .put(this.url(id))
        .send({ data })
        .end((err, res) => {
          if (err || !res.ok) return reject(err)

          this.parseResponse(res).then((item) => {
            this.set(id, item)
            resolve(item)
          }).catch(reject)
        })
    })

    return promise
  }

  /**
   * Sends to the server a DELETE call to .url(id), and unloads
   *
   * @param {String} id
   * @return {Promise} fetch
   * @api public
   */
  destroy (id) {
    let item = this.item.get(id)
    if (!item) {
      return this.findOne(id).then(() => {
        return this.destroy(id)
      })
    }

    if (this._destroys.get(id)) return this._destroys.get(id)

    let destroy = new Promise((resolve, reject) => {
      request
        .del(this.url(id))
        .end((err, res) => {
          this._destroys.remove(id)

          if (err || !res.ok) return reject(err)

          this.unset(id)

          resolve(item)

          this.busEmit('destroy', item)
          this.busEmit(`destroy:${id}`, item)
        })
    })

    this._destroys.set(id, destroy)

    return destroy
  }

  /**
   * Parse res object from backend
   *
   * @param {Object} res
   * @return {Promise} res
   * @api public
   */
  parseResponse (res) {
    if (Array.isArray(res.body)) {
      return Promise.all(res.body.map(this.parse))
    } else {
      return this.parse(res.body)
    }
  }

  /**
   * Fetch an item from backend
   *
   * @param {String} id
   * @return {Promise} fetch
   * @api protected
   */
  _fetch (url) {
    if (this._fetches.get(url)) return this._fetches.get(url)

    let fetch = new Promise((resolve, reject) => {
      let req = request
        .get(url)
        .end((err, res) => {
          this._fetches.remove(url)
          this._fetchRequests.remove(url)

          if (err) return reject(err)

          this.parseResponse(res)
            .then(resolve)
            .catch(reject)
        })

      this._fetchRequests.set(url, req)
    })

    this._fetches.set(url, fetch)

    return fetch
  }

  /**
   * Aborts a currently running fetch to the server
   *
   * @param {String} id
   * @api protected
   */
  _fetchAbort (url) {
    let req = this._fetchRequests.get(url)
    if (req) req.abort()
  }

  findAllSuffix () {
    return 'all'
  }

  /**
   * Method to find a list of Models from the Database and cache them.
   *
   * @param {String} id
   * @return {Promise} fetch
   * @api public
   */
  findAll (...args) {
    if (this.findAllSuffix()) args.unshift(this.findAllSuffix())
    let url = this.url(...args)

    if (this._findAllCache.url === url) {
      return Promise.resolve(this._findAllCache.items)
    }

    if (this._fetches.get(url)) return this._fetches.get(url)

    let fetch = this._fetch(url)

    fetch.then((items) => {
      this._findAllCache = {
        url: url,
        items: items
      }
      this.busEmit('update:all', items)
    }).catch((err) => {
      this.log('Found error', err)
    })

    return fetch
  }
}