text: const ObservableStore = require('obs-store')
  const { warn } = require('loglevel')
  
  // By default, poll every 3 minutes
  const DEFAULT_INTERVAL = 180 * 1000
  
  /**
   * A controller that polls for token exchange
   * rates based on a user's current token list
   */
  class TokenRatesController {
    /**
     * Creates a TokenRatesController
     *
     * @param {Object} [config] - Options to configure controller
     */
    constructor ({ interval = DEFAULT_INTERVAL, preferences } = {}) {
      this.store = new ObservableStore()
      this.preferences = preferences
      this.interval = interval
    }
  
    /**
     * Updates exchange rates for all tokens
     */
    async updateExchangeRates () {
      if (!this.isActive) { return }
      const contractExchangeRates = {}
      for (const i in this._tokens) {
        if (this._tokens[i]) {
          const address = this._tokens[i].address
          contractExchangeRates[address] = await this.fetchExchangeRate(address)
        }
      }
      this.store.putState({ contractExchangeRates })
    }
  
    /**
     * Fetches a token exchange rate by address
     *
     * @param {String} address - Token contract address
     */
    async fetchExchangeRate (address) {
      try {
        const response = await fetch(`https://metamask.balanc3.net/prices?from=${address}&to=ETH&autoConversion=false&summaryOnly=true`)
        const json = await response.json()
        return json && json.length ? json[0].averagePrice : 0
      } catch (error) {
        warn(`XinPay - TokenRatesController exchange rate fetch failed for ${address}.`, error)
        return 0
      }
    }
  
    /**
     * @type {Number}
     */
    set interval (interval) {
      this._handle && clearInterval(this._handle)
      if (!interval) { return }
      this._handle = setInterval(() => { this.updateExchangeRates() }, interval)
    }
  
    /**
     * @type {Object}
     */
    set preferences (preferences) {
      this._preferences && this._preferences.unsubscribe()
      if (!preferences) { return }
      this._preferences = preferences
      this.tokens = preferences.getState().tokens
      preferences.subscribe(({ tokens = [] }) => { this.tokens = tokens })
    }
  
    /**
     * @type {Array}
     */
    set tokens (tokens) {
      this._tokens = tokens
      this.updateExchangeRates()
    }
  }
  
  module.exports = TokenRatesController
  