Maintain token prices using a background service

2 files changed, 83 insertions, 0 deletions

diff --git a/app/scripts/controllers/token-rates.js b/app/scripts/controllers/token-rates.js
new file mode 100644
index 000000000..85a8ca24e
--- /dev/null
+++ b/app/scripts/controllers/token-rates.js
@@ -0,0 +1,76 @@
+const ObservableStore = require('obs-store')
+
+// 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 () {
+    const contractExchangeRates = {}
+    for (const i in this._tokens) {
+      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://exchanges.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) { }
+  }
+
+  /**
+   * @type {Number} - Interval used to poll for exchange rates
+   */
+  set interval (interval) {
+    this._handle && clearInterval(this._handle)
+    if (!interval) { return }
+    this._handle = setInterval(() => { this.updateExchangeRates() }, interval)
+  }
+
+  /**
+   * @type {Object} - Preferences controller instance
+   */
+  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} - Array of token objects with contract addresses
+   */
+  set tokens (tokens) {
+    this._tokens = tokens
+    this.updateExchangeRates()
+  }
+}
+
+module.exports = TokenRatesController
diff --git a/app/scripts/metamask-controller.js b/app/scripts/metamask-controller.js
index fa7890c50..750a97b86 100644
--- a/app/scripts/metamask-controller.js
+++ b/app/scripts/metamask-controller.js
@@ -34,6 +34,7 @@ const PersonalMessageManager = require('./lib/personal-message-manager')
 const TypedMessageManager = require('./lib/typed-message-manager')
 const TransactionController = require('./controllers/transactions')
 const BalancesController = require('./controllers/computed-balances')
+const TokenRatesController = require('./controllers/token-rates')
 const ConfigManager = require('./lib/config-manager')
 const nodeify = require('./lib/nodeify')
 const accountImporter = require('./account-import-strategies')
@@ -104,6 +105,11 @@ module.exports = class MetamaskController extends EventEmitter {
     this.provider = this.initializeProvider()
     this.blockTracker = this.provider._blockTracker
 
+    // token exchange rate tracker
+    this.tokenRatesController = new TokenRatesController({
+      preferences: this.preferencesController.store,
+    })
+
     this.recentBlocksController = new RecentBlocksController({
       blockTracker: this.blockTracker,
       provider: this.provider,
@@ -201,6 +207,7 @@ module.exports = class MetamaskController extends EventEmitter {
       AccountTracker: this.accountTracker.store,
       TxController: this.txController.memStore,
       BalancesController: this.balancesController.store,
+      TokenRatesController: this.tokenRatesController.store,
       MessageManager: this.messageManager.memStore,
       PersonalMessageManager: this.personalMessageManager.memStore,
       TypesMessageManager: this.typedMessageManager.memStore,