add coinbase ticker

lib/plugins/ticker/bitstamp/bitstamp.js

@@ -1,5 +1,5 @@
 const BN = require('../../../bn')
-const common = require('../common/bitstamp')
+const common = require('../../common/bitstamp')
 
 function ticker (account, fiatCode, cryptoCode) {
   return Promise.resolve()

lib/plugins/ticker/coinbase/coinbase.js

@@ -0,0 +1,55 @@
+const _ = require('lodash/fp')
+const axios = require('axios')
+
+const BN = require('../../../bn')
+
+function getBuyPrice (obj) {
+  const currencyPair = obj.currencyPair
+
+  return axios({
+    method: 'get',
+    url: `https://api.coinbase.com/v2/prices/${currencyPair}/buy`,
+    headers: {'CB-Version': '2017-07-10'}
+  })
+  .then(r => r.data)
+}
+
+function getSellPrice (obj) {
+  const currencyPair = obj.currencyPair
+
+  return axios({
+    method: 'get',
+    url: `https://api.coinbase.com/v2/prices/${currencyPair}/sell`,
+    headers: {'CB-Version': '2017-07-10'}
+  })
+  .then(r => r.data)
+}
+
+function ticker (account, fiatCode, cryptoCode) {
+  return Promise.resolve()
+  .then(() => {
+    if (!_.includes(cryptoCode, ['BTC', 'ETH', 'LTC'])) {
+      throw new Error('Unsupported crypto: ' + cryptoCode)
+    }
+  })
+  .then(() => {
+    const currencyPair = `${cryptoCode}-${fiatCode}`
+    const promises = [
+      getBuyPrice({currencyPair}),
+      getSellPrice({currencyPair})
+    ]
+
+    return Promise.all(promises)
+  })
+  .then(([buyPrice, sellPrice]) => ({
+    rates: {
+      ask: BN(buyPrice.data.amount),
+      bid: BN(sellPrice.data.amount)
+    }
+  }))
+}
+
+module.exports = {
+  ticker
+}
+