Support itbit exchange/ticker. Additions (#232)

* Initial itBit implementation

* Add tests for calculatePrice in exchange/itbit.js

* Add etherium to supported crypto codes in common/itbit.js

* Apply standardjs to itbit files

* itbit trade test. not important

* test getCurrencyRates in ticker/itbit.js

lib/plugins/common/itbit.js

@@ -0,0 +1,92 @@
+'use strict'
+
+const querystring = require('querystring')
+const axios = require('axios')
+const crypto = require('crypto')
+const _ = require('lodash/fp')
+
+const API_ENDPOINT = 'https://api.itbit.com/v1'
+
+let counter = -1
+let lastTimestamp = Date.now()
+
+function generateNonce () {
+  const timestamp = Date.now()
+  if (timestamp !== lastTimestamp) counter = -1
+  lastTimestamp = timestamp
+  counter = (counter + 1) % 1000
+  return timestamp.toString() + counter.toString()
+}
+
+function authRequest (account, method, path, data) {
+  if (!account.userId || !account.walletId || !account.clientKey || !account.clientSecret) {
+    const err = new Error('Must provide user ID, wallet ID, client key, and client secret')
+    return Promise.reject(err)
+  }
+
+  const url = buildURL(method, path, data)
+  const dataString = method !== 'GET' && !_.isEmpty(data) ? JSON.stringify(data) : ''
+  const nonce = generateNonce()
+  const timestamp = Date.now()
+  const message = nonce + JSON.stringify([method, url, dataString, nonce.toString(), timestamp.toString()])
+
+  const hashBuffer = crypto
+    .createHash('sha256')
+    .update(message).digest()
+
+  const bufferToHash = Buffer.concat([Buffer.from(url), hashBuffer])
+
+  const signature = crypto
+    .createHmac('sha512', Buffer.from(account.clientSecret))
+    .update(bufferToHash)
+    .digest('base64')
+
+  return request(method, path, data, {
+    'Authorization': account.clientKey + ':' + signature,
+    'X-Auth-Timestamp': timestamp,
+    'X-Auth-Nonce': nonce
+  })
+}
+
+function request (method, path, data, auth) {
+  const options = {
+    method: method,
+    url: buildURL(method, path, data),
+    headers: {
+      'User-Agent': 'Lamassu itBit node.js client',
+      ...(auth)
+    },
+    ...(method !== 'GET' && { data: data })
+  }
+
+  return axios(options)
+    .then(r => r.data)
+    .catch(e => {
+      var description = _.get(e, 'response.data.description')
+      throw new Error(description || e.message)
+    })
+}
+
+const cryptoCodeTranslations = { 'BTC': 'XBT', 'ETH': 'ETH' }
+function buildMarket (fiatCode, cryptoCode) {
+  const translatedCryptoCode = cryptoCodeTranslations[cryptoCode]
+  if (!translatedCryptoCode) {
+    throw new Error('Unsupported crypto: ' + cryptoCode)
+  }
+
+  if (!_.includes(fiatCode, ['USD', 'EUR', 'SGD'])) {
+    throw new Error('Unsupported fiat: ' + fiatCode)
+  }
+
+  return translatedCryptoCode + fiatCode
+}
+
+function buildURL (method, path, data) {
+  let url = API_ENDPOINT + path
+  if (method === 'GET' && !_.isEmpty(data)) {
+    url += '?' + querystring.stringify(data)
+  }
+  return url
+}
+
+module.exports = { authRequest, request, buildMarket }