Consolidate some stats server functions

server/StatsServer.js

@@ -0,0 +1,78 @@
+const redis = require('redis')
+const invariant = require('invariant')
+
+const RedisURL = process.env.REDIS_URL
+
+invariant(
+  RedisURL,
+  'Missing the $REDIS_URL environment variable'
+)
+
+const db = redis.createClient(RedisURL)
+
+const sumValues = (array) =>
+  array.reduce((memo, n) => memo + (parseInt(n, 10) || 0), 0)
+
+const getKeyValues = (keys) =>
+  new Promise((resolve, reject) => {
+    db.mget(keys, (error, values) => {
+      if (error) {
+        reject(error)
+      } else {
+        resolve(values)
+      }
+    })
+  })
+
+const sumKeys = (keys) =>
+  getKeyValues(keys).then(sumValues)
+
+const createScoresMap = (array) => {
+  const map = {}
+
+  for (let i = 0; i < array.length; i += 2)
+    map[array[i]] = parseInt(array[i + 1], 10)
+
+  return map
+}
+
+const getTopScores = (key, n = 10) =>
+  new Promise((resolve, reject) => {
+    db.zrevrange(key, 0, n, 'withscores', (error, value) => {
+      if (error) {
+        reject(error)
+      } else {
+        resolve(createScoresMap(value))
+      }
+    })
+  })
+
+const sumTopScores = (keys, n) =>
+  Promise.all(keys.map(key => getTopScores(key, n))).then(values => {
+    return values.reduce((memo, map) => {
+      Object.keys(map).forEach(key => {
+        memo[key] = (memo[key] || 0) + map[key]
+      })
+
+      return memo
+    }, {})
+  })
+
+const createDayKey = (date) =>
+  `${date.getUTCFullYear()}-${date.getUTCMonth()}-${date.getUTCDate()}`
+
+const createHourKey = (date) =>
+  `${createDayKey(date)}-${date.getUTCHours()}`
+
+const createMinuteKey = (date) =>
+  `${createDayKey(date)}-${date.getUTCMinutes()}`
+
+module.exports = {
+  getKeyValues,
+  sumKeys,
+  getTopScores,
+  sumTopScores,
+  createDayKey,
+  createHourKey,
+  createMinuteKey
+}