add Time, reducing some duplication

common/GameCommon.js

@@ -1,5 +1,6 @@
 import Geometry from './Geometry.js'
 import Protocol from './Protocol.js'
+import Time from './Time.js'
 import Util from './Util.js'
 
 // Map<gameId, GameObject>
@@ -89,14 +90,14 @@ function playerExists(gameId, playerId) {
 }
 
 function getRelevantPlayers(gameId, ts) {
-  const minTs = ts - 30000
+  const minTs = ts - 30 * Time.SEC
   return getAllPlayers(gameId).filter(player => {
     return player.ts >= minTs || player.points > 0
   })
 }
 
 function getActivePlayers(gameId, ts) {
-  const minTs = ts - 30000
+  const minTs = ts - 30 * Time.SEC
   return getAllPlayers(gameId).filter(player => {
     return player.ts >= minTs
   })

common/Time.js

@@ -0,0 +1,45 @@
+const MS = 1
+const SEC = MS * 1000
+const MIN = SEC * 60
+const HOUR = MIN * 60
+const DAY = HOUR * 24
+
+export const timestamp = () => {
+  const d = new Date();
+  return Date.UTC(
+    d.getUTCFullYear(),
+    d.getUTCMonth(),
+    d.getUTCDate(),
+    d.getUTCHours(),
+    d.getUTCMinutes(),
+    d.getUTCSeconds(),
+    d.getUTCMilliseconds(),
+  )
+}
+
+export const timeDiffStr = (from, to) => {
+  let diff = to - from
+  const d = Math.floor(diff / DAY)
+  diff = diff % DAY
+
+  const h = Math.floor(diff / HOUR)
+  diff = diff % HOUR
+
+  const m = Math.floor(diff / MIN)
+  diff = diff % MIN
+
+  const s = Math.floor(diff / SEC)
+
+  return `${d}d ${h}h ${m}m ${s}s`
+}
+
+export default {
+  MS,
+  SEC,
+  MIN,
+  HOUR,
+  DAY,
+
+  timestamp,
+  timeDiffStr,
+}

common/Util.js

@@ -69,19 +69,6 @@ export const shuffle = (
   return arr
 }
 
-export const timestamp = () => {
-  const d = new Date();
-  return Date.UTC(
-    d.getUTCFullYear(),
-    d.getUTCMonth(),
-    d.getUTCDate(),
-    d.getUTCHours(),
-    d.getUTCMinutes(),
-    d.getUTCSeconds(),
-    d.getUTCMilliseconds(),
-  )
-}
-
 function encodeShape(data) {
   if (typeof data === 'number') {
       return data
@@ -224,7 +211,6 @@ export default {
   choice,
   throttle,
   shuffle,
-  timestamp,
 
   encodeShape,
   decodeShape,