Current and Longest streak calculation fixed

Minor refactoring and unit tests added

After CR: user-stats file moved to util folder, export keywork added to exported functions, new line added at the end of gulp file

User-stats-test file moved to replicate user-stats path in test folder

server/utils/user-stats.js

@@ -0,0 +1,46 @@
+import moment from 'moment';
+import { dayCount } from '../utils/date-utils';
+
+const daysBetween = 1.5;
+
+export function calcCurrentStreak(cals) {
+  const revCals = cals.slice().reverse();
+
+  if (dayCount([moment(), revCals[0]]) > daysBetween) {
+    return 0;
+  }
+
+  let streakBroken = false;
+  const lastDayInStreak = revCals
+    .reduce((current, cal, index) => {
+      const before = revCals[index === 0 ? 0 : index - 1];
+      if (
+        !streakBroken &&
+        moment(before).diff(cal, 'days', true) < daysBetween
+        ) {
+        return index;
+      }
+      streakBroken = true;
+      return current;
+    }, 0);
+
+  const lastTimestamp = revCals[lastDayInStreak];
+  return dayCount([moment(), lastTimestamp]);
+}
+
+export function calcLongestStreak(cals) {
+  let tail = cals[0];
+  const longest = cals.reduce((longest, head, index) => {
+    const last = cals[index === 0 ? 0 : index - 1];
+    // is streak broken
+    if (moment(head).diff(last, 'days', true) > daysBetween) {
+      tail = head;
+    }
+    if (dayCount(longest) < dayCount([head, tail])) {
+      return [head, tail];
+    }
+    return longest;
+  }, [cals[0], cals[0]]);
+
+  return dayCount(longest);
+}