begin implementing new preenUserHistory method: port current code to es6 and setup tests

common/script/preenUserHistory.js

@@ -0,0 +1,66 @@
+import _ from 'lodash';
+import moment from 'moment';
+/*
+ Preen history for users with > 7 history entries
+ This takes an infinite array of single day entries [day day day day day...], and turns it into a condensed array
+ of averages, condensing more the further back in time we go. Eg, 7 entries each for last 7 days; 1 entry each week
+ of this month; 1 entry for each month of this year; 1 entry per previous year: [day*7 week*4 month*12 year*infinite]
+ */
+function _preenHistory (history) {
+  history = _.filter(history, h => {
+    return Boolean(h); // filter missing entries
+  });
+  let newHistory = [];
+
+  function _preen (amount, groupBy) {
+    let groups = _.chain(history).groupBy(h => {
+      return moment(h.date).format(groupBy);
+    }).sortBy((h, k) => {
+      return k;
+    }).value();
+    groups = groups.slice(-amount);
+    groups.pop();
+
+    return _.each(groups, group => {
+      newHistory.push({
+        date: moment(group[0].date).toDate(),
+        value: _.reduce(group, (m, obj) => {
+          return m + obj.value;
+        }, 0) / group.length,
+      });
+    });
+  }
+
+  _preen(50, 'YYYY');
+  _preen(moment().format('MM'), 'YYYYMM');
+
+  let thisMonth = moment().format('YYYYMM');
+  newHistory = newHistory.concat(_.filter(history, h => {
+    return moment(h.date).format('YYYYMM') === thisMonth;
+  }));
+
+  return newHistory;
+}
+
+export default function (user, minHistLen = 7) {
+  _.each(user.habits.concat(user.dailys), (task, index) => {
+    if (task.history && task.history.length > minHistLen) {
+      task.history = _preenHistory(task.history);
+      user.markModified(`user.${task.type}s.${index}.history`);
+    }
+  });
+
+  _.defaults(user.history, {
+    todos: [],
+    exp: [],
+  });
+
+  if (user.history.exp.length > minHistLen) {
+    user.history.exp = _preenHistory(user.history.exp);
+    user.markModified('user.history.exp');
+  }
+  if (user.history.todos.length > minHistLen) {
+    user.history.todos = _preenHistory(user.history.todos);
+    user.markModified('user.history.todos');
+  }
+}