add date interval module

src/helpers/index_interval.js

@@ -0,0 +1,37 @@
+import moment from 'moment';
+
+export const intervals = [
+  'y',
+  'M',
+  'w',
+  'd',
+  'h',
+  'm'
+];
+
+export const intervalNames = [
+  'year',
+  'month',
+  'week',
+  'day',
+  'hour',
+  'minute'
+];
+
+export default function getTimestamp(intervalStr) {
+  const index = intervals.indexOf(intervalStr);
+  if (index === -1) throw new Error('Invalid index interval: ', intervalStr);
+
+  const startType = intervalNames[intervalStr];
+  const m = moment();
+  m.startOf(startType);
+
+  let dateString = 'YYYY-MM-DD';
+  if (startType === 'hour') {
+    dateString += '-HH';
+  }
+  if (startType === 'minute') {
+    dateString += '-HH-mm';
+  }
+  return m.format(dateString);
+}