fix: adjust TimeGutter for DST (#2205)

Handle memoization of 'start' and 'end' to prevent infinite useEffect, and add DST fix back to the TimeGutter

Author: cutterbl

src/TimeGutter.js

@@ -1,10 +1,26 @@
-import React, { useState, useEffect } from 'react'
+import React, { useState, useEffect, useCallback, useMemo } from 'react'
 import clsx from 'clsx'
 import PropTypes from 'prop-types'
 
-import * as TimeSlotUtils from './utils/TimeSlots'
+import { getSlotMetrics } from './utils/TimeSlots'
 import TimeSlotGroup from './TimeSlotGroup'
 
+/**
+ * Since the TimeGutter only displays the 'times' of slots in a day, and is separate
+ * from the Day Columns themselves, we check to see if the range contains an offset difference
+ * and, if so, change the beginning and end 'date' by a day to properly display the slots times
+ * used.
+ */
+function adjustForDST({ min, max, localizer }) {
+  if (localizer.getTimezoneOffset(min) !== localizer.getTimezoneOffset(max)) {
+    return {
+      start: localizer.add(min, -1, 'day'),
+      end: localizer.add(max, -1, 'day'),
+    }
+  }
+  return { start: min, end: max }
+}
+
 const TimeGutter = ({
   min,
   max,
@@ -17,10 +33,15 @@ const TimeGutter = ({
   getters,
   gutterRef,
 }) => {
+  const { start, end } = useMemo(
+    () => adjustForDST({ min, max, localizer }),
+    // eslint-disable-next-line react-hooks/exhaustive-deps
+    [min?.toISOString(), max?.toISOString(), localizer]
+  )
   const [slotMetrics, setSlotMetrics] = useState(
-    TimeSlotUtils.getSlotMetrics({
-      min,
-      max,
+    getSlotMetrics({
+      min: start,
+      max: end,
       timeslots,
       step,
       localizer,
@@ -31,8 +52,8 @@ const TimeGutter = ({
     if (slotMetrics) {
       setSlotMetrics(
         slotMetrics.update({
-          min,
-          max,
+          min: start,
+          max: end,
           timeslots,
           step,
           localizer,
@@ -43,18 +64,21 @@ const TimeGutter = ({
      * We don't want this to fire when slotMetrics is updated as it would recursively bomb
      */
     // eslint-disable-next-line react-hooks/exhaustive-deps
-  }, [min, max, timeslots, step])
+  }, [start?.toISOString(), end?.toISOString(), timeslots, step])
 
-  const renderSlot = (value, idx) => {
-    if (idx) return null // don't return the first (0) idx
+  const renderSlot = useCallback(
+    (value, idx) => {
+      if (idx) return null // don't return the first (0) idx
 
-    const isNow = slotMetrics.dateIsInGroup(getNow(), idx)
-    return (
-      <span className={clsx('rbc-label', isNow && 'rbc-now')}>
-        {localizer.format(value, 'timeGutterFormat')}
-      </span>
-    )
-  }
+      const isNow = slotMetrics.dateIsInGroup(getNow(), idx)
+      return (
+        <span className={clsx('rbc-label', isNow && 'rbc-now')}>
+          {localizer.format(value, 'timeGutterFormat')}
+        </span>
+      )
+    },
+    [slotMetrics, localizer, getNow]
+  )
 
   return (
     <div className="rbc-time-gutter rbc-time-column" ref={gutterRef}>