fix: Correct display of beginning DST

This corrects jquense#1617, fixing the display of the TimeGutter times as well as correcting event layouts from the momentLocalizer, while maintaining date math within the localizers.

src/TimeGutter.js

@@ -5,22 +5,45 @@ import React, { Component } from 'react'
 import * as TimeSlotUtils 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 }
+}
+
 export default class TimeGutter extends Component {
   constructor(...args) {
     super(...args)
 
     const { min, max, timeslots, step, localizer } = this.props
+    const { start, end } = adjustForDST({ min, max, localizer })
     this.slotMetrics = TimeSlotUtils.getSlotMetrics({
-      min,
-      max,
+      min: start,
+      max: end,
       timeslots,
       step,
       localizer,
     })
   }
 
   UNSAFE_componentWillReceiveProps(nextProps) {
-    this.slotMetrics = this.slotMetrics.update(nextProps)
+    const { min, max, localizer } = nextProps
+    const { start, end } = adjustForDST({ min, max, localizer })
+    this.slotMetrics = this.slotMetrics.update({
+      ...nextProps,
+      min: start,
+      max: end,
+    })
   }
 
   renderSlot = (value, idx) => {

src/less/time-grid.less

@@ -25,6 +25,7 @@
 
   .rbc-time-gutter {
     white-space: nowrap;
+    text-align: right;
   }
 
   .rbc-allday-cell {
@@ -95,9 +96,9 @@
     border-right: 1px solid @cell-border;
   }
 
-  >.rbc-row.rbc-row-resource {
-      border-bottom: 1px solid @cell-border;
-      flex-shrink: 0;
+  > .rbc-row.rbc-row-resource {
+    border-bottom: 1px solid @cell-border;
+    flex-shrink: 0;
   }
 }
 

src/localizer.js

@@ -172,6 +172,9 @@ export class DateLocalizer {
     this.visibleDays = spec.visibleDays || visibleDays
 
     this.getSlotDate = spec.getSlotDate || getSlotDate
+    this.getTimezoneOffset =
+      spec.getTimezoneOffset || (value => value.getTimezoneOffset())
+    this.getDstOffset = spec.getDstOffset || getDstOffset
     this.getTotalMin = spec.getTotalMin || getTotalMin
     this.getMinutesFromMidnight =
       spec.getMinutesFromMidnight || getMinutesFromMidnight

src/localizers/moment.js

@@ -53,6 +53,37 @@ function fixUnit(unit) {
 export default function(moment) {
   const locale = (m, c) => (c ? m.locale(c) : m)
 
+  function getTimezoneOffset(date) {
+    // ensures this gets cast to timezone
+    return moment(date)
+      .toDate()
+      .getTimezoneOffset()
+  }
+
+  function getDstOffset(start, end) {
+    // convert to moment, in case
+    const st = moment(start)
+    const ed = moment(end)
+    // if not using moment timezone
+    if (!moment.tz) {
+      return st.toDate().getTimezoneOffset() - ed.toDate().getTimezoneOffset()
+    }
+    /**
+     * If using moment-timezone, and a timezone has been applied, then
+     * use this to get the proper timezone offset, otherwise default
+     * the timezone to the browser local
+     */
+    const tzName = st?._z?.name ?? moment.tz.guess()
+    const startOffset = moment.tz.zone(tzName).utcOffset(+st)
+    const endOffset = moment.tz.zone(tzName).utcOffset(+ed)
+    return startOffset - endOffset
+  }
+
+  function getDayStartDstOffset(start) {
+    const dayStart = moment(start).startOf('day')
+    return getDstOffset(dayStart, start)
+  }
+
   /*** BEGIN localized date arithmetic methods with moment ***/
   function defineComparators(a, b, unit) {
     const datePart = fixUnit(unit)
@@ -242,7 +273,7 @@ export default function(moment) {
   function getMinutesFromMidnight(start) {
     const dayStart = moment(start).startOf('day')
     const day = moment(start)
-    return day.diff(dayStart, 'minutes')
+    return day.diff(dayStart, 'minutes') + getDayStartDstOffset(start)
   }
 
   // These two are used by DateSlotMetrics
@@ -358,6 +389,8 @@ export default function(moment) {
     minutes,
 
     getSlotDate,
+    getTimezoneOffset,
+    getDstOffset,
     getTotalMin,
     getMinutesFromMidnight,
     continuesPrior,

src/sass/time-grid.scss

@@ -25,6 +25,7 @@
 
   .rbc-time-gutter {
     white-space: nowrap;
+    text-align: right;
   }
 
   .rbc-allday-cell {
@@ -95,9 +96,9 @@
     border-right: 1px solid $cell-border;
   }
 
-  >.rbc-row.rbc-row-resource {
-      border-bottom: 1px solid $cell-border;
-      flex-shrink: 0;
+  > .rbc-row.rbc-row-resource {
+    border-bottom: 1px solid $cell-border;
+    flex-shrink: 0;
   }
 }
 

src/utils/TimeSlots.js

@@ -44,7 +44,9 @@ export function getSlotMetrics({
   )
 
   function positionFromDate(date) {
-    const diff = localizer.getTotalMin(start, date)
+    const diff =
+      localizer.diff(start, date, 'minutes') +
+      localizer.getDstOffset(start, date)
     return Math.min(diff, totalMin)
   }