fix: month grouping error in timeline page (#2861)

web/src/components/ActivityCalendar.tsx

 import { Tooltip } from "@mui/joy";
 import classNames from "classnames";
-import { getNormalizedDateString } from "@/helpers/datetime";
+import { getNormalizedDateString, getDateWithOffset } from "@/helpers/datetime";
 
 interface Props {
   // Format: 2021-1
@@ -26,8 +26,8 @@ const getCellAdditionalStyles = (count: number, maxCount: number) => {
 
 const ActivityCalendar = (props: Props) => {
   const { month: monthStr, data, onClick } = props;
-  const year = new Date(monthStr).getFullYear();
-  const month = new Date(monthStr).getMonth() + 1;
+  const year = new Date(monthStr).getUTCFullYear();
+  const month = new Date(monthStr).getUTCMonth() + 1;
   const dayInMonth = new Date(year, month, 0).getDate();
   const firstDay = new Date(year, month - 1, 1).getDay();
   const lastDay = new Date(year, month - 1, dayInMonth).getDay();
@@ -47,7 +47,9 @@ const ActivityCalendar = (props: Props) => {
   return (
     <div className={classNames("w-36 h-auto p-0.5 shrink-0 grid grid-cols-7 grid-flow-row gap-1")}>
       {days.map((day, index) => {
-        const date = getNormalizedDateString(`${year}-${String(month).padStart(2, "0")}-${String(day).padStart(2, "0")}`);
+        const date = getNormalizedDateString(
+          getDateWithOffset(`${year}-${String(month).padStart(2, "0")}-${String(day).padStart(2, "0")}`),
+        );
         const count = data[date] || 0;
         const isToday = new Date().toDateString() === new Date(date).toDateString();
         const tooltipText = count ? `${count} memos in ${date}` : date;

web/src/helpers/datetime.ts

@@ -169,3 +169,15 @@ export function isFutureDate(t?: Date | number | string): boolean {
   const timestamp = getTimeStampByDate(t ? t : Date.now());
   return timestamp > Date.now();
 }
+
+/**
+ * Calculates a new Date object by adjusting the provided date, timestamp, or date string
+ * based on the current timezone offset.
+ *
+ * @param t - The input date, timestamp, or date string (optional). If not provided,
+ *            the current date and time will be used.
+ * @returns A new Date object adjusted by the current timezone offset.
+ */
+export function getDateWithOffset(t?: Date | number | string): Date {
+  return new Date(getTimeStampByDate(t) + new Date().getTimezoneOffset() * 60 * 1000);
+}

web/src/pages/Timeline.tsx

@@ -148,9 +148,9 @@ const Timeline = () => {
                   <div className={classNames("flex shrink-0", md ? "flex-col w-40 pr-4 pl-2 pb-8" : "flex-row w-full pl-1 mt-2 mb-2")}>
                     <div className={classNames("w-full flex flex-col", md && "mt-4 mb-2")}>
                       <span className="font-medium text-3xl leading-none mb-1">
-                        {new Date(group.month).toLocaleString(i18n.language, { month: "short" })}
+                        {new Date(group.month).toLocaleString(i18n.language, { month: "short", timeZone: "UTC" })}
                       </span>
-                      <span className="opacity-60">{new Date(group.month).getFullYear()}</span>
+                      <span className="opacity-60">{new Date(group.month).getUTCFullYear()}</span>
                       <span className="text-xs opacity-40">Total: {sum(Object.values(group.data))}</span>
                     </div>
                     <ActivityCalendar month={group.month} data={group.data} onClick={(date) => setSelectedDay(date)} />