🐛 Fix navigation issue with disabled dates in date picker

- Resolved the issue where navigating to a month with a previously selected date that is now disabled prevents using arrow keys (Tab) to navigate
- Fixed by pre-selecting the first enabled date in the same month.

Closes Hacker0x01#5147

src/calendar.tsx

@@ -1,4 +1,5 @@
 import { clsx } from "clsx";
+import { differenceInDays } from "date-fns";
 import React, { Component, createRef } from "react";
 
 import CalendarContainer from "./calendar_container";
@@ -40,6 +41,9 @@ import {
   DEFAULT_YEAR_ITEM_NUMBER,
   getMonthInLocale,
   type Locale,
+  getStartOfMonth,
+  getEndOfMonth,
+  isDayDisabled,
 } from "./date_utils";
 import InputTime from "./input_time";
 import Month from "./month";
@@ -379,14 +383,42 @@ export default class Calendar extends Component<CalendarProps, CalendarState> {
     this.props.setPreSelection && this.props.setPreSelection(date);
   };
 
+  getEnabledPreSelectionDateForMonth = (date: Date) => {
+    if (!isDayDisabled(date, this.props)) {
+      return date;
+    }
+
+    const startOfMonth = getStartOfMonth(date);
+    const endOfMonth = getEndOfMonth(date);
+
+    const totalDays = differenceInDays(endOfMonth, startOfMonth);
+
+    let preSelectedDate = null;
+
+    for (let dayIdx = 0; dayIdx <= totalDays; dayIdx++) {
+      const processingDate = addDays(startOfMonth, dayIdx);
+
+      if (!isDayDisabled(processingDate, this.props)) {
+        preSelectedDate = processingDate;
+        break;
+      }
+    }
+
+    return preSelectedDate;
+  };
+
   handleMonthChange = (date: Date): void => {
-    this.handleCustomMonthChange(date);
+    const enabledPreSelectionDate =
+      this.getEnabledPreSelectionDateForMonth(date) ?? date;
+
+    this.handleCustomMonthChange(enabledPreSelectionDate);
     if (this.props.adjustDateOnChange) {
-      this.props.onSelect(date);
+      this.props.onSelect(enabledPreSelectionDate);
       this.props.setOpen?.(true);
     }
 
-    this.props.setPreSelection && this.props.setPreSelection(date);
+    this.props.setPreSelection &&
+      this.props.setPreSelection(enabledPreSelectionDate);
   };
 
   handleCustomMonthChange = (date: Date): void => {
@@ -478,8 +510,7 @@ export default class Calendar extends Component<CalendarProps, CalendarState> {
         date: subYears(
           date,
           this.props.showYearPicker
-            ? (this.props.yearItemNumber ??
-                Calendar.defaultProps.yearItemNumber)
+            ? this.props.yearItemNumber ?? Calendar.defaultProps.yearItemNumber
             : 1,
         ),
       }),
@@ -593,8 +624,7 @@ export default class Calendar extends Component<CalendarProps, CalendarState> {
         date: addYears(
           date,
           this.props.showYearPicker
-            ? (this.props.yearItemNumber ??
-                Calendar.defaultProps.yearItemNumber)
+            ? this.props.yearItemNumber ?? Calendar.defaultProps.yearItemNumber
             : 1,
         ),
       }),

src/test/calendar_test.test.tsx

@@ -3,6 +3,7 @@
  */
 
 import { render, fireEvent, act, waitFor } from "@testing-library/react";
+import { setDate, startOfMonth, eachDayOfInterval, endOfMonth } from "date-fns";
 import { endOfYear } from "date-fns/endOfYear";
 import { isSunday } from "date-fns/isSunday";
 import { eo } from "date-fns/locale/eo";
@@ -28,6 +29,8 @@ import {
   isSameDay,
   subMonths,
   subYears,
+  addDays,
+  getDate,
 } from "../date_utils";
 import DatePicker from "../index";
 
@@ -2257,6 +2260,112 @@ describe("Calendar", () => {
         currentMonth === 0 ? 11 : currentMonth - 1,
       );
     });
+
+    describe("pre-selection & disabled dates", () => {
+      it("should update the pre-selected dates to the first enabled day in a month when the next month is selected", () => {
+        const selected = new Date("2024-06-01");
+        const excludeDate = addMonths(selected, 1);
+
+        const { container } = render(
+          <DatePicker selected={selected} excludeDates={[excludeDate]} />,
+        );
+        const input = safeQuerySelector<HTMLInputElement>(container, "input");
+        fireEvent.focus(input);
+
+        const nextButton = safeQuerySelector<HTMLButtonElement>(
+          container,
+          ".react-datepicker__navigation--next",
+        );
+        fireEvent.click(nextButton);
+
+        const preSelectedNewDate = safeQuerySelector(
+          container,
+          ".react-datepicker__day--keyboard-selected",
+        ).textContent;
+        const expectedPreSelectedNewDate = addDays(excludeDate, 1);
+
+        expect(Number(preSelectedNewDate)).toBe(
+          getDate(expectedPreSelectedNewDate),
+        );
+      });
+
+      it("should update the pre-selected dates to the first enabled day in a month when the previous month is selected", () => {
+        const selected = new Date("2024-06-08");
+        const excludeDate = addMonths(selected, 1);
+
+        const { container } = render(
+          <DatePicker selected={selected} excludeDates={[excludeDate]} />,
+        );
+        const input = safeQuerySelector<HTMLInputElement>(container, "input");
+        fireEvent.focus(input);
+
+        const nextButton = safeQuerySelector<HTMLButtonElement>(
+          container,
+          ".react-datepicker__navigation--next",
+        );
+        fireEvent.click(nextButton);
+
+        const preSelectedNewDate = safeQuerySelector(
+          container,
+          ".react-datepicker__day--keyboard-selected",
+        ).textContent;
+        const expectedPreSelectedNewDate = setDate(excludeDate, 1);
+
+        expect(Number(preSelectedNewDate)).toBe(
+          getDate(expectedPreSelectedNewDate),
+        );
+      });
+
+      it("shouldn't set pre-select any date if all dates of a next month is disabled", () => {
+        const selected = new Date("2024-06-08");
+        const nextMonth = addMonths(selected, 1);
+        const excludeDates = eachDayOfInterval({
+          start: startOfMonth(nextMonth),
+          end: endOfMonth(nextMonth),
+        });
+
+        const { container } = render(
+          <DatePicker selected={selected} excludeDates={excludeDates} />,
+        );
+        const input = safeQuerySelector<HTMLInputElement>(container, "input");
+        fireEvent.focus(input);
+
+        const nextButton = safeQuerySelector<HTMLButtonElement>(
+          container,
+          ".react-datepicker__navigation--next",
+        );
+        fireEvent.click(nextButton);
+
+        expect(
+          container.querySelector(".react-datepicker__day--keyboard-selected"),
+        ).toBeNull();
+      });
+
+      it("shouldn't set pre-select any date if all dates of a last month is disabled", () => {
+        const selected = new Date("2024-06-08");
+        const lastMonth = subMonths(selected, 1);
+        const excludeDates = eachDayOfInterval({
+          start: startOfMonth(lastMonth),
+          end: endOfMonth(lastMonth),
+        });
+
+        const { container } = render(
+          <DatePicker selected={selected} excludeDates={excludeDates} />,
+        );
+        const input = safeQuerySelector<HTMLInputElement>(container, "input");
+        fireEvent.focus(input);
+
+        const nextButton = safeQuerySelector<HTMLButtonElement>(
+          container,
+          ".react-datepicker__navigation--previous",
+        );
+        fireEvent.click(nextButton);
+
+        expect(
+          container.querySelector(".react-datepicker__day--keyboard-selected"),
+        ).toBeNull();
+      });
+    });
   });
 
   describe("showTimeSelect", () => {