fix: Improve behaviour of highlight dates with swapRange

src/day.tsx

@@ -67,6 +67,7 @@ interface DayProps
   locale?: Locale;
   monthShowsDuplicateDaysEnd?: boolean;
   monthShowsDuplicateDaysStart?: boolean;
+  swapRange?: boolean;
 }
 
 /**
@@ -288,6 +289,7 @@ export default class Day extends Component<DayProps> {
       selectsRange,
       selectsDisabledDaysInRange,
       startDate,
+      swapRange,
       endDate,
     } = this.props;
 
@@ -317,13 +319,18 @@ export default class Day extends Component<DayProps> {
       return isDayInRange(day, startDate, selectingDate);
     }
 
-    if (
-      selectsRange &&
-      startDate &&
-      !endDate &&
-      (isAfter(selectingDate, startDate) || isEqual(selectingDate, startDate))
-    ) {
-      return isDayInRange(day, startDate, selectingDate);
+    if (selectsRange && startDate && !endDate) {
+      if (isEqual(selectingDate, startDate)) {
+        return isDayInRange(day, startDate, selectingDate);
+      }
+
+      if (isAfter(selectingDate, startDate)) {
+        return isDayInRange(day, startDate, selectingDate);
+      }
+
+      if (swapRange && isBefore(selectingDate, startDate)) {
+        return isDayInRange(day, selectingDate, startDate);
+      }
     }
 
     return false;
@@ -334,29 +341,49 @@ export default class Day extends Component<DayProps> {
       return false;
     }
 
-    const { day, startDate, selectsStart } = this.props;
+    const { day, startDate, selectsStart, swapRange, selectsRange } =
+      this.props;
     const selectingDate = this.props.selectingDate ?? this.props.preSelection;
 
     if (selectsStart) {
       return isSameDay(day, selectingDate);
-    } else {
-      return isSameDay(day, startDate);
     }
+
+    if (selectsRange && swapRange && startDate && selectingDate) {
+      return isSameDay(
+        day,
+        isBefore(selectingDate, startDate) ? selectingDate : startDate,
+      );
+    }
+
+    return isSameDay(day, startDate);
   };
 
   isSelectingRangeEnd = () => {
     if (!this.isInSelectingRange()) {
       return false;
     }
 
-    const { day, endDate, selectsEnd, selectsRange } = this.props;
+    const { day, endDate, selectsEnd, selectsRange, swapRange, startDate } =
+      this.props;
     const selectingDate = this.props.selectingDate ?? this.props.preSelection;
 
-    if (selectsEnd || selectsRange) {
+    if (selectsEnd) {
+      return isSameDay(day, selectingDate);
+    }
+
+    if (selectsRange && swapRange && startDate && selectingDate) {
+      return isSameDay(
+        day,
+        isBefore(selectingDate, startDate) ? startDate : selectingDate,
+      );
+    }
+
+    if (selectsRange) {
       return isSameDay(day, selectingDate);
-    } else {
-      return isSameDay(day, endDate);
     }
+
+    return isSameDay(day, endDate);
   };
 
   isRangeStart = () => {

src/test/day_test.test.tsx

@@ -896,6 +896,151 @@ describe("Day", () => {
         ).toBe(true);
       });
     });
+
+    describe("for a date picker with selectsRange and swapRange prop", () => {
+      it("should select range from startDate to selectingDate if selectingDate is after startDate", () => {
+        const startDate = newDate();
+        const dayInRange = addDays(startDate, 1);
+        const selectingDate = addDays(startDate, 2);
+
+        const containerStartDay = renderDay(dayInRange, {
+          startDate,
+          selectingDate,
+          selectsRange: true,
+          swapRange: true,
+        });
+        expect(
+          containerStartDay
+            .querySelector(".react-datepicker__day")
+            ?.classList.contains(rangeDayClassName),
+        ).toBe(true);
+      });
+
+      it("should select range from selectingDate to startDate if selectingDate is before startDate", () => {
+        const startDate = newDate();
+        const dayInRange = subDays(startDate, 1);
+        const selectingDate = subDays(startDate, 2);
+
+        const containerStartDay = renderDay(dayInRange, {
+          startDate,
+          selectingDate,
+          selectsRange: true,
+          swapRange: true,
+        });
+        expect(
+          containerStartDay
+            .querySelector(".react-datepicker__day")
+            ?.classList.contains(rangeDayClassName),
+        ).toBe(true);
+      });
+
+      it("should select as range if selectingDate is equal to startDate", () => {
+        const startDate = newDate();
+        const selectingDate = startDate;
+
+        const containerStartDay = renderDay(startDate, {
+          startDate,
+          selectingDate,
+          selectsRange: true,
+          swapRange: true,
+        });
+        expect(
+          containerStartDay
+            .querySelector(".react-datepicker__day")
+            ?.classList.contains(rangeDayClassName),
+        ).toBe(true);
+      });
+
+      it("should set selectingDate as the start of range and startDate as the end of range if selectingDate is before startDate", () => {
+        const startDate = newDate();
+        const selectingDate = subDays(startDate, 1);
+
+        const containerStartDay = renderDay(selectingDate, {
+          startDate,
+          selectingDate,
+          selectsRange: true,
+          swapRange: true,
+        });
+        expect(
+          containerStartDay
+            .querySelector(".react-datepicker__day")
+            ?.classList.contains(rangeDayStartClassName),
+        ).toBe(true);
+
+        const containerEndDay = renderDay(startDate, {
+          startDate,
+          selectingDate,
+          selectsRange: true,
+          swapRange: true,
+        });
+
+        expect(
+          containerEndDay
+            .querySelector(".react-datepicker__day")
+            ?.classList.contains(rangeDayEndClassName),
+        ).toBe(true);
+      });
+
+      it("should set selectingDate as the end of range and startDate as the start of range if selectingDate is after startDate", () => {
+        const startDate = newDate();
+        const selectingDate = addDays(startDate, 1);
+
+        const containerStartDay = renderDay(startDate, {
+          startDate,
+          selectingDate,
+          selectsRange: true,
+          swapRange: true,
+        });
+        expect(
+          containerStartDay
+            .querySelector(".react-datepicker__day")
+            ?.classList.contains(rangeDayStartClassName),
+        ).toBe(true);
+
+        const containerEndDay = renderDay(selectingDate, {
+          startDate,
+          selectingDate,
+          selectsRange: true,
+          swapRange: true,
+        });
+
+        expect(
+          containerEndDay
+            .querySelector(".react-datepicker__day")
+            ?.classList.contains(rangeDayEndClassName),
+        ).toBe(true);
+      });
+
+      it("should set startDate as the end and start range if selectionDate equal startDate", () => {
+        const startDate = newDate();
+        const selectingDate = startDate;
+
+        const containerStartDay = renderDay(startDate, {
+          startDate,
+          selectingDate,
+          selectsRange: true,
+          swapRange: true,
+        });
+        expect(
+          containerStartDay
+            .querySelector(".react-datepicker__day")
+            ?.classList.contains(rangeDayStartClassName),
+        ).toBe(true);
+
+        const containerEndDay = renderDay(selectingDate, {
+          startDate,
+          selectingDate,
+          selectsRange: true,
+          swapRange: true,
+        });
+
+        expect(
+          containerEndDay
+            .querySelector(".react-datepicker__day")
+            ?.classList.contains(rangeDayEndClassName),
+        ).toBe(true);
+      });
+    });
   });
 
   describe("today", () => {