Add + use getFirstDateFromMonth plus tests

acusti · Apr 29, 2024 · 0f8e51e · 0f8e51e
1 parent 7d017b0
commit 0f8e51e
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Showing 2 changed files with 29 additions and 5 deletions.
diff --git a/packages/date-picker/src/utils.test.ts b/packages/date-picker/src/utils.test.ts
@@ -1,6 +1,7 @@
 import { describe, expect, it } from 'vitest';
 
 import {
+    getFirstDateFromMonth,
     getMonthFromDate,
     getMonthNameFromMonth,
     getLastDateFromMonth,
@@ -69,6 +70,26 @@ describe('@acusti/date-picker', () => {
             });
         });
 
+        describe('getFirstDateFromMonth', () => {
+            it('returns the date of the first day for a post-unix epoch month', () => {
+                expect(
+                    getFirstDateFromMonth(getMonthFromDate(new Date(2008, 2, 13))),
+                ).toEqual(new Date(2008, 2, 1));
+            });
+
+            it('returns the correct date for a pre-unix epoch month', () => {
+                expect(
+                    getFirstDateFromMonth(getMonthFromDate(new Date(1865, 5, 2))),
+                ).toEqual(new Date(1865, 5, 1));
+            });
+
+            it('returns an invalid date if given NaN (e.g. if dealing with an Invalid Date)', () => {
+                expect(getFirstDateFromMonth(getMonthFromDate(INVALID_DATE))).toEqual(
+                    INVALID_DATE,
+                );
+            });
+        });
+
         describe('getLastDateFromMonth', () => {
             it('returns the date of the last day for a post-unix epoch month', () => {
                 expect(

diff --git a/packages/date-picker/src/utils.ts b/packages/date-picker/src/utils.ts
@@ -36,10 +36,13 @@ export const getMonthAbbreviationFromMonth = (month: number) => {
     return monthName.substring(0, 3);
 };
 
+export const getFirstDateFromMonth = (month: number) => {
+    const monthIn12 = month < 0 ? (12 - Math.abs(month % 12)) % 12 : month % 12;
+    return new Date(getYearFromMonth(month), monthIn12, 1);
+};
+
 export const getLastDateFromMonth = (month: number) => {
-    const nextMonth = month + 1;
-    const nextMonthIn12 = nextMonth < 0 ? (12 - Math.abs(nextMonth % 12)) % 12 : nextMonth % 12;
-    const lastDate = new Date(getYearFromMonth(nextMonth), nextMonthIn12, 1);
-    lastDate.setDate(lastDate.getDate() - 1);
-    return lastDate;
+    const date = getFirstDateFromMonth(month + 1);
+    date.setDate(date.getDate() - 1);
+    return date;
 };