fix(getPrevDate): the wrong result was sometimes returned for months …

…with less than 31 days

Closes #313

Signed-off-by: Pascal Sthamer <10992664+P4sca1@users.noreply.github.com>

src/cron.ts

@@ -424,7 +424,7 @@ export class Cron {
 		}
 
 		// We try every month within the past 5 years to make sure that we tried to
-		// find a matching date insidde a whole leap year.
+		// find a matching date inside a whole leap year.
 		const maxIterations = this.reversed.months.length * 5
 
 		for (let i = 0; i < maxIterations; i++) {
@@ -444,7 +444,10 @@ export class Cron {
 				'prev',
 				year,
 				month,
-				isStartMonth ? startDateElements.day : 31,
+				isStartMonth
+					? startDateElements.day
+					: // Start searching from the last day of the month.
+						getDaysInMonth(year, month),
 			)
 			let isStartDay = isStartMonth && day === startDateElements.day
 

test/cron.test.ts

@@ -433,6 +433,16 @@ describe('getPrevDate(s)', () => {
 				new Date(2020, 9, 5, 18, 50, 2),
 			),
 		).toStrictEqual(new Date(2019, 11, 31, 0, 0, 0))
+
+		// https://github.com/P4sca1/cron-schedule/issues/313
+		// Cron: every Wednesday at 10:00
+		// Start date: 01.05.2025 10:00:00
+		// Expected: 24.04.2024 10:00:00
+		expect(
+			parseCronExpression('0 10 * * 3').getPrevDate(
+				new Date(2024, 4, 1, 9, 0, 0),
+			),
+		).toStrictEqual(new Date(2024, 3, 24, 10, 0, 0))
 	})
 
 	test('Should correctly get the previous dates', () => {