feat: add Date.subMonths method (#764)

Lendable · Aug 21, 2024 · 55f2859 · 55f2859
1 parent 4e1566f
commit 55f2859
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Showing 2 changed files with 78 additions and 6 deletions.
diff --git a/lib/Date.php b/lib/Date.php
@@ -121,13 +121,29 @@ public function addMonths(int $increment): self
             $year++;
         }
 
-        // @infection-ignore-all (IncrementInteger)
-        $daysInNewMonth = (int) DateTimeFactory::immutableFromFormat(
-            'Y-m-d',
-            \sprintf('%d-%02d-%02d', $year, $month, 1),
-        )->format('t');
+        return new self($year, $month, \min($this->day, $this->numberOfDaysInMonth($year, $month)));
+    }
+
+    /**
+     * @return self Instance decremented by the specified number of months.
+     *              If the resulting month has fewer days than the current day, the day will be the last day of that month.
+     *
+     * @throws \InvalidArgumentException if $decrement is less than 1
+     */
+    public function subMonths(int $decrement): self
+    {
+        if ($decrement < 1) {
+            throw new \InvalidArgumentException('Months decrement must be greater than 0.');
+        }
+
+        $month = $this->month - $decrement;
+        $year = $this->year;
+        while ($month < 1) {
+            $month += 12;
+            $year--;
+        }
 
-        return new self($year, $month, \min($this->day, $daysInNewMonth));
+        return new self($year, $month, \min($this->day, $this->numberOfDaysInMonth($year, $month)));
     }
 
     public function offsetByDays(int $days): self
@@ -217,4 +233,13 @@ private function modify(string $modification): self
     {
         return self::fromDateTime($this->startOfDay()->modify($modification));
     }
+
+    private function numberOfDaysInMonth(int $year, int $month): int
+    {
+        // @infection-ignore-all (IncrementInteger)
+        return (int) DateTimeFactory::immutableFromFormat(
+            'Y-m-d',
+            \sprintf('%d-%02d-%02d', $year, $month, 1),
+        )->format('t');
+    }
 }
diff --git a/tests/unit/DateTest.php b/tests/unit/DateTest.php
@@ -569,6 +569,15 @@ public function it_throws_when_incrementing_month_by_less_than_1(int $increment)
         Date::fromYearMonthDay(2018, 10, 10)->addMonths($increment);
     }
 
+    #[Test]
+    #[DataProvider('provideInvalidDateMonthIncrements')]
+    public function it_throws_when_decrementing_month_by_less_than_1(int $decrement): void
+    {
+        $this->expectExceptionObject(new \InvalidArgumentException('Months decrement must be greater than 0.'));
+
+        Date::fromYearMonthDay(2018, 10, 10)->subMonths($decrement);
+    }
+
     /**
      * @return iterable<array{int}>
      */
@@ -579,6 +588,44 @@ public static function provideInvalidDateMonthIncrements(): iterable
         yield [-10];
     }
 
+    #[Test]
+    #[DataProvider('provideDatesForMonthDecrement')]
+    public function it_will_correctly_sub_months(
+        string $currentDate,
+        int $decrement,
+        string $expectedDate,
+    ): void {
+        $this->assertSame(
+            $expectedDate,
+            Date::fromYearMonthDayString($currentDate)->subMonths($decrement)->toYearMonthDayString(),
+        );
+    }
+
+    /**
+     * @return iterable<array{string, positive-int, string}>
+     */
+    public static function provideDatesForMonthDecrement(): iterable
+    {
+        yield ['2019-02-05', 1, '2019-01-05'];
+        yield ['2020-01-31', 1, '2019-12-31'];
+        yield ['2019-03-31', 1, '2019-02-28'];
+
+        yield ['2019-07-05', 6, '2019-01-05'];
+        yield ['2020-03-31', 5, '2019-10-31'];
+        yield ['2020-02-29', 6, '2019-08-29'];
+        yield ['2020-03-31', 6, '2019-09-30'];
+
+        yield ['2020-01-05', 12, '2019-01-05'];
+        yield ['2020-10-31', 12, '2019-10-31'];
+        yield ['2020-08-31', 12, '2019-08-31'];
+        yield ['2020-10-31', 12, '2019-10-31'];
+
+        yield ['2021-07-05', 30, '2019-01-05'];
+        yield ['2022-03-31', 30, '2019-09-30'];
+        yield ['2022-02-28', 30, '2019-08-28'];
+        yield ['2022-04-30', 30, '2019-10-30'];
+    }
+
     #[Test]
     #[DataProvider('provideValidDateDayChanges')]
     public function it_can_change_day(int $day): void