fix rounding issues with microseconds calculation

src/PhpSpreadsheet/Shared/Date.php

@@ -223,13 +223,27 @@ public static function excelToDateTimeObject(float|int $excelTimestamp, null|Dat
         }
         $days = floor($excelTimestamp);
         $partDay = $excelTimestamp - $days;
-        $hms = 86400 * $partDay;
-        $microseconds = (int) round(fmod($hms, 1) * 1000000);
-        $hms = (int) floor($hms);
-        $hours = intdiv($hms, 3600);
-        $hms -= $hours * 3600;
-        $minutes = intdiv($hms, 60);
-        $seconds = $hms % 60;
+        $hoursInMs = 86400 * $partDay;
+        $wholeSeconds = (int) floor($hoursInMs);
+
+        // flooring here might lose data due to precision issues, hence round it
+        $microseconds = (int) round(($hoursInMs - $wholeSeconds) * 1_000_000);
+        $microseconds = (int) round($microseconds, -2);
+
+        // rounding may lead to edge cases
+        if ($microseconds === 1_000_000) {
+            $microseconds = 0;
+            ++$wholeSeconds;
+        }
+        if ($wholeSeconds >= 86400) {
+            $wholeSeconds = 0;
+            ++$days;
+        }
+
+        $hours = intdiv($wholeSeconds, 3600);
+        $remainingSeconds = $wholeSeconds % 3600;
+        $minutes = intdiv($remainingSeconds, 60);
+        $seconds = $remainingSeconds % 60;
 
         if ($days >= 0) {
             $days = '+' . $days;

tests/PhpSpreadsheetTests/Reader/Xlsx/ExplicitDateTest.php

@@ -4,7 +4,11 @@
 
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
 
+use DateTime;
 use PhpOffice\PhpSpreadsheet\IOFactory;
+use PhpOffice\PhpSpreadsheet\Shared\Date;
+use PhpOffice\PhpSpreadsheet\Spreadsheet;
+use PhpOffice\PhpSpreadsheet\Writer\Xlsx;
 
 class ExplicitDateTest extends \PHPUnit\Framework\TestCase
 {
@@ -20,7 +24,7 @@
             self::fail('Unable to read file');
         } else {
             // confirm that file contains type "d" cells
             self::assertStringContainsString('<c r="A3" s="1" t="d"><v>2021-12-31T23:44:51.894</v></c>', $data);
             self::assertStringContainsString('<c r="B3" s="2" t="d"><v>2021-12-31</v></c>', $data);
             self::assertStringContainsString('<c r="C3" s="3" t="d"><v>23:44:51.894</v></c>', $data);
         }
@@ -40,12 +44,55 @@
         $formatted = $sheet->getCell('B3')->getFormattedValue();
         self::assertEquals(44561, $value);
         self::assertSame('2021-12-31', $formatted);
-        // Time only
+        // Time only, with seconds
         $value = $sheet->getCell('C3')->getValue();
         $formatted = $sheet->getCell('C3')->getFormattedValue();
         self::assertEqualsWithDelta(0.98948, $value, 0.00001);
         self::assertSame('23:44:52', $formatted);
+        // Time only, full minute
+        $value = $sheet->getCell('F3')->getValue();
+        $formatted = $sheet->getCell('F3')->getFormattedValue();
+        self::assertEqualsWithDelta(0.5673611, $value, 0.00001);
+        self::assertSame('13:37', $formatted);
 
         $spreadsheet->disconnectWorksheets();
     }
+
+    public function testThatDateTimesCanBePersistedAndReread(): void
+    {
+        $originalDateTime = new DateTime('2020-10-21T14:55:31');
+
+        $dateTimeFromSpreadsheet = $this->getDateTimeFrom($this->excelSheetWithDateTime($originalDateTime));
+        $dateTimeFromSpreadsheetAfterPersistAndReread = $this->getDateTimeFrom($this->persistAndReread($this->excelSheetWithDateTime($originalDateTime)));
+
+        self::assertEquals($originalDateTime, $dateTimeFromSpreadsheet);
+        self::assertEquals($originalDateTime, $dateTimeFromSpreadsheetAfterPersistAndReread);
+    }
+
+    private function excelSheetWithDateTime(DateTime $dateTime): Spreadsheet
+    {
+        $spreadsheet = new Spreadsheet();
+        $spreadsheet->getActiveSheet()->setCellValue('A1', Date::dateTimeToExcel($dateTime));
+
+        return $spreadsheet;
+    }
+
+    public function getDateTimeFrom(Spreadsheet $spreadsheet): DateTime
+    {
+        $value = $spreadsheet->getSheet(0)->getCell('A1')->getCalculatedValue();
+        self::assertIsNumeric($value);
+        $value = (float) $value;
+
+        return Date::excelToDateTimeObject($value);
+    }
+
+    private function persistAndReread(Spreadsheet $spreadsheet): Spreadsheet
+    {
+        $tempPointer = tmpfile();
+        $tempFileName = stream_get_meta_data($tempPointer)['uri'] ?? null;
+        self::assertNotNull($tempFileName, 'Temp file not created');
+        (new Xlsx($spreadsheet))->save($tempFileName);
+
+        return (new \PhpOffice\PhpSpreadsheet\Reader\Xlsx())->load($tempFileName);
+    }
 }