Task::updateDatePlan

private function updateDatePlan(array $fields): array
{
	if (!$this->needCorrectDatePlan)
	{
		return $fields;
	}

	$taskData = $this->getFullTaskData();
	if (!$taskData)
	{
		return $fields;
	}

	$fieldHandler = new TaskFieldHandler($this->userId, $fields, $taskData);

	$parentChanged = $fieldHandler->isParentChanged();
	$datesChanged = $fieldHandler->isDatesChanged();
	$followDatesChanged = $fieldHandler->isFollowDates();

	if ($parentChanged)
	{
		// task was attached previously, and now it is being unattached or reattached to smth else
		// then we need to recalculate its previous parent...
		$scheduler = BitrixTasksProcessorTaskScheduler::getInstance($this->userId);
		$shiftResultPrev = $scheduler->processEntity(
			$this->taskId,
			$taskData,
			array(
				'MODE' => 'BEFORE_DETACH',
			)
		);
		if ($shiftResultPrev->isSuccess())
		{
			$shiftResultPrev->save(array('!ID' => $this->taskId));
		}
	}
	else
	{
		if (array_key_exists('PARENT_ID', $fields))
		{
			unset($fields['PARENT_ID']);
		}
	}

	// when updating end or start date plan, we need to be sure the time is correct
	if (
		$parentChanged
		|| $datesChanged
		|| $followDatesChanged
	)
	{
		$scheduler = BitrixTasksProcessorTaskScheduler::getInstance($this->userId);
		$this->shiftResult = $scheduler->processEntity(
			$this->taskId,
			$fields,
			[
				'MODE' => $parentChanged ? 'BEFORE_ATTACH' : '',
			]
		);
		if (!$this->shiftResult->isSuccess())
		{
			return $fields;
		}

		$shiftData = $this->shiftResult->getImpactById($this->taskId);
		if ($shiftData)
		{
			$fields['START_DATE_PLAN'] = $shiftData['START_DATE_PLAN'];
			if (
				isset($fields['START_DATE_PLAN'])
				&& $shiftData['START_DATE_PLAN'] === null
			)
			{
				$fields['START_DATE_PLAN'] = false;
			}

			$fields['END_DATE_PLAN'] = $shiftData['END_DATE_PLAN'];
			if (
				isset($fields['END_DATE_PLAN'])
				&& $shiftData['END_DATE_PLAN'] === null
			)
			{
				$fields['END_DATE_PLAN'] = false;
			}

			$fields['DURATION_PLAN_SECONDS'] = $shiftData['DURATION_PLAN_SECONDS'];
			$this->legacyOperationResultData['SHIFT_RESULT'] = $this->shiftResult->getData();
		}
	}

	if (
		isset($fields['END_DATE_PLAN'])
		&& (string) $fields['END_DATE_PLAN'] === ''
	)
	{
		$fields['DURATION_PLAN'] = 0;
	}

	$taskData = $this->getFullTaskData() ?? [];
	$fields = (new TaskFieldHandler($this->userId, $fields, $taskData))
		->prepareDurationPlanFields()
		->getFields();

	return $fields;
}