Append row in a spreadsheet as the values were user entered - php

Question

I have an array of strings and I need to append it in a spreadsheet, from the first to the n-th column according to the size of the array.
The strings could represent several type of values, e.g. numbers, dates and so on, so they must be put in the sheet as user entered to keep their meaning.
As far as I understand, the Google APIs offer two ways to append values, but none of them seems to be suitable for this case. Here's the issues I encountered:
Using Google_Service_Sheets_AppendCellsRequest
The problem with this method is that I cannot find a way to set the values as user entered. Here is a code sample:
// Build the CellData array
$values = array();
foreach( $ary_values AS $d ) {
$cellData = new Google_Service_Sheets_CellData();
$value = new Google_Service_Sheets_ExtendedValue();
$value->setStringValue($d);
$cellData->setUserEnteredValue($value);
$values[] = $cellData;
}
// Build the RowData
$rowData = new Google_Service_Sheets_RowData();
$rowData->setValues($values);
// Prepare the request
$append_request = new Google_Service_Sheets_AppendCellsRequest();
$append_request->setSheetId(0);
$append_request->setRows($rowData);
$append_request->setFields('userEnteredValue');
// Set the request
$request = new Google_Service_Sheets_Request();
$request->setAppendCells($append_request);
(full working code is here)
Even using CellData.setUserEnteredValue, the data is interpreted as string because one have to set the values using ExtendedValue.setStringValue (or the other supported methods, i.e. setBoolValue, setFormulaValue, setNumberValue).
Using spreadsheets.values.append
Using this method I can have the data rendered as user entered, but the "appending" is done in the wrong place in several cases. As stated in the documentation:
The input range is used to search for
existing data and find a "table" within that range. Values will be
appended to the next row of the table, starting with the first column
of the table.
So this method is meant to behave in a different way from the previous one, and that leads to problem for me.
This is a piece of code that should do what I want:
$body = new Google_Service_Sheets_ValueRange([
'values' => [ $array_values ]
]);
$params = [
'valueInputOption' => 'USER_ENTERED'
];
// the n-th column
$end_column = chr( ord('A') + count($array_values));
$result = $sheet_service->spreadsheets_values->append(
$fileId,
$sheetName . "!A1:" . $end_column . "1",
$body,
$params
);
Indeed, it works fine but with some exceptions, e.g.:
if the cell A1 is empty, the append method will put the values starting at column 2 (see this example to understand why).
if I have some written rows, then an empty row, then other written rows, the append method will "fill the gap" instead of putting the values after the very last written row.
Am I doing some errors? Is there a way to make what I want using either one or the other method?
To recap:
the values must be considered as user entered (e.g. a number or a date should be interpreted as such)
the values must be written in the row after the last non-empty cell, starting at column one
the append operation must be atomic (i.e. sending one request to get the last non-empty cell row and then sending another request to write data into that is not an option, because in the meantime another user could put data there)
Any advice is welcome!