Issue #1810 fix weird gen warning

[JoerivanEngelen]

Fixes #1810

Description

This fixes confusing warning about incorrect IPF headers when loading GEN files.

• Move _infer_delim_whitespace to a imod.formats.common.py module
• Throw warning only in IPF module

Checklist

• Links to correct issue
• Update changelog, if changes affect users
• PR title starts with Issue #nr, e.g. Issue #737
• Unit tests were added
• If feature added: Added/extended example
• If feature added: Added feature to API documentation
• If pixi.lock was changed: Ran pixi run generate-sbom and committed changes

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[Manangka]

This method does 2 things. From the name it isn't clear that it also does a column check.
You could make the name more generic and return a namedtuple.

The method signature than also contains the return type which makes it clearer what it does

class DelimiterInfo(NamedTuple):
    is_whitespace: bool
    has_expected_cols: bool


def infer_delimiter_info(line: str, ncol: int) -> DelimiterInfo:
    """
    Infer whether the line is delimited by whitespace or commas, and whether
    the number of comma-delimited columns matches the expected count.

    Parameters
    ----------
    line : str
        The line to analyze.
    ncol : int
        The expected number of columns if line is delimited by commas.

    Returns
    -------
    DelimiterInfo
        is_whitespace : bool
            Whether the line is delimited by whitespace.
        has_expected_cols : bool
            Whether the line has the expected number of columns if delimited by commas.
    """
    n_elem = len(next(csv.reader([line])))
    if n_elem == 1:
        return DelimiterInfo(is_whitespace=True, has_expected_cols=True)
    elif n_elem == ncol:
        return DelimiterInfo(is_whitespace=False, has_expected_cols=True)
    else:
        return DelimiterInfo(is_whitespace=False, has_expected_cols=False)

On the calling side you can then use the named tuple:

delimiter_info = infer_delimiter_info(line, ncol)`
delimiter_info.is_whitespace
delimiter_info.has_expected_cols

or directly unpack it:
has_whitespace, has_expected_cols = infer_delimiter_info(line, ncol)

[Manangka]

infer_line_delimiter_info could also be a good name with the named tuple then being LineDelimiterInfo

[Manangka]

This test assert many things.
Consider using test cases to make it clearer what you're testing

@pytest.mark.parametrize(
    "line, ncol, expected",
    [
        ("1 2 3", 3, (True, True)),    # whitespace-delimited, correct ncol
        ("1 2 3", 2, (True, True)),    # whitespace-delimited, wrong ncol: ncol is ignored
        ("1\t2\t3", 3, (True, True)),  # tab-delimited (csv.reader sees 1 element -> whitespace branch)
        ("1,2,3", 3, (False, True)),   # comma-delimited, correct cols
        ("1, 2, 3", 3, (False, True)), # comma-delimited with spaces, correct cols
        ("1,2,3", 4, (False, False)),  # comma-delimited, wrong number of cols
        ("1 2,3", 3, (False, False)),  # mixed delimiters, unexpected col count
    ],
)
def test_infer_delimiter_info(line, ncol, expected):
    assert infer_delimiter_info(line, ncol) == expected