def METHOD_NAME(source_dir: str, prefix: Optional[str] = None) -> Tuple[int, int]:
    """Get size and file count of a directory.
    Parameters
    ----------
    source_dir: str
        Directory path
    Returns
    -------
    Tuple[int, int]
        Size in megabytes and file count
    """
    size = 0
    count = 0
    for root, _, files in os.walk(source_dir, topdown=True):
        for f in files:
            if prefix and not f.startswith(prefix):
                continue
            full_path = os.path.join(root, f)
            size += os.path.getsize(full_path)
            count += 1
    return (size, count)