public static int GetFontIndex(SpreadsheetDocument document, Font f)
{
XElement font = f.GetXElement();
XDocument styles = document.WorkbookPart.WorkbookStylesPart.GetXDocument();
XElement fonts = styles.Root.Element(S.fonts);
int index = Array.FindIndex(fonts.Elements(S.font).ToArray(),
z => XElement.DeepEquals(z, font));
if (index != -1)
return index;
fonts.Add(font);
fonts.Attribute(NoNamespace.count).Value = fonts.Elements(S.font).Count().ToString();
document.WorkbookPart.WorkbookStylesPart.PutXDocument();
return fonts.Elements(S.font).Count() - 1;
}