consider header/footer specs `hf_spec()`

[jmbarbone]

probably would be better to do something like :

hf_spec <- function(type = c("header", "footer"), default = NULL, odd = default, even = default, first = default, last = default) {
  type <- match.arg(type)
  ...
  structure(ls, class = "header_footer_spec")
}

# fun printing
print.header_footer_spec <- function(x, ...) {
  ... 
  invisible(x)
}

And handle the header and footer separately. Would be easy then to toggle:

# even only:
hf_spec("header", odd = "odd_header_here")

# skip first page:
hf_spec("header", "default_spec_here", first = NULL)

... and etc, etc.

• make it easy to set header and footer text
• consider ability to use an image (e.g. company logo) (perhaps something like hf_spec("header", "{image1} Header text {image2}", images = list(image1 = filepath1.png, image2 = filepath2.png))? But I don't really know how this is done with the xml

[JanMarvin]

I quickly drafted an example and had a look at the xml: logo_hf.xlsx

<headerFooter>
<!-- left header: P is current Page, N is number of pages -->
<!-- center header: current date and time 2022-03-13 00:04 CET in dd.mm.yy hh:mm notation -->
<!-- right header: the graphic rId1 -->
<oddHeader>&L&P/&N&C&"System Font,Regular"&10&K000000&D &T&R&G</oddHeader>
</headerFooter>
<legacyDrawingHF r:id="rId1"/>

Needs the following (should all be copyable from insertImage)

• content_types entries: png,
• media
• vmlDrawing
• vmlDrawing_rel pointing to media
• legacy drawing entry in worksheet
• worksheet_rel entry pointing to vml_drawing

Guess we can use all of the insertImage code, but instead of adding it somewhere in the worksheet, we add it to the header. But that's as far I am about to go with this issue 😄

[Edit] "Only one picture can be inserted in each section of the header."

[JanMarvin]

ofc duplication should be minimised, maybe we can simply extract the media to workbook part and make the include image to worksheet/header part special cases