Feature request: Allow citar to add multiple files to library item/citeky via citar-add-file-to-library

[deen1]

While setting the citar-file-additional-files-separator variable to non-nil allows a library item to have multiple associated files under the same cite-key -- e.g. {cite-key}_{cite-year}.pdf, {cite-key}_{cite-year}-1.pdf, {cite-key}_{cite-year}-2.pdf -- it is currently only possible to add an additional file to an item only by renaming the file and moving it to the directory manually. Otherwise, running M-x citar-add-file-to-library will produce the File ... exists, overwrite? (y or n) prompt in the minibuffer, and answering will either overwrite the existing file (y) or cancel the operation (n).

Via @bdarcus in #820 (comment)_, the following code needs to change:

citar/citar.el

Lines 1337 to 1360 in 885b86f

	(defun citar-save-file-to-library (citekey source-plist)
	"Use as `citar-add-file-function' to save files to `citar-library-paths'.
	Save the file with the filename CITEKEY.EXTENSION to a directory
	from `citar-library-paths'. If there are multiple such
	directories, prompt the user to choose one. If SOURCE-PLIST has
	an :extension key, use its value as EXTENSION; otherwise prompt
	the user. If the file already exists, confirm before overwriting
	it.
	SOURCE-PLIST must be as specified in the documentation of
	`citar-add-file-sources'."
	(let* ((directory (if (cdr citar-library-paths)
	(completing-read "Directory: " citar-library-paths)
	(car citar-library-paths)))
	(extension (or (plist-get source-plist :extension)
	(read-string "File extension: ")))
	(destfile (expand-file-name citekey directory))
	(destfile (if (string-empty-p extension)
	destfile
	(concat destfile "." extension)))
	;; an integer means to confirm before overwriting
	(ok-if-already-exists 1))
	(funcall (plist-get source-plist :write-file)

I would say that

 (destfile (expand-file-name citekey directory)) 
          (destfile (if (string-empty-p extension) 
                        destfile 
                      (concat destfile "." extension))) 
          ;; an integer means to confirm before overwriting 
          (ok-if-already-exists 1)

needs to change to prompt the user to either overwrite the existing file (y), or add the new file with an appended filename (a), or cancel (c/q/n).

If the user chooses to add with an appended filename, then citar should check if the -1, -2 ... -n. versions of the filename are in use, before adding the file with filename {cite_key}_{cite_year}-{n+1}.ext.

[bdarcus]

... needs to change to prompt the user to either overwrite the existing file (y), or add the new file with an appended filename (a), or cancel (c/q/n).

If the user chooses to add with an appended filename, then citar should check if the -1, -2 ... -n. versions of the filename are in use, before adding the file with filename {cite_key}_{cite_year}-{n+1}.ext.

This makes sense to me, so suggest whoever gets to this start here.

The only amendment I would make is this should only work like this if the file separator variable is set.