Override org-insert-link for those that match a pattern

Question

I often need to keep track of conversations that happen in Slack, so I wrote a small elisp package that retrieves all message info (channel, timestamps, message(s)) for a given Slack permalink.

Then I convert the data to org-element using org-element-interpret-data.

Now, I need to find a way to either override org-insert-link so whenever I want to insert a link and it happens to match a pattern, it would not insert link as is, but extracts Slack data using my method and inserts that instead.

What's the best way of doing something like this?

Answer 1

Usually advising functions can be used to change the behavior of a function. But for this interactive function it would get complicated when looking at the source.

Fortunately org-mode (version 9.1+) has a built-in method to add custom link types which is the preferred way in this case:

(org-link-set-parameters TYPE &rest PARAMETERS)

An example that should come close to what you have in mind:

(defun my-org-link-insert-slack-data (&optional arg)
  "Get the slack link and insert the data."
  (let ((slack-link (read-string "slack link: ")))
    ;; Use your function here to insert the slack data.
    (insert slack-link)))

(org-link-set-parameters "slack" :complete #'my-org-link-insert-slack-data)

Evaluate the example code and then run M-x org-insert-link. The custom link type slack can be selected:

Then it prompts you for the slack link and inserts the text entered at point.

Usually the completing function has to return a string. But as long as I have understood your question correctly you don't really want to insert a link. Therefore the function just inserts the text itself. Org will show an user error in the minibuffer (wrong type argument: stringp, nil) but it still works.

It would probably be better to just use a function for this and not rely on org-insert-link at all.