convert time into HH:MM:SS.sss

[Emanuel Berg <incal@dataswamp.org>]

HH:MM:SS, MM:SS.sss and MM:SS are converted into HH:MM:SS.sss
in the below code.

But for example HH:MM:SS:ss isn't given an extra zero at
the end.

That can be dealt with as well using the same method, just
more cases are needed. It is absolutely doable, it is just
that too many cases is often a sign one should think in a new
way instead of just adding more and more.

One can also think - should one do anything about for example
H:M:S.sss - which is also easy, just left-pad zeroes to
incomplete data - but, maybe one shouldn't bother trying to
rescue what is likely incorrect input from the user to
begin with?

Another thing one maybe would like is to warn for bogus time,
that is more than 59 minutes and the same for seconds seconds.

Maybe one shouldn't do this with regexps to begin with,
instead read data as data as one goes along, warn for bogus
data, and print it back with the desire format when assessed?

This is what happens right now:

;; 11:22:33.444 -> 11:22:33.444  (complete so no change)
;; 11:22:33     -> 11:22:33.000  (add milliseconds)
;; 22:33.444    -> 00:22:33.444  (add hours)
;; 22:33        -> 00:22:33.000  (add hours and milliseconds)

;;; -*- lexical-binding: t -*-

(defun convert-time ()
  "Convert incomplete time data,
that is all of either HH:MM:SS, MM:SS.sss or MM:SS,
into HH:MM:SS.sss.
When converting, pad with zero hours (00:) and/or zero milliseconds (.000)."
  (interactive)
  (goto-char (point-min))
  (while (re-search-forward "\\([[:digit:]]\\{2\\}:[[:digit:]]\\{2\\}\\)" nil t)
    (goto-char (match-beginning 0))
    (if (looking-at "[[:digit:]]\\{2\\}:[[:digit:]]\\{2\\}:[[:digit:]]\\{2\\}.[[:digit:]]\\{3\\}")
        (goto-char (match-end 0))
      (if (looking-at "\\([[:digit:]]\\{2\\}:[[:digit:]]\\{2\\}:[[:digit:]]\\{2\\}\\)")
          (replace-match "\\1.000")
        (if (looking-at "\\([[:digit:]]\\{2\\}:[[:digit:]]\\{2\\}.[[:digit:]]\\{3\\}\\)")
            (replace-match "00:\\1")
          (replace-match "00:\\1.000") )))))

(defalias 'ct #'convert-time)

;; 11:22:33.444 -> 11:22:33.444  (complete so no change)
;; 11:22:33     -> 11:22:33.000  (add milliseconds)
;; 22:33.444    -> 00:22:33.444  (add hours)
;; 22:33        -> 00:22:33.000  (add hours and milliseconds)

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