Re: calculating relative time until a day of week

[Emanuel Berg <incal@dataswamp.org>]

Michael Heerdegen via Users list for the GNU Emacs text editor wrote:

>> Hi, I want to make an Emacs timer that runs a command once
>> a week, every Tuesday at 4am. I could do this with
>> run-at-time and a relative time, but I would need to
>> calculate how many seconds until Tuesday 4am. Is there an
>> easy way to calcuate that?
>
> Depending on what that command is for, an answer might be
> "Use diary and appointments" Or org-mode.

Here is a bunch of time stuff, maybe some of it can be
modified for that purpose.

;;; -*- lexical-binding: t -*-
;;
;; this file:
;;   https://dataswamp.org/~incal/emacs-init/time-cmp.el

(require 'cl-lib)
(require 'pcase)

(defun wall-clock-time (h1 m1 s1 h2 m2 s2)
  (let*((y 1978) (m 05) (d 08) ; arbitrary date, 1978-05-08
        (total-seconds-1 (float-time (encode-time s1 m1 h1 d m y)))
        (total-seconds-2 (float-time (encode-time s2 m2 h2 d m y)))
        (s-diff (- total-seconds-2 total-seconds-1)) )
    (format-seconds "%.2h:%.2m:%.2s" s-diff) ))

(defalias 'wct #'wall-clock-time)

;; (wct 09 35 10 23 00 00) ; 13:24:50

(defun days (y1 m1 d1 y2 m2 d2)
  (let*((then (float-time (encode-time 0 0 0 d1 m1 y1)))
        (now  (float-time (encode-time 0 0 0 d2 m2 y2)))
        (diff (- now then)) )
    (string-to-number (format-seconds "%d" diff)) ))

;; (days 1958 04 13 1958 08 30) ; 139 days between Tahiti Nui 2 & 3

(defun days-date (date1 date2)
  (pcase-let*(
      (sep "-")
      (`(,y1 ,m1 ,d1) (cl-map 'list #'string-to-number (split-string date1 sep)))
      (`(,y2 ,m2 ,d2) (cl-map 'list #'string-to-number (split-string date2 sep))) )
    (days y1 m1 d1 y2 m2 d2) ))

;; (days-date "2021-03-19" "2021-04-20") ;     31
;; (days-date "1964-07-26" "2021-03-22") ; 20 693

(defun get-time-since (y m d)
  (interactive "nyear: \nnmonth: \nnday: ")
  (message "%s"
    (format-seconds "%yy %dd"
      (float-time
        (time-since (encode-time 0 0 0 d m y)) ))))

;; (get-time-since 2011 09 27) ; 10y 172d [2022-03-15]

(defun days-since (y m d)
  (string-to-number
    (format-seconds "%d"
      (float-time (time-since (encode-time 0 0 0 d m y))) )))

;; (days-since 1 1 1) ; 738 228 days from 0001-01-01 [2022-03-15]

(provide 'time-cmp)

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