;;; -*- lexical-binding: t -*-
;;;
;;; this file:
;;;   http://user.it.uu.se/~embe8573/emacs-init/time-cmp.el
;;;   https://dataswamp.org/~incal/emacs-init/time-cmp.el

(defun wall-clock-time (h1 m1 s1 h2 m2 s2)
  (let*((d   08) ; arbitrary day to use below, any would do
        (m   05) ; actually something cool happened that day
        (y 1978) ; in the history of climbing
        (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
;; (wct 09 35 10 09 35 20) ; 00:00:10

(defun time-between-times (y1 m1 d1 h1 min1 s1
                           y2 m2 d2 h2 min2 s2)
  (let*((s-then  (float-time (encode-time s1 min1 h1 d1 m1 y1)))
        (s-now   (float-time (encode-time s2 min2 h2 d2 m2 y2)))
        (s-diff  (- s-now s-then)) )
    (format-seconds "%yy %dd %hh %mm %ss" s-diff)))
;; DNC:
;;   (time-between-times 1958  4 13 1958 8 30) ; Tahiti Nui 2 -> 3, 139 days

(defun get-time-since (year month day)
  (interactive "nyear: \nnmonth: \nnday: ")
  (message "%s"
           (format-seconds
            "%yy %dd"
            (float-time
             (time-since (encode-time 0 0 0 day month year)) ))))
;; (get-time-since 2011 09 27) ; 8y 228d @ 2020-05-10

(defun dope (boxes pills dose &optional from)
  (interactive "nboxes: \nnpills/box: \nnpills/day: ")
  (let*((days (/ (* boxes pills) dose))
        (done (time-add (when from
                          (date-to-time (concat from "T00:00+01:00")) )
                        (days-to-time (1- days)) ))
        (str  (format-time-string "%F" done))
        (more (format-time-string "%F" (time-add done (days-to-time -10)))) )
    (insert (format "%s  [%s]   %s" ; don't change
                    (or from (format-time-string "%F")) more str) )))