;;; -*- 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

(require 'cl-lib)
(defun days-from-date (d1 d2)
  (let*((sep     "-")
        (d1-data (cl-map 'list #'string-to-number (split-string d1 sep)))
        (d2-data (cl-map 'list #'string-to-number (split-string d2 sep)))
        (y1      (car   d1-data))
        (m1      (cadr  d1-data))
        (d1      (caddr d1-data))
        (y2      (car   d2-data))
        (m2      (cadr  d2-data))
        (d2      (caddr d2-data)) )
    (days-from y1 m1 d1 y2 m2 d2) ))
;; (days-from-date "2021-03-19" "2021-04-20") ; 31
;; (days-from-date "1964-07-26" "2021-03-22")

(defun days-from (y1 m1 d1 y2 m2 d2)
  (let*((s-then (float-time (encode-time 0 0 0 d1 m1 y1)))
        (s-now  (float-time (encode-time 0 0 0 d2 m2 y2)))
        (s-diff (- s-now s-then)) )
    (string-to-number (format-seconds "%d" s-diff) )))
;; (days-from 2021 03 19 2021 04 20) ; 31

(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
(defalias 'time-from #'time-between-times)

(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 (from boxes pills dose)
  (interactive
   (list
    (read-string "from: " (format-time-string "%F"))
    (read-number "boxes: ")
    (read-number "pills/box: " 50)
    (read-number "pills/day: "  6) ))
  (let*((days (/ (* boxes pills) dose))
        (done (time-add (date-to-time (format "%sT00:00+01:00" from))
                        (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" from more str) )))