Repeat tasks M-F but not weekends on Emacs org-mode, see https://stackoverflow.com/questions/28369833/emacs-org-mode-repeat-tasks-m-f-but-not-weekends

my-workday-todo-schedule.el

;; START: my :workday: todo task schedule update
(require 'org)
(require 'calendar)

(defun my-is-repeating-workday-task-p ()
  "Check if the current TODO task is a repeating workday task.
A repeating workday task is defined as a task that has the tag :workday:
and a SCHEDULED property with a repeater interval of +1d/++1d/.+1d."
  (save-excursion
    (org-back-to-heading t)
    (let ((tags (org-get-tags))
	  (scheduled (org-entry-get (point) "SCHEDULED")))
      (and scheduled
	   (member "workday" tags)
	   (or
	    (string-match-p "\\+1d" scheduled) ; exact 1 day
	    (string-match-p "\\.+1d" scheduled) ; 1 day from today
	    (string-match-p "\\++1d" scheduled)) ; 1 day from today
	   ))))

(defun my-is-one-day-repeater-p ()
  "Check the repeater for current TASK.

Return t for a 1-day-repeater, nil for at-least-1-day-repeater."
  (interactive)
  (let* ((element (org-element-at-point))
	 (schedule (org-element-property :scheduled element))
	 (repeater-type (and schedule (org-element-property :repeater-type schedule)))
	 (repeater-value (and schedule (org-element-property :repeater-value schedule)))
	 (repeater-unit (and schedule (org-element-property :repeater-unit schedule)))
	 )
    ;; (message "%s" schedule)
    ;; (message "%s" repeater-type)
    ;; (message "%s" repeater-value)
    ;; (message "%s" repeater-unit)
    (when (and (= repeater-value 1)
	       (string= repeater-unit "day"))
      (if (or (string= repeater-type "catch-up") (string= repeater-type "restart"))
	  nil
	t))))

(defun my/schedule-workday-todo ()
  "Set the SCHEDULED date of a repeating :workday: TODO to the next workday
if the current SCHEDULED date is Mon-Thu, or to the next Monday if it's Fri-Sun.
Display a colored message in the minibuffer."
  (interactive)
  (save-excursion
    (org-back-to-heading t)
    (when (my-is-repeating-workday-task-p)
      (if (my-is-one-day-repeater-p)
	  (let* ((scheduled (org-entry-get (point) "SCHEDULED"))
		 (date (org-parse-time-string scheduled))
		 (day-of-week (nth 6 (decode-time (apply 'encode-time date)))))
	    ;; (message "%s" date)
	    ;; (message "%s" day-of-week)
	    (my-update-schedule-date date day-of-week))
	;; Return the current day of the week as a number (1 for Monday, 7 for Sunday)
	(let ((date (decode-time (current-time)))
	      (day-of-week (string-to-number (format-time-string "%u"))))
	  (if (= day-of-week 7)
	      0  ;; Convert Sunday from 7 to 0
	    day-of-week)
	  ;; (message "%s" day-of-week)
	  (my-update-schedule-date date day-of-week))
	))))

(defun my-update-schedule-date (date day-of-week)
  (cond
   ((<= 1 day-of-week 4)  ; Monday to Thursday (0 = Sunday, 1 = Monday, ..., 6 = Saturday)
    (let* ((new-date (time-add (apply 'encode-time date) (* 86400 1))) ; 86400 seconds in a day
	   (new-date-string (format-time-string "%Y-%m-%d" new-date)) ; Format without time
	   (new-date-with-day (format-time-string "%a" new-date))) ; Day of the week (e.g., Mon, Tue)
      (org-schedule nil new-date-string)
      (my-insert-properties-entry "LAST_REPEAT" (format-time-string "[%Y-%m-%d %a %H:%M]"))
      (my-insert-drawer-content "LOGBOOK"
				(format "- State \"DONE\"       from \"TODO\"       [%s]"
					(format-time-string "%Y-%m-%d %a %H:%M")))
      (message (propertize (format "Scheduled date updated to %s (%s)" new-date-string new-date-with-day)
			   'face '(:foreground "green")))))
   (t  ; Friday to Sunday
    (let* ((days-to-next-monday (- 8 day-of-week)) ; Calculate days to next Monday
	   (new-date (time-add (apply 'encode-time date) (* 86400 days-to-next-monday))) ; 86400 seconds in a day
	   (new-date-string (format-time-string "%Y-%m-%d" new-date)) ; Format without time
	   (new-date-with-day (format-time-string "%a" new-date))) ; Day of the week (e.g., Mon, Tue)
      (org-schedule nil new-date-string)
      (my-insert-properties-entry "LAST_REPEAT" (format-time-string "[%Y-%m-%d %a %H:%M]"))
      (my-insert-drawer-content "LOGBOOK"
				(format "- State \"DONE\"       from \"TODO\"       [%s]"
					(format-time-string "%Y-%m-%d %a %H:%M")))
      (message (propertize (format "Scheduled date updated to %s (%s)" new-date-string new-date-with-day)
			   'face '(:foreground "green")))))))

(defun my-org-entry-has-drawer (drawer)
  "Check if the current Org entry has a specific DRAWER as a standalone line."
  (save-excursion
    (org-back-to-heading t)
    (let ((end (save-excursion (outline-next-heading) (point))))
      (re-search-forward (format "^:%s:$" drawer) end t))))

(defun my-insert-properties-entry (property value)
  "Insert or update PROPERTY with VALUE in the :PROPERTIES: drawer."
  (interactive)
  (save-excursion
    (org-back-to-heading t)
    (if (org-entry-get (point) property)
	;; if PROPERTY exists
	(progn
	  (org-delete-property property)
	  (org-set-property property value)
	  )
      ;; if PROPERTY does not exist
      (org-set-property property value))))
;; (my-insert-properties-entry "LAST_REPEAT" (format-time-string "[%Y-%m-%d %a %H:%M]"))

(defun my-insert-drawer-content (drawer content)
  "Insert a LOGBOOK entry below the current task if it doesn't already exist,
or add to the existing LOGBOOK drawer if it does."
  (interactive)
  (save-excursion
    (org-back-to-heading t)
    (if (my-org-entry-has-drawer drawer)
	;; If DRAWER exists, check if entry already exists
	(progn
	  (re-search-forward (format "^:%s:$" drawer))
	  (forward-line 1)
	  (insert (format "%s\n" content)))
      ;; Otherwise, create DRAWER and insert content
      (progn
	(org-end-of-meta-data t)
	(org-insert-drawer nil drawer)
	(insert content)))))
;; (my-insert-drawer-content "LOGBOOK" (format "- State \"DONE\"       from \"TODO\"       [%s]" (format-time-string "%Y-%m-%d %a %H:%M")))

(defun my-org-todo ()
  "Change TODO state and reschedule if necessary."
  (interactive)
  (if (my-is-repeating-workday-task-p)
      (my/schedule-workday-todo)
    (org-todo)))

;; Override the key binding for C-c C-t to use my/org-todo-and-reschedule
(define-key org-mode-map (kbd "C-c C-t") 'my-org-todo)
;; END: my :workday: todo task schedule update