;;; gnus-diary.el --- Wrapper around the NNDiary Gnus back end  -*- lexical-binding: t; -*-

;; Copyright (C) 1999-2022 Free Software Foundation, Inc.

;; Author:        Didier Verna <didier@didierverna.net>
;; Created:       Tue Jul 20 10:42:55 1999
;; Keywords:      calendar mail news

;; This file is part of GNU Emacs.

;; GNU Emacs is free software: you can redistribute it and/or modify
;; it under the terms of the GNU General Public License as published by
;; the Free Software Foundation, either version 3 of the License, or
;; (at your option) any later version.

;; GNU Emacs is distributed in the hope that it will be useful,
;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
;; GNU General Public License for more details.

;; You should have received a copy of the GNU General Public License
;; along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.

;;; Commentary:

;; Contents management by FCM version 0.1.

;; gnus-diary is a utility toolkit used on top of the nndiary back end.  It is
;; now fully documented in the Gnus manual.

;;; Code:

(require 'nndiary)
(require 'message)
(require 'gnus-art)

(defgroup gnus-diary nil
  "Utilities on top of the nndiary back end for Gnus."
  :version "22.1"
  :group 'gnus)

(defcustom gnus-diary-summary-line-format "%U%R%z %uD: %(%s%) (%ud)\n"
  "Summary line format for nndiary groups."
  :type 'string
  :group 'gnus-diary
  :group 'gnus-summary-format)

(defcustom gnus-diary-time-format "%a, %b %e %y, %H:%M"
  "Time format to display appointments in nndiary summary buffers.
Please refer to `format-time-string' for information on possible values."
  :type 'string)

(defcustom gnus-diary-delay-format-function 'gnus-diary-delay-format-english
  "Function called to format a diary delay string.
It is passed two arguments.  The first one is non-nil if the delay is in
the past.  The second one is of the form ((NUM . UNIT) ...) where NUM is
an integer and UNIT is one of `year' `month' `week' `day' `hour' or `minute'.
It should return strings like \"In 2 months, 3 weeks\", \"3 hours,
1 minute ago\" and so on.

There are currently two built-in format functions:
`gnus-diary-delay-format-english' (the default)
`gnus-diary-delay-format-french'"
  :type '(choice (const  :tag "english" gnus-diary-delay-format-english)
		 (const  :tag "french"  gnus-diary-delay-format-french)
		 (symbol :tag "other")))

(defconst gnus-diary-version nndiary-version
  "Current Diary back end version.")


;; Compatibility functions ==================================================

(defun gnus-diary-kill-entire-line ()
  (beginning-of-line)
  (let ((kill-whole-line t))
    (kill-line)))


;; Summary line format ======================================================

(defun gnus-diary-delay-format-french (past delay)
  (if (null delay)
      "maintenant!"
    ;; Keep only a precision of two degrees
    (and (> (length delay) 1) (setcdr (cdr delay) nil))
    (concat (if past "il y a " "dans ")
	    (let ((str "")
		  del)
	      (while (setq del (pop delay))
		(setq str (concat str
				  (int-to-string (car del)) " "
				  (cond ((eq (cdr del) 'year)
					 "an")
					((eq (cdr del) 'month)
					 "mois")
					((eq (cdr del) 'week)
					 "semaine")
					((eq (cdr del) 'day)
					 "jour")
					((eq (cdr del) 'hour)
					 "heure")
					((eq (cdr del) 'minute)
					 "minute"))
				  (unless (or (eq (cdr del) 'month)
					      (= (car del) 1))
				    "s")
				  (if delay ", "))))
	      str))))


(defun gnus-diary-delay-format-english (past delay)
  (if (null delay)
      "now!"
    ;; Keep only a precision of two degrees
    (and (> (length delay) 1) (setcdr (cdr delay) nil))
    (concat (unless past "in ")
	    (let ((str "")
		  del)
	      (while (setq del (pop delay))
		(setq str (concat str
				  (int-to-string (car del)) " "
				  (symbol-name (cdr del))
				  (and (> (car del) 1) "s")
				  (if delay ", "))))
	      str)
	    (and past " ago"))))


(defun gnus-diary-header-schedule (headers)
  ;; Same as `nndiary-schedule', but given a set of headers HEADERS
  (mapcar
   (lambda (elt)
     (let ((head (cdr (assoc (intern (format "X-Diary-%s" (car elt)))
			     headers))))
       (when head
	 (nndiary-parse-schedule-value head (cadr elt) (car (cddr elt))))))
   nndiary-headers))

;; #### NOTE: Gnus sometimes gives me a HEADER not corresponding to any
;; message, with all fields set to nil here. I don't know what it is for, and
;; I just ignore it.
;;;###autoload
(defun gnus-user-format-function-d (header)
  ;; Return an approximate delay string for the next occurrence of this
  ;; message. The delay is given only in the first non zero unit.
  ;; Code partly stolen from article-make-date-line
  (let* ((extras (mail-header-extra header))
	 (sched (gnus-diary-header-schedule extras))
	 (now (current-time))
	 (occur (nndiary-next-occurrence sched now))
	 (real-time (time-subtract occur now)))
    (let* ((sec (time-convert real-time 'integer))
	   (past (< sec 0))
	   delay)
      (and past (setq sec (- sec)))
      (unless (zerop sec)
	;; This is a bit convoluted, but basically we go through the time
	;; units for years, weeks, etc, and divide things to see whether
	;; that results in positive answers.
	(let ((units `((year . ,(round (* 365.25 24 3600)))
		       (month . ,(* 31 24 3600))
		       (week . ,(* 7 24 3600))
		       (day . ,(* 24 3600))
		       (hour . 3600)
		       (minute . 60)))
	      unit num)
	  (while (setq unit (pop units))
	    (unless (zerop (setq num (floor sec (cdr unit))))
	      (setq delay (append delay `((,num . ,(car unit))))))
	    (setq sec (mod sec (cdr unit))))))
      (funcall gnus-diary-delay-format-function past delay))))

;; #### NOTE: Gnus sometimes gives me a HEADER not corresponding to any
;; message, with all fields set to nil here. I don't know what it is for, and
;; I just ignore it.
;;;###autoload
(defun gnus-user-format-function-D (header)
  ;; Returns a formatted time string for the next occurrence of this message.
  (let* ((extras (mail-header-extra header))
	 (sched (gnus-diary-header-schedule extras))
	 (occur (nndiary-next-occurrence sched (current-time))))
    (format-time-string gnus-diary-time-format occur)))


;; Article sorting functions ================================================

(defun gnus-article-sort-by-schedule (h1 h2)
  (let* ((now (current-time))
	 (e1 (mail-header-extra h1))
	 (e2 (mail-header-extra h2))
	 (s1 (gnus-diary-header-schedule e1))
	 (s2 (gnus-diary-header-schedule e2))
	 (o1 (nndiary-next-occurrence s1 now))
	 (o2 (nndiary-next-occurrence s2 now)))
    (if (and (= (car o1) (car o2)) (= (cadr o1) (cadr o2)))
	(< (mail-header-number h1) (mail-header-number h2))
      (time-less-p o1 o2))))


(defun gnus-thread-sort-by-schedule (h1 h2)
  (gnus-article-sort-by-schedule (gnus-thread-header h1)
				 (gnus-thread-header h2)))

(defun gnus-summary-sort-by-schedule (&optional reverse)
  "Sort nndiary summary buffers by schedule of appointments.
Optional prefix (or REVERSE argument) means sort in reverse order."
  (interactive "P" gnus-summary-mode)
  (gnus-summary-sort 'schedule reverse))

(defvar gnus-summary-misc-menu) ;; Avoid byte compiler warning.
(add-hook 'gnus-summary-menu-hook
	  (lambda ()
	    (easy-menu-add-item gnus-summary-misc-menu
				'("Sort")
				["Sort by schedule"
				 gnus-summary-sort-by-schedule
				 (eq (car (gnus-find-method-for-group
					   gnus-newsgroup-name))
				     'nndiary)]
				"Sort by number")))



;; Group parameters autosetting =============================================

(defun gnus-diary-update-group-parameters (group)
  ;; Ensure that nndiary groups have convenient group parameters:
  ;; - a posting style containing X-Diary headers
  ;; - a nice summary line format
  ;; - NNDiary specific sorting by schedule functions
  ;; In general, try not to mess with what the user might have modified.

  ;; Posting style:
  (let ((posting-style (gnus-group-get-parameter group 'posting-style t))
	(headers nndiary-headers)
	header)
    (while headers
      (setq header (format "X-Diary-%s" (caar headers))
	    headers (cdr headers))
      (unless (assoc header posting-style)
	(setq posting-style (append posting-style (list (list header "*"))))))
    (gnus-group-set-parameter group 'posting-style posting-style))
  ;; Summary line format:
  (unless (gnus-group-get-parameter group 'gnus-summary-line-format t)
    (gnus-group-set-parameter group 'gnus-summary-line-format
			      `(,gnus-diary-summary-line-format)))
  ;; Sorting by schedule:
  (unless (gnus-group-get-parameter group 'gnus-article-sort-functions)
    (gnus-group-set-parameter group 'gnus-article-sort-functions
			      '((append gnus-article-sort-functions
					(list
					 'gnus-article-sort-by-schedule)))))
  (unless (gnus-group-get-parameter group 'gnus-thread-sort-functions)
    (gnus-group-set-parameter group 'gnus-thread-sort-functions
			      '((append gnus-thread-sort-functions
					(list
					 'gnus-thread-sort-by-schedule))))))

;; Called when a group is subscribed. This is needed because groups created
;; because of mail splitting are *not* created with the back end function.
;; Thus, `nndiary-request-create-group-functions' is inoperative.
(defun gnus-diary-maybe-update-group-parameters (group)
  (when (eq (car (gnus-find-method-for-group group)) 'nndiary)
    (gnus-diary-update-group-parameters group)))

(add-hook 'nndiary-request-create-group-functions
	  #'gnus-diary-update-group-parameters)
;; Now that we have `gnus-subscribe-newsgroup-functions', this is not needed
;; anymore. Maybe I should remove this completely.
(add-hook 'nndiary-request-update-info-functions
	  #'gnus-diary-update-group-parameters)
(add-hook 'gnus-subscribe-newsgroup-functions
	  #'gnus-diary-maybe-update-group-parameters)


;; Diary Message Checking ===================================================

(defvar gnus-diary-header-value-history nil
  ;; History variable for header value prompting
  )

(defun gnus-diary-narrow-to-headers ()
  "Narrow the current buffer to the header part.
Point is left at the beginning of the region.
The buffer is assumed to contain a message, but the format is unknown."
  (cond ((eq major-mode 'message-mode)
	 (message-narrow-to-headers))
	(t
	 (goto-char (point-min))
	 (when (search-forward "\n\n" nil t)
	   (narrow-to-region (point-min) (- (point) 1))
	   (goto-char (point-min))))
	))

(defun gnus-diary-add-header (str)
  "Add a header to the current buffer.
The buffer is assumed to contain a message, but the format is unknown."
  (cond ((eq major-mode 'message-mode)
	 (message-add-header str))
	(t
	 (save-restriction
	   (gnus-diary-narrow-to-headers)
	   (goto-char (point-max))
	   (if (string-match "\n$" str)
	       (insert str)
	     (insert str ?\n))))
	))

(defun gnus-diary-check-message (arg)
  "Ensure that the current message is a valid for NNDiary.
This function checks that all NNDiary required headers are present and
valid, and prompts for values / correction otherwise.

If ARG (or prefix) is non-nil, force prompting for all fields."
  (interactive "P" gnus-summary-mode)
  (save-excursion
    (mapcar
     (lambda (head)
       (let ((header (concat "X-Diary-" (car head)))
	     (ask arg)
	     value invalid)
	 ;; First, try to find the header, and checks for validity:
	 (save-restriction
	   (gnus-diary-narrow-to-headers)
	   (when (re-search-forward (concat "^" header ":") nil t)
	     (unless (eq (char-after) ? )
	       (insert " "))
	     (setq value (buffer-substring (point) (point-at-eol)))
	     (and (string-match "[ \t]*\\([^ \t]+\\)[ \t]*" value)
		  (setq value (match-string 1 value)))
	     (condition-case ()
		 (nndiary-parse-schedule-value value
					       (nth 1 head) (nth 2 head))
	       (error
		(setq invalid t)))
	     ;; #### NOTE: this (along with the `gnus-diary-add-header'
	     ;; function) could be rewritten in a better way, in particular
	     ;; not to blindly remove an already present header and reinsert
	     ;; it somewhere else afterwards.
	     (when (or ask invalid)
	       (gnus-diary-kill-entire-line))
	     ))
	 ;; Now, loop until a valid value is provided:
	 (while (or ask (not value) invalid)
	   (let ((prompt (concat (and invalid
				      (prog1 "(current value invalid) "
					(beep)))
				 header ": ")))
	     (setq value
		   (if (listp (nth 1 head))
		       (gnus-completing-read prompt (cons "*" (mapcar #'car (nth 1 head)))
                                             t value
                                             'gnus-diary-header-value-history)
		     (read-string prompt value
				  'gnus-diary-header-value-history))))
	   (setq ask nil)
	   (setq invalid nil)
	   (condition-case ()
	       (nndiary-parse-schedule-value value
					     (nth 1 head) (nth 2 head))
	     (error
	      (setq invalid t))))
	 (gnus-diary-add-header (concat header ": " value))
	 ))
     nndiary-headers)
    ))

(add-hook 'nndiary-request-accept-article-functions
	  (lambda () (gnus-diary-check-message nil)))

(define-key message-mode-map "\C-c\C-fd" 'gnus-diary-check-message)
(define-key gnus-article-edit-mode-map "\C-c\C-fd" 'gnus-diary-check-message)


;; The end ==================================================================

(defun gnus-diary-version ()
  "Current Diary back end version."
  (interactive)
  (message "NNDiary version %s" nndiary-version))

(provide 'gnus-diary)

;;; gnus-diary.el ends here
