;;; gnosis.el --- Learning tool for GNU Emacs  -*- lexical-binding: t; -*-

;; Copyright (C) 2023  Thanos Apollo

;; Author: Thanos Apollo <public@thanosapollo.org>
;; Keywords: extensions
;; URL: https://git.thanosapollo.org/gnosis
;; Version: 0.0.1

;; Package-Requires: ((emacs "27.2") (compat "29.1.4.2"))

;; This program 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.

;; This program 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 this program.  If not, see <https://www.gnu.org/licenses/>.

;;; Commentary:

;; Work in progress

;;; Code:

;; TODO: Create cloze question type & make it easily extensible for
;; other types


(require 'emacsql)
(require 'cl-lib)
(require 'animate)

(defgroup gnosis nil
  "Spaced repetition learning tool."
  :group 'external
  :prefix "gnosis-")

(defvar gnosis-db (emacsql-sqlite (concat user-emacs-directory "gnosis.db")))

(cl-defun gnosis--select (value table &optional (restrictions '1=1))
  "Select VALUE from TABLE, optionally with RESTRICTIONS."
  (emacsql gnosis-db `[:select ,value :from ,table :where ,restrictions]))

(cl-defun gnosis--create-table (table &optional values)
  "Create TABLE for VALUES."
  (emacsql gnosis-db `[:create-table ,table ,values]))

(cl-defun gnosis--drop-table (table)
  "Drop TABLE from gnosis-db."
  (emacsql gnosis-db `[:drop-table ,table]))

(cl-defun gnosis--insert-into (table values)
  "Insert VALUES to TABLE."
  (emacsql gnosis-db `[:insert :into ,table :values ,values]))

(defun gnosis-get (value table &optional restrictions)
  "Get VALUE from TABLE, optionally with where RESTRICTIONS."
  (caar (gnosis--select value table restrictions)))

(defun gnosis--delete (table value)
  "From TABLE use where to delete VALUE."
  (emacsql gnosis-db `[:delete :from ,table :where ,value]))

(defun gnosis--display-question (id)
  "Display main row for question ID."
  (let ((question (gnosis-get 'main 'notes `(= id ,id))))
    ;; Animate.el is used only for testing purposes.
    (animate-string question 1)))

(defun gnosis--ask-input (prompt)
  "PROMPT user for input until `q' is given.

The user is prompted to provide input for the 'PROMPT' message, and
the returns the list of inputs in reverse order."
  (let ((input nil))
    (while (not (equal (car input) "q"))
      (add-to-list 'input (read-string (concat prompt " (q for quit): "))))
    (when (equal (car input) "q")
      (pop input))
    (reverse input)))

(defun gnosis-add-deck (name)
  "Create deck with NAME."
  (interactive (list (read-string "Deck Name: ")))
  (gnosis--insert-into 'decks `([nil ,name])))

(defun gnosis--get-deck-name ()
  "Get name from table DECKS."
  (when (equal (gnosis--select 'name 'decks) nil)
    (error "No decks found"))
  (completing-read "Deck: " (gnosis--select 'name 'decks)))

(defun gnosis--get-deck-id ()
  "Select id for deck name."
  (let ((deck (gnosis--get-deck-name)))
    (gnosis-get 'id 'decks `(= name ,deck))))

(defun gnosis-delete-deck (id)
  "Delete deck with id value of ID."
  (interactive (list (gnosis--get-deck-id)))
  (gnosis--delete 'decks `(= id ,id)))

(cl-defun gnosis-add-note-mcq (&key deck question choices correct-answer tags)
  "Create a NOTE with a list of multiple CHOICES.

MCQ type consists of a main `QUESTION' that is displayed to the user.
The user will be prompted to select the correct answer from a list of
`CHOICES'. The `CORRECT-ANSWER' should be the index of the correct
choice in the `CHOICES' list. Each note must correspond to one `DECK'.
TAGS are used to organize questions."
  (interactive
   (list :deck (gnosis--get-deck-id)
	 :question (read-string "Question: ")
         :choices (gnosis--ask-input "Choices")
         :correct-answer (string-to-number (read-string "Which is the correct answer (number)? "))
	 :tags (when (equal (gnosis--ask-input "Tags") nil) 'untagged)))
  (when (equal (numberp correct-answer) nil)
    (error "The correct answer must be the number of the correct answer"))
  (gnosis--insert-into 'notes `([nil "mcq" ,question ,choices ,correct-answer ,tags ,deck]))
  ;; Get last inserted note-id
  (let ((note-id (caar (last (gnosis--select 'id 'notes)))))
    (gnosis--insert-into 'review `([,note-id ,gnosis-ef ,gnosis-ff 0 0 0]))))

(defun gnosis-add-note (type)
  "Create note as TYPE."
  (interactive (list (completing-read "Type: " '(MCQ Cloze Basic))))
  (pcase type
    ("MCQ" (call-interactively 'gnosis-add-note-mcq))
    ("Cloze" (message "Not ready yet."))
    ("Basic" (message "Not ready yet."))
    (_ (message "No such type."))))

(defun gnosis-mcq-answer (id)
  "Choose the correct answer, from mcq choices for question ID."
  (let ((choices (gnosis-get 'options 'notes `(= id ,id)))
	(history-add-new-input nil)) ;; Disable history
    (completing-read "Answer: " choices)))

(defun gnosis-review-mcq-choices (id)
  "Display multiple choice answers for question ID."
  (let ((answer (gnosis-get 'answer 'notes `(= id ,id)))
	(choices (gnosis-get 'options 'notes `(= id ,id)))
	(user-choice (gnosis-mcq-answer id)))
    (if (equal (nth (- answer 1) choices) user-choice)
	(message "Correct!")
      (message "False"))))

(defun gnosis-review (id)
  "Start review for question ID."
  (let ((type (gnosis-get 'type 'notes `(= id id))))
    (pcase type
      ("mcq" (gnosis-review-mcq-choices id))
      ("basic" (message "Not Ready yet."))
      ("cloze" (message "Not Ready yet."))
      (_ (error "Malformed note type")))))

;; Database Schemas
(defvar gnosis-db-decks-schema '([(id integer :primary-key :autoincrement)
				  (name text :not-null)]))

(defvar gnosis-db-notes-schema '([(id integer :primary-key :autoincrement)
				  (type text :not-null)
				  (main text :not-null)
				  (options text :not-null)
				  (answer text :not-null)
				  (tags text :default untagged)
				  (deck-id integer)]
				 (:foreign-key [deck-id] :references decks [id]
					       :on-delete :cascade)))

(defvar gnosis-db-review-schema '([(id integer :not-null) ;; note-id
				   (ef integer :not-null) ;; Easiness factor
				   (ff integer :not-null) ;; Forgetting factor
				   (n integer :not-null) ;; Number of reviews
				   (failures integer :not-null) ;; Number of consecutive review failures
				   (interval integer :not-null)] ;; Interval
				  (:foreign-key [id] :references notes [id]
						:on-delete :cascade)))


;; testing
(defun gnosis-test-buffer ()
  "Create testing buffer."
  (interactive)
  (with-current-buffer
      (switch-to-buffer (get-buffer-create "*gnosis*"))
    (read-only-mode 0)
    (erase-buffer)
    (gnosis--display-question 4)
    (gnosis-review 4)
    (gnosis-mode)))

(defun gnosis-init ()
  "Create notes content table."
  (interactive)
  ;;(make-directory (concat user-emacs-directory "gnosis"))
  (condition-case nil
      (gnosis--drop-table 'notes)
    (error (message "No NOTES table to drop.")))
  (condition-case nil
      (gnosis--drop-table 'decks)
    (error (message "No NOTES table to drop.")))
  (condition-case nil
      (gnosis--drop-table 'review)
    (error (message "No REVIEW table to drop.")))
  ;; Enable foreign_keys
  (emacsql gnosis-db "PRAGMA foreign_keys = ON")
  ;; Create decks table
  (gnosis--create-table 'decks gnosis-db-decks-schema)
  ;; Create notes table
  (gnosis--create-table 'notes gnosis-db-notes-schema)
  ;; Create review table
  (gnosis--create-table 'review gnosis-db-review-schema)
  (gnosis-add-deck "Anatomy"))

;; Gnosis mode ;;
;;;;;;;;;;;;;;;;;

(define-derived-mode gnosis-mode special-mode "Gnosis"
  "Gnosis Mode."
  :interactive t
  (display-line-numbers-mode 0)
  :lighter " gnosis-mode")

;; Gnosis Algorithm ;;
;;;;;;;;;;;;;;;;;;;;;;

(defcustom gnosis-interval '(1 3)
  "Gnosis initial interval.

Interval by which a new question is displayed or when it's ef is at 1.3.

First item: First interval
Second item: Second interval."
  :group 'gnosis
  :type 'list)

(defcustom gnosis-ef '(0.3 0.3)
  "Gnosis easiness factor.

First item : Increase factor
Second item: Decrease factor"
  :group 'gnosis
  :type 'list)

(defcustom gnosis-ff 0.5
  "Gnosis forgetting factor.

Used to calcuate new interval for failed questions."
  :group 'gnosis
  :type 'float)

(defun gnosis-current-date (&optional offset)
  "Return the current date in a list (year month day).
Optional integer OFFSET is a number of days from the current date."
  (let* ((now (decode-time))
         (now (list (decoded-time-month now)
                    (decoded-time-day now)
                    (decoded-time-year now))))
    (let ((date (if (zerop (or offset 0))
                    now
                  (calendar-gregorian-from-absolute
                   (+ offset (calendar-absolute-from-gregorian now))))))
      (list (nth 2 date) (nth 0 date) (nth 1 date)))))

(defun gnosis-calculate-e-factor (ef quality)
  "Calculate new e-factor given existing EF and binary QUALITY, 0 or 1."
  (cond
   ((not (numberp quality))
    (error "Invalid argument passed to gnosis-calculate-e-factor"))
   ((= quality 0) ;; If the quality score is 0 (fail), decrease the ef by a small penalty
    (max 1.3 (- ef (cadr gnosis-ef))))
   ((= quality 1) ;; If the quality score is 1 (pass), increase the ef by a small reward
    (+ ef (car gnosis-ef)))
   (t (error "Invalid quality score passed to gnosis-calculate-e-factor"))))

(defun gnosis-calculate-next-interval (last-interval n ef success ff)
  "Calculate next interval.
- LAST-INTERVAL : The number of days since the item was last reviewed.
- N : Number of times the item has been reviewed.
- EF : The 'easiness factor'.
- SUCCESS : Success of the recall, ranges from 0 (unsuccessful) to 1
  (successful).
- FF: Failure factor

Returns a tuple: (INTERVAL N EF) where,
- INTERVAL : The number of days until the item should next be reviewed.
- N : Incremented by 1.
- EF : Modified based on the recall success for the item."
  (cl-assert (and (>= success 0)
		  (<= success 1)))
  ;; Calculate the next easiness factor.
  (let* ((next-ef (gnosis-calculate-e-factor ef success))
         ;; Calculate the next interval.
         (interval
          (cond
	   ;; Show item same day on the first review
	   ((= n 0) 0)
           ;; Immediately next day if it's the first time review.
           ((<= n 1) (car gnosis-interval))
           ;; After 3 days if it's second review.
           ((= n 2) (cadr gnosis-interval))
           ;; Increase last interval by 1 if recall was successful. Keep last interval if unsuccessful.
           (t (if (= success 1)
                  (* ef last-interval)
                (* ff last-interval))))))
    (list (round interval) (1+ n) next-ef)))


(provide 'gnosis)
;;; gnosis.el ends here