From 43bb7ab15c37b452418e1a9095e01e56d56c5ef8 Mon Sep 17 00:00:00 2001
From: Leon Rische <leon.rische@me.com>
Date: Sun, 7 Mar 2021 15:53:14 +0100
Subject: Extract core functions

---
 org-fc-algo-sm2.el        |   2 +
 org-fc-audio.el           |   2 +-
 org-fc-awk.el             |   3 +
 org-fc-cache.el           |   2 +
 org-fc-core.el            | 611 +++++++++++++++++++++++++++++++++++++++++
 org-fc-dashboard.el       |   6 +
 org-fc-diff.el            |   2 +
 org-fc-hydra.el           |   3 +-
 org-fc-keymap-hint.el     |   3 +-
 org-fc-review.el          |  53 +++-
 org-fc-type-cloze.el      |   2 +
 org-fc-type-double.el     |   2 +
 org-fc-type-normal.el     |   2 +
 org-fc-type-text-input.el |   1 +
 org-fc-type-vocab.el      |   1 +
 org-fc.el                 | 678 +---------------------------------------------
 16 files changed, 699 insertions(+), 674 deletions(-)
 create mode 100644 org-fc-core.el

diff --git a/org-fc-algo-sm2.el b/org-fc-algo-sm2.el
index 743afde..1283bd8 100644
--- a/org-fc-algo-sm2.el
+++ b/org-fc-algo-sm2.el
@@ -28,6 +28,8 @@
 
 (require 'cl-lib)
 
+(require 'org-fc-core)
+
 (defmacro org-fc-property (symbol standard doc &rest args)
   (let (defcustom-args property reader)
     (while args
diff --git a/org-fc-audio.el b/org-fc-audio.el
index a947bc4..2e95f7a 100644
--- a/org-fc-audio.el
+++ b/org-fc-audio.el
@@ -35,7 +35,7 @@
 ;;
 ;;; Code:
 
-(require 'org-fc)
+(require 'org-fc-core)
 
 (defcustom org-fc-audio-before-setup-property "FC_AUDIO_BEFORE_SETUP"
   "Name of the property to use for storing before-setup audio files."
diff --git a/org-fc-awk.el b/org-fc-awk.el
index 24d010b..1f060e6 100644
--- a/org-fc-awk.el
+++ b/org-fc-awk.el
@@ -25,6 +25,9 @@
 ;;
 ;;
 ;;; Code:
+
+(require 'org-fc-core)
+
 ;;;; Shell wrappers
 
 (defun org-fc-awk--find (paths)
diff --git a/org-fc-cache.el b/org-fc-cache.el
index e64f08e..83fee37 100644
--- a/org-fc-cache.el
+++ b/org-fc-cache.el
@@ -32,6 +32,8 @@
 
 ;;; Code:
 
+(require 'org-fc-core)
+
 ;;; Queue / Processing of Files
 
 (defvar org-fc-cache
diff --git a/org-fc-core.el b/org-fc-core.el
new file mode 100644
index 0000000..3fde3f8
--- /dev/null
+++ b/org-fc-core.el
@@ -0,0 +1,611 @@
+;;; org-fc-core.el --- Core functions of org-fc -*- lexical-binding: t; -*-
+
+;; Copyright (C) 2020-2021  Leon Rische
+
+;; Author: Leon Rische <emacs@leonrische.me>
+;; Url: https://www.leonrische.me/pages/org_flashcards.html
+;; Package-requires: ((emacs "26.3") (org "9.3"))
+;; Version: 0.1.0
+
+;; 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:
+;;
+;;; Code:
+
+(require 'org-indent)
+(require 'org-element)
+(require 'outline)
+
+;;; Helper Functions
+
+(defun org-fc-member-p (path)
+  "Check if PATH is member of one of the `org-fc-directories'."
+  (setq path (expand-file-name path))
+  (and (string= (file-name-extension path) "org")
+       (cl-some
+        (lambda (dir) (string-prefix-p (expand-file-name dir) path))
+        org-fc-directories)))
+
+(defun org-fc-noop ()
+  "Noop-function.")
+
+(defun org-fc-timestamp-now ()
+  "ISO8601 timestamp of the current time in the UTC timezone."
+  (format-time-string "%FT%TZ" nil "UTC"))
+
+(defun org-fc-show-latex ()
+  "Show latex fragments of heading at point."
+  (org-latex-preview 4))
+
+(defun org-fc-back-heading-position ()
+  "Return point at the beginning of an entries 'Back' subheading.
+Return nil if there is no such heading.
+This is expected to be called on an card entry heading."
+  (let ((found nil)
+        (level (cl-first (org-heading-components))))
+    (org-map-entries
+     (lambda ()
+       (when (let ((comps (org-heading-components)))
+               (and
+                (string= (cl-fifth comps) "Back")
+                (= (cl-first comps) (1+ level))))
+         (setq found (point))))
+     t 'tree)
+    found))
+
+(defun org-fc-has-back-heading-p ()
+  "Check if the entry at point has a 'Back' subheading.
+Used to determine if a card uses the compact style."
+  (not (null (org-fc-back-heading-position))))
+
+(defun org-fc-sorted-random (n)
+  "Generate a list of N sorted random numbers."
+  (sort (cl-loop for i below n collect (cl-random 1.0)) #'>))
+
+(defun org-fc-zip (as bs)
+  "Zip two lists AS and BS."
+  (cl-loop for a in as for b in bs collect (cons a b)))
+
+;; File-scoped variant of `org-id-goto'
+(defun org-fc-id-goto (id file)
+  "Go to the heading with ID in FILE."
+  (let ((position (org-id-find-id-in-file id file)))
+    (if position
+        (goto-char (cdr position))
+      (error "ID %s not found in %s" id file))))
+
+(defun org-fc-timestamp-in (interval)
+  "Generate an `org-mode' timestamp INTERVAL days from now."
+  (let ((seconds (* interval 60 60 24))
+        (now (time-to-seconds)))
+    (format-time-string
+     org-fc-timestamp-format
+     (seconds-to-time (+ now seconds))
+     "UTC0")))
+
+(defun org-fc-deemphasize (string)
+  "Remove org emphasis markers from STRING.
+Returns a pair (marker . body)."
+  (if (or (string-match org-emph-re string)
+          (string-match org-verbatim-re string))
+      (cons (match-string 3 string) (match-string 4 string))
+    (cons nil string)))
+
+(defun org-fc-emphasize (string)
+  "Apply org emphasis faces to STRING."
+  (with-temp-buffer
+    (insert string)
+    (goto-char (point-min))
+    (org-do-emphasis-faces (point-max))
+    (buffer-string)))
+
+(defun org-fc-indent ()
+  "Run `org-indent' on the current headline.
+Usually org-indent runs with a delay, so when reviewing a card in
+a new file, the cards contents jump to the right (are indented)
+during the review.  We can get around this by synchronously
+indenting the current heading."
+  (if org-indent-mode
+      (let ((el (org-element-at-point)))
+        (org-indent-add-properties
+         (org-element-property :begin el)
+         (org-element-property :end el)))))
+
+(defmacro org-fc-with-point-at-entry (&rest body)
+  "Execute BODY with point at the card heading.
+If point is not inside a flashcard entry, an error is raised."
+  `(save-excursion
+     (org-fc-goto-entry-heading)
+     ,@body))
+
+(defmacro org-fc-with-point-at-back-heading (&rest body)
+  "Execute BODY with point at the card's back heading.
+If point is not inside a flashcard entry, an error is raised."
+  `(if-let ((pos (org-fc-back-heading-position)))
+       (save-excursion
+         (goto-char pos)
+         ,@body)))
+
+;;; Checking for / going to flashcard headings
+
+(defun org-fc-entry-p ()
+  "Check if the current heading is a flashcard."
+  (member org-fc-flashcard-tag (org-get-tags nil 'local)))
+
+(defun org-fc-suspended-entry-p ()
+  "Check if the current heading is a suspended flashcard."
+  (let ((tags (org-get-tags nil 'local)))
+    (and (member org-fc-flashcard-tag tags)
+         (member org-fc-suspended-tag tags))))
+
+(defun org-fc-part-of-entry-p ()
+  "Check if the current heading belongs to a flashcard."
+  (member org-fc-flashcard-tag (org-get-tags nil)))
+
+(defun org-fc-goto-entry-heading ()
+  "Move up to the parent heading marked as a flashcard."
+  (unless (org-fc-part-of-entry-p)
+    (error "Not inside a flashcard entry"))
+  (unless (org-at-heading-p)
+    (org-back-to-heading))
+  (while (not (org-fc-entry-p))
+    (unless (org-up-heading-safe)
+      (error "Cannot find a parent heading that is marked as a flashcard"))))
+
+;;; Adding / Removing Tags
+
+(defun org-fc--add-tag (tag)
+  "Add TAG to the heading at point."
+  (org-set-tags
+   (cl-remove-duplicates
+    (cons tag (org-get-tags nil 'local))
+    :test #'string=)))
+
+(defun org-fc--remove-tag (tag)
+  "Add TAG to the heading at point."
+  (org-set-tags
+   (remove tag (org-get-tags nil 'local))))
+
+;;; Card Initialization
+
+(defun org-fc--init-card (type)
+  "Initialize the current card as a flashcard.
+Should only be used by the init functions of card TYPEs."
+  (if (org-fc-entry-p)
+      (error "Headline is already a flashcard"))
+  (org-back-to-heading)
+  (org-set-property
+   org-fc-created-property
+   (org-fc-timestamp-now))
+  (org-set-property org-fc-type-property type)
+  (org-id-get-create)
+  (org-fc--add-tag org-fc-flashcard-tag))
+
+;;; Card Types
+;;;; Type Management
+
+(defvar org-fc-types '()
+  "Alist for registering card types.
+Entries should be lists (name handler-fn update-fn).
+Use `org-fc-register-type' for adding card types.")
+
+(defun org-fc-register-type (name setup-fn flip-fn update-fn)
+  "Register a new card type.
+Argument NAME Name of the new type.
+Argument SETUP-FN Function for initializing a new card of this type.
+Argument FLIP-FN Function for flipping a card during review.
+Argument UPDATE-FN Function to update a card when it's contents have changed."
+  (push
+   (list name setup-fn flip-fn update-fn)
+   org-fc-types))
+
+(defun org-fc-type-setup-fn (type)
+  "Get the review function for a card of TYPE."
+  (let ((entry (alist-get type org-fc-types nil nil #'string=)))
+    (if entry
+        (cl-first entry)
+      (error "No such flashcard type: %s" type))))
+
+(defun org-fc-type-flip-fn (type)
+  "Get the flip function for a card of TYPE."
+  (let ((entry (alist-get type org-fc-types nil nil #'string=)))
+    (if entry
+        (cl-second entry)
+      (error "No such flashcard type: %s" type))))
+
+(defun org-fc-type-update-fn (type)
+  "Get the update function for a card of TYPE."
+  (let ((entry (alist-get type org-fc-types nil nil #'string=)))
+    (if entry
+        (cl-third entry)
+      (error "No such flashcard type: %s" type))))
+
+;;; Working with Overlays / Hiding Text
+;;;; Showing / Hiding Overlays
+
+(defun org-fc-remove-overlays ()
+  "Remove all org-fc overlays in the current buffer."
+  (interactive)
+  (remove-overlays (point-min) (point-max) 'category 'org-fc))
+
+;; Based on `outline-flag-region'
+(defun org-fc-hide-region (from to &optional text face)
+  "Hide region FROM ... TO, optionally replacing it with TEXT.
+FACE can be used to set the text face of the overlay, e.g. to
+make it bold."
+  ;; (remove-overlays from to 'category 'org-fc)
+  (let ((o (make-overlay from to nil 'front-advance)))
+    (overlay-put o 'category 'org-fc)
+    (overlay-put o 'evaporate t)
+    (if face (overlay-put o 'face face))
+    (if (stringp text)
+        (progn
+          (overlay-put o 'invisible nil)
+          (overlay-put o 'display text))
+      (overlay-put o 'invisible t))
+    o))
+
+(defun org-fc-make-overlay (begin end &rest props)
+  "Create an overlay from BEGIN to END with PROPS."
+  (let ((o (make-overlay begin end)))
+    (overlay-put o 'category 'org-fc)
+    (cl-loop for (prop value) on props by #'cddr do
+             (overlay-put o prop value))
+    o))
+
+(defun org-fc-overlay-surround (o before after &optional face)
+  "Surround O with strings BEFORE and AFTER with optional FACE."
+  (overlay-put o 'before-string (propertize before 'face face))
+  (overlay-put o 'after-string (propertize after 'face face))
+  o)
+
+;;;; Hiding Drawers
+
+(defun org-fc-hide-keyword-times ()
+  "Hide all timestamp keywords (e.g. DEADLINE) after point."
+  (save-excursion
+    (while (re-search-forward org-keyword-time-regexp nil t)
+      (let ((start (1- (match-beginning 0)))
+            (end (match-end 0)))
+        (org-fc-hide-region start end)))))
+
+(defun org-fc-hide-drawers ()
+  "Hide all drawers except ones in `org-fc-drawer-whitelist' after point."
+  (let ((bound (org-element-property :end (org-element-at-point))))
+    (save-excursion
+      (while (re-search-forward org-drawer-regexp bound t)
+        (let ((start (1- (match-beginning 0)))
+              (name (match-string 1))
+              (end))
+          (if (re-search-forward ":END:" bound t)
+              (setq end (point))
+            (error "No :END: found for drawer"))
+          (if (member name org-fc-drawer-whitelist)
+              (org-flag-drawer nil nil start end)
+            (org-fc-hide-region start end)))))))
+
+;;;; Hiding Headings / Section Contents
+
+(defun org-fc-hide-heading (&optional text)
+  "Hide the title of the headline at point.
+If TEXT is non-nil, the heading is replaced with TEXT."
+  ;; Case sensitive search
+  (let ((case-fold-search nil))
+    (save-excursion
+      (beginning-of-line)
+      (if (looking-at org-complex-heading-regexp)
+          (org-fc-hide-region (match-beginning 4) (match-end 4) (or text "..."))
+        (error "Point is not on a heading")))))
+
+(defun org-fc-hide-content (&optional text)
+  "Hide the main text of a heading *before* the first subheading.
+If TEXT is non-nil, the content is replaced with TEXT."
+  (let (start end)
+    (save-excursion
+      (org-back-to-heading)
+      (forward-line)
+      (setq start (point)))
+    (save-excursion
+      (outline-next-heading)
+      (setq end (point)))
+    (org-fc-hide-region start end text)))
+
+;;;; Outline Trees
+
+(defcustom org-fc-narrow-visibility 'ancestors
+  "Visibility of the current heading during review.
+See `org-show-set-visibility' for possible values"
+  :group 'org-fc
+  :type 'symbol
+  :options '(ancestors lineage minimal local tree canonical))
+
+(defun org-fc-narrow ()
+  "Narrow the outline tree.
+Only parent headings of the current heading remain visible."
+  (interactive)
+  (let* ((tags (org-get-tags nil 'local)))
+    ;; Find the first heading with a :narrow: tag or the top level
+    ;; ancestor of the current heading and narrow to its region
+    (save-excursion
+      (while (org-up-heading-safe))
+      (org-narrow-to-subtree)
+      (outline-hide-subtree))
+    ;; Show only the ancestors of the current card
+    (org-show-set-visibility org-fc-narrow-visibility)
+    (if (member "noheading" tags) (org-fc-hide-heading))))
+
+;;; Updating Cards
+
+(defun org-fc-map-cards (fn &optional scope)
+  "Call FN for each flashcard headline in SCOPE.
+FN is called with point at the headline and no arguments.
+If SCOPE is nil, it defaults to the full buffer.
+Other useful values are:
+- tree
+- region"
+  (org-map-entries
+   (lambda () (if (org-fc-entry-p) (funcall fn)))
+   nil
+   scope))
+
+;;;###autoload
+(defun org-fc-update ()
+  "Re-process the current flashcard."
+  (interactive)
+  (org-fc-with-point-at-entry
+   (let ((type (org-entry-get (point) "FC_TYPE")))
+     (funcall (org-fc-type-update-fn type)))))
+
+;;;###autoload
+(defun org-fc-update-all ()
+  "Re-process all flashcards in the current buffer."
+  (interactive)
+  (org-fc-map-cards 'org-fc-update))
+
+;;; Suspending / Unsuspending Cards
+
+;;;###autoload
+(defun org-fc-suspend-card ()
+  "Suspend the headline at point if it is a flashcard."
+  (interactive)
+  (org-fc-with-point-at-entry
+   (org-fc--add-tag org-fc-suspended-tag)))
+
+;;;###autoload
+(defun org-fc-suspend-tree ()
+  "Suspend all cards in the subtree at point."
+  (interactive)
+  (org-fc-map-cards 'org-fc-suspend-card 'tree))
+
+;;;###autoload
+(defun org-fc-suspend-buffer ()
+  "Suspend all cards in the current buffer."
+  (interactive)
+  (org-fc-map-cards 'org-fc-suspend-card))
+
+;;;###autoload
+(defun org-fc-suspend-region ()
+  "Suspend all cards in the current region."
+  (interactive)
+  (org-fc-map-cards 'org-fc-suspend-card 'region))
+
+;;;###autoload
+(defun org-fc-unsuspend-card ()
+  "Unsuspend the headline at point.
+Checks if the headline is a suspended card first."
+  (interactive)
+  (org-fc--remove-tag org-fc-suspended-tag))
+
+;;;###autoload
+(defun org-fc-unsuspend-tree ()
+  "Un-suspend all cards in the subtree at point."
+  (interactive)
+  (org-fc-map-cards 'org-fc-unsuspend-card 'tree))
+
+;;;###autoload
+(defun org-fc-unsuspend-buffer ()
+  "Un-suspend all cards in the current buffer."
+  (interactive)
+  (org-fc-map-cards 'org-fc-unsuspend-card))
+
+;;;###autoload
+(defun org-fc-unsuspend-region ()
+  "Un-suspend all cards in the current region."
+  (interactive)
+  (org-fc-map-cards 'org-fc-unsuspend-card 'region))
+
+;;; Indexing Cards
+;;;; Card Filters
+
+(defun org-fc--compile-filter (filter)
+  "Compile FILTER into a lambda function.
+Filters can be combinations of the following expressions:
+
+- `(and ex1 ex2 ...)'
+- `(or ex1 ex2 ...)'
+- `(not ex)'
+- `(tag \"tag\")'
+- `(type card-type)' or `(type \"card-type\")'
+
+For example, to match all double cards with tag \"math\",
+use `(and (type double) (tag \"math\"))'."
+  (let ((card-var (gensym)))
+    (cl-labels
+        ((check-arity-exact
+          (filter n)
+          (unless (= (length filter) (1+ n))
+            (error
+             (format "Filter '%s' expects %d argument(s)" filter n))))
+         (compile-inner
+          (filter)
+          (cl-case (car filter)
+            ('and `(and ,@(mapcar #'compile-inner (cdr filter))))
+            ('or `(or ,@(mapcar #'compile-inner (cdr filter))))
+            ('not
+             (check-arity-exact filter 1)
+             `(not ,(compile-inner (cadr filter))))
+            ('tag
+             (check-arity-exact filter 1)
+             `(member ,(cadr filter) (plist-get ,card-var :tags)))
+            ('type
+             (check-arity-exact filter 1)
+             `(eq ',(if (stringp (cadr filter))
+                        (intern (cadr filter))
+                      (cadr filter))
+                  (plist-get ,card-var :type))))))
+      `(lambda (,card-var)
+         ,(compile-inner filter)))))
+
+(defun org-fc-index (context)
+  "Create an index for review CONTEXT."
+  (let ((paths (plist-get context :paths))
+        (filter (plist-get context :filter)))
+    ;; Handle path formats / symbols
+    (cond
+     ((or (null paths) (eq paths 'all)) (setq paths org-fc-directories))
+     ((eq paths 'buffer) (setq paths (list (buffer-file-name))))
+     ((stringp paths) (setq paths (list paths))))
+
+    (if filter (setq filter (org-fc--compile-filter filter)))
+
+    (funcall org-fc-index-function paths filter)))
+
+(defun org-fc-index-flatten-card (card)
+  "Flatten CARD into a list of positions.
+Relevant data from the card is included in each position
+element."
+  (mapcar
+   (lambda (pos)
+     (list
+      :filetitle (plist-get card :filetitle)
+      :tags (plist-get card :tags)
+      :path (plist-get card :path)
+      :id (plist-get card :id)
+      :type (plist-get card :type)
+      :due (plist-get pos :due)
+      :position (plist-get pos :position)))
+   (plist-get card :positions)))
+
+(defun org-fc-index-filter-due (index)
+  "Filter INDEX to include only unsuspended due positions.
+Cards with no positions are removed from the index."
+  (let (res (now (current-time)))
+    (dolist (card index)
+      (unless (plist-get card :suspended)
+        (let ((due
+               (cl-remove-if-not
+                (lambda (pos)
+                  (time-less-p (plist-get pos :due) now))
+                (plist-get card :positions))))
+          (unless (null due)
+            (plist-put
+             card :positions
+             (if (or (not org-fc-bury-siblings)
+                     (member (plist-get card :cloze-type) '(single enumeration)))
+                 due (list (car due))))
+            (push card res)))))
+    res))
+
+(defun org-fc-index-positions (index)
+  "Return all positions in INDEX."
+  (mapcan (lambda (card) (org-fc-index-flatten-card card)) index))
+
+(defun org-fc-index-shuffled-positions (index)
+  "Return all positions in INDEX in random order.
+Positions are shuffled in a way that preserves the order of the
+  positions for each card."
+  ;; 1. assign each position a random number
+  ;; 2. flatten the list
+  ;; 3. sort by the random number
+  ;; 4. remove the random numbers from the result
+  (let ((positions
+         (mapcan
+          (lambda (card)
+            (let ((pos (org-fc-index-flatten-card card)))
+              (org-fc-zip
+               (org-fc-sorted-random (length pos))
+               pos)))
+          index)))
+    (mapcar
+     #'cdr
+     (sort positions (lambda (a b) (> (car a) (car b)))))))
+
+;;; Demo Mode
+
+;;;###autoload
+(defun org-fc-demo ()
+  "Start a review of the demo file."
+  (interactive)
+  (let ((path (expand-file-name "demo.org" org-fc-source-path)))
+    (with-current-buffer (find-file path)
+      (org-fc-review-buffer))))
+
+;;; Header Line
+
+(defvar org-fc-original-header-line-format nil
+  "`header-line-format' before it was set by org-fc.")
+
+(defun org-fc-set-header-line ()
+  "Set the header-line for review."
+  (let* ((remaining (1+ (length (oref org-fc--session cards))))
+         (current (oref org-fc--session current-item))
+         (title
+          (unless (member "notitle" (plist-get current :tags))
+            (plist-get current :filetitle))))
+    (setq org-fc-original-header-line-format header-line-format)
+    (setq-local
+     header-line-format
+     `((org-fc-review-flip-mode "Flip")
+       (org-fc-review-rate-mode "Rate")
+       (org-fc-review-edit-mode "Edit")
+       ,(format " (%d) " remaining)
+       ,title))))
+
+(defun org-fc-reset-header-line ()
+  "Reset the header-line to its original value."
+  (setq-local header-line-format org-fc-original-header-line-format))
+
+;;; Contexts
+
+(defvar org-fc-custom-contexts '()
+  "User-defined review contexts.")
+
+(defvar org-fc-context-all '(:paths all)
+  "Default context for all cards.")
+(defvar org-fc-context-buffer '(:paths buffer)
+  "Default context for the current buffer.")
+
+(defun org-fc-contexts ()
+  "List of all contexts."
+  (cl-list*
+   (cons 'all org-fc-context-all)
+   (cons 'buffer org-fc-context-buffer)
+   org-fc-custom-contexts))
+
+(defun org-fc-select-context ()
+  "Select a review context."
+  (let ((context (completing-read
+                  "Context: "
+                  (mapcar (lambda (c) (car c)) (org-fc-contexts))
+                  nil
+                  :require-match)))
+    (unless (string= context "")
+      (alist-get (intern context) (org-fc-contexts)))))
+
+;;; Footer
+
+(provide 'org-fc-core)
+
+;;; org-fc-core.el ends here
diff --git a/org-fc-dashboard.el b/org-fc-dashboard.el
index aaa9742..024142a 100644
--- a/org-fc-dashboard.el
+++ b/org-fc-dashboard.el
@@ -26,6 +26,12 @@
 ;; the current context.
 ;;
 ;;; Code:
+
+(require 'svg)
+
+(require 'org-fc-core)
+(require 'org-fc-awk)
+
 ;;; Customization
 
 (defcustom org-fc-dashboard-bar-chart-width 400
diff --git a/org-fc-diff.el b/org-fc-diff.el
index b8b28d1..5330388 100644
--- a/org-fc-diff.el
+++ b/org-fc-diff.el
@@ -31,6 +31,8 @@
 
 (require 'cl-lib)
 
+(require 'org-fc-core)
+
 (defcustom org-fc-diff-filler ?-
   "Character for filling diffs when the input was too short."
   :type 'character
diff --git a/org-fc-hydra.el b/org-fc-hydra.el
index 890e37e..9a192fa 100644
--- a/org-fc-hydra.el
+++ b/org-fc-hydra.el
@@ -27,9 +27,10 @@
 ;;
 ;;; Code:
 
-(require 'org-fc)
 (require 'hydra)
 
+(require 'org-fc)
+
 (defhydra org-fc-hydra ()
   ("m" org-fc-dashboard "Dashboard" :exit t)
   ("r" org-fc-review "Start Review" :exit t)
diff --git a/org-fc-keymap-hint.el b/org-fc-keymap-hint.el
index 04df5e9..84abec8 100644
--- a/org-fc-keymap-hint.el
+++ b/org-fc-keymap-hint.el
@@ -27,9 +27,10 @@
 ;;
 ;;; Code:
 
-(require 'org-fc)
 (require 'edmacro)
 
+(require 'org-fc)
+
 (defun org-fc-keymap-hint--symbol-name (name)
   "Remove org-fc- prefixes from symbol NAME."
   (setq name (symbol-name name))
diff --git a/org-fc-review.el b/org-fc-review.el
index 998cbb5..c371a61 100644
--- a/org-fc-review.el
+++ b/org-fc-review.el
@@ -35,6 +35,52 @@
 ;;
 ;;; Code:
 
+(require 'eieio)
+
+(require 'org-fc-core)
+
+;;; Hooks
+
+(defcustom org-fc-before-setup-hook '()
+  "Functions run before a card is set up for review."
+  :type 'hook
+  :group 'org-fc)
+
+(defcustom org-fc-after-setup-hook '()
+  "Functions run after a card is set up for review."
+  :type 'hook
+  :group 'org-fc)
+
+(defcustom org-fc-after-flip-hook '()
+  "Functions run after a card is flipped during review."
+  :type 'hook
+  :group 'org-fc)
+
+(defcustom org-fc-before-review-hook '()
+  "Functions run when a review session is started."
+  :type 'hook
+  :group 'org-fc)
+
+(defcustom org-fc-after-review-hook '()
+  "Functions run when a review session ends / is quit."
+  :type 'hook
+  :group 'org-fc)
+
+;;; Variables
+
+(defvar org-fc-review--session nil
+  "Current review session.")
+
+(defvar org-fc-review--timestamp nil
+  "Time the last card was flipped.
+Used to calculate the time needed for reviewing a card.")
+
+(defvar org-fc-reviewing-existing-buffer nil
+  "Track if the current buffer was open before the review.")
+(make-variable-buffer-local 'org-fc-reviewing-existing-buffer)
+
+;;; Main Review Functions
+
 ;;;###autoload
 (defun org-fc-review (context)
   "Start a review session for all cards in CONTEXT.
@@ -113,7 +159,7 @@ If RESUMING is non-nil, some parts of the buffer setup are skipped."
                 (org-display-inline-images)
                 (run-hooks 'org-fc-before-setup-hook)
 
-                (setq org-fc-timestamp (time-to-seconds (current-time)))
+                (setq org-fc-review--timestamp (time-to-seconds (current-time)))
                 (let ((step (funcall (org-fc-type-setup-fn type) position)))
                   (run-hooks 'org-fc-after-setup-hook)
 
@@ -166,7 +212,7 @@ same ID as the current card in the session."
                (id (plist-get card :id))
                (position (plist-get card :position))
                (now (time-to-seconds (current-time)))
-               (delta (- now org-fc-timestamp)))
+               (delta (- now org-fc-review--timestamp)))
           (org-fc-review-add-rating org-fc-review--session rating)
           (org-fc-review-update-data path id position rating delta)
           (org-fc-review-reset)
@@ -424,9 +470,6 @@ removed."
       ('easy (cl-incf (cl-getf ratings :easy) 1)))
     (cl-incf (cl-getf ratings :total 1))))
 
-(defvar org-fc-review--session nil
-  "Current review session.")
-
 ;;; Modes
 
 (defvar org-fc-review-flip-mode-map
diff --git a/org-fc-type-cloze.el b/org-fc-type-cloze.el
index 9f0cffd..78b76ee 100644
--- a/org-fc-type-cloze.el
+++ b/org-fc-type-cloze.el
@@ -24,6 +24,8 @@
 ;;
 ;;; Code:
 
+(require 'org-fc-core)
+
 (defcustom org-fc-type-cloze-type-property "FC_CLOZE_TYPE"
   "Property used to store the card's subtype for cloze cards."
   :type 'string
diff --git a/org-fc-type-double.el b/org-fc-type-double.el
index 1a71075..81c7568 100644
--- a/org-fc-type-double.el
+++ b/org-fc-type-double.el
@@ -27,6 +27,8 @@
 ;;
 ;;; Code:
 
+(require 'org-fc-core)
+
 (defvar org-fc-type-double--overlay '())
 
 (defun org-fc-type-double-init ()
diff --git a/org-fc-type-normal.el b/org-fc-type-normal.el
index 011541f..2325e3e 100644
--- a/org-fc-type-normal.el
+++ b/org-fc-type-normal.el
@@ -24,6 +24,8 @@
 ;;
 ;;; Code:
 
+(require 'org-fc-core)
+
 (defun org-fc-type-normal-init ()
   "Mark headline as card of the normal type."
   (interactive)
diff --git a/org-fc-type-text-input.el b/org-fc-type-text-input.el
index 1327633..4def806 100644
--- a/org-fc-type-text-input.el
+++ b/org-fc-type-text-input.el
@@ -24,6 +24,7 @@
 ;;
 ;;; Code:
 
+(require 'org-fc-core)
 (require 'org-fc-diff)
 
 (defun org-fc-text-input-content ()
diff --git a/org-fc-type-vocab.el b/org-fc-type-vocab.el
index 7c74e26..6740851 100644
--- a/org-fc-type-vocab.el
+++ b/org-fc-type-vocab.el
@@ -30,6 +30,7 @@
 ;;
 ;;; Code:
 
+(require 'org-fc-core)
 (require 'org-fc-diff)
 (require 'org-fc-audio)
 
diff --git a/org-fc.el b/org-fc.el
index 7c99049..1a03975 100644
--- a/org-fc.el
+++ b/org-fc.el
@@ -27,17 +27,24 @@
 ;;; Code:
 
 (require 'cl-lib)
-(require 'eieio)
 (require 'org-id)
-(require 'org-indent)
-(require 'org-element)
-(require 'outline)
 (require 'parse-time)
 (require 'subr-x)
-(require 'svg)
 
 (require 'org-fc-compat)
 
+(require 'org-fc-awk)
+(require 'org-fc-cache)
+(require 'org-fc-algo-sm2)
+
+(require 'org-fc-dashboard)
+(require 'org-fc-review)
+
+(require 'org-fc-type-normal)
+(require 'org-fc-type-double)
+(require 'org-fc-type-text-input)
+(require 'org-fc-type-cloze)
+
 ;;; Customization
 
 (defgroup org-fc nil
@@ -139,667 +146,6 @@ Does not apply to cloze single and cloze enumeration cards."
   :type 'boolean
   :group 'org-fc)
 
-;;;; Hooks
-
-(defcustom org-fc-before-setup-hook '()
-  "Functions run before a card is set up for review."
-  :type 'hook
-  :group 'org-fc)
-
-(defcustom org-fc-after-setup-hook '()
-  "Functions run after a card is set up for review."
-  :type 'hook
-  :group 'org-fc)
-
-(defcustom org-fc-after-flip-hook '()
-  "Functions run after a card is flipped during review."
-  :type 'hook
-  :group 'org-fc)
-
-(defcustom org-fc-before-review-hook '()
-  "Functions run when a review session is started."
-  :type 'hook
-  :group 'org-fc)
-
-(defcustom org-fc-after-review-hook '()
-  "Functions run when a review session ends / is quit."
-  :type 'hook
-  :group 'org-fc)
-
-;;; Variables
-
-;; Not customizable because the indexers / filters expect ISO8601
-(defvar org-fc-timestamp-format "%FT%TZ"
-  "Format to use for storing timestamps.
-Defaults to ISO8601")
-
-(defvar org-fc-reviewing-existing-buffer nil
-  "Track if the current buffer was open before the review.")
-(make-variable-buffer-local 'org-fc-reviewing-existing-buffer)
-
-(defvar org-fc-original-header-line-format nil
-  "`header-line-format' before it was set by org-fc.")
-
-(defvar org-fc-timestamp nil
-  "Time the last card was flipped.
-Used to calculate the time needed for reviewing a card.")
-
-;;; Helper Functions
-
-(defun org-fc-member-p (path)
-  "Check if PATH is member of one of the `org-fc-directories'."
-  (setq path (expand-file-name path))
-  (and (string= (file-name-extension path) "org")
-       (cl-some
-        (lambda (dir) (string-prefix-p (expand-file-name dir) path))
-        org-fc-directories)))
-
-(defun org-fc-noop ()
-  "Noop-function.")
-
-(defun org-fc-timestamp-now ()
-  "ISO8601 timestamp of the current time in the UTC timezone."
-  (format-time-string org-fc-timestamp-format nil "UTC"))
-
-(defun org-fc-days-overdue (ts)
-  "Number of days between now and the ISO8601 timestamp TS."
-  (/ (- (time-to-seconds)
-        (time-to-seconds (date-to-time ts)))
-     (* 24 60 60)))
-
-(defun org-fc-show-latex ()
-  "Show latex fragments of heading at point."
-  (org-latex-preview 4))
-
-(defun org-fc-back-heading-position ()
-  "Return point at the beginning of an entries 'Back' subheading.
-Return nil if there is no such heading.
-This is expected to be called on an card entry heading."
-  (let ((found nil)
-        (level (cl-first (org-heading-components))))
-    (org-map-entries
-     (lambda ()
-       (when (let ((comps (org-heading-components)))
-               (and
-                (string= (cl-fifth comps) "Back")
-                (= (cl-first comps) (1+ level))))
-         (setq found (point))))
-     t 'tree)
-    found))
-
-(defun org-fc-has-back-heading-p ()
-  "Check if the entry at point has a 'Back' subheading.
-Used to determine if a card uses the compact style."
-  (not (null (org-fc-back-heading-position))))
-
-(defun org-fc-shuffle (list)
-  "Randomize the order of elements in LIST.
-This mutates / destroys the input list."
-  (sort list (lambda (_a _b) (< (cl-random 1.0) 0.5))))
-
-(defun org-fc-sorted-random (n)
-  "Generate a list of N sorted random numbers."
-  (sort (cl-loop for i below n collect (cl-random 1.0)) #'>))
-
-(defun org-fc-zip (as bs)
-  "Zip two lists AS and BS."
-  (cl-loop for a in as for b in bs collect (cons a b)))
-
-;; File-scoped variant of `org-id-goto'
-(defun org-fc-id-goto (id file)
-  "Go to the heading with ID in FILE."
-  (let ((position (org-id-find-id-in-file id file)))
-    (if position
-        (goto-char (cdr position))
-      (error "ID %s not found in %s" id file))))
-
-(defun org-fc-timestamp-in (interval)
-  "Generate an `org-mode' timestamp INTERVAL days from now."
-  (let ((seconds (* interval 60 60 24))
-        (now (time-to-seconds)))
-    (format-time-string
-     org-fc-timestamp-format
-     (seconds-to-time (+ now seconds))
-     "UTC0")))
-
-(defun org-fc-deemphasize (string)
-  "Remove org emphasis markers from STRING.
-Returns a pair (marker . body)."
-  (if (or (string-match org-emph-re string)
-          (string-match org-verbatim-re string))
-      (cons (match-string 3 string) (match-string 4 string))
-    (cons nil string)))
-
-(defun org-fc-emphasize (string)
-  "Apply org emphasis faces to STRING."
-  (with-temp-buffer
-    (insert string)
-    (goto-char (point-min))
-    (org-do-emphasis-faces (point-max))
-    (buffer-string)))
-
-(defun org-fc-indent ()
-  "Run `org-indent' on the current headline.
-Usually org-indent runs with a delay, so when reviewing a card in
-a new file, the cards contents jump to the right (are indented)
-during the review.  We can get around this by synchronously
-indenting the current heading."
-  (if org-indent-mode
-      (let ((el (org-element-at-point)))
-        (org-indent-add-properties
-         (org-element-property :begin el)
-         (org-element-property :end el)))))
-
-(defmacro org-fc-with-point-at-entry (&rest body)
-  "Execute BODY with point at the card heading.
-If point is not inside a flashcard entry, an error is raised."
-  `(save-excursion
-     (org-fc-goto-entry-heading)
-     ,@body))
-
-(defmacro org-fc-with-point-at-back-heading (&rest body)
-  "Execute BODY with point at the card's back heading.
-If point is not inside a flashcard entry, an error is raised."
-  `(if-let ((pos (org-fc-back-heading-position)))
-       (save-excursion
-         (goto-char pos)
-         ,@body)))
-
-;;; Checking for / going to flashcard headings
-
-(defun org-fc-entry-p ()
-  "Check if the current heading is a flashcard."
-  (member org-fc-flashcard-tag (org-get-tags nil 'local)))
-
-(defun org-fc-suspended-entry-p ()
-  "Check if the current heading is a suspended flashcard."
-  (let ((tags (org-get-tags nil 'local)))
-    (and (member org-fc-flashcard-tag tags)
-         (member org-fc-suspended-tag tags))))
-
-(defun org-fc-part-of-entry-p ()
-  "Check if the current heading belongs to a flashcard."
-  (member org-fc-flashcard-tag (org-get-tags nil)))
-
-(defun org-fc-goto-entry-heading ()
-  "Move up to the parent heading marked as a flashcard."
-  (unless (org-fc-part-of-entry-p)
-    (error "Not inside a flashcard entry"))
-  (unless (org-at-heading-p)
-    (org-back-to-heading))
-  (while (not (org-fc-entry-p))
-    (unless (org-up-heading-safe)
-      (error "Cannot find a parent heading that is marked as a flashcard"))))
-
-;;; Adding / Removing Tags
-
-(defun org-fc--add-tag (tag)
-  "Add TAG to the heading at point."
-  (org-set-tags
-   (cl-remove-duplicates
-    (cons tag (org-get-tags nil 'local))
-    :test #'string=)))
-
-(defun org-fc--remove-tag (tag)
-  "Add TAG to the heading at point."
-  (org-set-tags
-   (remove tag (org-get-tags nil 'local))))
-
-;;; Card Indexing (AWK)
-
-(require 'org-fc-awk)
-
-;;; Card Initialization
-
-(defun org-fc--init-card (type)
-  "Initialize the current card as a flashcard.
-Should only be used by the init functions of card TYPEs."
-  (if (org-fc-entry-p)
-      (error "Headline is already a flashcard"))
-  (org-back-to-heading)
-  (org-set-property
-   org-fc-created-property
-   (org-fc-timestamp-now))
-  (org-set-property org-fc-type-property type)
-  (org-id-get-create)
-  (org-fc--add-tag org-fc-flashcard-tag))
-
-;;; Card Types
-;;;; Type Management
-
-(defvar org-fc-types '()
-  "Alist for registering card types.
-Entries should be lists (name handler-fn update-fn).
-Use `org-fc-register-type' for adding card types.")
-
-(defun org-fc-register-type (name setup-fn flip-fn update-fn)
-  "Register a new card type.
-Argument NAME Name of the new type.
-Argument SETUP-FN Function for initializing a new card of this type.
-Argument FLIP-FN Function for flipping a card during review.
-Argument UPDATE-FN Function to update a card when it's contents have changed."
-  (push
-   (list name setup-fn flip-fn update-fn)
-   org-fc-types))
-
-(defun org-fc-type-setup-fn (type)
-  "Get the review function for a card of TYPE."
-  (let ((entry (alist-get type org-fc-types nil nil #'string=)))
-    (if entry
-        (cl-first entry)
-      (error "No such flashcard type: %s" type))))
-
-(defun org-fc-type-flip-fn (type)
-  "Get the flip function for a card of TYPE."
-  (let ((entry (alist-get type org-fc-types nil nil #'string=)))
-    (if entry
-        (cl-second entry)
-      (error "No such flashcard type: %s" type))))
-
-(defun org-fc-type-update-fn (type)
-  "Get the update function for a card of TYPE."
-  (let ((entry (alist-get type org-fc-types nil nil #'string=)))
-    (if entry
-        (cl-third entry)
-      (error "No such flashcard type: %s" type))))
-
-(require 'org-fc-type-normal)
-(require 'org-fc-type-double)
-(require 'org-fc-type-text-input)
-(require 'org-fc-type-cloze)
-
-;;; Working with Overlays / Hiding Text
-;;;; Showing / Hiding Overlays
-
-(defun org-fc-remove-overlays ()
-  "Remove all org-fc overlays in the current buffer."
-  (interactive)
-  (remove-overlays (point-min) (point-max) 'category 'org-fc))
-
-;; Based on `outline-flag-region'
-(defun org-fc-hide-region (from to &optional text face)
-  "Hide region FROM ... TO, optionally replacing it with TEXT.
-FACE can be used to set the text face of the overlay, e.g. to
-make it bold."
-  ;; (remove-overlays from to 'category 'org-fc)
-  (let ((o (make-overlay from to nil 'front-advance)))
-    (overlay-put o 'category 'org-fc)
-    (overlay-put o 'evaporate t)
-    (if face (overlay-put o 'face face))
-    (if (stringp text)
-        (progn
-          (overlay-put o 'invisible nil)
-          (overlay-put o 'display text))
-      (overlay-put o 'invisible t))
-    o))
-
-(defun org-fc-overlay-region (from to &optional face)
-  "Wrap region FROM ... TO in an overlay for later hiding.
-FACE can be used to set the text face of the overlay."
-  ;; (remove-overlays from to 'category 'org-fc)
-  (let ((o (make-overlay from to)))
-    (overlay-put o 'evaporate t)
-    (if face (overlay-put o 'face face))
-    (overlay-put o 'invisible nil)
-    (overlay-put o 'category 'org-fc)
-    o))
-
-(defun org-fc-make-overlay (begin end &rest props)
-  "Create an overlay from BEGIN to END with PROPS."
-  (let ((o (make-overlay begin end)))
-    (overlay-put o 'category 'org-fc)
-    (cl-loop for (prop value) on props by #'cddr do
-             (overlay-put o prop value))
-    o))
-
-(defun org-fc-overlay-surround (o before after &optional face)
-  "Surround O with strings BEFORE and AFTER with optional FACE."
-  (overlay-put o 'before-string (propertize before 'face face))
-  (overlay-put o 'after-string (propertize after 'face face))
-  o)
-
-;;;; Hiding Drawers
-
-(defun org-fc-hide-keyword-times ()
-  "Hide all timestamp keywords (e.g. DEADLINE) after point."
-  (save-excursion
-    (while (re-search-forward org-keyword-time-regexp nil t)
-      (let ((start (1- (match-beginning 0)))
-            (end (match-end 0)))
-        (org-fc-hide-region start end)))))
-
-(defun org-fc-hide-drawers ()
-  "Hide all drawers except ones in `org-fc-drawer-whitelist' after point."
-  (let ((bound (org-element-property :end (org-element-at-point))))
-    (save-excursion
-      (while (re-search-forward org-drawer-regexp bound t)
-        (let ((start (1- (match-beginning 0)))
-              (name (match-string 1))
-              (end))
-          (if (re-search-forward ":END:" bound t)
-              (setq end (point))
-            (error "No :END: found for drawer"))
-          (if (member name org-fc-drawer-whitelist)
-              (org-flag-drawer nil nil start end)
-            (org-fc-hide-region start end)))))))
-
-;;;; Hiding Headings / Section Contents
-
-(defun org-fc-hide-heading (&optional text)
-  "Hide the title of the headline at point.
-If TEXT is non-nil, the heading is replaced with TEXT."
-  ;; Case sensitive search
-  (let ((case-fold-search nil))
-    (save-excursion
-      (beginning-of-line)
-      (if (looking-at org-complex-heading-regexp)
-          (org-fc-hide-region (match-beginning 4) (match-end 4) (or text "..."))
-        (error "Point is not on a heading")))))
-
-(defun org-fc-hide-content (&optional text)
-  "Hide the main text of a heading *before* the first subheading.
-If TEXT is non-nil, the content is replaced with TEXT."
-  (let (start end)
-    (save-excursion
-      (org-back-to-heading)
-      (forward-line)
-      (setq start (point)))
-    (save-excursion
-      (outline-next-heading)
-      (setq end (point)))
-    (org-fc-hide-region start end text)))
-
-;;;; Outline Trees
-
-(defcustom org-fc-narrow-visibility 'ancestors
-  "Visibility of the current heading during review.
-See `org-show-set-visibility' for possible values"
-  :group 'org-fc
-  :type 'symbol
-  :options '(ancestors lineage minimal local tree canonical))
-
-(defun org-fc-narrow ()
-  "Narrow the outline tree.
-Only parent headings of the current heading remain visible."
-  (interactive)
-  (let* ((tags (org-get-tags nil 'local)))
-    ;; Find the first heading with a :narrow: tag or the top level
-    ;; ancestor of the current heading and narrow to its region
-    (save-excursion
-      (while (org-up-heading-safe))
-      (org-narrow-to-subtree)
-      (outline-hide-subtree))
-    ;; Show only the ancestors of the current card
-    (org-show-set-visibility org-fc-narrow-visibility)
-    (if (member "noheading" tags) (org-fc-hide-heading))))
-
-;;; Updating Cards
-
-(defun org-fc-map-cards (fn &optional scope)
-  "Call FN for each flashcard headline in SCOPE.
-FN is called with point at the headline and no arguments.
-If SCOPE is nil, it defaults to the full buffer.
-Other useful values are:
-- tree
-- region"
-  (org-map-entries
-   (lambda () (if (org-fc-entry-p) (funcall fn)))
-   nil
-   scope))
-
-;;;###autoload
-(defun org-fc-update ()
-  "Re-process the current flashcard."
-  (interactive)
-  (org-fc-with-point-at-entry
-   (let ((type (org-entry-get (point) "FC_TYPE")))
-     (funcall (org-fc-type-update-fn type)))))
-
-;;;###autoload
-(defun org-fc-update-all ()
-  "Re-process all flashcards in the current buffer."
-  (interactive)
-  (org-fc-map-cards 'org-fc-update))
-
-;;; Suspending / Unsuspending Cards
-
-;;;###autoload
-(defun org-fc-suspend-card ()
-  "Suspend the headline at point if it is a flashcard."
-  (interactive)
-  (org-fc-with-point-at-entry
-   (org-fc--add-tag org-fc-suspended-tag)))
-
-;;;###autoload
-(defun org-fc-suspend-tree ()
-  "Suspend all cards in the subtree at point."
-  (interactive)
-  (org-fc-map-cards 'org-fc-suspend-card 'tree))
-
-;;;###autoload
-(defun org-fc-suspend-buffer ()
-  "Suspend all cards in the current buffer."
-  (interactive)
-  (org-fc-map-cards 'org-fc-suspend-card))
-
-;;;###autoload
-(defun org-fc-suspend-region ()
-  "Suspend all cards in the current region."
-  (interactive)
-  (org-fc-map-cards 'org-fc-suspend-card 'region))
-
-;;;###autoload
-(defun org-fc-unsuspend-card ()
-  "Unsuspend the headline at point.
-Checks if the headline is a suspended card first."
-  (interactive)
-  (org-fc--remove-tag org-fc-suspended-tag))
-
-;;;###autoload
-(defun org-fc-unsuspend-tree ()
-  "Un-suspend all cards in the subtree at point."
-  (interactive)
-  (org-fc-map-cards 'org-fc-unsuspend-card 'tree))
-
-;;;###autoload
-(defun org-fc-unsuspend-buffer ()
-  "Un-suspend all cards in the current buffer."
-  (interactive)
-  (org-fc-map-cards 'org-fc-unsuspend-card))
-
-;;;###autoload
-(defun org-fc-unsuspend-region ()
-  "Un-suspend all cards in the current region."
-  (interactive)
-  (org-fc-map-cards 'org-fc-unsuspend-card 'region))
-
-;;; Indexing Cards
-;;;; Card Filters
-
-(defun org-fc--compile-filter (filter)
-  "Compile FILTER into a lambda function.
-Filters can be combinations of the following expressions:
-
-- `(and ex1 ex2 ...)'
-- `(or ex1 ex2 ...)'
-- `(not ex)'
-- `(tag \"tag\")'
-- `(type card-type)' or `(type \"card-type\")'
-
-For example, to match all double cards with tag \"math\",
-use `(and (type double) (tag \"math\"))'."
-  (let ((card-var (gensym)))
-    (cl-labels
-        ((check-arity-exact
-          (filter n)
-          (unless (= (length filter) (1+ n))
-            (error
-             (format "Filter '%s' expects %d argument(s)" filter n))))
-         (compile-inner
-          (filter)
-          (cl-case (car filter)
-            ('and `(and ,@(mapcar #'compile-inner (cdr filter))))
-            ('or `(or ,@(mapcar #'compile-inner (cdr filter))))
-            ('not
-             (check-arity-exact filter 1)
-             `(not ,(compile-inner (cadr filter))))
-            ('tag
-             (check-arity-exact filter 1)
-             `(member ,(cadr filter) (plist-get ,card-var :tags)))
-            ('type
-             (check-arity-exact filter 1)
-             `(eq ',(if (stringp (cadr filter))
-                        (intern (cadr filter))
-                      (cadr filter))
-                  (plist-get ,card-var :type))))))
-      `(lambda (,card-var)
-         ,(compile-inner filter)))))
-
-(defun org-fc-index (context)
-  "Create an index for review CONTEXT."
-  (let ((paths (plist-get context :paths))
-        (filter (plist-get context :filter)))
-    ;; Handle path formats / symbols
-    (cond
-     ((or (null paths) (eq paths 'all)) (setq paths org-fc-directories))
-     ((eq paths 'buffer) (setq paths (list (buffer-file-name))))
-     ((stringp paths) (setq paths (list paths))))
-
-    (if filter (setq filter (org-fc--compile-filter filter)))
-
-    (funcall org-fc-index-function paths filter)))
-
-(defun org-fc-index-flatten-card (card)
-  "Flatten CARD into a list of positions.
-Relevant data from the card is included in each position
-element."
-  (mapcar
-   (lambda (pos)
-     (list
-      :filetitle (plist-get card :filetitle)
-      :tags (plist-get card :tags)
-      :path (plist-get card :path)
-      :id (plist-get card :id)
-      :type (plist-get card :type)
-      :due (plist-get pos :due)
-      :position (plist-get pos :position)))
-   (plist-get card :positions)))
-
-(defun org-fc-index-filter-due (index)
-  "Filter INDEX to include only unsuspended due positions.
-Cards with no positions are removed from the index."
-  (let (res (now (current-time)))
-    (dolist (card index)
-      (unless (plist-get card :suspended)
-        (let ((due
-               (cl-remove-if-not
-                (lambda (pos)
-                  (time-less-p (plist-get pos :due) now))
-                (plist-get card :positions))))
-          (unless (null due)
-            (plist-put
-             card :positions
-             (if (or (not org-fc-bury-siblings)
-                     (member (plist-get card :cloze-type) '(single enumeration)))
-                 due (list (car due))))
-            (push card res)))))
-    res))
-
-(defun org-fc-index-positions (index)
-  "Return all positions in INDEX."
-  (mapcan (lambda (card) (org-fc-index-flatten-card card)) index))
-
-(defun org-fc-index-shuffled-positions (index)
-  "Return all positions in INDEX in random order.
-Positions are shuffled in a way that preserves the order of the
-  positions for each card."
-  ;; 1. assign each position a random number
-  ;; 2. flatten the list
-  ;; 3. sort by the random number
-  ;; 4. remove the random numbers from the result
-  (let ((positions
-         (mapcan
-          (lambda (card)
-            (let ((pos (org-fc-index-flatten-card card)))
-              (org-fc-zip
-               (org-fc-sorted-random (length pos))
-               pos)))
-          index)))
-    (mapcar
-     #'cdr
-     (sort positions (lambda (a b) (> (car a) (car b)))))))
-
-;;; Review & Spacing
-
-(require 'org-fc-algo-sm2)
-
-;;;; Demo Mode
-
-;;;###autoload
-(defun org-fc-demo ()
-  "Start a review of the demo file."
-  (interactive)
-  (let ((path (expand-file-name "demo.org" org-fc-source-path)))
-    (with-current-buffer (find-file path)
-      (org-fc-review-buffer))))
-
-;;; Header Line
-
-(defun org-fc-set-header-line ()
-  "Set the header-line for review."
-  (let* ((remaining (1+ (length (oref org-fc--session cards))))
-         (current (oref org-fc--session current-item))
-         (title
-          (unless (member "notitle" (plist-get current :tags))
-            (plist-get current :filetitle))))
-    (setq org-fc-original-header-line-format header-line-format)
-    (setq-local
-     header-line-format
-     `((org-fc-review-flip-mode "Flip")
-       (org-fc-review-rate-mode "Rate")
-       (org-fc-review-edit-mode "Edit")
-       ,(format " (%d) " remaining)
-       ,title))))
-
-(defun org-fc-reset-header-line ()
-  "Reset the header-line to its original value."
-  (setq-local header-line-format org-fc-original-header-line-format))
-
-;;; Contexts
-
-(defvar org-fc-custom-contexts '()
-  "User-defined review contexts.")
-
-(defvar org-fc-context-all '(:paths all)
-  "Default context for all cards.")
-(defvar org-fc-context-buffer '(:paths buffer)
-  "Default context for the current buffer.")
-
-(defun org-fc-contexts ()
-  "List of all contexts."
-  (cl-list*
-   (cons 'all org-fc-context-all)
-   (cons 'buffer org-fc-context-buffer)
-   org-fc-custom-contexts))
-
-(defun org-fc-select-context ()
-  "Select a review context."
-  (let ((context (completing-read
-                  "Context: "
-                  (mapcar (lambda (c) (car c)) (org-fc-contexts))
-                  nil
-                  :require-match)))
-    (unless (string= context "")
-      (alist-get (intern context) (org-fc-contexts)))))
-
-;;; Dashboard
-
-(require 'org-fc-dashboard)
-
-;;; Cache
-
-(require 'org-fc-cache)
-
 ;;; Footer
 
 (provide 'org-fc)
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