feat(tools/passively): Implement automatic passive learning in Emacs r/3142

Adds all the functionality described in the README in cl/4066.

This code is very closely related to //users/tazjin/russian/russian.el

Change-Id: I14f1052cebfbe4886e75e8efc730eacbf8773f29

2 files changed, 128 insertions, 0 deletions

diff --git a/tools/emacs-pkgs/passively/default.nix b/tools/emacs-pkgs/passively/default.nix
new file mode 100644
index 0000000000..ec59cc85fd
--- /dev/null
+++ b/tools/emacs-pkgs/passively/default.nix
@@ -0,0 +1,8 @@
+{ depot, ... }:
+
+depot.tools.emacs-pkgs.buildEmacsPackage {
+  pname = "passively";
+  version = "1.0";
+  src = ./passively.el;
+  externalRequires = (epkgs: with epkgs; [ ht ]);
+}
diff --git a/tools/emacs-pkgs/passively/passively.el b/tools/emacs-pkgs/passively/passively.el
new file mode 100644
index 0000000000..75586e4e3f
--- /dev/null
+++ b/tools/emacs-pkgs/passively/passively.el
@@ -0,0 +1,120 @@
+;;; passively.el --- Passively learn new information -*- lexical-binding: t; -*-
+;;
+;; SPDX-License-Identifier: MIT
+;; Copyright (C) 2020 The TVL Contributors
+;;
+;; Author: Vincent Ambo <tazjin@tvl.su>
+;; Version: 1.0
+;; Package-Requires: (ht seq)
+;; URL: https://code.tvl.fyi/about/tools/emacs-pkgs/passively/
+;;
+;; This file is not part of GNU Emacs.
+
+(require 'ht)
+(require 'seq)
+
+;; Customisation options
+
+(defgroup passively nil
+  "Customisation options for passively"
+  :group 'applications)
+
+(defcustom passively-learn-terms nil
+  "Terms that passively should randomly display to the user. The
+format of this variable is a hash table with a string key that
+uniquely identifies the term, and a string value that is
+displayed to the user.
+
+For example, a possible value could be:
+
+   (ht (\"забыть\" \"забыть - to forget\")
+       (\"действительно\" \"действительно - indeed, really\")))
+"
+  ;; TODO(tazjin): No hash-table type in customization.el?
+  :type '(sexp)
+  :group 'passively)
+
+(defcustom passively-store-state (format "%spassively.el" user-emacs-directory)
+  "File in which passively should store its state (e.g. known terms)"
+  :type '(file)
+  :group 'passively)
+
+(defcustom passively-show-after-idle-for 4
+  "Number of seconds after Emacs goes idle that passively should
+wait before displaying a term."
+  :type '(integer)
+  :group 'passively)
+
+;; Implementation of state persistence
+(defvar passively-last-displayed nil
+  "Key of the last displayed passively term.")
+
+(defvar passively--known-terms (make-hash-table)
+  "Set of terms that are already known.")
+
+(defun passively--persist-known-terms ()
+  "Persist the set of known passively terms to disk."
+  (with-temp-file passively-store-state
+    (insert (prin1-to-string (ht-keys passively--known-terms)))))
+
+(defun passively--load-known-terms ()
+  "Load the set of known passively terms from disk."
+  (with-temp-buffer
+    (insert-file-contents passively-store-state)
+    (let ((keys (read (current-buffer))))
+      (setq passively--known-terms (make-hash-table))
+      (seq-do
+       (lambda (key) (ht-set passively--known-terms key t))
+       keys)))
+  (message "passively: loaded %d known words"
+           (seq-length (ht-keys passively--known-terms))))
+
+(defun passively-mark-last-as-known ()
+  "Mark the last term that passively displayed as known. It will
+not be displayed again."
+  (interactive)
+
+  (ht-set passively--known-terms passively-last-displayed t)
+  (passively--persist-known-terms)
+  (message "passively: Marked '%s' as known" passively-last-displayed))
+
+;; Implementation of main display logic
+(defvar passively--display-timer nil
+  "idle-timer used for displaying terms by passively")
+
+(defun passively--random-term (timeout)
+  ;; This is stupid, calculate set intersections instead.
+  (if (< 1000 timeout)
+      (error "It seems you already know all the terms?")
+    (seq-random-elt (ht-keys passively-learn-terms))))
+
+(defun passively--display-random-term ()
+  (let* ((timeout 1)
+         (term (passively--random-term timeout)))
+    (while (ht-contains? passively--known-terms term)
+      (setq timeout (+ 1 timeout))
+      (setq term (passively--random-term timeout)))
+    (setq passively-last-displayed term)
+    (message (ht-get passively-learn-terms term))))
+
+(defun passively-enable ()
+  "Enable automatic display of terms via passively."
+  (interactive)
+  (if passively--display-timer
+      (error "passively: Already running!")
+    (setq passively--display-timer
+          (run-with-idle-timer passively-show-after-idle-for t
+                               #'passively--display-random-term))
+    (message "passively: Now running after %s seconds of idle time"
+             passively-show-after-idle-for)))
+
+(defun passively-disable ()
+  "Turn off automatic display of terms via passively."
+  (interactive)
+  (unless passively--display-timer
+    (error "passively: Not running!"))
+  (cancel-timer passively--display-timer)
+  (setq passively--display-timer nil)
+  (message "passively: Now disabled"))
+
+(provide 'passively)