From 9b173af80d53b36acb382966a7dd9525cd97fbc7 Mon Sep 17 00:00:00 2001
From: Chris Barrett <chris@walrus.cool>
Date: Mon, 29 Aug 2022 20:28:49 +1200
Subject: [PATCH] Add lib that advises backlinks buffer to build previews
 lazily

---
 Readme.org                     |  4 ++
 lisp/org-roam-lazy-previews.el | 76 ++++++++++++++++++++++++++++++++++
 2 files changed, 80 insertions(+)
 create mode 100644 lisp/org-roam-lazy-previews.el

diff --git a/Readme.org b/Readme.org
index 66bcac6..2840872 100644
--- a/Readme.org
+++ b/Readme.org
@@ -62,6 +62,10 @@ and provides integrations with org-capture.
 ** SPIKE [[file:lisp/org-roam-refill-previews.el][org-roam-refill-previews]] /(spike)/
 Refill previews in the backlinks buffer so they fit the window.
 
+** SPIKE [[file:lisp/org-roam-lazy-previews.el][org-roam-lazy-previews]] /(spike)/
+Compute previews lazily for much better performance in buffers with many
+backlinks or reflinks.
+
 * Installation
 Most packages should be manually installable via =package.el=, assuming you have
 [[https://melpa.org/#/getting-started][MELPA]] set up. But honestly, you're better off just cloning this repo and putting
diff --git a/lisp/org-roam-lazy-previews.el b/lisp/org-roam-lazy-previews.el
new file mode 100644
index 0000000..7ecfd4d
--- /dev/null
+++ b/lisp/org-roam-lazy-previews.el
@@ -0,0 +1,76 @@
+;;; org-roam-lazy-previews.el --- Make previews in org-roam buffer lazy for better performance  -*- lexical-binding: t; -*-
+
+;; Copyright (C) 2022  Chris Barrett
+
+;; Author: Chris Barrett <chris@walrus.cool>
+
+;; 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 <http://www.gnu.org/licenses/>.
+
+;;; Commentary:
+
+;; Changes previews in the org-roam buffer to be lazily computed, improving
+;; responsiveness in buffers with many backlinks and reflinks.
+;;
+;; Example configuration:
+;;
+;;   (use-package org-roam-lazy-previews
+;;     :after org-roam
+;;     :demand t)
+
+;;; Code:
+
+(require 'cl-lib)
+(require 'magit-section)
+(require 'org)
+(require 'org-roam)
+(require 'subr-x)
+
+(autoload 'org-roam-review-insert-preview "org-roam-review")
+
+(defgroup org-roam-lazy-previews nil
+  "Change org-roam node previews to be lazy for performance."
+  :group 'productivity
+  :prefix "org-roam-lazy-previews-")
+
+(defcustom org-roam-lazy-previews-title-formatter #'org-roam-lazy-previews-custom-title-formatter
+  "A function to format a node's title for the backlinks buffer.
+
+It is passed the same arguments as
+`org-roam-node-insert-section', and should return a string."
+  :group 'org-roam-lazy-previews
+  :type 'function)
+
+(cl-defun org-roam-lazy-previews-custom-title-formatter (&key source-node properties &allow-other-keys)
+  (let* ((outline (when-let* ((outline (plist-get properties :outline)))
+                    (mapconcat #'org-link-display-format outline " > ")))
+         (title (org-roam-node-title source-node)))
+    (concat (propertize title 'font-lock-face 'org-roam-title)
+            (when (and outline (not (equal title outline)))
+              (format " > %s" (propertize outline 'font-lock-face 'org-roam-olp))))))
+
+(define-advice org-roam-node-insert-section (:override (&rest args) lazy-previews)
+  (cl-destructuring-bind (&key source-node point &allow-other-keys) args
+    (magit-insert-section section (org-roam-node-section (org-roam-node-id source-node) t)
+      (magit-insert-heading (apply org-roam-lazy-previews-title-formatter args))
+      (oset section node source-node)
+      ;; KLUDGE: Mofified macro-expansion of `magit-insert-section-body' that
+      ;; avoids unsetting the parent section's keymap.
+      (oset section washer
+            (lambda ()
+              (org-roam-review-insert-preview source-node :point point)
+              (magit-section-maybe-remove-visibility-indicator section))))))
+
+(provide 'org-roam-lazy-previews)
+
+;;; org-roam-lazy-previews.el ends here