From 0451b5b7d10a86f0c2c28103aa7ff7aa2f59061d Mon Sep 17 00:00:00 2001
From: John Lorentzson <john_lorentzson@yahoo.com>
Date: Thu, 31 Jul 2025 13:23:52 +0200
Subject: [PATCH] Add page up and page down commands to the editor

---
 editor/editor.lisp | 40 +++++++++++++++++++++++++++++++++++++++-
 1 file changed, 39 insertions(+), 1 deletion(-)

diff --git a/editor/editor.lisp b/editor/editor.lisp
index 91ba88d..d933b2d 100644
--- a/editor/editor.lisp
+++ b/editor/editor.lisp
@@ -805,6 +805,42 @@ Additionally ensures correct line numbers on the way, as a bonus."
                      (char= (char (line-content line) (1- column)) #\Space)))
     (update-buffer-cursor buffer)))
 
+(defun com-next-page ()
+  (with-editor-accessors *editor* (:current-line line
+                                   :current-buffer buffer)
+    (let ((view (buffer-view buffer)))
+      (cond ((or (null (bottom-line view))
+                 (eql line (bottom-line view)))
+             (feep))
+            ((< (view-line-number view (bottom-line view))
+                (height view))
+             (setf line (bottom-line view))
+             (update-buffer-cursor buffer))
+            (t
+             (setf line (bottom-line view))
+             (setf (top-line view) (bottom-line view))
+             (update-buffer-cursor buffer)
+             (redisplay-view (current-view *editor*)))))))
+
+(defun com-previous-page ()
+  (with-editor-accessors *editor* (:current-line cursor-line
+                                   :current-buffer buffer)
+    (let ((view (buffer-view buffer)))
+      (cond ((eql cursor-line (first-line buffer))
+             (feep))
+            ((line-in-view (first-line buffer) view)
+             (setf cursor-line (first-line buffer))
+             (update-buffer-cursor buffer))
+            (t
+             (loop :repeat (height view)
+                   :for current-line := cursor-line
+                     :then (prev-line current-line)
+                   :until (null current-line)
+                   :do (setf cursor-line current-line
+                             (top-line view) current-line))
+             (update-buffer-cursor buffer)
+             (redisplay-view view))))))
+
 (defun com-new-buffer ()
   (setf (current-buffer *editor*)
         (make-instance 'buffer))
@@ -979,7 +1015,9 @@ Additionally ensures correct line numbers on the way, as a bonus."
     ((:m . #\f) com-forward-word)
     ((:c . #\w) com-forward-word)
     ((:m . #\b) com-backward-word)
-    ((:c . #\q) com-backward-word)))
+    ((:c . #\q) com-backward-word)
+    (:page-down com-next-page)
+    (:page-up com-previous-page)))
 
 (defun key-command-dispatch (key)
   (when (numberp key)