From 791397f051aa6533f6f8c58d3a75ac77bc21f90b Mon Sep 17 00:00:00 2001
From: Ivan Prikaznov <77636647+Prikaz98@users.noreply.github.com>
Date: Mon, 10 Feb 2025 12:11:06 +0100
Subject: [PATCH] recenter-top-bottom (emacs-mode) (#1767)

* recenter-top-bottom

Emacs default behavior of (C-l recenter-top-bottom)

* fix: window-recenter-top-bottom should return smt

* return prev keymap

* removed unused variable
---
 src/commands/window.lisp     |  7 +++++++
 src/internal-packages.lisp   |  1 +
 src/window/virtual-line.lisp | 14 ++++++++++++++
 3 files changed, 22 insertions(+)

diff --git a/src/commands/window.lisp b/src/commands/window.lisp
index 19b0da718..8337c0c5f 100644
--- a/src/commands/window.lisp
+++ b/src/commands/window.lisp
@@ -124,6 +124,13 @@
   (redraw-display)
   t)
 
+(define-command recenter-top-bottom (p) (:universal-nil)
+  "Scroll so that the cursor is in the middle/top/bottom."
+  (clear-screens-of-window-list)
+  (unless p (window-recenter-top-bottom (current-window)))
+  (redraw-display)
+  t)
+
 (define-command split-active-window-vertically (&optional n) (:universal-nil)
   "Split the current window vertically."
   (split-window-vertically (current-window) :height n)
diff --git a/src/internal-packages.lisp b/src/internal-packages.lisp
index 41c2416f7..724edba1d 100644
--- a/src/internal-packages.lisp
+++ b/src/internal-packages.lisp
@@ -353,6 +353,7 @@
   ;; virtual-line
   (:export
    :window-recenter
+   :window-recenter-top-bottom
    :window-cursor-x
    :window-cursor-y
    :backward-line-wrap
diff --git a/src/window/virtual-line.lisp b/src/window/virtual-line.lisp
index 381c69783..3d314759b 100644
--- a/src/window/virtual-line.lisp
+++ b/src/window/virtual-line.lisp
@@ -21,6 +21,20 @@ If FROM-BOTTOM is T, start counting from the bottom."
       (window-scroll window n)
       n)))
 
+(defun window-recenter-top-bottom (window)
+  "In first call recenter WINDOW to the middle line.
+If cursor is already in the middle of WINDOW then move cursor in the top position.
+If cursor is on top then move move WINDOW to the bottom."
+  (let* ((line (window-cursor-y window))
+         (window-height (window-height-without-modeline window))
+         (middle (floor window-height 2))
+         (scrolloff (min (floor (/ (window-height window) 2)) 0))
+         (top 0))
+    (cond
+      ((= line middle) (window-recenter window :line scrolloff :from-bottom nil))
+      ((= line top) (window-recenter window :line scrolloff :from-bottom t))
+      (t (window-recenter window :line nil :from-bottom nil)))))
+
 (defun %calc-window-cursor-x (point window)
   "Return (values cur-x next). the 'next' is a flag if the cursor goes to
 next line because it is at the end of width."