From 2a13a3315f9f07819da638ce6b3f8a02d4ca2c6f Mon Sep 17 00:00:00 2001
From: Nimish Jha <nimish.jha@gmail.com>
Date: Thu, 24 Oct 2024 08:24:08 +1100
Subject: [PATCH] implement nano-like page up/page down functionality

---
 internal/action/actions.go  | 48 +++++++++++++++++++++++--------------
 internal/config/settings.go |  2 ++
 runtime/help/options.md     |  7 ++++++
 3 files changed, 39 insertions(+), 18 deletions(-)

diff --git a/internal/action/actions.go b/internal/action/actions.go
index 2c7157c48..ce6ee0667 100644
--- a/internal/action/actions.go
+++ b/internal/action/actions.go
@@ -1676,50 +1676,62 @@ func (h *BufPane) PageDown() bool {
 
 // SelectPageUp selects up one page
 func (h *BufPane) SelectPageUp() bool {
+	pageOverlap := int(h.Buf.Settings["pageoverlap"].(float64))
+	scrollAmount := h.BufView().Height - pageOverlap
 	if !h.Cursor.HasSelection() {
 		h.Cursor.OrigSelection[0] = h.Cursor.Loc
 	}
-	h.MoveCursorUp(h.BufView().Height)
-	h.Cursor.SelectTo(h.Cursor.Loc)
+	h.MoveCursorUp(scrollAmount)
+	if h.Cursor.Num == 0 {
+		h.Cursor.SelectTo(h.Cursor.Loc)
+	}
+	h.ScrollUp(scrollAmount)
 	h.Relocate()
 	return true
 }
 
 // SelectPageDown selects down one page
 func (h *BufPane) SelectPageDown() bool {
+	pageOverlap := int(h.Buf.Settings["pageoverlap"].(float64))
+	scrollAmount := h.BufView().Height - pageOverlap
 	if !h.Cursor.HasSelection() {
 		h.Cursor.OrigSelection[0] = h.Cursor.Loc
 	}
-	h.MoveCursorDown(h.BufView().Height)
-	h.Cursor.SelectTo(h.Cursor.Loc)
+	h.MoveCursorDown(scrollAmount)
+	if h.Cursor.Num == 0 {
+		h.Cursor.SelectTo(h.Cursor.Loc)
+	}
+	h.ScrollDown(scrollAmount)
+	h.ScrollAdjust()
 	h.Relocate()
 	return true
 }
 
-// CursorPageUp places the cursor a page up
+// CursorPageUp places the cursor a page up,
+// moving the view to keep cursor at the same relative position in the view
 func (h *BufPane) CursorPageUp() bool {
 	h.Cursor.Deselect(true)
-
-	if h.Cursor.HasSelection() {
-		h.Cursor.Loc = h.Cursor.CurSelection[0]
-		h.Cursor.ResetSelection()
-		h.Cursor.StoreVisualX()
+	pageOverlap := int(h.Buf.Settings["pageoverlap"].(float64))
+	scrollAmount := h.BufView().Height - pageOverlap
+	h.MoveCursorUp(scrollAmount)
+	if h.Cursor.Num == 0 {
+		h.ScrollUp(scrollAmount)
 	}
-	h.MoveCursorUp(h.BufView().Height)
 	h.Relocate()
 	return true
 }
 
-// CursorPageDown places the cursor a page up
+// CursorPageDown places the cursor a page down,
+// moving the view to keep cursor at the same relative position in the view
 func (h *BufPane) CursorPageDown() bool {
 	h.Cursor.Deselect(false)
-
-	if h.Cursor.HasSelection() {
-		h.Cursor.Loc = h.Cursor.CurSelection[1]
-		h.Cursor.ResetSelection()
-		h.Cursor.StoreVisualX()
+	pageOverlap := int(h.Buf.Settings["pageoverlap"].(float64))
+	scrollAmount := h.BufView().Height - pageOverlap
+	h.MoveCursorDown(scrollAmount)
+	if h.Cursor.Num == 0 {
+		h.ScrollDown(scrollAmount)
+		h.ScrollAdjust()
 	}
-	h.MoveCursorDown(h.BufView().Height)
 	h.Relocate()
 	return true
 }
diff --git a/internal/config/settings.go b/internal/config/settings.go
index 910a3072c..ca6d27deb 100644
--- a/internal/config/settings.go
+++ b/internal/config/settings.go
@@ -32,6 +32,7 @@ var optionValidators = map[string]optionValidator{
 	"helpsplit":       validateChoice,
 	"matchbracestyle": validateChoice,
 	"multiopen":       validateChoice,
+	"pageoverlap":     validateNonNegativeValue,
 	"reload":          validateChoice,
 	"scrollmargin":    validateNonNegativeValue,
 	"scrollspeed":     validateNonNegativeValue,
@@ -76,6 +77,7 @@ var defaultCommonSettings = map[string]interface{}{
 	"matchbraceleft":  true,
 	"matchbracestyle": "underline",
 	"mkparents":       false,
+	"pageoverlap":     float64(2),
 	"permbackup":      false,
 	"readonly":        false,
 	"reload":          "prompt",
diff --git a/runtime/help/options.md b/runtime/help/options.md
index 0ea3b4ee1..c925d52e0 100644
--- a/runtime/help/options.md
+++ b/runtime/help/options.md
@@ -285,6 +285,13 @@ Here are the available options:
 
     default value: `tab`
 
+* `pageoverlap`: the number of lines from the current view to keep in view
+   when paging up or down. If this is set to 2, for instance, and you page
+   down, the last two lines of the previous page will be the first two lines
+   of the next page.
+
+    default value: `2`
+
 * `paste`: treat characters sent from the terminal in a single chunk as a paste
    event rather than a series of manual key presses. If you are pasting using
    the terminal keybinding (not `Ctrl-v`, which is micro's default paste