From 7fb91cc12527f530b28a455150dc2a59c508371f Mon Sep 17 00:00:00 2001
From: Dion Moult <dion@thinkmoult.com>
Date: Mon, 23 Dec 2024 12:50:43 +1100
Subject: [PATCH] Implement scroll up and down sequences

---
 pyte/escape.py  |  6 ++++++
 pyte/screens.py | 36 ++++++++++++++++++++++++++++++++++++
 pyte/streams.py |  4 +++-
 3 files changed, 45 insertions(+), 1 deletion(-)

diff --git a/pyte/escape.py b/pyte/escape.py
index 7dfd6b8..3cfc1e7 100644
--- a/pyte/escape.py
+++ b/pyte/escape.py
@@ -150,3 +150,9 @@
 
 #: *Horizontal position adjust*: Same as :data:`CHA`.
 HPA = "'"
+
+#: *Scroll up*: scroll up
+SU = "S"
+
+#: *Scroll down*: scroll up
+SD = "T"
diff --git a/pyte/screens.py b/pyte/screens.py
index ebbac7c..7f655bf 100644
--- a/pyte/screens.py
+++ b/pyte/screens.py
@@ -576,6 +576,28 @@ def reverse_index(self) -> None:
         else:
             self.cursor_up()
 
+    def scroll_up(self, count: Optional[int] = None) -> None:
+        """Scroll the screen up # lines. Cursor does not move.
+        """
+        for _ in range(count or 1):
+            top, bottom = self.margins or Margins(0, self.lines - 1)
+            # TODO: mark only the lines within margins?
+            self.dirty.update(range(self.lines))
+            for y in range(top, bottom):
+                self.buffer[y] = self.buffer[y + 1]
+            self.buffer.pop(bottom, None)
+
+    def scroll_down(self, count: Optional[int] = None) -> None:
+        """Scroll the screen down # lines. Cursor does not move.
+        """
+        for _ in range(count or 1):
+            top, bottom = self.margins or Margins(0, self.lines - 1)
+            # TODO: mark only the lines within margins?
+            self.dirty.update(range(self.lines))
+            for y in range(bottom, top, -1):
+                self.buffer[y] = self.buffer[y - 1]
+            self.buffer.pop(top, None)
+
     def linefeed(self) -> None:
         """Perform an index and, if :data:`~pyte.modes.LNM` is set, a
         carriage return.
@@ -1230,6 +1252,20 @@ def reverse_index(self) -> None:
 
         super(HistoryScreen, self).reverse_index()
 
+    def scroll_up(self, count: Optional[int] = None) -> None:
+        """Overloaded to update top history with the removed lines."""
+        for _ in range(count or 1):
+            top, bottom = self.margins or Margins(0, self.lines - 1)
+            self.history.top.append(self.buffer[top])
+            super(HistoryScreen, self).scroll_up()
+
+    def scroll_down(self, count: Optional[int] = None) -> None:
+        """Overloaded to update bottom history with the removed lines."""
+        for _ in range(count or 1):
+            top, bottom = self.margins or Margins(0, self.lines - 1)
+            self.history.bottom.append(self.buffer[bottom])
+            super(HistoryScreen, self).scroll_down()
+
     def prev_page(self) -> None:
         """Move the screen page up through the history buffer. Page
         size is defined by ``history.ratio``, so for instance
diff --git a/pyte/streams.py b/pyte/streams.py
index cd0f51c..012d334 100644
--- a/pyte/streams.py
+++ b/pyte/streams.py
@@ -121,7 +121,9 @@ class Stream:
         esc.SGR: "select_graphic_rendition",
         esc.DSR: "report_device_status",
         esc.DECSTBM: "set_margins",
-        esc.HPA: "cursor_to_column"
+        esc.HPA: "cursor_to_column",
+        esc.SU: "scroll_up",
+        esc.SD: "scroll_down"
     }
 
     #: A set of all events dispatched by the stream.