From 1a72e2b3127ae2516b64f5153c76d14f12c19416 Mon Sep 17 00:00:00 2001
From: Kyle Isom <kyle@imap.cc>
Date: Sat, 29 Nov 2025 22:48:31 -0800
Subject: [PATCH] Add undo/redo infrastructure and buffer management additions.

---
 .idea/workspace.xml     |  24 +-
 CMakeLists.txt          |   4 +
 Command.cc              | 648 ++++++++++++++++++++++++++++++++++++----
 Command.h               |  16 +-
 Editor.h                |  42 ++-
 GUIInputHandler.cc      | 101 ++++++-
 GUIInputHandler.h       |   2 +
 KKeymap.cc              |  39 +++
 TerminalFrontend.cc     |  23 +-
 TerminalFrontend.h      |   4 +
 TerminalInputHandler.cc |   2 +-
 UndoNode.cc             |  15 +
 UndoNode.h              |  83 +++++
 UndoTree.cc             |  47 +++
 UndoTree.h              |  20 ++
 kte-cloc                |   3 +
 16 files changed, 1000 insertions(+), 73 deletions(-)
 create mode 100644 UndoNode.cc
 create mode 100644 UndoNode.h
 create mode 100644 UndoTree.cc
 create mode 100644 UndoTree.h
 create mode 100755 kte-cloc

diff --git a/.idea/workspace.xml b/.idea/workspace.xml
index afd40db..7414c9f 100644
--- a/.idea/workspace.xml
+++ b/.idea/workspace.xml
@@ -34,10 +34,30 @@
   </component>
   <component name="ChangeListManager">
     <list default="true" id="e1fe3ab0-3650-4fca-8664-a247d5dfa457" name="Changes" comment="">
+      <change afterPath="$PROJECT_DIR$/UndoNode.cc" afterDir="false" />
+      <change afterPath="$PROJECT_DIR$/UndoNode.h" afterDir="false" />
+      <change afterPath="$PROJECT_DIR$/UndoTree.cc" afterDir="false" />
+      <change afterPath="$PROJECT_DIR$/UndoTree.h" afterDir="false" />
+      <change afterPath="$PROJECT_DIR$/kte-cloc" afterDir="false" />
+      <change beforePath="$PROJECT_DIR$/.idea/workspace.xml" beforeDir="false" afterPath="$PROJECT_DIR$/.idea/workspace.xml" afterDir="false" />
+      <change beforePath="$PROJECT_DIR$/Buffer.cc" beforeDir="false" afterPath="$PROJECT_DIR$/Buffer.cc" afterDir="false" />
+      <change beforePath="$PROJECT_DIR$/CMakeLists.txt" beforeDir="false" afterPath="$PROJECT_DIR$/CMakeLists.txt" afterDir="false" />
       <change beforePath="$PROJECT_DIR$/Command.cc" beforeDir="false" afterPath="$PROJECT_DIR$/Command.cc" afterDir="false" />
       <change beforePath="$PROJECT_DIR$/Command.h" beforeDir="false" afterPath="$PROJECT_DIR$/Command.h" afterDir="false" />
+      <change beforePath="$PROJECT_DIR$/Editor.cc" beforeDir="false" afterPath="$PROJECT_DIR$/Editor.cc" afterDir="false" />
+      <change beforePath="$PROJECT_DIR$/Editor.h" beforeDir="false" afterPath="$PROJECT_DIR$/Editor.h" afterDir="false" />
+      <change beforePath="$PROJECT_DIR$/GUIFrontend.cc" beforeDir="false" afterPath="$PROJECT_DIR$/GUIFrontend.cc" afterDir="false" />
+      <change beforePath="$PROJECT_DIR$/GUIInputHandler.cc" beforeDir="false" afterPath="$PROJECT_DIR$/GUIInputHandler.cc" afterDir="false" />
+      <change beforePath="$PROJECT_DIR$/GUIInputHandler.h" beforeDir="false" afterPath="$PROJECT_DIR$/GUIInputHandler.h" afterDir="false" />
+      <change beforePath="$PROJECT_DIR$/GUIRenderer.cc" beforeDir="false" afterPath="$PROJECT_DIR$/GUIRenderer.cc" afterDir="false" />
+      <change beforePath="$PROJECT_DIR$/GapBuffer.cc" beforeDir="false" afterPath="$PROJECT_DIR$/GapBuffer.cc" afterDir="false" />
       <change beforePath="$PROJECT_DIR$/KKeymap.cc" beforeDir="false" afterPath="$PROJECT_DIR$/KKeymap.cc" afterDir="false" />
+      <change beforePath="$PROJECT_DIR$/PieceTable.cc" beforeDir="false" afterPath="$PROJECT_DIR$/PieceTable.cc" afterDir="false" />
+      <change beforePath="$PROJECT_DIR$/TerminalFrontend.cc" beforeDir="false" afterPath="$PROJECT_DIR$/TerminalFrontend.cc" afterDir="false" />
+      <change beforePath="$PROJECT_DIR$/TerminalFrontend.h" beforeDir="false" afterPath="$PROJECT_DIR$/TerminalFrontend.h" afterDir="false" />
       <change beforePath="$PROJECT_DIR$/TerminalInputHandler.cc" beforeDir="false" afterPath="$PROJECT_DIR$/TerminalInputHandler.cc" afterDir="false" />
+      <change beforePath="$PROJECT_DIR$/TerminalRenderer.cc" beforeDir="false" afterPath="$PROJECT_DIR$/TerminalRenderer.cc" afterDir="false" />
+      <change beforePath="$PROJECT_DIR$/main.cc" beforeDir="false" afterPath="$PROJECT_DIR$/main.cc" afterDir="false" />
     </list>
     <option name="SHOW_DIALOG" value="false" />
     <option name="HIGHLIGHT_CONFLICTS" value="true" />
@@ -73,6 +93,8 @@
   <component name="ProjectViewState">
     <option name="hideEmptyMiddlePackages" value="true" />
     <option name="showLibraryContents" value="true" />
+    <option name="sortByType" value="true" />
+    <option name="sortKey" value="BY_TYPE" />
   </component>
   <component name="PropertiesComponent"><![CDATA[{
   "keyToString": {
@@ -142,7 +164,7 @@
       <option name="number" value="Default" />
       <option name="presentableId" value="Default" />
       <updated>1764457173148</updated>
-      <workItem from="1764457174208" duration="22512000" />
+      <workItem from="1764457174208" duration="26658000" />
     </task>
     <servers />
   </component>
diff --git a/CMakeLists.txt b/CMakeLists.txt
index d7a312c..d4615d8 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -58,6 +58,8 @@ set(COMMON_SOURCES
         TerminalInputHandler.cc
         TerminalRenderer.cc
         TerminalFrontend.cc
+        #        UndoNode.cc
+        #        UndoTree.cc
 )
 
 set(COMMON_HEADERS
@@ -74,6 +76,8 @@ set(COMMON_HEADERS
         TerminalRenderer.h
         Frontend.h
         TerminalFrontend.h
+        #        UndoNode.h
+        #        UndoTree.h
 )
 
 # kte (terminal-first) executable
diff --git a/Command.cc b/Command.cc
index 8eb47e8..1868c00 100644
--- a/Command.cc
+++ b/Command.cc
@@ -82,6 +82,163 @@ ensure_at_least_one_line(Buffer &buf)
 }
 
 
+// Helper: compute ordered region between mark and cursor. Returns false if no mark set or zero-length.
+static bool
+compute_mark_region(Buffer &buf, std::size_t &sx, std::size_t &sy, std::size_t &ex, std::size_t &ey)
+{
+	if (!buf.MarkSet())
+		return false;
+	std::size_t cx = buf.Curx();
+	std::size_t cy = buf.Cury();
+	std::size_t mx = buf.MarkCurx();
+	std::size_t my = buf.MarkCury();
+	if (cy < my || (cy == my && cx < mx)) {
+		sy = cy;
+		sx = cx;
+		ey = my;
+		ex = mx;
+	} else {
+		sy = my;
+		sx = mx;
+		ey = cy;
+		ex = cx;
+	}
+	if (sy == ey && sx == ex)
+		return false; // empty region
+	return true;
+}
+
+
+// Helper: extract text from [sx,sy) to [ex,ey) without modifying buffer. Newlines inserted between lines.
+static std::string
+extract_region_text(const Buffer &buf, std::size_t sx, std::size_t sy, std::size_t ex, std::size_t ey)
+{
+	const auto &rows = buf.Rows();
+	if (sy >= rows.size())
+		return std::string();
+	if (ey >= rows.size())
+		ey = rows.size() - 1;
+	if (sy == ey) {
+		const auto &line = rows[sy];
+		std::size_t xs   = std::min(sx, line.size());
+		std::size_t xe   = std::min(ex, line.size());
+		if (xe < xs)
+			std::swap(xs, xe);
+		return line.substr(xs, xe - xs);
+	}
+	std::string out;
+	// first line tail
+	{
+		const auto &line = rows[sy];
+		std::size_t xs   = std::min(sx, line.size());
+		out += line.substr(xs);
+		out += '\n';
+	}
+	// middle lines full
+	for (std::size_t y = sy + 1; y < ey; ++y) {
+		out += rows[y];
+		out += '\n';
+	}
+	// last line head
+	{
+		const auto &line = rows[ey];
+		std::size_t xe   = std::min(ex, line.size());
+		out += line.substr(0, xe);
+	}
+	return out;
+}
+
+
+// Helper: delete region and leave cursor at start (sx,sy). Adjust lines appropriately.
+static void
+delete_region(Buffer &buf, std::size_t sx, std::size_t sy, std::size_t ex, std::size_t ey)
+{
+	auto &rows = buf.Rows();
+	if (rows.empty())
+		return;
+	if (sy >= rows.size())
+		return;
+	if (ey >= rows.size())
+		ey = rows.size() - 1;
+	if (sy == ey) {
+		auto &line     = rows[sy];
+		std::size_t xs = std::min(sx, line.size());
+		std::size_t xe = std::min(ex, line.size());
+		if (xe < xs)
+			std::swap(xs, xe);
+		line.erase(xs, xe - xs);
+	} else {
+		// Keep prefix of first and suffix of last then join
+		std::string prefix = rows[sy].substr(0, std::min(sx, rows[sy].size()));
+		std::string suffix;
+		{
+			const auto &last = rows[ey];
+			std::size_t xe   = std::min(ex, last.size());
+			suffix           = last.substr(xe);
+		}
+		rows[sy] = prefix + suffix;
+		// erase middle lines and the last line
+		rows.erase(rows.begin() + static_cast<std::ptrdiff_t>(sy + 1),
+		           rows.begin() + static_cast<std::ptrdiff_t>(ey + 1));
+	}
+	buf.SetCursor(sx, sy);
+	buf.SetDirty(true);
+}
+
+
+// Insert arbitrary text at cursor, supporting newlines. Updates cursor position.
+static void
+insert_text_at_cursor(Buffer &buf, const std::string &text)
+{
+	auto &rows    = buf.Rows();
+	std::size_t y = buf.Cury();
+	std::size_t x = buf.Curx();
+	if (y > rows.size())
+		y = rows.size();
+	if (rows.empty())
+		rows.emplace_back("");
+	if (y >= rows.size())
+		rows.emplace_back("");
+
+	std::size_t cur_y = y;
+	std::size_t cur_x = x;
+
+	std::string remain = text;
+	while (true) {
+		auto pos = remain.find('\n');
+		if (pos == std::string::npos) {
+			// insert remaining into current line
+			if (cur_y >= rows.size())
+				rows.emplace_back("");
+			if (cur_x > rows[cur_y].size())
+				cur_x = rows[cur_y].size();
+			rows[cur_y].insert(cur_x, remain);
+			cur_x += remain.size();
+			break;
+		}
+		// insert segment before newline
+		std::string seg = remain.substr(0, pos);
+		if (cur_x > rows[cur_y].size())
+			cur_x = rows[cur_y].size();
+		rows[cur_y].insert(cur_x, seg);
+		// split line at cur_x + seg.size()
+		cur_x += seg.size();
+		std::string after = rows[cur_y].substr(cur_x);
+		rows[cur_y].erase(cur_x);
+		// create new line after current with the 'after' tail
+		rows.insert(rows.begin() + static_cast<std::ptrdiff_t>(cur_y + 1), after);
+		// move to start of next line
+		cur_y += 1;
+		cur_x = 0;
+		// advance remain after newline
+		remain.erase(0, pos + 1);
+	}
+
+	buf.SetCursor(cur_x, cur_y);
+	buf.SetDirty(true);
+}
+
+
 static std::size_t
 inverse_render_to_source_col(const std::string &line, std::size_t rx_target, std::size_t tabw)
 {
@@ -457,6 +614,99 @@ cmd_open_file_start(CommandContext &ctx)
 }
 
 
+// --- Buffers: switch/next/prev/close ---
+static bool
+cmd_buffer_switch_start(CommandContext &ctx)
+{
+	// If only one (or zero) buffer is open, do nothing per spec
+	if (ctx.editor.BufferCount() <= 1) {
+		ctx.editor.SetStatus("No other buffers open.");
+		return true;
+	}
+	ctx.editor.StartPrompt(Editor::PromptKind::BufferSwitch, "Buffer", "");
+	ctx.editor.SetStatus("Buffer: ");
+	return true;
+}
+
+
+static std::string
+buffer_display_name(const Buffer &b)
+{
+	if (!b.Filename().empty())
+		return b.Filename();
+	return std::string("<untitled>");
+}
+
+
+static std::string
+buffer_basename(const Buffer &b)
+{
+	const std::string &p = b.Filename();
+	if (p.empty())
+		return std::string("<untitled>");
+	auto pos = p.find_last_of("/\\");
+	if (pos == std::string::npos)
+		return p;
+	return p.substr(pos + 1);
+}
+
+
+static bool
+cmd_buffer_next(CommandContext &ctx)
+{
+	const auto cnt = ctx.editor.BufferCount();
+	if (cnt <= 1) {
+		ctx.editor.SetStatus("No other buffers open.");
+		return true;
+	}
+	std::size_t idx = ctx.editor.CurrentBufferIndex();
+	idx             = (idx + 1) % cnt;
+	ctx.editor.SwitchTo(idx);
+	const Buffer *b = ctx.editor.CurrentBuffer();
+	ctx.editor.SetStatus(std::string("Switched: ") + (b ? buffer_display_name(*b) : std::string("")));
+	return true;
+}
+
+
+static bool
+cmd_buffer_prev(CommandContext &ctx)
+{
+	const auto cnt = ctx.editor.BufferCount();
+	if (cnt <= 1) {
+		ctx.editor.SetStatus("No other buffers open.");
+		return true;
+	}
+	std::size_t idx = ctx.editor.CurrentBufferIndex();
+	idx             = (idx + cnt - 1) % cnt;
+	ctx.editor.SwitchTo(idx);
+	const Buffer *b = ctx.editor.CurrentBuffer();
+	ctx.editor.SetStatus(std::string("Switched: ") + (b ? buffer_display_name(*b) : std::string("")));
+	return true;
+}
+
+
+static bool
+cmd_buffer_close(CommandContext &ctx)
+{
+	if (ctx.editor.BufferCount() == 0)
+		return true;
+	std::size_t idx  = ctx.editor.CurrentBufferIndex();
+	const Buffer *b  = ctx.editor.CurrentBuffer();
+	std::string name = b ? buffer_display_name(*b) : std::string("");
+	ctx.editor.CloseBuffer(idx);
+	if (ctx.editor.BufferCount() == 0) {
+		// Open a fresh empty buffer
+		Buffer empty;
+		ctx.editor.AddBuffer(std::move(empty));
+		ctx.editor.SwitchTo(0);
+	}
+	const Buffer *cur = ctx.editor.CurrentBuffer();
+	ctx.editor.SetStatus(std::string("Closed: ") + name + std::string("  Now: ")
+	                     + (cur ? buffer_display_name(*cur) : std::string("")));
+	return true;
+}
+
+
 // --- Editing ---
 static bool
 cmd_insert_text(CommandContext &ctx)
@@ -468,6 +718,45 @@ cmd_insert_text(CommandContext &ctx)
 	}
 	// If a prompt is active, edit prompt text
 	if (ctx.editor.PromptActive()) {
+		// Special-case: buffer switch prompt supports Tab-completion
+		if (ctx.editor.CurrentPromptKind() == Editor::PromptKind::BufferSwitch && ctx.arg == "\t") {
+			// Complete against buffer names (path and basename)
+			const std::string prefix = ctx.editor.PromptText();
+			std::vector<std::pair<std::string, std::size_t> > cands; // name, index
+			const auto &bs = ctx.editor.Buffers();
+			for (std::size_t i = 0; i < bs.size(); ++i) {
+				std::string full = buffer_display_name(bs[i]);
+				std::string base = buffer_basename(bs[i]);
+				if (full.rfind(prefix, 0) == 0) {
+					cands.emplace_back(full, i);
+				}
+				if (base.rfind(prefix, 0) == 0 && base != full) {
+					cands.emplace_back(base, i);
+				}
+			}
+			if (cands.empty()) {
+				// no change
+			} else if (cands.size() == 1) {
+				ctx.editor.SetPromptText(cands[0].first);
+			} else {
+				// extend to longest common prefix
+				std::string lcp = cands[0].first;
+				for (std::size_t i = 1; i < cands.size(); ++i) {
+					const std::string &s = cands[i].first;
+					std::size_t j        = 0;
+					while (j < lcp.size() && j < s.size() && lcp[j] == s[j])
+						++j;
+					lcp.resize(j);
+					if (lcp.empty())
+						break;
+				}
+				if (!lcp.empty() && lcp != ctx.editor.PromptText())
+					ctx.editor.SetPromptText(lcp);
+			}
+			ctx.editor.SetStatus(ctx.editor.PromptLabel() + ": " + ctx.editor.PromptText());
+			return true;
+		}
+
 		ctx.editor.AppendPromptText(ctx.arg);
 		// If it's a search prompt, mirror text to search state
 		if (ctx.editor.CurrentPromptKind() == Editor::PromptKind::Search) {
@@ -576,6 +865,35 @@ cmd_newline(CommandContext &ctx)
 			} else {
 				ctx.editor.SetStatus(std::string("Opened ") + value);
 			}
+		} else if (kind == Editor::PromptKind::BufferSwitch) {
+			// Resolve to a buffer index by exact match against path or basename;
+			// if multiple partial matches, prefer exact; if none, keep status.
+			const auto &bs = ctx.editor.Buffers();
+			std::vector<std::size_t> matches;
+			for (std::size_t i = 0; i < bs.size(); ++i) {
+				if (value == buffer_display_name(bs[i]) || value == buffer_basename(bs[i])) {
+					matches.push_back(i);
+				}
+			}
+			if (matches.empty()) {
+				// Try prefix match if no exact
+				for (std::size_t i = 0; i < bs.size(); ++i) {
+					const std::string full = buffer_display_name(bs[i]);
+					const std::string base = buffer_basename(bs[i]);
+					if ((!value.empty() && full.rfind(value, 0) == 0) || (
+						    !value.empty() && base.rfind(value, 0) == 0)) {
+						matches.push_back(i);
+					}
+				}
+			}
+			if (matches.empty()) {
+				ctx.editor.SetStatus("No such buffer: " + value);
+			} else {
+				ctx.editor.SwitchTo(matches[0]);
+				const Buffer *cur = ctx.editor.CurrentBuffer();
+				ctx.editor.SetStatus(std::string("Switched: ")
+				                     + (cur ? buffer_display_name(*cur) : std::string("")));
+			}
 		} else if (kind == Editor::PromptKind::SaveAs) {
 			// Optional: not wired yet
 			ctx.editor.SetStatus("Save As not implemented");
@@ -723,74 +1041,252 @@ cmd_delete_char(CommandContext &ctx)
 static bool
 cmd_kill_to_eol(CommandContext &ctx)
 {
-    Buffer *buf = ctx.editor.CurrentBuffer();
-    if (!buf) {
-        ctx.editor.SetStatus("No buffer to edit");
-        return false;
-    }
-    ensure_at_least_one_line(*buf);
-    auto &rows    = buf->Rows();
-    std::size_t y = buf->Cury();
-    std::size_t x = buf->Curx();
-    int repeat    = ctx.count > 0 ? ctx.count : 1;
-    for (int i = 0; i < repeat; ++i) {
-        if (y >= rows.size())
-            break;
-        if (x < rows[y].size()) {
-            // delete from cursor to end of line
-            rows[y].erase(x);
-        } else if (y + 1 < rows.size()) {
-            // at EOL: delete the newline (join with next line)
-            rows[y] += rows[y + 1];
-            rows.erase(rows.begin() + static_cast<std::ptrdiff_t>(y + 1));
-        } else {
-            // nothing to delete
-            break;
-        }
-    }
-    buf->SetDirty(true);
-    ensure_cursor_visible(ctx.editor, *buf);
-    return true;
+	Buffer *buf = ctx.editor.CurrentBuffer();
+	if (!buf) {
+		ctx.editor.SetStatus("No buffer to edit");
+		return false;
+	}
+	ensure_at_least_one_line(*buf);
+	auto &rows    = buf->Rows();
+	std::size_t y = buf->Cury();
+	std::size_t x = buf->Curx();
+	int repeat    = ctx.count > 0 ? ctx.count : 1;
+	std::string killed_total;
+	for (int i = 0; i < repeat; ++i) {
+		if (y >= rows.size())
+			break;
+		if (x < rows[y].size()) {
+			// delete from cursor to end of line
+			killed_total += rows[y].substr(x);
+			rows[y].erase(x);
+		} else if (y + 1 < rows.size()) {
+			// at EOL: delete the newline (join with next line)
+			killed_total += "\n";
+			rows[y] += rows[y + 1];
+			rows.erase(rows.begin() + static_cast<std::ptrdiff_t>(y + 1));
+		} else {
+			// nothing to delete
+			break;
+		}
+	}
+	buf->SetDirty(true);
+	ensure_cursor_visible(ctx.editor, *buf);
+	if (!killed_total.empty()) {
+		if (ctx.editor.KillChain())
+			ctx.editor.KillRingAppend(killed_total);
+		else
+			ctx.editor.KillRingPush(killed_total);
+		ctx.editor.SetKillChain(true);
+	}
+	return true;
 }
 
 
 static bool
 cmd_kill_line(CommandContext &ctx)
 {
-    Buffer *buf = ctx.editor.CurrentBuffer();
-    if (!buf) {
-        ctx.editor.SetStatus("No buffer to edit");
-        return false;
-    }
-    ensure_at_least_one_line(*buf);
-    auto &rows    = buf->Rows();
-    std::size_t y = buf->Cury();
-    std::size_t x = buf->Curx();
-    (void)x; // cursor x will be reset to 0
-    int repeat = ctx.count > 0 ? ctx.count : 1;
-    for (int i = 0; i < repeat; ++i) {
-        if (rows.empty())
-            break;
-        if (rows.size() == 1) {
-            // last remaining line: clear its contents
-            rows[0].clear();
-            y = 0;
-        } else if (y < rows.size()) {
-            // erase current line; keep y pointing at the next line
-            rows.erase(rows.begin() + static_cast<std::ptrdiff_t>(y));
-            if (y >= rows.size()) {
-                // deleted last line; move to previous
-                y = rows.size() - 1;
-            }
-        } else {
-            // out of range
-            y = rows.empty() ? 0 : rows.size() - 1;
-        }
-    }
-    buf->SetCursor(0, y);
-    buf->SetDirty(true);
-    ensure_cursor_visible(ctx.editor, *buf);
-    return true;
+	Buffer *buf = ctx.editor.CurrentBuffer();
+	if (!buf) {
+		ctx.editor.SetStatus("No buffer to edit");
+		return false;
+	}
+	ensure_at_least_one_line(*buf);
+	auto &rows    = buf->Rows();
+	std::size_t y = buf->Cury();
+	std::size_t x = buf->Curx();
+	(void) x; // cursor x will be reset to 0
+	int repeat = ctx.count > 0 ? ctx.count : 1;
+	std::string killed_total;
+	for (int i = 0; i < repeat; ++i) {
+		if (rows.empty())
+			break;
+		if (rows.size() == 1) {
+			// last remaining line: clear its contents
+			killed_total += rows[0];
+			rows[0].clear();
+			y = 0;
+		} else if (y < rows.size()) {
+			// erase current line; keep y pointing at the next line
+			killed_total += rows[y];
+			killed_total += "\n";
+			rows.erase(rows.begin() + static_cast<std::ptrdiff_t>(y));
+			if (y >= rows.size()) {
+				// deleted last line; move to previous
+				y = rows.size() - 1;
+			}
+		} else {
+			// out of range
+			y = rows.empty() ? 0 : rows.size() - 1;
+		}
+	}
+	buf->SetCursor(0, y);
+	buf->SetDirty(true);
+	ensure_cursor_visible(ctx.editor, *buf);
+	if (!killed_total.empty()) {
+		if (ctx.editor.KillChain())
+			ctx.editor.KillRingAppend(killed_total);
+		else
+			ctx.editor.KillRingPush(killed_total);
+		ctx.editor.SetKillChain(true);
+	}
+	return true;
+}
+
+
+static bool
+cmd_yank(CommandContext &ctx)
+{
+	Buffer *buf = ctx.editor.CurrentBuffer();
+	if (!buf) {
+		ctx.editor.SetStatus("No buffer to edit");
+		return false;
+	}
+	std::string text = ctx.editor.KillRingHead();
+	if (text.empty()) {
+		ctx.editor.SetStatus("Kill ring is empty");
+		return false;
+	}
+	ensure_at_least_one_line(*buf);
+	int repeat = ctx.count > 0 ? ctx.count : 1;
+	for (int i = 0; i < repeat; ++i) {
+		insert_text_at_cursor(*buf, text);
+	}
+	ensure_cursor_visible(ctx.editor, *buf);
+	// Start a new kill chain only from kill commands; yanking should break it
+	ctx.editor.SetKillChain(false);
+	return true;
+}
+
+
+// --- Marks/Regions and File boundaries ---
+static bool
+cmd_move_file_start(CommandContext &ctx)
+{
+	Buffer *buf = ctx.editor.CurrentBuffer();
+	if (!buf)
+		return false;
+	ensure_at_least_one_line(*buf);
+	buf->SetCursor(0, 0);
+	ensure_cursor_visible(ctx.editor, *buf);
+	return true;
+}
+
+
+static bool
+cmd_move_file_end(CommandContext &ctx)
+{
+	Buffer *buf = ctx.editor.CurrentBuffer();
+	if (!buf)
+		return false;
+	ensure_at_least_one_line(*buf);
+	auto &rows    = buf->Rows();
+	std::size_t y = rows.empty() ? 0 : rows.size() - 1;
+	std::size_t x = rows.empty() ? 0 : rows[y].size();
+	buf->SetCursor(x, y);
+	ensure_cursor_visible(ctx.editor, *buf);
+	return true;
+}
+
+
+static bool
+cmd_toggle_mark(CommandContext &ctx)
+{
+	Buffer *buf = ctx.editor.CurrentBuffer();
+	if (!buf)
+		return false;
+	if (buf->MarkSet()) {
+		buf->ClearMark();
+		ctx.editor.SetStatus("Mark cleared");
+	} else {
+		buf->SetMark(buf->Curx(), buf->Cury());
+		ctx.editor.SetStatus("Mark set");
+	}
+	return true;
+}
+
+
+static bool
+cmd_jump_to_mark(CommandContext &ctx)
+{
+	Buffer *buf = ctx.editor.CurrentBuffer();
+	if (!buf)
+		return false;
+	if (!buf->MarkSet()) {
+		ctx.editor.SetStatus("Mark not set");
+		return false;
+	}
+	std::size_t cx = buf->Curx();
+	std::size_t cy = buf->Cury();
+	std::size_t mx = buf->MarkCurx();
+	std::size_t my = buf->MarkCury();
+	buf->SetCursor(mx, my);
+	buf->SetMark(cx, cy);
+	ensure_cursor_visible(ctx.editor, *buf);
+	return true;
+}
+
+
+static bool
+cmd_kill_region(CommandContext &ctx)
+{
+	Buffer *buf = ctx.editor.CurrentBuffer();
+	if (!buf)
+		return false;
+	ensure_at_least_one_line(*buf);
+	std::size_t sx, sy, ex, ey;
+	if (!compute_mark_region(*buf, sx, sy, ex, ey)) {
+		ctx.editor.SetStatus("No region to kill");
+		return false;
+	}
+	std::string text = extract_region_text(*buf, sx, sy, ex, ey);
+	delete_region(*buf, sx, sy, ex, ey);
+	ensure_cursor_visible(ctx.editor, *buf);
+	if (!text.empty()) {
+		if (ctx.editor.KillChain())
+			ctx.editor.KillRingAppend(text);
+		else
+			ctx.editor.KillRingPush(text);
+		ctx.editor.SetKillChain(true);
+	}
+
+	buf->ClearMark();
+	return true;
+}
+
+
+static bool
+cmd_copy_region(CommandContext &ctx)
+{
+	Buffer *buf = ctx.editor.CurrentBuffer();
+	if (!buf)
+		return false;
+	ensure_at_least_one_line(*buf);
+	std::size_t sx, sy, ex, ey;
+	if (!compute_mark_region(*buf, sx, sy, ex, ey)) {
+		ctx.editor.SetStatus("No region to copy");
+		return false;
+	}
+	std::string text = extract_region_text(*buf, sx, sy, ex, ey);
+	if (!text.empty()) {
+		if (ctx.editor.KillChain())
+			ctx.editor.KillRingAppend(text);
+		else
+			ctx.editor.KillRingPush(text);
+		ctx.editor.SetKillChain(true);
+	}
+
+	buf->ClearMark();
+	return true;
+}
+
+
+static bool
+cmd_flush_kill_ring(CommandContext &ctx)
+{
+	ctx.editor.KillRingClear();
+	ctx.editor.SetKillChain(false);
+	ctx.editor.SetStatus("Kill ring cleared");
+	return true;
 }
 
 
@@ -1275,6 +1771,14 @@ InstallDefaultCommands()
 	CommandRegistry::Register({
 		CommandId::OpenFileStart, "open-file-start", "Begin open-file prompt", cmd_open_file_start
 	});
+	// Buffers
+	CommandRegistry::Register({
+		CommandId::BufferSwitchStart, "buffer-switch-start", "Begin buffer switch prompt",
+		cmd_buffer_switch_start
+	});
+	CommandRegistry::Register({CommandId::BufferNext, "buffer-next", "Switch to next buffer", cmd_buffer_next});
+	CommandRegistry::Register({CommandId::BufferPrev, "buffer-prev", "Switch to previous buffer", cmd_buffer_prev});
+	CommandRegistry::Register({CommandId::BufferClose, "buffer-close", "Close current buffer", cmd_buffer_close});
 	// Editing
 	CommandRegistry::Register({
 		CommandId::InsertText, "insert", "Insert text at cursor (no newlines)", cmd_insert_text
@@ -1284,6 +1788,21 @@ InstallDefaultCommands()
 	CommandRegistry::Register({CommandId::DeleteChar, "delete-char", "Delete char at cursor", cmd_delete_char});
 	CommandRegistry::Register({CommandId::KillToEOL, "kill-to-eol", "Delete to end of line", cmd_kill_to_eol});
 	CommandRegistry::Register({CommandId::KillLine, "kill-line", "Delete entire line", cmd_kill_line});
+	CommandRegistry::Register({CommandId::Yank, "yank", "Yank from kill ring", cmd_yank});
+	// Marks/regions and file boundaries
+	CommandRegistry::Register({
+		CommandId::MoveFileStart, "file-start", "Move to beginning of file", cmd_move_file_start
+	});
+	CommandRegistry::Register({CommandId::MoveFileEnd, "file-end", "Move to end of file", cmd_move_file_end});
+	CommandRegistry::Register({CommandId::ToggleMark, "toggle-mark", "Toggle mark at cursor", cmd_toggle_mark});
+	CommandRegistry::Register({
+		CommandId::JumpToMark, "jump-to-mark", "Jump to mark (swap mark)", cmd_jump_to_mark
+	});
+	CommandRegistry::Register({CommandId::KillRegion, "kill-region", "Kill region to kill ring", cmd_kill_region});
+	CommandRegistry::Register({CommandId::CopyRegion, "copy-region", "Copy region to kill ring", cmd_copy_region});
+	CommandRegistry::Register({
+		CommandId::FlushKillRing, "flush-kill-ring", "Flush kill ring", cmd_flush_kill_ring
+	});
 	// Navigation
 	CommandRegistry::Register({CommandId::MoveLeft, "left", "Move cursor left", cmd_move_left});
 	CommandRegistry::Register({CommandId::MoveRight, "right", "Move cursor right", cmd_move_right});
@@ -1312,6 +1831,11 @@ Execute(Editor &ed, CommandId id, const std::string &arg, int count)
 	if (ed.QuitConfirmPending() && id != CommandId::Quit && id != CommandId::KPrefix) {
 		ed.SetQuitConfirmPending(false);
 	}
+	// Reset kill chain unless this is a kill-like command (so consecutive kills append)
+	if (id != CommandId::KillToEOL && id != CommandId::KillLine && id != CommandId::KillRegion && id !=
+	    CommandId::CopyRegion) {
+		ed.SetKillChain(false);
+	}
 	CommandContext ctx{ed, arg, count};
 	return cmd->handler ? cmd->handler(ctx) : false;
 }
diff --git a/Command.h b/Command.h
index 0e796c7..5fc124b 100644
--- a/Command.h
+++ b/Command.h
@@ -24,13 +24,27 @@ enum class CommandId {
 	KPrefix, // show "C-k _" prompt in status when entering k-command
 	FindStart, // begin incremental search (placeholder)
 	OpenFileStart, // begin open-file prompt
+	// Buffers
+	BufferSwitchStart, // begin buffer switch prompt
+	BufferClose,
+	BufferNext,
+	BufferPrev,
 	// Editing
 	InsertText, // arg: text to insert at cursor (UTF-8, no newlines)
 	Newline, // insert a newline at cursor
 	Backspace, // delete char before cursor (may join lines)
 	DeleteChar, // delete char at cursor (may join lines)
 	KillToEOL, // delete from cursor to end of line; if at EOL, delete newline
-	KillLine,  // delete the entire current line (including newline)
+	KillLine, // delete the entire current line (including newline)
+	Yank, // insert most recently killed text at cursor
+	// Region/mark and file-boundary navigation
+	MoveFileStart, // move to beginning of file
+	MoveFileEnd, // move to end of file
+	ToggleMark, // toggle mark at cursor
+	JumpToMark, // jump to mark, set mark to previous cursor
+	KillRegion, // kill region between mark and cursor (to kill ring)
+	CopyRegion, // copy region to kill ring (Alt-w)
+	FlushKillRing, // clear kill ring
 	// Navigation (basic)
 	MoveLeft,
 	MoveRight,
diff --git a/Editor.h b/Editor.h
index f42e060..ed1b5b1 100644
--- a/Editor.h
+++ b/Editor.h
@@ -69,6 +69,42 @@ public:
 	}
 
 
+	// Kill ring API
+	void KillRingClear()
+	{
+		kill_ring_.clear();
+	}
+
+
+	void KillRingPush(const std::string &text)
+	{
+		if (text.empty())
+			return;
+		// push to front
+		kill_ring_.insert(kill_ring_.begin(), text);
+		if (kill_ring_.size() > kill_ring_max_)
+			kill_ring_.resize(kill_ring_max_);
+	}
+
+
+	void KillRingAppend(const std::string &text)
+	{
+		if (text.empty())
+			return;
+		if (kill_ring_.empty()) {
+			KillRingPush(text);
+		} else {
+			kill_ring_.front() += text;
+		}
+	}
+
+
+	[[nodiscard]] std::string KillRingHead() const
+	{
+		return kill_ring_.empty() ? std::string() : kill_ring_.front();
+	}
+
+
 	void SetDirtyEx(int d)
 	{
 		dirtyex_ = d;
@@ -254,7 +290,7 @@ public:
 
 
 	// --- Generic Prompt subsystem (for search, open-file, save-as, etc.) ---
-	enum class PromptKind { None = 0, Search, OpenFile, SaveAs, Confirm };
+	enum class PromptKind { None = 0, Search, OpenFile, SaveAs, Confirm, BufferSwitch };
 
 
 	void StartPrompt(PromptKind kind, const std::string &label, const std::string &initial)
@@ -382,6 +418,10 @@ private:
 	std::vector<Buffer> buffers_;
 	std::size_t curbuf_ = 0; // index into buffers_
 
+	// Kill ring (Emacs-like)
+	std::vector<std::string> kill_ring_;
+	std::size_t kill_ring_max_ = 60;
+
 	// Quit state
 	bool quit_requested_       = false;
 	bool quit_confirm_pending_ = false;
diff --git a/GUIInputHandler.cc b/GUIInputHandler.cc
index 3871f1c..aba369c 100644
--- a/GUIInputHandler.cc
+++ b/GUIInputHandler.cc
@@ -5,12 +5,42 @@
 
 
 static bool
-map_key(const SDL_Keycode key, const SDL_Keymod mod, bool &k_prefix, MappedInput &out)
+map_key(const SDL_Keycode key, const SDL_Keymod mod, bool &k_prefix, bool &esc_meta, MappedInput &out)
 {
 	// Ctrl handling
 	const bool is_ctrl = (mod & KMOD_CTRL) != 0;
 	const bool is_alt  = (mod & (KMOD_ALT | KMOD_LALT | KMOD_RALT)) != 0;
 
+	// If previous key was ESC, interpret this as Meta via ESC keymap
+	if (esc_meta) {
+		int ascii_key = 0;
+		if (key >= SDLK_a && key <= SDLK_z) {
+			ascii_key = static_cast<int>('a' + (key - SDLK_a));
+		} else if (key == SDLK_COMMA) {
+			ascii_key = '<';
+		} else if (key == SDLK_PERIOD) {
+			ascii_key = '>';
+		} else if (key == SDLK_LESS) {
+			ascii_key = '<';
+		} else if (key == SDLK_GREATER) {
+			ascii_key = '>';
+		}
+		if (ascii_key != 0) {
+			ascii_key = KLowerAscii(ascii_key);
+			CommandId id;
+			if (KLookupEscCommand(ascii_key, id)) {
+				// Only consume the ESC-meta prefix if we actually mapped a command
+				esc_meta = false;
+				out      = {true, id, "", 0};
+				return true;
+			}
+		}
+		// Unhandled meta chord at KEYDOWN: do not clear esc_meta here.
+		// Leave it set so SDL_TEXTINPUT fallback can translate and suppress insertion.
+		out.hasCommand = false;
+		return true;
+	}
+
 	// Movement and basic keys
 	switch (key) {
 	case SDLK_LEFT:
@@ -56,7 +86,8 @@ map_key(const SDL_Keycode key, const SDL_Keymod mod, bool &k_prefix, MappedInput
 		return true;
 	case SDLK_ESCAPE:
 		k_prefix = false;
-		out = {true, CommandId::Refresh, "", 0};
+		esc_meta       = true; // next key will be treated as Meta
+		out.hasCommand = false; // no immediate command for bare ESC in GUI
 		return true;
 	default:
 		break;
@@ -108,8 +139,19 @@ map_key(const SDL_Keycode key, const SDL_Keymod mod, bool &k_prefix, MappedInput
 
 	// Alt/Meta bindings (ESC f/b equivalent)
 	if (is_alt) {
+		int ascii_key = 0;
 		if (key >= SDLK_a && key <= SDLK_z) {
-			int ascii_key = static_cast<int>('a' + (key - SDLK_a));
+			ascii_key = static_cast<int>('a' + (key - SDLK_a));
+		} else if (key == SDLK_COMMA) {
+			ascii_key = '<';
+		} else if (key == SDLK_PERIOD) {
+			ascii_key = '>';
+		} else if (key == SDLK_LESS) {
+			ascii_key = '<';
+		} else if (key == SDLK_GREATER) {
+			ascii_key = '>';
+		}
+		if (ascii_key != 0) {
 			CommandId id;
 			if (KLookupEscCommand(ascii_key, id)) {
 				out = {true, id, "", 0};
@@ -133,13 +175,14 @@ GUIInputHandler::ProcessSDLEvent(const SDL_Event &e)
 	case SDL_KEYDOWN: {
 		// Remember whether we were in k-prefix before handling this key
 		bool was_k_prefix     = k_prefix_;
+		bool was_esc_meta     = esc_meta_;
 		SDL_Keymod mods       = SDL_Keymod(e.key.keysym.mod);
 		const SDL_Keycode key = e.key.keysym.sym;
-		produced              = map_key(key, mods, k_prefix_, mi);
+		produced              = map_key(key, mods, k_prefix_, esc_meta_, mi);
 		// Suppress the immediate following SDL_TEXTINPUT only in cases where
 		// SDL would also emit a text input for the same physical keystroke:
 		//  - k-prefix printable suffix keys (no Ctrl), and
-		//  - Alt/Meta modified printable letters.
+		//  - Alt/Meta modified printable letters (or ESC+letter/symbol).
 		// Do NOT suppress for non-text keys like Tab/Enter/Backspace/arrows/etc.,
 		// otherwise the next normal character would be dropped.
 		if (produced && mi.hasCommand) {
@@ -159,7 +202,14 @@ GUIInputHandler::ProcessSDLEvent(const SDL_Event &e)
 					should_suppress = true;
 				}
 				// Alt/Meta + letter can also generate TEXTINPUT on some platforms
-				if (is_alt && key >= SDLK_a && key <= SDLK_z) {
+				const bool is_meta_symbol = (
+					key == SDLK_COMMA || key == SDLK_PERIOD || key == SDLK_LESS || key ==
+					SDLK_GREATER);
+				if (is_alt && ((key >= SDLK_a && key <= SDLK_z) || is_meta_symbol)) {
+					should_suppress = true;
+				}
+				// ESC-as-meta followed by printable
+				if (was_esc_meta && (is_printable_letter || is_meta_symbol)) {
 					should_suppress = true;
 				}
 			}
@@ -176,6 +226,45 @@ GUIInputHandler::ProcessSDLEvent(const SDL_Event &e)
 			produced                  = true; // consumed input
 			break;
 		}
+		// Handle ESC-as-meta fallback on TEXTINPUT: some platforms emit only TEXTINPUT
+		// for the printable part after ESC. If esc_meta_ is set, translate first char.
+		if (esc_meta_) {
+			esc_meta_       = false; // consume meta prefix
+			const char *txt = e.text.text;
+			if (txt && *txt) {
+				// Parse first UTF-8 codepoint (we care only about common ASCII cases)
+				unsigned char c0 = static_cast<unsigned char>(txt[0]);
+				// Map a few common symbols/letters used in our ESC map
+				int ascii_key = 0;
+				if (c0 < 0x80) {
+					// ASCII path
+					ascii_key = static_cast<int>(c0);
+					ascii_key = KLowerAscii(ascii_key);
+				} else {
+					// Basic handling for macOS Option combos that might produce ≤/≥
+					// Compare the UTF-8 prefix for these two symbols
+					std::string s(txt);
+					if (s.rfind("\xE2\x89\xA4", 0) == 0) {
+						// U+2264 '≤'
+						ascii_key = '<';
+					} else if (s.rfind("\xE2\x89\xA5", 0) == 0) {
+						// U+2265 '≥'
+						ascii_key = '>';
+					}
+				}
+				if (ascii_key != 0) {
+					CommandId id;
+					if (KLookupEscCommand(ascii_key, id)) {
+						mi       = {true, id, "", 0};
+						produced = true;
+						break;
+					}
+				}
+			}
+			// If we get here, swallow the TEXTINPUT (do not insert stray char)
+			produced = true;
+			break;
+		}
 		if (!k_prefix_ && e.text.text[0] != '\0') {
 			mi.hasCommand = true;
 			mi.id         = CommandId::InsertText;
diff --git a/GUIInputHandler.h b/GUIInputHandler.h
index cb25f13..483ab2c 100644
--- a/GUIInputHandler.h
+++ b/GUIInputHandler.h
@@ -27,6 +27,8 @@ private:
 	std::mutex mu_;
 	std::queue<MappedInput> q_;
 	bool k_prefix_ = false;
+	// Treat ESC as a Meta prefix: next key is looked up via ESC keymap
+	bool esc_meta_ = false;
 	// When a printable keydown generated a non-text command, suppress the very next SDL_TEXTINPUT
 	// event produced by SDL for the same keystroke to avoid inserting stray characters.
 	bool suppress_text_input_once_ = false;
diff --git a/KKeymap.cc b/KKeymap.cc
index a623de3..197e0e0 100644
--- a/KKeymap.cc
+++ b/KKeymap.cc
@@ -23,21 +23,42 @@ KLookupKCommand(const int ascii_key, const bool ctrl, CommandId &out) -> bool
 		}
 	} else {
 		switch (k) {
+		case 'j':
+			out = CommandId::JumpToMark;
+			return true; // C-k j
+		case 'f':
+			out = CommandId::FlushKillRing;
+			return true; // C-k f
 		case 'd':
 			out = CommandId::KillToEOL;
 			return true; // C-k d
+		case 'y':
+			out = CommandId::Yank;
+			return true; // C-k y
 		case 's':
 			out = CommandId::Save;
 			return true; // C-k s
 		case 'e':
 			out = CommandId::OpenFileStart;
 			return true; // C-k e (open file)
+		case 'b':
+			out = CommandId::BufferSwitchStart;
+			return true; // C-k b (switch buffer by name)
+		case 'c':
+			out = CommandId::BufferClose;
+			return true; // C-k c (close current buffer)
+		case 'n':
+			out = CommandId::BufferPrev;
+			return true; // C-k n (switch to previous buffer)
 		case 'x':
 			out = CommandId::SaveAndQuit;
 			return true; // C-k x
 		case 'q':
 			out = CommandId::Quit;
 			return true; // C-k q
+		case 'p':
+			out = CommandId::BufferNext;
+			return true; // C-k p (switch to next buffer)
 		default:
 			break;
 		}
@@ -51,6 +72,12 @@ KLookupCtrlCommand(const int ascii_key, CommandId &out) -> bool
 {
 	const int k = KLowerAscii(ascii_key);
 	switch (k) {
+	case 'w':
+		out = CommandId::KillRegion; // C-w
+		return true;
+	case 'y':
+		out = CommandId::Yank; // C-y
+		return true;
 	case 'd':
 		out = CommandId::DeleteChar; // C-d
 		return true;
@@ -96,6 +123,18 @@ KLookupEscCommand(const int ascii_key, CommandId &out) -> bool
 {
 	const int k = KLowerAscii(ascii_key);
 	switch (k) {
+	case '<':
+		out = CommandId::MoveFileStart; // Esc <
+		return true;
+	case '>':
+		out = CommandId::MoveFileEnd; // Esc >
+		return true;
+	case 'm':
+		out = CommandId::ToggleMark; // Esc m
+		return true;
+	case 'w':
+		out = CommandId::CopyRegion; // Esc w (Alt-w)
+		return true;
 	case 'b':
 		out = CommandId::WordPrev;
 		return true;
diff --git a/TerminalFrontend.cc b/TerminalFrontend.cc
index b897d45..2c6d3f5 100644
--- a/TerminalFrontend.cc
+++ b/TerminalFrontend.cc
@@ -10,11 +10,27 @@
 bool
 TerminalFrontend::Init(Editor &ed)
 {
-	// Ensure Ctrl-S/Ctrl-Q reach the application by disabling XON/XOFF flow control
+	// Ensure Control keys reach the app: disable XON/XOFF and dsusp/susp bindings (e.g., ^S/^Q, ^Y on macOS)
 	{
 		struct termios tio{};
 		if (tcgetattr(STDIN_FILENO, &tio) == 0) {
+			// Save original to restore on shutdown
+			orig_tio_      = tio;
+			have_orig_tio_ = true;
+			// Disable software flow control so C-s/C-q work
 			tio.c_iflag &= static_cast<unsigned long>(~IXON);
+#ifdef IXOFF
+			tio.c_iflag &= static_cast<unsigned long>(~IXOFF);
+#endif
+			// Disable dsusp/susp characters so C-y (VDSUSP on macOS) and C-z don't signal-stop the app
+#ifdef _POSIX_VDISABLE
+#ifdef VSUSP
+			tio.c_cc[VSUSP] = _POSIX_VDISABLE;
+#endif
+#ifdef VDSUSP
+			tio.c_cc[VDSUSP] = _POSIX_VDISABLE;
+#endif
+#endif
 			(void) tcsetattr(STDIN_FILENO, TCSANOW, &tio);
 		}
 	}
@@ -78,5 +94,10 @@ TerminalFrontend::Step(Editor &ed, bool &running)
 void
 TerminalFrontend::Shutdown()
 {
+	// Restore original terminal settings if we changed them
+	if (have_orig_tio_) {
+		(void) tcsetattr(STDIN_FILENO, TCSANOW, &orig_tio_);
+		have_orig_tio_ = false;
+	}
 	endwin();
 }
diff --git a/TerminalFrontend.h b/TerminalFrontend.h
index 2d38ff9..e1a1efd 100644
--- a/TerminalFrontend.h
+++ b/TerminalFrontend.h
@@ -7,6 +7,7 @@
 #include "Frontend.h"
 #include "TerminalInputHandler.h"
 #include "TerminalRenderer.h"
+#include <termios.h>
 
 
 class TerminalFrontend final : public Frontend {
@@ -26,6 +27,9 @@ private:
 	TerminalRenderer renderer_{};
 	int prev_r_ = 0;
 	int prev_c_ = 0;
+	// Saved terminal attributes to restore on shutdown
+	bool have_orig_tio_ = false;
+	struct termios orig_tio_{};
 };
 
 #endif // KTE_TERMINAL_FRONTEND_H
diff --git a/TerminalInputHandler.cc b/TerminalInputHandler.cc
index e501f0d..0bd8f03 100644
--- a/TerminalInputHandler.cc
+++ b/TerminalInputHandler.cc
@@ -108,7 +108,7 @@ map_key_to_command(const int ch, bool &k_prefix, bool &esc_meta, MappedInput &ou
 	// IMPORTANT: if we're in k-prefix, the very next key must be interpreted
 	// via the C-k keymap first, even if it's a Control chord like C-d.
 	if (k_prefix) {
-		k_prefix = false; // consume the prefix for this one key
+		k_prefix      = false; // consume the prefix for this one key
 		bool ctrl     = false;
 		int ascii_key = ch;
 		if (ch >= 1 && ch <= 26) {
diff --git a/UndoNode.cc b/UndoNode.cc
new file mode 100644
index 0000000..3576e30
--- /dev/null
+++ b/UndoNode.cc
@@ -0,0 +1,15 @@
+#include "UndoNode.h"
+
+
+void
+UndoNode::DeleteNext() const
+{
+	const UndoNode *node = next_;
+	const UndoNode *next = nullptr;
+
+	while (node != nullptr) {
+		next = node->Next();
+		delete node;
+		node = next;
+	}
+}
diff --git a/UndoNode.h b/UndoNode.h
new file mode 100644
index 0000000..2df4bfd
--- /dev/null
+++ b/UndoNode.h
@@ -0,0 +1,83 @@
+#ifndef KTE_UNDONODE_H
+#define KTE_UNDONODE_H
+
+#include <cstddef>
+#include <cstddef>
+
+
+enum UndoKind {
+	UNDO_INSERT,
+	UNDO_DELETE,
+};
+
+
+class UndoNode {
+public:
+	explicit UndoNode(const UndoKind kind, const size_t row, const size_t col)
+		: kind_(kind), row_(row), col_(col) {}
+
+
+	~UndoNode() = default;
+
+
+	[[nodiscard]] UndoKind Kind() const
+	{
+		return kind_;
+	}
+
+
+	[[nodiscard]] UndoNode *Next() const
+	{
+		return next_;
+	}
+
+
+	void Next(UndoNode *next)
+	{
+		next_ = next;
+	}
+
+
+	[[nodiscard]] UndoNode *Child() const
+	{
+		return child_;
+	}
+
+
+	void Child(UndoNode *child)
+	{
+		child_ = child;
+	}
+
+
+	void SetRowCol(const std::size_t row, const std::size_t col)
+	{
+		this->row_ = row;
+		this->col_ = col;
+	}
+
+
+	[[nodiscard]] std::size_t Row() const
+	{
+		return row_;
+	}
+
+
+	[[nodiscard]] std::size_t Col() const
+	{
+		return col_;
+	}
+
+
+	void DeleteNext() const;
+
+private:
+	[[maybe_unused]] UndoKind kind_;
+	[[maybe_unused]] UndoNode *next_{nullptr};
+	[[maybe_unused]] UndoNode *child_{nullptr};
+
+	[[maybe_unused]] std::size_t row_{}, col_{};
+};
+
+
+#endif // KTE_UNDONODE_H
diff --git a/UndoTree.cc b/UndoTree.cc
new file mode 100644
index 0000000..c090182
--- /dev/null
+++ b/UndoTree.cc
@@ -0,0 +1,47 @@
+#include "UndoTree.h"
+
+#include <cassert>
+
+
+void
+UndoTree::Begin(const UndoKind kind, const size_t row, const size_t col)
+{
+	if (this->pending != nullptr) {
+		if (this->pending->Kind() == kind) {
+			return;
+		}
+		this->Commit();
+	}
+
+	assert(this->pending == nullptr);
+	this->pending = new UndoNode(kind, row, col);
+	assert(this->pending != nullptr);
+}
+
+
+void
+UndoTree::Commit()
+{
+	if (this->pending == nullptr) {
+		return;
+	}
+
+	if (this->root == nullptr) {
+		assert(this->current == nullptr);
+
+		this->root    = this->pending;
+		this->current = this->pending;
+		this->pending = nullptr;
+
+		return;
+	}
+
+	assert(this->current != nullptr);
+	if (this->current->Next() != nullptr) {
+		this->current->DeleteNext();
+	}
+
+	this->current->Next(this->pending);
+	this->current = this->pending;
+	this->pending = nullptr;
+}
diff --git a/UndoTree.h b/UndoTree.h
new file mode 100644
index 0000000..9ff8ea5
--- /dev/null
+++ b/UndoTree.h
@@ -0,0 +1,20 @@
+#ifndef KTE_UNDOTREE_H
+#define KTE_UNDOTREE_H
+
+#include "UndoNode.h"
+
+class UndoTree {
+	UndoTree() : root{nullptr}, current{nullptr}, pending{nullptr} {}
+
+	void Begin(UndoKind kind, size_t row, size_t col);
+
+	void Commit();
+
+private:
+	UndoNode *root{nullptr};
+	UndoNode *current{nullptr};
+	UndoNode *pending{nullptr};
+};
+
+
+#endif // KTE_UNDOTREE_H
diff --git a/kte-cloc b/kte-cloc
new file mode 100755
index 0000000..08bc3b1
--- /dev/null
+++ b/kte-cloc
@@ -0,0 +1,3 @@
+#!/usr/bin/env bash
+
+ls -1 *.cc *.h | grep -v '^Font.h$' | xargs cloc -fmt 3