add undo docs

+ editor removes per-buffer fields.
+ switching from internal use of 'int' to 'size_t'.
+ deleting old code
+ double checking relevancy of comments. A lot has changed in
  5 years, even more so in the past week.
+ fixing a few vestigal memory errors from the overhaul.
+ fixing search behavior

CMakeLists.txt

@@ -2,7 +2,7 @@ cmake_minimum_required(VERSION 3.15)
 project(ke C)  # Specify C language explicitly
 
 set(CMAKE_C_STANDARD 99)
-set(KE_VERSION "2.0.1")
+set(KE_VERSION "2.1.0")
 
 set(CMAKE_C_FLAGS "-Wall -Wextra -pedantic -Wshadow -Werror -std=c99 -g -Werror=stringop-truncation")
 set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -D_DEFAULT_SOURCE -D_XOPEN_SOURCE")
@@ -28,6 +28,8 @@ add_executable(ke
         core.c
         core.h
         main.c
+        undo.h
+        undo.c
 )
 target_compile_definitions(ke PRIVATE KE_VERSION="ke version ${KE_VERSION}")
 install(TARGETS ke RUNTIME DESTINATION bin)

abuf.c

@@ -1,6 +1,7 @@
 #include <assert.h>
 #include <stdlib.h>
 #include <string.h>
+#include <stdint-gcc.h>
 
 #include "abuf.h"
 #include "core.h"
@@ -28,19 +29,34 @@ ab_init(abuf *buf)
 void
 ab_init_cap(abuf *buf, const size_t cap)
 {
-	buf->b    = calloc(cap, 1);
-	buf->size = 0;
-	buf->cap  = cap;
+	ab_init(buf);
+
+	if (cap > 0) {
+		ab_resize(buf, cap);
+	}
+}
+
+
+void
+ab_init_str(abuf *buf, const char *s)
+{
+	size_t	 len = kstrnlen(s, SIZE_MAX);
+
+	ab_init_cap(buf, len);
+	ab_append(buf, s, len);
 }
 
 
 void
 ab_resize(abuf *buf, size_t cap)
 {
-	cap = cap_growth(buf->cap, cap);
-	buf->b = realloc(buf->b, cap);
-	assert(buf->b != NULL);
+	char	*newbuf = NULL;
+
+	cap = cap_growth(buf->cap, cap) + 1;
+	newbuf = realloc(buf->b, cap);
+	assert(newbuf != NULL);
 	buf->cap = cap;
+	buf->b   = newbuf;
 }
 
 
@@ -66,6 +82,18 @@ ab_append(abuf *buf, const char *s, size_t len)
 }
 
 
+void
+ab_append_ab(abuf *buf, abuf *other)
+{
+	assert(buf != NULL && other != NULL);
+	if (other->size == 0) {
+		return;
+	}
+
+	ab_append(buf, other->b, other->size);
+}
+
+
 void
 ab_prependch(abuf *buf, const char c)
 {
@@ -92,6 +120,18 @@ ab_prepend(abuf *buf, const char *s, const size_t len)
 }
 
 
+void
+ab_prepend_ab(abuf *buf, abuf *other)
+{
+	assert(buf != NULL && other != NULL);
+	if (other->size == 0) {
+		return;
+	}
+
+	ab_prepend(buf, other->b, other->size);
+}
+
+
 void
 ab_free(abuf *buf)
 {

abuf.h

@@ -1,8 +1,8 @@
 /*
  * abuf.h - append/prepend buffer utilities
  */
-#ifndef ABUF_H
-#define ABUF_H
+#ifndef KE_ABUF_H
+#define KE_ABUF_H
 
 #include <stddef.h>
 
@@ -19,11 +19,14 @@ typedef struct abuf {
 
 void		 ab_init(abuf *buf);
 void		 ab_init_cap(abuf *buf, size_t cap);
+void		 ab_init_str(abuf *buf, const char *s);
 void		 ab_resize(abuf *buf, size_t cap);
 void		 ab_appendch(abuf *buf, char c);
 void		 ab_append(abuf *buf, const char *s, size_t len);
-void		 ab_prependch(abuf *buf, const char c);
-void		 ab_prepend(abuf *buf, const char *s, const size_t len);
+void		 ab_append_ab(abuf *buf, abuf *other);
+void		 ab_prependch(abuf *buf, char c);
+void		 ab_prepend(abuf *buf, const char *s, size_t len);
+void		 ab_prepend_ab(abuf *buf, abuf *other);
 void		 ab_free(abuf *buf);
 
 

buffer.c

@@ -35,12 +35,13 @@ static int
 buffer_find_exact_by_name(const char *name)
 {
 	buffer	*b = NULL;
+	size_t   i = 0;
 
 	if (name == NULL) {
 		return -1;
 	}
 
-	for (int i = 0; i < editor.bufcount; i++) {
+	for (i = 0; i < editor.bufcount; i++) {
 		b                = editor.buffers[i];
 		const char *full = b->filename;
 		const char *base = buf_basename(full);
@@ -66,11 +67,12 @@ static int
 buffer_collect_prefix_matches(const char *prefix, int *out_idx, const int max_out)
 {
 	buffer	*b       = NULL;
-	int	 count   = 0;
-	int	 matched = 0;
+	int      count   = 0;
+	int      matched = 0;
+	size_t   i       = 0;
 	size_t	 plen    = (prefix ? strlen(prefix) : 0);
 
-	for (int i = 0; i < editor.bufcount; i++) {
+	for (i = 0; i < editor.bufcount; i++) {
 		matched = 0;
 		b = editor.buffers[i];
 
@@ -206,49 +208,6 @@ buffer_switch_prompt_cb(char *buf, const int16_t key)
 }
 
 
-static void
-buffer_bind_to_editor(const buffer *b)
-{
-	if (b == NULL) {
-		return;
-	}
-
-	editor.curx      = b->curx;
-	editor.cury      = b->cury;
-	editor.rx        = b->rx;
-	editor.nrows     = b->nrows;
-	editor.rowoffs   = b->rowoffs;
-	editor.coloffs   = b->coloffs;
-	editor.row       = b->row;
-	editor.filename  = b->filename;
-	editor.dirty     = b->dirty;
-	editor.mark_set  = b->mark_set;
-	editor.mark_curx = b->mark_curx;
-	editor.mark_cury = b->mark_cury;
-}
-
-
-static void
-buffer_extract_from_editor(buffer *b)
-{
-	if (b == NULL) {
-		return;
-	}
-
-	b->curx      = editor.curx;
-	b->cury      = editor.cury;
-	b->rx        = editor.rx;
-	b->nrows     = editor.nrows;
-	b->rowoffs   = editor.rowoffs;
-	b->coloffs   = editor.coloffs;
-	b->row       = editor.row;
-	b->filename  = editor.filename;
-	b->dirty     = editor.dirty;
-	b->mark_set  = editor.mark_set;
-	b->mark_curx = editor.mark_curx;
-	b->mark_cury = editor.mark_cury;
-}
-
 const char *
 buffer_name(buffer *b)
 {
@@ -263,12 +222,12 @@ buffer_name(buffer *b)
 void
 buffers_init(void)
 {
-	int	 idx = 0;
+    int	 idx = 0;
 
-	editor.buffers  = NULL;
-	editor.bufcount = 0;
-	editor.curbuf   = -1;
-	editor.bufcap	= 0;
+ editor.buffers  = NULL;
+ editor.bufcount = 0;
+ editor.curbuf   = 0;
+ editor.bufcap	= 0;
 
 	idx = buffer_add_empty();
 	buffer_switch(idx);
@@ -278,28 +237,28 @@ buffers_init(void)
 static void
 buffer_list_resize(void)
 {
-	buffer	**newlist = NULL;
+    buffer	**newlist = NULL;
 
-	if (editor.bufcount == (int)editor.bufcap) {
-		editor.bufcap = cap_growth((int)editor.bufcap, editor.bufcount + 1);
+    if (editor.bufcount == editor.bufcap) {
+        editor.bufcap = (size_t)cap_growth((int)editor.bufcap, (int)editor.bufcount + 1);
 
-		newlist = realloc(editor.buffers, sizeof(buffer *) * editor.bufcap);
-		assert(newlist != NULL);
-		editor.buffers = newlist;
-	}
+        newlist = realloc(editor.buffers, sizeof(buffer *) * editor.bufcap);
+        assert(newlist != NULL);
+        editor.buffers = newlist;
+    }
 }
 
 
 int
 buffer_add_empty(void)
 {
-	buffer	 *buf    = NULL;
-	int	 idx     = 0;
+    buffer	 *buf    = NULL;
+    int	 idx     = 0;
 
-	buffer_list_resize();
+    buffer_list_resize();
 
-	buf = calloc(1, sizeof(buffer));
-	assert(buf != NULL);
+    buf = calloc(1, sizeof(buffer));
+    assert(buf != NULL);
 
 	buf->curx      = 0;
 	buf->cury      = 0;
@@ -312,36 +271,32 @@ buffer_add_empty(void)
 	buf->dirty     = 0;
 	buf->mark_set  = 0;
 	buf->mark_curx = 0;
-	buf->mark_cury = 0;
+ buf->mark_cury = 0;
+ /* initialize undo tree for this buffer */
+ undo_tree_init(&buf->undo);
 
-	editor.buffers[editor.bufcount] = buf;
-	idx                             = editor.bufcount;
-	editor.bufcount++;
-	return idx;
+    editor.buffers[editor.bufcount] = buf;
+    idx                             = (int)editor.bufcount;
+    editor.bufcount++;
+    return idx;
 }
 
 
 void
 buffer_save_current(void)
 {
-	buffer	*b = NULL;
-
-	if (editor.curbuf < 0 || editor.curbuf >= editor.bufcount) {
-		return;
-	}
-
-	b = editor.buffers[editor.curbuf];
-	buffer_extract_from_editor(b);
+    /* No-op: editor no longer mirrors per-buffer fields */
+    (void)editor;
 }
 
 
 buffer *
 buffer_current(void)
 {
-	if (editor.curbuf < 0 || editor.curbuf >= editor.bufcount) {
-		return NULL;
-	}
-	return editor.buffers[editor.curbuf];
+    if (editor.bufcount == 0 || editor.curbuf >= editor.bufcount) {
+        return NULL;
+    }
+    return editor.buffers[editor.curbuf];
 }
 
 
@@ -375,89 +330,85 @@ buffer_is_unnamed_and_empty(const buffer *b)
 void
 buffer_switch(const int idx)
 {
-	buffer	*b = NULL;
+    buffer	*b = NULL;
 
-	if (idx < 0 || idx >= editor.bufcount) {
-		return;
-	}
+    if (idx < 0 || (size_t)idx >= editor.bufcount) {
+        return;
+    }
 
-	if (editor.curbuf == idx) {
-		return;
-	}
+    if (editor.curbuf == (size_t)idx) {
+        return;
+    }
 
-	if (editor.curbuf >= 0) {
-		buffer_save_current();
-	}
-
-	b = editor.buffers[idx];
-	buffer_bind_to_editor(b);
-	editor.curbuf  = idx;
-	editor.dirtyex = 1;
-	editor_set_status("Switched to buffer %d: %s", editor.curbuf, buffer_name(b));
+    b = editor.buffers[idx];
+    editor.curbuf  = (size_t)idx;
+    editor.dirtyex = 1;
+    editor_set_status("Switched to buffer %d: %s", editor.curbuf, buffer_name(b));
 }
 
 
 void
 buffer_next(void)
 {
-	int idx = 0;
+    size_t idx = 0;
 
-	if (editor.bufcount <= 1) {
-		return;
-	}
+    if (editor.bufcount <= 1) {
+        return;
+    }
 
-	idx = (editor.curbuf + 1) % editor.bufcount;
-	buffer_switch(idx);
+    idx = (editor.curbuf + 1) % editor.bufcount;
+    buffer_switch((int)idx);
 }
 
 
 void
 buffer_prev(void)
 {
-	int	 idx = 0;
+    size_t	 idx = 0;
 
-	if (editor.bufcount <= 1) {
-		return;
-	}
+    if (editor.bufcount <= 1) {
+        return;
+    }
 
-	idx = (editor.curbuf - 1 + editor.bufcount) % editor.bufcount;
-	buffer_switch(idx);
+    idx = (editor.curbuf == 0) ? (editor.bufcount - 1) : (editor.curbuf - 1);
+    buffer_switch((int)idx);
 }
 
 
 void
 buffer_close_current(void)
 {
-	buffer	*b   = NULL;
-	int	 closing = 0;
-	int	 target  = 0;
-	int	 nb      = 0;
+    buffer	*b   = NULL;
+    size_t	 closing = 0;
+    int	 target  = 0;
+    int	 nb      = 0;
 
 	/* sanity check */
-	if (editor.curbuf < 0 || editor.curbuf >= editor.bufcount) {
+	if (editor.bufcount == 0 || editor.curbuf >= editor.bufcount) {
 		editor_set_status("No buffer to close.");
 		return;
 	}
 
 	closing = editor.curbuf;
 
-	target = -1;
 	if (editor.bufcount > 1) {
-		target = (closing - 1 >= 0) ? (closing - 1) : (closing + 1);
+		target = (closing > 0) ? (int) (closing - 1) : (int) (closing + 1);
 		buffer_switch(target);
 	} else {
 		nb = buffer_add_empty();
 		buffer_switch(nb);
 	}
 
-	b = editor.buffers[closing];
-	if (b) {
-		if (b->row) {
-			for (int i = 0; i < b->nrows; i++) {
-				ab_free(&b->row[i]);
-			}
-			free(b->row);
-		}
+ b = editor.buffers[closing];
+ if (b) {
+     /* free undo tree resources before freeing buffer */
+     undo_tree_free(&b->undo);
+     if (b->row) {
+         for (size_t i = 0; i < b->nrows; i++) {
+             ab_free(&b->row[i]);
+         }
+         free(b->row);
+     }
 
 		if (b->filename) {
 			free(b->filename);
@@ -466,11 +417,11 @@ buffer_close_current(void)
 	}
 
 	memmove(&editor.buffers[closing], &editor.buffers[closing + 1],
-	        sizeof(buffer *) * (editor.bufcount - closing - 1));
+		sizeof(buffer *) * (editor.bufcount - closing - 1));
 
 	editor.bufcount--;
 	if (editor.bufcount == 0) {
-		editor.curbuf = -1;
+		editor.curbuf = 0;
 	} else {
 		if (editor.curbuf > closing) {
 			editor.curbuf--;
@@ -479,7 +430,7 @@ buffer_close_current(void)
 
 	editor.dirtyex = 1;
 	editor_set_status("Closed buffer. Now on %s",
-	                  buffer_name(editor.buffers[editor.curbuf]));
+			  buffer_name(editor.buffers[editor.curbuf]));
 }
 
 
@@ -512,7 +463,7 @@ buffer_switch_by_name(void)
 	if (idx >= 0) {
 		buffer_switch(idx);
 	} else {
-		editor_set_status("No such buffer: %s", name);
+		editor_set_status("No open buffer: %s", name);
 	}
 
 	free(name);

buffer.h

@@ -1,19 +1,21 @@
-#ifndef BUFFER_H
-#define BUFFER_H
+#ifndef KE_BUFFER_H
+#define KE_BUFFER_H
 
 #include "abuf.h"
+#include "undo.h"
 
 
 typedef struct buffer {
-	int	 curx, cury;
-	int	 rx;
-	int	 nrows;
-	int	 rowoffs, coloffs;
-	abuf	*row;
-	char	*filename;
-	int	 dirty;
-	int	 mark_set;
-	int	 mark_curx, mark_cury;
+	size_t		 curx, cury;
+	size_t		 rx;
+	size_t		 nrows;
+	size_t		 rowoffs, coloffs;
+	abuf		*row;
+	char		*filename;
+	int		 dirty;
+	int		 mark_set;
+	size_t		 mark_curx, mark_cury;
+	undo_tree	 undo;
 } buffer;
 
 /* Access current buffer and convenient aliases for file-specific fields */

core.c

@@ -35,19 +35,8 @@ strnstr(const char *s, const char *find, size_t slen)
 #endif
 
 
-char
-nibble_to_hex(char c)
-{
-	c &= 0xf;
-	if (c < 10) {
-		return (char)('0' + c);
-	}
-	return (char)('A' + (c - 10));
-}
-
-
 void
-swap_int(int *first, int *second)
+swap_size_t(size_t *first, size_t *second)
 {
 	*first ^= *second;
 	*second ^= *first;

core.h

@@ -4,7 +4,6 @@
 #include <stddef.h>
 
 
-#define		calloc1(sz)		calloc(1, sz)
 #define		INITIAL_CAPACITY	8
 
 
@@ -29,10 +28,9 @@ char	*strnstr(const char *s, const char *find, size_t slen);
 #define	INCLUDE_STRNSTR
 #endif
 
-char		 nibble_to_hex(char c);
-void		 swap_int(int *first, int *second);
-int		 next_power_of_2(int n);
-int		 cap_growth(int cap, int sz);
+void		 swap_size_t(size_t *first, size_t *second);
+int 		 next_power_of_2(int n);
+int 		 cap_growth(int cap, int sz);
 size_t		 kstrnlen(const char *buf, size_t max);
 void		 kwrite(int fd, const char *buf, int len);
 void		 die(const char *s);

editor.c

@@ -16,31 +16,20 @@
  * Global editor instance
  */
 struct editor editor = {
-	.cols = 0,
-	.rows = 0,
-	.curx = 0,
-	.cury = 0,
-	.rx = 0,
-	.mode = 0,
-	.nrows = 0,
-	.rowoffs = 0,
-	.coloffs = 0,
-	.row = NULL,
+    .cols = 0,
+	.rows     = 0,
+	.mode     = 0,
 	.killring = NULL,
-	.kill = 0,
-	.no_kill = 0,
-	.filename = NULL,
-	.dirty = 0,
-	.dirtyex = 0,
-	.mark_set = 0,
-	.mark_curx = 0,
-	.mark_cury = 0,
-	.uarg = 0,
-	.ucount = 0,
-	.msgtm = 0,
-	.buffers = NULL,
+	.kill     = 0,
+	.no_kill  = 0,
+	.dirtyex  = 0,
+	.uarg     = 0,
+	.ucount   = 0,
+	.msgtm    = 0,
+	.buffers  = NULL,
 	.bufcount = 0,
-	.curbuf = -1,
+	.curbuf   = 0,
+	.bufcap   = 0,
 };
 
 
@@ -69,26 +58,15 @@ init_editor(void)
 	editor.rows--; /* status bar */
 	editor.rows--; /* message line */
 
-	editor.curx = editor.cury = 0;
-	editor.rx   = 0;
-
-	editor.nrows   = 0;
-	editor.rowoffs = editor.coloffs = 0;
-	editor.row     = NULL;
-
 	/* don't clear out the kill ring:
 	 * killing / yanking across files is helpful, and killring
 	 * is initialized to NULL at program start.
 	 */
-	editor.kill    = 0;
+	editor.kill = 0;
 	editor.no_kill = 0;
 
 	editor.msg[0] = '\0';
-	editor.msgtm  = 0;
-
-	editor.dirty     = 0;
-	editor.mark_set  = 0;
-	editor.mark_cury = editor.mark_curx = 0;
+	editor.msgtm = 0;
 
 	/* initialize buffer system on first init */
 	if (editor.buffers == NULL && editor.bufcount == 0) {
@@ -101,25 +79,31 @@ init_editor(void)
 void
 reset_editor(void)
 {
-	/* Clear current working set. Notably, does not reset terminal
-	 * or buffers list. */
-	for (int i = 0; i < editor.nrows; i++) {
-		ab_free(&editor.row[i]);
-	}
-	free(editor.row);
-
-	editor.row     = NULL;
-	editor.nrows   = 0;
-	editor.rowoffs = editor.coloffs = 0;
-	editor.curx    = editor.cury    = 0;
-	editor.rx      = 0;
-
-	if (editor.filename != NULL) {
-		free(editor.filename);
-		editor.filename = NULL;
+	/* Reset the current buffer's contents/state. */
+	buffer *b = buffer_current();
+	if (b == NULL) {
+		return;
 	}
 
-	editor.dirty     = 0;
-	editor.mark_set  = 0;
-	editor.mark_cury = editor.mark_curx = 0;
+	if (b->row) {
+		for (size_t i = 0; i < b->nrows; i++) {
+			ab_free(&b->row[i]);
+		}
+		free(b->row);
+	}
+	b->row = NULL;
+	b->nrows = 0;
+	b->rowoffs = 0;
+	b->coloffs = 0;
+	b->rx = 0;
+	b->curx = 0;
+	b->cury = 0;
+	if (b->filename) {
+		free(b->filename);
+		b->filename = NULL;
+	}
+	b->dirty = 0;
+	b->mark_set = 0;
+	b->mark_curx = 0;
+	b->mark_cury = 0;
 }

editor.h

@@ -1,5 +1,5 @@
-#ifndef EDITOR_H
-#define EDITOR_H
+#ifndef KE_EDITOR_H
+#define KE_EDITOR_H
 
 #include <termios.h>
 #include <time.h>
@@ -9,32 +9,19 @@
 #include "buffer.h"
 
 
-/* TODO(kyle): remove the "per-buffer" fields completely from the editor. */
-
 struct editor {
-	int		  rows, cols;
-	int		  curx, cury;		/* per-buffer */
-	int		  rx;			/* per-buffer */
+	size_t		  rows, cols;
 	int		  mode;
-	int		  nrows;		/* per-buffer */
-	int		  rowoffs, coloffs;	/* per-buffer */
-	abuf		 *row;			/* per-buffer */
 	abuf		 *killring;
 	int		  kill;			/* KILL CHAIN (\m/) */
 	int		  no_kill;		/* don't kill in delete_row */
-	char		 *filename;		/* per-buffer */
-	int		  dirty;		/* per-buffer */
 	int		  dirtyex;
 	char		  msg[80];
-	int		  mark_set;		/* per-buffer */
-	int		  mark_curx, mark_cury;	/* per-buffer */
 	int		  uarg, ucount;		/* C-u support */
 	time_t		  msgtm;
-
-	/* Multi-buffer support */
 	struct buffer	**buffers;  /* array of buffers */
-	int		  bufcount; /* number of buffers */
-	int		  curbuf;   /* current buffer index */
+	size_t		  bufcount; /* number of buffers */
+	size_t		  curbuf;   /* current buffer index */
 	size_t		  bufcap;   /* current buffer capacity */
 };
 
@@ -45,4 +32,4 @@ void			 init_editor(void);
 void			 reset_editor(void);
 
 
-#endif /* EDITOR_H */
+#endif /* KE_EDITOR_H */

ke.1

@@ -65,9 +65,9 @@ Reload the current buffer from disk.
 .It C-k s
 Save the file, prompting for a filename if needed. Also C-k C-s.
 .It C-k u
-Undo changes (not implemented; marking this k-command as taken).
+Undo changes.
 .It C-k U
-Redo changes (not implemented; marking this k-command as taken).
+Redo changes.
 .It C-k x
 save the file and exit. Also C-k C-x.
 .It C-k y

scratch.c

@@ -2,15 +2,20 @@
  * scratch.c - ideas in progress
  */
 
+#include "buffer.h"
+#include "abuf.h"
+#include <ctype.h>
+#include <string.h>
+
 #define REFLOW_MARGIN		72
 
 void
 reflow_region(void)
 {
-	int		 start_row, end_row, i, col, wlen, this_len;
-	struct erow	*row;
-	struct abuf	 buf = ABUF_INIT;
-	struct abuf	 out = ABUF_INIT;
+ int		 start_row, end_row, i, col, wlen, this_len;
+ abuf		*row;
+ struct abuf	 buf = ABUF_INIT;
+ struct abuf	 out = ABUF_INIT;
 	int		 in_paragraph = 0;
 	int		 indent_len = 0;
 	char		 indent[REFLOW_MARGIN + 1];
@@ -19,38 +24,38 @@ reflow_region(void)
 	char		*p = NULL;
 	char		*s = NULL;
 
-	if (editor.mark_set) {
-		if (editor.mark_cury < editor.cury ||
-			(editor.mark_cury == editor.cury &&
-				editor.mark_curx < editor.curx)) {
-			start_row = editor.mark_cury;
-			end_row = editor.cury;
-		} else {
-			start_row = editor.cury;
-			end_row = editor.mark_cury;
-		}
-	} else {
-		start_row = end_row = editor.cury;
-		while (start_row > 0 && editor.row[start_row - 1].size > 0) {
-			start_row--;
-		}
+ if (EMARK_SET) {
+        if (EMARK_CURY < ECURY ||
+            (EMARK_CURY == ECURY &&
+                EMARK_CURX < ECURX)) {
+            start_row = EMARK_CURY;
+            end_row = ECURY;
+        } else {
+            start_row = ECURY;
+            end_row = EMARK_CURY;
+        }
+    } else {
+        start_row = end_row = ECURY;
+        while (start_row > 0 && EROW[start_row - 1].size > 0) {
+            start_row--;
+        }
 
-		while (end_row < editor.nrows - 1 &&
-			editor.row[end_row + 1].size > 0) {
-			end_row++;
-		}
-	}
+        while (end_row < ENROWS - 1 &&
+            EROW[end_row + 1].size > 0) {
+            end_row++;
+        }
+    }
 
-	if (start_row >= editor.nrows) {
-		return;
-	}
+ if (start_row >= ENROWS) {
+        return;
+    }
 
-	if (end_row >= editor.nrows) {
-		end_row = editor.nrows - 1;
-	}
+ if (end_row >= ENROWS) {
+        end_row = ENROWS - 1;
+    }
 
-	for (i = start_row; i <= end_row; i++) {
-		row = &editor.row[i];
+ for (i = start_row; i <= end_row; i++) {
+        row = &EROW[i];
 
 		if (row->size == 0) {
 			if (in_paragraph) {
@@ -62,21 +67,21 @@ reflow_region(void)
 			continue;
 		}
 
-		if (!in_paragraph) {
-			indent_len = 0;
-			while (indent_len < row->size &&
-				(row->line[indent_len] == ' ' ||
-					row->line[indent_len] == '\t')) {
-				indent[indent_len] = row->line[indent_len], indent_len++;
-			}
+        if (!in_paragraph) {
+            indent_len = 0;
+            while (indent_len < (int)row->size &&
+                (row->b[indent_len] == ' ' ||
+                    row->b[indent_len] == '\t')) {
+                indent[indent_len] = row->b[indent_len], indent_len++;
+            }
 
-			indent[indent_len] = '\0';
-			in_paragraph = 1;
-		}
+            indent[indent_len] = '\0';
+            in_paragraph = 1;
+        }
 
-		ab_append(&buf, row->line + indent_len, row->size - indent_len);
-		ab_append(&buf, " ", 1);
-	}
+        ab_append(&buf, row->b + indent_len, row->size - indent_len);
+        ab_append(&buf, " ", 1);
+    }
 
 	if (in_paragraph) {
 		ab_append(&buf, "\n", 1);
@@ -145,18 +150,57 @@ reflow_region(void)
 	ab_free(&out);
 
 
-	for (i = end_row; i >= start_row; i--) {
-		delete_row(i);
-	}
+ for (i = end_row; i >= start_row; i--) {
+        delete_row(i);
+    }
 
-	s = buf.b;
-	while ((e = strchr(s, '\n'))) {
-		erow_insert(start_row++, s, e - s);
-		s = e + 1;
-	}
+ s = buf.b;
+ while ((e = strchr(s, '\n'))) {
+     erow_insert(start_row++, s, e - s);
+     s = e + 1;
+ }
 
 	ab_free(&buf);
 
-	editor.dirty++;
-	editor_set_status("Region reflowed to %d columns", REFLOW_MARGIN);
+    EDIRTY++;
+    editor_set_status("Region reflowed to %d columns", REFLOW_MARGIN);
+}
+
+
+static inline
+void clamp_curx_to_row(void)
+{
+	abuf	*row  = NULL;
+	int	 maxx = 0;
+
+	if (ECURY >= ENROWS) {
+		return;
+	}
+
+	row = &EROW[ECURY];
+	if (ECURX < 0) {
+		ECURX = 0;
+	}
+
+	maxx = (int) row->size;
+	if (ECURX > maxx) {
+		ECURX = maxx;
+	}
+}
+
+static inline
+void set_cursor(int col, int row)
+{
+	if (row < 0) {
+		row = 0;
+	}
+
+	if (row > ENROWS) {
+		row = ENROWS;
+	}
+	
+	ECURY = row;
+	ECURX = col;
+	
+	clamp_curx_to_row();
 }

term.c

@@ -71,16 +71,16 @@ setup_terminal(void)
 
 
 int
-get_winsz(int *rows, int *cols)
+get_winsz(size_t *rows, size_t *cols)
 {
-	struct winsize ws;
+    struct winsize ws;
 
-	if (ioctl(STDOUT_FILENO, TIOCGWINSZ, &ws) == -1 || ws.ws_col == 0) {
-		return -1;
-	}
+    if (ioctl(STDOUT_FILENO, TIOCGWINSZ, &ws) == -1 || ws.ws_col == 0) {
+        return -1;
+    }
 
-	*cols = ws.ws_col;
-	*rows = ws.ws_row;
+    *cols = (size_t)ws.ws_col;
+    *rows = (size_t)ws.ws_row;
 
-	return 0;
+    return 0;
 }

term.h

@@ -1,5 +1,5 @@
-#ifndef TERM_H
-#define TERM_H
+#ifndef KE_TERM_H
+#define KE_TERM_H
 
 #include "abuf.h"
 
@@ -17,6 +17,6 @@ void display_clear(abuf *ab);
  * on this for now because it's bloaty and this works on OpenBSD and
  * Linux, at least.
  */
-int  get_winsz(int *rows, int *cols);
+int  get_winsz(size_t *rows, size_t *cols);
 
-#endif /* TERM_H */
+#endif /* KE_TERM_H */

undo.c

@@ -1,8 +1,13 @@
+#include <assert.h>
+#include <stdlib.h>
+#include <string.h>
 #include "abuf.h"
+#include "editor.h"
+#include "buffer.h"
 #include "undo.h"
 
 
-undo_node
+undo_node *
 undo_node_new(undo_kind kind)
 {
 	undo_node	*node = NULL;
@@ -13,24 +18,23 @@ undo_node_new(undo_kind kind)
 	node->kind = kind;
 	node->row = node->col = 0;
 
-	abuf_init(node->text);
+	ab_init(&node->text);
 	
 	node->next = NULL;
 	node->parent = NULL;
+
+	return node;
 }
 
 
 void
 undo_node_free(undo_node *node)
 {
-	undo_node	*next = NULL;
-
 	if (node == NULL) {
-		return NULL;
+		return;
 	}
 
-	abuf_free(node-text);
-	next = node->next;
+	ab_free(&node->text);
 }
 
 
@@ -44,9 +48,10 @@ undo_node_free_all(undo_node *node)
 	}
 
 	while (node != NULL) {
+		next = node->next;
 		undo_node_free(node);
 		free(node);
-		node = node->next;
+		node = next;
 	}
 }
 
@@ -65,7 +70,7 @@ undo_tree_init(undo_tree *tree)
 void
 undo_tree_free(undo_tree *tree)
 {
-	assert(tree == NULL);
+	assert(tree != NULL);
 
 	undo_node_free(tree->pending);
 	undo_node_free_all(tree->root);
@@ -86,19 +91,286 @@ undo_begin(undo_tree *tree, undo_kind kind)
 		undo_commit(tree);
 	}
 
-	pending = undo_new_new(kind);
+	pending = undo_node_new(kind);
 	assert(pending != NULL);
 
 	tree->pending = pending;
 }
 
 
-void		 undo_prepend(abuf *buf);
-void		 undo_append(buf *buf);
-void		 undo_prependch(char c);
-void		 undo_appendch(char c);
-void		 undo_commit(void);
-void		 undo_apply(undo_node *node);
-void		 editor_undo(void);
-void		 editor_redo(void);
+void
+undo_prepend(undo_tree *tree, abuf *buf)
+{
+	assert(tree != NULL);
+	assert(tree->pending != NULL);
+
+	ab_prepend_ab(&tree->pending->text, buf);
+}
+
+
+void
+undo_append(undo_tree *tree, abuf *buf)
+{
+	assert(tree != NULL);
+	assert(tree->pending != NULL);
+
+	ab_append_ab(&tree->pending->text, buf);
+}
+
+
+void
+undo_prependch(undo_tree *tree, char c)
+{
+	assert(tree != NULL);
+	assert(tree->pending != NULL);
+
+	ab_prependch(&tree->pending->text, c);
+}
+
+
+void
+undo_appendch(undo_tree *tree, char c)
+{
+	assert(tree != NULL);
+	assert(tree->pending != NULL);
+
+	ab_appendch(&tree->pending->text, c);
+}
+
+
+void
+undo_commit(undo_tree *tree)
+{
+	assert(tree != NULL);
+
+	if (tree->pending == NULL) {
+		return;
+	}
+
+	if (tree->root == NULL) {
+		tree->root = tree->pending;
+		tree->current = tree->pending;
+		tree->pending = NULL;
+		return;
+	}
+
+	undo_node_free_all(tree->current->next);
+	tree->current->next = tree->pending;
+	tree->pending->parent = tree->current;
+	tree->current = tree->pending;
+	tree->pending = NULL;
+}
+
+
+/* --- Helper functions for applying undo/redo operations --- */
+static void
+row_insert_at(buffer *b, size_t at, const char *s, size_t len)
+{
+    abuf *newrows = realloc(b->row, sizeof(abuf) * (b->nrows + 1));
+    assert(newrows != NULL);
+    b->row = newrows;
+
+    if (at < b->nrows) {
+        memmove(&b->row[at + 1], &b->row[at], sizeof(abuf) * (b->nrows - at));
+    }
+    ab_init(&b->row[at]);
+    if (len > 0) {
+        ab_append(&b->row[at], s, len);
+    }
+    b->nrows++;
+    b->dirty++;
+}
+
+static void
+ensure_row_exists(buffer *b, size_t r)
+{
+    while (r >= b->nrows) {
+        row_insert_at(b, b->nrows, "", 0);
+    }
+}
+
+static void
+row_insert_ch_at(abuf *row, size_t col, char ch)
+{
+    if (col > row->size) {
+        col = row->size;
+    }
+    ab_resize(row, row->size + 2);
+    memmove(&row->b[col + 1], &row->b[col], row->size - col + 1);
+    row->b[col] = ch;
+    row->size++;
+    row->b[row->size] = '\0';
+}
+
+static void
+row_delete_ch_at(abuf *row, size_t col)
+{
+    if (col >= row->size) {
+        return;
+    }
+    memmove(&row->b[col], &row->b[col + 1], row->size - col);
+    row->size--;
+    row->b[row->size] = '\0';
+}
+
+static void
+split_row_at(buffer *b, size_t r, size_t c)
+{
+    ensure_row_exists(b, r);
+    abuf *row = &b->row[r];
+    if (c > row->size) c = row->size;
+    size_t rhs_len = row->size - c;
+    char *rhs = NULL;
+    if (rhs_len > 0) {
+        rhs = malloc(rhs_len);
+        assert(rhs != NULL);
+        memcpy(rhs, &row->b[c], rhs_len);
+    }
+    row->size = c;
+    if (row->cap <= row->size) {
+        ab_resize(row, row->size + 1);
+    }
+    row->b[row->size] = '\0';
+
+    row_insert_at(b, r + 1, rhs ? rhs : "", rhs_len);
+    if (rhs) free(rhs);
+    b->dirty++;
+}
+
+static void
+join_with_next_row(buffer *b, size_t r, size_t c)
+{
+    if (r >= b->nrows) return;
+    abuf *row = &b->row[r];
+    if (c > row->size) c = row->size;
+    if (r + 1 >= b->nrows) return;
+    abuf *next = &b->row[r + 1];
+
+    /* Make room in current row at end if needed (we append next->b after position c). */
+    size_t tail_len = row->size - c;
+    size_t add_len = next->size;
+    ab_resize(row, row->size + add_len + 1);
+    /* Move tail to make room for next content */
+    memmove(&row->b[c + add_len], &row->b[c], tail_len);
+    memcpy(&row->b[c], next->b, add_len);
+    row->size += add_len;
+    row->b[row->size] = '\0';
+
+    /* Delete next row */
+    ab_free(next);
+    if (b->nrows - (r + 2) > 0) {
+        memmove(&b->row[r + 1], &b->row[r + 2], sizeof(abuf) * (b->nrows - (r + 2)));
+    }
+    b->nrows--;
+    b->dirty++;
+}
+
+static void
+buffer_insert_text(buffer *b, size_t row, size_t col, const char *s, size_t len)
+{
+    ensure_row_exists(b, row);
+    size_t r = row;
+    size_t c = col;
+    if (c > b->row[r].size) c = b->row[r].size;
+    for (size_t i = 0; i < len; i++) {
+        char ch = s[i];
+        if (ch == '\n') {
+            split_row_at(b, r, c);
+            r++;
+            c = 0;
+        } else {
+            row_insert_ch_at(&b->row[r], c, ch);
+            c++;
+        }
+        b->dirty++;
+    }
+}
+
+static void
+buffer_delete_text(buffer *b, size_t row, size_t col, const char *s, size_t len)
+{
+    if (row >= b->nrows) return;
+    size_t r = row;
+    size_t c = col;
+    if (c > b->row[r].size) c = b->row[r].size;
+    for (size_t i = 0; i < len; i++) {
+        char ch = s[i];
+        if (ch == '\n') {
+            /* delete newline at (r,c): join row r with next */
+            join_with_next_row(b, r, c);
+        } else {
+            row_delete_ch_at(&b->row[r], c);
+            /* c stays the same because character at c is removed */
+        }
+        b->dirty++;
+        if (r >= b->nrows) break; /* safety */
+        if (c > b->row[r].size) c = b->row[r].size;
+    }
+}
+
+void
+undo_apply(struct buffer *buf, int direction) {
+	undo_tree	*tree = &buf->undo;
+	undo_node	*node = NULL;
+	undo_commit(tree);
+
+	if (tree->root == NULL) {
+		return;
+	}
+
+	if (direction < 0) {
+		/* UNDO: apply inverse of current node, then move back */
+		node = tree->current;
+		if (node == NULL) {
+			return;
+		}
+		switch (node->kind) {
+			/* support insert first */
+			case UNDO_INSERT:
+				buffer_delete_text(buf, node->row, node->col,
+						   node->text.b, node->text.size);
+				break;
+			default:
+				/* unknown type: do nothing */
+				break;
+		}
+
+		tree->current = node->parent; /* move back in history */
+	} else if (direction > 0) {
+		/* REDO: move forward then apply node */
+		undo_node *next = (tree->current == NULL)
+				  ? tree->root
+				  : tree->current->next;
+		if (next == NULL) {
+			return; /* nothing to redo */
+		}
+
+		switch (next->kind) {
+			/* support insert first */
+			case UNDO_INSERT:
+				buffer_insert_text(buf, next->row, next->col,
+						   next->text.b, next->text.size);
+				break;
+			default:
+				/* unknown type: do nothing */
+				break;
+		}
+
+		tree->current = next; /* move forward in history */
+	}
+}
+
+
+void
+editor_undo(struct buffer *buf)
+{
+	undo_apply(buf, -1);
+}
+
+
+void
+editor_redo(struct buffer *buf)
+{
+	undo_apply(buf, 1);
+}
 

undo.h

@@ -1,5 +1,14 @@
-#ifndef KE_UNDO
-#define KE_UNDO
+#include <stddef.h>
+
+#include "abuf.h"
+#include "buffer.h"
+
+
+#ifndef KE_UNDO_H
+#define KE_UNDO_H
+
+
+struct buffer;
 
 
 typedef enum undo_kind {
@@ -9,7 +18,7 @@ typedef enum undo_kind {
 
 
 typedef struct undo_node {
-	undo_kind		 op;
+	undo_kind		 kind;
 	size_t			 row, col;
 	abuf			 text;
 
@@ -31,14 +40,14 @@ void		 undo_node_free(undo_node *node);
 void		 undo_tree_init(undo_tree *tree);
 void		 undo_tree_free(undo_tree *tree);
 void		 undo_begin(undo_tree *tree, undo_kind kind);
-void		 undo_prepend(abuf *buf);
-void		 undo_append(buf *buf);
-void		 undo_prependch(char c);
-void		 undo_appendch(char c);
+void		 undo_prepend(undo_tree *tree, abuf *buf);
+void		 undo_append(undo_tree *tree, abuf *buf);
+void		 undo_prependch(undo_tree *tree, char c);
+void		 undo_appendch(undo_tree *tree, char c);
 void		 undo_commit(undo_tree *tree);
-void		 undo_apply(undo_node *node);
-void		 editor_undo(void);
-void		 editor_redo(void);
+void		 undo_apply(struct buffer *buf, int direction);
+void		 editor_undo(struct buffer *buf);
+void		 editor_redo(struct buffer *buf);
 
 
 #endif

undo.md

@@ -0,0 +1,64 @@
+# Towards an Undo System
+
+date  
+2025-11-27 20:14
+
+tags  
+ked, hacks, text-editors
+
+I've been thinking about building an undo system for
+[ke](https://git.wntrmute.dev/kyle/ke). The first pass is going to be a
+linear system. Let's start with the basic definitions for an undo
+system:
+
+``` c
+typedef enum undo_kind {
+    UNDO_INSERT  = 1 << 0,
+    UNDO_UNKNOWN = 1 << 1,
+    /* more types to follow */
+} undo_kind;
+
+
+typedef struct undo_node {
+    undo_kind        op;
+    size_t           row, col;
+    abuf             text;
+    struct undo_node    *next;
+    struct undo_node    *parent;
+} undo_node;
+
+
+typedef struct undo_tree {
+    /* the start of the undo sequence */
+    undo_node   *root;
+    /* where we are currently at */
+    undo_node   *current;
+    /* the current undo operations being built */
+    undo_node   *pending;
+} undo_tree;
+```
+
+The root is anchored at the last time the file was saved; when saving,
+the tree is freed. Current points to the end of the history, and pending
+is the sequence being built.
+
+The lifecycle looks something like:
+
+- `undo_tree_new` and `undo_tree_free` --- called in `init_editor` and
+  `deathknell`, respectively. The tree is initialized with all nodes set
+  to `NULL`.
+- Once the user starts doing undoable things, `undo_begin(undo_kind)`
+  gets called, calling `undo_node_new(undo_kind)` if needed to set up
+  `tree->pending`. It may need to call `undo_commit` (below) if needed.
+- Until an `undo_commit` is called, some form of `undo_append` or
+  `undo_prepend` is called.
+- Finally, at some point `undo_commit` is called. This needs to do a few
+  things:
+  1.  If `tree->current->next` is not `NULL`, it must be freed.
+  2.  Set `tree->current->next` as pending, set `tree->current` to
+      `tree->current->next`.
+  3.  Set `tree->pending` to `NULL`.
+
+Once the e
+
+- `undo_node_new(undo_kind)` and `undo_node_free`