vis: make `cw` and `cW` more vim compatible

If the starting position is:

 * on a space or tab use the `w` motion

 * on the last letter of a word use `l` or `e` depending on whether
   a count was given. This also applies for single letter words.

 * otherwise use the `e` motion

As in vim `cw` and `dw` behave differently, whether that is desirable
remains to be seen.

Might fix #521

2 files changed, 57 insertions, 2 deletions

diff --git a/vis-motions.c b/vis-motions.c
index f8baf1d..3e7f269 100644
--- a/vis-motions.c
+++ b/vis-motions.c
@@ -56,6 +56,51 @@ static size_t search_backward(Vis *vis, Text *txt, size_t pos) {
 	return pos;
 }
 
+static size_t common_word_next(Vis *vis, Text *txt, size_t pos, enum VisMotion end_next) {
+	char c;
+	Iterator it = text_iterator_get(txt, pos);
+	if (!text_iterator_byte_get(&it, &c))
+		return pos;
+	const Movement *motion = NULL;
+	int count = vis_count_get_default(vis, 1);
+	if (c == ' ' || c == '\t') {
+		motion = &vis_motions[VIS_MOVE_WORD_START_NEXT];
+	} else if (text_iterator_char_next(&it, &c) && (c == ' ' || c == '\t')) {
+		/* we are on the last character of a word */
+		if (count == 1) {
+			/* map `cw` to `cl` */
+			motion = &vis_motions[VIS_MOVE_CHAR_NEXT];
+		} else {
+			/* map `c{n}w` to `c{n-1}e` */
+			count--;
+			motion = &vis_motions[end_next];
+		}
+	} else {
+		/* map `cw` to `ce` */
+		motion = &vis_motions[end_next];
+	}
+
+	while (count--) {
+		size_t newpos = motion->txt(txt, pos);
+		if (newpos == pos)
+			break;
+		pos = newpos;
+	}
+
+	if (motion->type & INCLUSIVE)
+		pos = text_char_next(txt, pos);
+
+	return pos;
+}
+
+static size_t word_next(Vis *vis, Text *txt, size_t pos) {
+	return common_word_next(vis, txt, pos, VIS_MOVE_WORD_END_NEXT);
+}
+
+static size_t longword_next(Vis *vis, Text *txt, size_t pos) {
+	return common_word_next(vis, txt, pos, VIS_MOVE_LONGWORD_END_NEXT);
+}
+
 static size_t mark_goto(Vis *vis, File *file, size_t pos) {
 	return text_mark_get(file->text, file->marks[vis->action.mark]);
 }
@@ -266,11 +311,11 @@ bool vis_motion(Vis *vis, enum VisMotion motion, ...) {
 	switch (motion) {
 	case VIS_MOVE_WORD_START_NEXT:
 		if (vis->action.op == &vis_operators[VIS_OP_CHANGE])
-			motion = VIS_MOVE_WORD_END_NEXT;
+			motion = VIS_MOVE_WORD_NEXT;
 		break;
 	case VIS_MOVE_LONGWORD_START_NEXT:
 		if (vis->action.op == &vis_operators[VIS_OP_CHANGE])
-			motion = VIS_MOVE_LONGWORD_END_NEXT;
+			motion = VIS_MOVE_LONGWORD_NEXT;
 		break;
 	case VIS_MOVE_SEARCH_FORWARD:
 	case VIS_MOVE_SEARCH_BACKWARD:
@@ -427,6 +472,10 @@ const Movement vis_motions[] = {
 		.txt = text_line_char_next,
 		.type = CHARWISE,
 	},
+	[VIS_MOVE_WORD_NEXT] = {
+		.vis = word_next,
+		.type = CHARWISE|IDEMPOTENT,
+	},
 	[VIS_MOVE_WORD_START_PREV] = {
 		.txt = text_word_start_prev,
 		.type = CHARWISE,
@@ -443,6 +492,10 @@ const Movement vis_motions[] = {
 		.txt = text_word_end_next,
 		.type = CHARWISE|INCLUSIVE,
 	},
+	[VIS_MOVE_LONGWORD_NEXT] = {
+		.vis = longword_next,
+		.type = CHARWISE|IDEMPOTENT,
+	},
 	[VIS_MOVE_LONGWORD_START_PREV] = {
 		.txt = text_longword_start_prev,
 		.type = CHARWISE,
diff --git a/vis.h b/vis.h
index 6c6e0fe..da1677c 100644
--- a/vis.h
+++ b/vis.h
@@ -268,10 +268,12 @@ enum VisMotion {
 	VIS_MOVE_CHAR_NEXT,
 	VIS_MOVE_LINE_CHAR_PREV,
 	VIS_MOVE_LINE_CHAR_NEXT,
+	VIS_MOVE_WORD_NEXT,
 	VIS_MOVE_WORD_START_NEXT,
 	VIS_MOVE_WORD_END_PREV,
 	VIS_MOVE_WORD_END_NEXT,
 	VIS_MOVE_WORD_START_PREV,
+	VIS_MOVE_LONGWORD_NEXT,
 	VIS_MOVE_LONGWORD_START_PREV,
 	VIS_MOVE_LONGWORD_START_NEXT,
 	VIS_MOVE_LONGWORD_END_PREV,