cutting: overhaul the pasting routine, to not make use of partitioning

This has the pleasing effect of not changing the linestructs of the
current line nor of the line after it (if any).

src/cut.c

@@ -325,59 +325,71 @@ void extract_segment(linestruct *top, size_t top_x, linestruct *bot, size_t bot_
  * at the current cursor position. */
 void ingraft_buffer(linestruct *topline)
 {
-	/* Remember whether the current line is at the top of the edit window. */
-	bool edittop_inside = (openfile->edittop == openfile->current);
+	size_t length = strlen(openfile->current->data);
+	size_t extralen = strlen(topline->data);
+	size_t xpos = openfile->current_x;
+	char *tailtext = copy_of(openfile->current->data + xpos);
+	linestruct *line = openfile->current;
 #ifndef NANO_TINY
-	/* Remember whether mark and cursor are on the same line, and their order. */
-	bool right_side_up = (openfile->mark && mark_is_before_cursor());
-	bool same_line = (openfile->mark == openfile->current);
+	bool placed_after = (openfile->mark == line && !mark_is_before_cursor());
 #endif
-	size_t was_x = openfile->current_x;
+	linestruct *botline = topline;
 
-	/* Partition the buffer so that it contains no text, then delete it.*/
-	partition_buffer(openfile->current, openfile->current_x,
-						openfile->current, openfile->current_x);
-	delete_node(openfile->filetop);
+	while (botline->next != NULL)
+		botline = botline->next;
 
-	/* Replace the current buffer with the passed buffer. */
-	openfile->filetop = topline;
-	openfile->filebot = topline;
-	while (openfile->filebot->next != NULL)
-		openfile->filebot = openfile->filebot->next;
+	/* Add the size of the text to be grafted to the buffer size. */
+	openfile->totsize += get_totsize(topline, botline);
 
-	/* Put the cursor at the end of the pasted text. */
-	openfile->current = openfile->filebot;
-	openfile->current_x = strlen(openfile->filebot->data);
+	if (topline != botline)
+		length = xpos;
 
-	/* When the pasted stuff contains no newline, adjust the cursor's
-	 * x coordinate for the text that is before the pasted stuff. */
-	if (openfile->filetop == openfile->filebot)
-		openfile->current_x += was_x;
-
-#ifndef NANO_TINY
-	/* When needed, refresh the mark's pointer and compensate the mark's
-	 * x coordinate for the change in the current line. */
-	if (same_line) {
-		if (!right_side_up) {
-			openfile->mark = openfile->filebot;
-			openfile->mark_x += openfile->current_x - was_x;
-		} else
-			openfile->mark = openfile->filetop;
+	if (extralen > 0) {
+		/* Insert the text of topline at the current cursor position. */
+		line->data = charealloc(line->data, length + extralen + 1);
+		memmove(line->data + xpos + extralen, line->data + xpos, length - xpos + 1);
+		strncpy(line->data + xpos, topline->data, extralen);
 	}
+
+	if (topline != botline) {
+		/* When inserting at end-of-buffer, update the relevant pointer. */
+		if (line->next == NULL)
+			openfile->filebot = botline;
+
+		line->data[xpos + extralen] = '\0';
+
+		/* Hook the grafted lines in after the current one. */
+		botline->next = openfile->current->next;
+		if (botline->next)
+			botline->next->prev = botline;
+		openfile->current->next = topline->next;
+		topline->next->prev = openfile->current;
+
+		/* Add the text after the cursor position at the end of botline. */
+		length = strlen(botline->data);
+		extralen = strlen(tailtext);
+		botline->data = charealloc(botline->data, length + extralen + 1);
+		strcpy(botline->data + length, tailtext);
+
+		/* Put the cursor at the end of the grafted text. */
+		openfile->current = botline;
+		openfile->current_x = length;
+	} else
+		openfile->current_x += extralen;
+
+#ifndef NANO_TINY
+	/* When needed, update the mark's pointer and position. */
+	if (placed_after && topline != botline) {
+		openfile->mark = botline;
+		openfile->mark_x += length - xpos;
+	} else if (placed_after)
+		openfile->mark_x += extralen;
 #endif
 
-	/* Add the number of characters in the copied text to the file size. */
-	openfile->totsize += get_totsize(openfile->filetop, openfile->filebot);
+	delete_node(topline);
+	free(tailtext);
 
-	/* If we pasted onto the first line of the edit window, the corresponding
-	 * record has been freed, so... point at the start of the copied text. */
-	if (edittop_inside)
-		openfile->edittop = openfile->filetop;
-
-	/* Weld the pasted text into the surrounding content of the buffer. */
-	unpartition_buffer();
-
-	renumber_from(topline);
+	renumber_from(line);
 
 	/* If the text doesn't end with a newline, and it should, add one. */
 	if (!ISSET(NO_NEWLINES) && openfile->filebot->data[0] != '\0')