display clients count in monocle symbol

- Replicate missing functionality from dwl to display the client count in monocle mode
  - Add ltsymbol field to Monitor struct
  - Display client count in monocle mode when greater than zero
- Tested with somebar and dwlb

dwl.c

@@ -190,6 +190,7 @@ struct Monitor {
 	unsigned int tagset[2];
 	double mfact;
 	int nmaster;
+	char ltsymbol[16];
 };
 
 typedef struct {
@@ -482,6 +483,8 @@ arrange(Monitor *m)
 	wlr_scene_node_set_enabled(&m->fullscreen_bg->node,
 			(c = focustop(m)) && c->isfullscreen);
 
+	if (m)
+		strncpy(m->ltsymbol, m->lt[m->sellt]->symbol, LENGTH(m->ltsymbol));
 	if (m && m->lt[m->sellt]->arrange)
 		m->lt[m->sellt]->arrange(m);
 	motionnotify(0);
@@ -970,6 +973,7 @@ createmon(struct wl_listener *listener, void *data)
 		wlr_output_layout_add_auto(output_layout, wlr_output);
 	else
 		wlr_output_layout_add(output_layout, wlr_output, m->m.x, m->m.y);
+	strncpy(m->ltsymbol, m->lt[m->sellt]->symbol, LENGTH(m->ltsymbol));
 }
 
 void
@@ -1592,12 +1596,16 @@ void
 monocle(Monitor *m)
 {
 	Client *c;
+	int n = 0;
 
 	wl_list_for_each(c, &clients, link) {
 		if (!VISIBLEON(c, m) || c->isfloating || c->isfullscreen)
 			continue;
 		resize(c, m->w, 0);
+		n++;
 	}
+	if (n)
+		snprintf(m->ltsymbol, LENGTH(m->ltsymbol), "[%d]", n);
 	if ((c = focustop(m)))
 		wlr_scene_node_raise_to_top(&c->scene->node);
 }
@@ -1851,7 +1859,7 @@ printstatus(void)
 		printf("%s selmon %u\n", m->wlr_output->name, m == selmon);
 		printf("%s tags %u %u %u %u\n", m->wlr_output->name, occ, m->tagset[m->seltags],
 				sel, urg);
-		printf("%s layout %s\n", m->wlr_output->name, m->lt[m->sellt]->symbol);
+		printf("%s layout %s\n", m->wlr_output->name, m->ltsymbol);
 	}
 	fflush(stdout);
 }
@@ -2044,7 +2052,7 @@ setlayout(const Arg *arg)
 		selmon->sellt ^= 1;
 	if (arg && arg->v)
 		selmon->lt[selmon->sellt] = (Layout *)arg->v;
-	/* TODO change layout symbol? */
+	strncpy(selmon->ltsymbol, selmon->lt[selmon->sellt]->symbol, LENGTH(selmon->ltsymbol));
 	arrange(selmon);
 	printstatus();
 }