truncatechars function
Truncate to at most max characters, adding ellipsis if truncated.
Implementation
String truncatechars(String s, int max, {String ellipsis = '...'}) {
if (max <= 0) return '';
if (s.length <= max) return s;
if (ellipsis.length >= max) return ellipsis.substring(0, max);
return s.substring(0, max - ellipsis.length) + ellipsis;
}