countdown-symfony/templates/admin/_start_form.html.twig

{% if counter.state is same as 'ready' %}
    <a class="btn" href="{{ path('app_admin_start', {'id': counter.id}) }}">{{ "start" | trans }}</a>
{% elseif counter.state is same as 'completed' %}
    <a class="btn" href="{{ path('app_admin_reset', {'id': counter.id}) }}">{{ "Reset" | trans }}</a>
{% endif %}