<% # expects subscription and current_user %>
<%= form_for([current_user, subscription],
  method: subscription.new_record? ? 'post' : 'delete',
  html: { 
    class: 'ajax-create-destroy', 
    data: { 
      create_value: ts('Subscribe'),
      destroy_value: ts('Unsubscribe')
    }
  }) do |f| %>
  <%= f.hidden_field :subscribable_id %>
  <%= f.hidden_field :subscribable_type %>
  <%= f.submit subscription.new_record? ? ts('Subscribe') : ts('Unsubscribe') %>
<% end %>