astuto/app/views/layouts/_header.html.erb

<nav class="navbar navbar-expand-lg navbar-light">
  <div class="container">
    <%= link_to "Astuto", root_path, class: "navbar-brand" %>
    <button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#navbarSupportedContent" aria-controls="navbarSupportedContent" aria-expanded="false" aria-label="Toggle navigation">
      <span class="navbar-toggler-icon"></span>
    </button>

    <div class="collapse navbar-collapse" id="navbarSupportedContent">
      <ul class="navbar-nav ml-auto">
        <% if user_signed_in? %>
          <% if current_user.moderator? || current_user.admin? %>
            <li class="nav-item">
              <%= link_to "Admin Panel", admin_root_path, class: "nav-link", 'data-turbolinks': 'false' %>
            </li>
          <% end %>
          <li class="nav-item dropdown">
            <a class="nav-link dropdown-toggle" href="#" id="navbarDropdown" role="button" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
              <%= image_tag(current_user.gravatar_url, class: "gravatar", alt: current_user.full_name, size: 24) %>
              <span class="fullname"><%= current_user.full_name %></span>
            </a>
            <div class="dropdown-menu" aria-labelledby="navbarDropdown">
              <%= link_to "Profile settings", edit_user_registration_path, class: "dropdown-item" %>
              <div class="dropdown-divider"></div>
              <%= link_to "Sign out", destroy_user_session_path, method: :delete, class: "dropdown-item" %>
            </div>
          </li>
        <% else %>
          <li class="nav-item">
            <%= link_to "Sign in / Sign up", new_user_session_path, class: "nav-link" %>
          </li>
        <% end %>
      </ul>
    </div>
  </div>
</nav>