Enable creation of subunits

app/views/units/_form.html.erb

@@ -1,6 +1,6 @@
 <%= fields_for @unit do |form| %>
   <tr id="<%= dom_id(@unit) %>" onkeydown="processKey(event)">
-    <td>
+    <td class="<%= class_names({subunit: @unit.base}) %>">
       <%= form.text_field :symbol, form: :unit_form, required: true, autofocus: true, size: 12,
         maxlength: @unit.class.columns_hash['symbol'].limit, autocomplete: "off" %>
     </td>
@@ -10,8 +10,9 @@
     </td>
     <td>
       <% unless @unit.base.nil? %>
-        <%= form.number_field :multiplier, form: :unit_form, step: "any", size: 10,
-          autocomplete: "off" %>
+        <%= form.hidden_field :base_id, form: :unit_form %>
+        <%= form.number_field :multiplier, form: :unit_form, required: true, step: "any",
+          size: 10, autocomplete: "off" %>
       <% end %>
     </td>
 
@@ -23,4 +24,3 @@
   </tr>
   <!-- TODO: display error_messages_for unit -->
 <% end %>
-

app/views/units/_unit.html.erb

@@ -1,11 +1,17 @@
-<tr>
-  <td class="link">
-    <%= link_to unit.symbol, edit_unit_path(unit), class: unit.base.nil? ? '' : 'subunit' %>
+<tr id="<%= dom_id(unit) %>">
+  <td class="<%= class_names('link', {subunit: unit.base}) %>">
+    <%= link_to unit.symbol, edit_unit_path(unit) %>
   </td>
   <td><%= unit.name %></td>
   <td class="number"><%= scientifize(unit.multiplier) if unit.multiplier %></td>
+
   <% if current_user.at_least(:active) %>
     <td class="actions">
+      <% if unit.base.nil? %>
+        <%= image_link_to t(".add_subunit"), "plus-outline", new_unit_path(unit),
+          onclick: 'this.blur();', data: {turbo_stream: true} %>
+      <% end %>
+
       <%= image_button_to t(".delete_unit"), "delete-outline", unit_path(unit),
         method: :delete %>
     </td>

app/views/units/new.turbo_stream.erb

@@ -1,5 +1,13 @@
-<%= turbo_stream.prepend :units do %>
-  <%= render partial: 'form' %>
+<%= turbo_stream.disable :add_unit %>
+<%= turbo_stream.disable_all 'td.actions .button' %>
+
+<% case %>
+<% when @unit.errors.present? %>
+  <%= turbo_stream.replace @unit, partial: 'form' %>
+<% when @unit.base.nil? %>
+  <%= turbo_stream.prepend :units, partial: 'form' %>
+<% else %>
+  <%= turbo_stream.after @unit.base, partial: 'form' %>
 <% end %>
 
 <%= turbo_stream.update :unit_form_frame do %>