Fix subtopics method

app/controllers/tag_controller.rb

@@ -242,6 +242,35 @@ def related
     render partial: 'tag/related', layout: false, locals: { tags: @tags }
   end
 
+  def subtopics
+    @topic = (params[:subtopic] || params[:topic] || params[:id]).to_s.strip
+    if @topic.blank?
+      @subtopics = []
+    else
+      parent_tag = Tag.find_by(name: "parent:#{@topic}")
+      node_subtopics = parent_tag ? parent_tag.nodes.where(status: 1) : []
+      node_slugs = node_subtopics.collect(&:slug).compact.uniq
+
+      if node_slugs.present?
+        @subtopics = Tag.where(name: node_slugs).or(Tag.where(parent: @topic)).order(:name)
+      else
+        @subtopics = Tag.where(parent: @topic).order(:name)
+      end
+
+      existing_names = @subtopics.collect(&:name)
+      missing_slugs = node_slugs - existing_names
+      if missing_slugs.present?
+        missing_tags = missing_slugs.map { |slug| Tag.new(name: slug) }
+        @subtopics = @subtopics.to_a + missing_tags
+        @subtopics.sort_by!(&:name)
+      end
+    end
+
+    render partial: 'tag/subtopics', layout: false, locals: { subtopics: @subtopics, topic: @topic }
+  end
+
+  def topic_tree; end
+
   def widget
     num = params[:n] || 4
     nids = Tag.find_nodes_by_type(params[:id], 'note', num).collect(&:nid)
@@ -566,6 +595,4 @@ def fetch_counts
       @nodes.size
     end
   end
-
-  def topic_tree; end
 end

app/views/tag/_subtopic.html.erb

@@ -0,0 +1 @@
+<%= render partial: 'tag/subtopics', locals: { subtopics: local_assigns[:subtopics] || @subtopics, topic: local_assigns[:topic] || @topic } %>

app/views/tag/_subtopics.html.erb

@@ -0,0 +1,19 @@
+<% list = local_assigns[:subtopics] || @subtopics %>
+<% if list.present? %>
+  <% list.each do |subtopic| %>
+    <% name = subtopic.respond_to?(:name) ? subtopic.name : (subtopic.respond_to?(:slug) ? subtopic.slug : subtopic.to_s) %>
+    <div class="topic-item" data-topic="<%= name %>">
+      <div class="list-group-item list-group-item-action d-flex align-items-center">
+        <span class="expand-btn" data-topic="<%= name %>" style="cursor: pointer; margin-right: 5px;" title="Expand subtopics">
+          &emsp;<i class="fa fa-chevron-right icon"></i>
+        </span>
+        <a href="/<%= name %>" style="color: inherit; text-decoration: none;" class="flex-grow-1">&nbsp;<%= name %></a>
+      </div>
+      <div class="subtopics-container list-group" style="display: none; margin-left: 20px;"></div>
+    </div>
+  <% end %>
+<% else %>
+  <div class="list-group-item text-muted" style="font-style: italic;">
+    &emsp;No subtopics found
+  </div>
+<% end %>

config/routes.rb

@@ -208,6 +208,8 @@
   get 'blog2/:id' => 'tag#blog2'
   get 'tags' => 'tag#index'
   get 'tags/related(/:id)' => 'tag#related'
+  get 'tags/subtopics(/:subtopic)' => 'tag#subtopics'
+  get 'tags/subtopic(/:subtopic)' => 'tag#subtopics'
   get 'tags/:id' => redirect('/tag/:id')
   post 'tag/suggested/:id' => 'tag#suggested'
   get 'tag/author/:id.json' => 'tag#author'

test/fixtures/node_tags.yml

@@ -284,3 +284,10 @@ sub_tag:
   tid: 37
   nid: 1
   uid: 2
+
+subtopic_node_tag:
+  tid: 38
+  uid: 1
+  nid: 2
+  date: <%= DateTime.now.to_i %>
+

test/fixtures/tags.yml

@@ -150,3 +150,12 @@ hidden_response_tag:
 subscribed_tag:
   tid: 37
   name: sub:tag
+
+subtopic_parent_tag:
+  tid: 38
+  name: parent:water
+
+subtopic_child_tag:
+  tid: 39
+  name: about
+

test/functional/tag_controller_test.rb

@@ -694,4 +694,52 @@ def setup
     assert_not_nil comments
     assert_template 'comments/_comments'
   end
+
+  test 'subtopics partial with parent column tag' do
+    get :subtopics, params: { subtopic: 'spectrometry' }
+    assert_response :success
+    assert_not_nil assigns(:subtopics)
+    assert_includes assigns(:subtopics).map(&:name), 'spectrometer'
+    assert_template partial: 'tag/_subtopics'
+    assert_select '.topic-item[data-topic="spectrometer"]'
+  end
+
+  test 'subtopics partial with parent:tagname on node' do
+    get :subtopics, params: { subtopic: 'water' }
+    assert_response :success
+    assert_not_nil assigns(:subtopics)
+    assert_includes assigns(:subtopics).map(&:name), 'about'
+    assert_template partial: 'tag/_subtopics'
+    assert_select '.topic-item[data-topic="about"]'
+  end
+
+  test 'subtopics accepts topic parameter alias' do
+    get :subtopics, params: { topic: 'water' }
+    assert_response :success
+    assert_not_nil assigns(:subtopics)
+    assert_includes assigns(:subtopics).map(&:name), 'about'
+  end
+
+  test 'subtopics with missing or empty parameter' do
+    get :subtopics, params: { subtopic: '' }
+    assert_response :success
+    assert_equal [], assigns(:subtopics)
+    assert_select '.text-muted'
+  end
+
+  test 'subtopics with nonexistent topic returns empty list message' do
+    get :subtopics, params: { subtopic: 'nonexistent-topic-xyz' }
+    assert_response :success
+    assert_equal [], assigns(:subtopics)
+    assert_select '.text-muted'
+  end
+
+  test 'topic_tree page renders correctly with expandable topics' do
+    get :topic_tree
+    assert_response :success
+    assert_select '#accordion'
+    assert_select '.topic-item'
+    assert_select '.expand-btn'
+    assert_select '.subtopics-container'
+  end
 end