feat: collapsable hierarchical view

lib/components_elixir/inventory/hierarchical.ex

@@ -275,4 +275,60 @@ defmodule ComponentsElixir.Inventory.Hierarchical do
       [child | sort_children_recursively(entities, child.id, parent_id_accessor_fn)]
     end)
   end
+
+  @doc """
+  Calculates component counts for an entity and all its descendants.
+  Returns a tuple of {self_count, children_count, total_count}.
+
+  ## Parameters
+    - entity_id: The ID of the entity to count for
+    - all_entities: List of all entities in the hierarchy
+    - parent_id_accessor_fn: Function to get parent_id from an entity
+    - count_fn: Function that takes an entity_id and returns the direct count for that entity
+
+  ## Examples
+      iex> count_fn = fn id -> MyRepo.count_components_for(id) end
+      iex> Hierarchical.count_with_descendants(1, entities, &(&1.parent_id), count_fn)
+      {3, 7, 10}  # 3 in self, 7 in children, 10 total
+  """
+  def count_with_descendants(entity_id, all_entities, parent_id_accessor_fn, count_fn) do
+    # Get direct count for this entity
+    self_count = count_fn.(entity_id)
+
+    # Get all descendant entity IDs (excluding self)
+    all_descendant_ids = descendant_ids(all_entities, entity_id, parent_id_accessor_fn)
+    descendant_ids_only = List.delete(all_descendant_ids, entity_id)
+
+    # Sum counts for all descendants
+    children_count = Enum.reduce(descendant_ids_only, 0, fn id, acc ->
+      acc + count_fn.(id)
+    end)
+
+    {self_count, children_count, self_count + children_count}
+  end
+
+  @doc """
+  Formats component count display based on expansion state.
+
+  When collapsed: Shows total count only: "10 components"
+  When expanded: Shows breakdown: "10 components (3 self, 7 children)"
+
+  ## Parameters
+    - self_count: Number of components directly in this entity
+    - children_count: Number of components in all descendant entities
+    - is_expanded: Whether the entity is currently expanded
+    - singular_noun: What to call a single item (default: "component")
+    - plural_noun: What to call multiple items (default: "components")
+  """
+  def format_count_display(self_count, children_count, is_expanded, singular_noun \\ "component", plural_noun \\ "components") do
+    total_count = self_count + children_count
+
+    count_noun = if total_count == 1, do: singular_noun, else: plural_noun
+
+    if is_expanded and children_count > 0 do
+      "#{total_count} #{count_noun} (#{self_count} self, #{children_count} children)"
+    else
+      "#{total_count} #{count_noun}"
+    end
+  end
 end