1 files changed, 86 insertions, 0 deletions

diff --git a/app/models/concerns/nested_tree.rb b/app/models/concerns/nested_tree.rb
new file mode 100644
index 0000000..9a2eb0e
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+++ b/app/models/concerns/nested_tree.rb
@@ -0,0 +1,86 @@
+# app/models/concerns/nested_tree.rb
+#
+# Minimal parent_id-based replacement for the tree-traversal subset of
+# awesome_nested_set actually used by this app (descendants, ancestors,
+# level, root, move_to_child_of)
+module NestedTree
+  extend ActiveSupport::Concern
+
+  included do
+    belongs_to :parent, class_name: name, foreign_key: :parent_id, optional: true, inverse_of: :children
+    has_many :children, -> { order(:id) }, class_name: name, foreign_key: :parent_id, inverse_of: :parent
+
+    before_destroy :delete_descendants
+  end
+
+  class_methods do
+    def root
+      roots.first
+    end
+
+    def roots
+      where(parent_id: nil)
+    end
+
+    def valid?
+      # Every non-root row's parent_id must point at a real, existing row.
+      where.not(parent_id: nil).where.missing(:parent).none?
+    end
+  end
+
+  def root?
+    parent_id.nil?
+  end
+
+  def ancestors
+    result = []
+    current = parent
+    while current
+      result << current
+      current = current.parent
+    end
+    result
+  end
+
+  def level
+    ancestors.size
+  end
+
+  def descendants
+    ids = []
+    queue = self.class.where(parent_id: id).pluck(:id)
+    until queue.empty?
+      ids.concat(queue)
+      queue = self.class.where(parent_id: queue).pluck(:id)
+    end
+    self.class.where(id: ids)
+  end
+
+  def self_and_descendants
+    self.class.where(id: [id] + descendants.pluck(:id))
+  end
+
+  def self_and_descendants_ordered_with_level
+    nodes = [self] + descendants.to_a
+    children_by_parent = nodes.group_by(&:parent_id)
+    children_by_parent.each_value { |list| list.sort_by!(&:id) }
+
+    result = []
+    visit = ->(node, level) do
+      result << [node, level]
+      (children_by_parent[node.id] || []).each { |child| visit.call(child, level + 1) }
+    end
+    visit.call(self, 0)
+    result
+  end
+
+  def move_to_child_of(new_parent)
+    update!(parent_id: new_parent.id)
+  end
+
+  private
+
+  def delete_descendants
+    self.class.where(id: descendants.pluck(:id)).delete_all
+  end
+end