module Pruning
  module Processing
    # Contains methods that store the tree and prune everything 
    # except the branches with requested indicator 
    class Pruner
      def initialize(tree)
        @tree = tree
      end

      def prune_tree(indicator_ids)
        pruned_tree = @tree
        prune_subtree(pruned_tree, indicator_ids)
        pruned_tree
      end

      private

      # Depth First Search implementation 
      # With pruning on the same sweep 
      def prune_subtree(nodes, indicator_ids)
        nodes_to_examine = nodes.dup
        nodes_to_examine.each do |node|
          if indicator_node?(node)
            indicator_not_wanted = !indicator_ids.include?(node['id'])
            nodes.delete(node) if indicator_not_wanted
          else
            no_wanted_children = prune_subtree(children(node), indicator_ids)
            nodes.delete(node) if no_wanted_children
          end
        end
        nodes.empty?
      end

      def children(node)
        node.fetch('sub_themes', false) ||
          node.fetch('categories', false) ||
          node.fetch('indicators', false) ||
          []
      end

      def indicator_node?(node)
        children(node).empty?
      end
    end
  end
end