class ActionText::PlainTextConversion::BottomUpReducer

def initialize(node)
  @node = node
  @values = {}
end

def reduce(&block)
  traverse_bottom_up(@node) do |n|
    child_values = @values.values_at(*n.children)
    @values[n] = block.call(n, child_values)
  end
  @values[@node]
end

def traverse_bottom_up(node, &block)
  call_stack, processing_stack = [ node ], []
  until call_stack.empty?
    node = call_stack.pop
    processing_stack.push(node)
    call_stack.concat node.children
  end
  processing_stack.reverse_each(&block)
end