Arbre content caching for ActiveAdmin

cache_arbre.rb

# Caches Arbre elements in the `Rails.cache`.
#
# Yielding the first time adds to the output buffer regardless of the
# returned value. A cache miss must be handled separately from a hit
# to avoid double rendering.
#
# Returns yielded Arbre on cache miss OR an HTML string wrapped in
# an text node on cache hit.
def cache_arbre(context, *args, &block)
  if controller.perform_caching
    if Rails.cache.exist?(*args)
      context.text_node(Rails.cache.read(*args))
    else
      Rails.cache.write(*args, arbre_appended_children_content(context, &block))
    end
  else
    yield
  end
end

# Returns HTML content for Arbre elements appended to a context.
#
# Due to the complexities of Arbre content buffering it is difficult to get
# the content of an arbitrary set of Arbre elements without the use of a
# wrapping element like a `div`.
#
# Example
#
#    Arbre::Context.new do
#      h1 "Capturing Children Content"
#
#      content = arbre_appended_children_content(self) do
#        para "Paragraph 1"
#        para "Paragraph 2"
#      end
#    end
#
#    content # => "<p>Paragraph 1</p>\n<p>Paragraph 2</p>\n"
#
# Unlike this simple example which only returns the content of Paragraph 2
# because it is the only object returned from the block.
#
#    Arbre::Context.new do
#      h1 "Example of "
#
#      content = begin
#        para "Vanishing Paragraph 1"
#        para "Paragraph 2"
#      end.to_s
#    end
#
#    content # => "<p>Paragraph 2</p>\n"
#
def arbre_appended_children_content(context)
  children      = context.current_arbre_element.children
  original_size = children.size
  content       = "".html_safe
  result        = yield

  if (children.size > original_size)
    content = "".html_safe

    children[original_size .. -1].each do |child|
      content << child.to_s
    end
  else
    # No children added, return the output from yield. This could be when
    # content was generated from a partial via `render`.
    content = result.to_s
  end

  content
end