module ActionView::CollectionCaching

def automatic_cache_eligible?
  single_template_render? && !callable_cache_key? &&
    @template.eligible_for_collection_caching?(as: @options[:as])
end

def cache_collection?
  @options.fetch(:cache, automatic_cache_eligible?)
end

def cache_collection_render
  return yield unless cache_collection?
  keyed_collection = collection_by_cache_keys
  partial_cache = collection_cache.read_multi(*keyed_collection.keys)
  @collection = keyed_collection.reject { |key, _| partial_cache.key?(key) }.values
  rendered_partials = @collection.any? ? yield.dup : []
  fetch_or_cache_partial(partial_cache, order_by: keyed_collection.each_key) do
    rendered_partials.shift
  end
end

def callable_cache_key?
  @options[:cache].respond_to?(:call)
end

def collection_by_cache_keys
  seed = callable_cache_key? ? @options[:cache] : ->(i) { i }
  @collection.each_with_object({}) do |item, hash|
    hash[expanded_cache_key(seed.call(item))] = item
  end
end

def expanded_cache_key(key)
  key = @view.fragment_cache_key(@view.cache_fragment_name(key, virtual_path: @template.virtual_path))
  key.frozen? ? key.dup : key # #read_multi & #write may require mutability, Dalli 2.6.0.
end

def fetch_or_cache_partial(cached_partials, order_by:)
  cache_options = @options[:cache_options] || @locals[:cache_options] || {}
  order_by.map do |key|
    cached_partials.fetch(key) do
      yield.tap do |rendered_partial|
        collection_cache.write(key, rendered_partial, cache_options)
      end
    end
  end
end

def single_template_render?
  @template # Template is only set when a collection renders one template.
end