require 'active_support/core_ext/object/try'

module ActionView
  module CollectionCaching # :nodoc:
    extend ActiveSupport::Concern

    included do
      # Fallback cache store if Action View is used without Rails.
      # Otherwise overridden in Railtie to use Rails.cache.
      mattr_accessor(:collection_cache) { ActiveSupport::Cache::MemoryStore.new }
    end

    private
      def cache_collection_render
        return yield unless cache_collection?

        keyed_collection = collection_by_cache_keys
        cached_partials = collection_cache.read_multi(*keyed_collection.keys)

        @collection = keyed_collection.reject { |key, _| cached_partials.key?(key) }.values
        rendered_partials = @collection.empty? ? [] : yield

        index = 0
        keyed_collection.map do |cache_key, _|
          cached_partials.fetch(cache_key) do
            rendered_partials[index].tap { index += 1 }
          end
        end
      end

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

      def automatic_cache_eligible?
        @template && @template.eligible_for_collection_caching?(as: @options[:as])
      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 collection_cache_rendered_partial(rendered_partial, key_by)
        if callable_cache_key?
          key = expanded_cache_key(@options[:cache].call(key_by))
          collection_cache.write(key, rendered_partial, @options[:cache_options])
        end
      end
  end
end