src/derails/reaction_blur/renderer/collection_renderer.rb
# frozen_string_literal: true

require "reaction_blur/renderer/partial_renderer"

module ReactionBlur
  class PartialIteration
    # The number of iterations that will be done by the partial.
    attr_reader :size

    # The current iteration of the partial.
    attr_reader :index

    def initialize(size)
      @size  = size
      @index = 0
    end

    # Check if this is the first iteration of the partial.
    def first?
      index == 0
    end

    # Check if this is the last iteration of the partial.
    def last?
      index == size - 1
    end

    def iterate! # :nodoc:
      @index += 1
    end
  end

  class CollectionRenderer < PartialRenderer # :nodoc:
    include ObjectRendering

    class CollectionIterator # :nodoc:
      include Enumerable

      def initialize(collection)
        @collection = collection
      end

      def each(&blk)
        @collection.each(&blk)
      end

      def size
        @collection.size
      end

      def length
        @collection.respond_to?(:length) ? @collection.length : size
      end

      def preload!
        # no-op
      end
    end

    class SameCollectionIterator < CollectionIterator # :nodoc:
      def initialize(collection, path, variables)
        super(collection)
        @path      = path
        @variables = variables
      end

      def from_collection(collection)
        self.class.new(collection, @path, @variables)
      end

      def each_with_info
        return enum_for(:each_with_info) unless block_given?
        variables = [@path] + @variables
        @collection.each { |o| yield(o, variables) }
      end
    end

    class PreloadCollectionIterator < SameCollectionIterator # :nodoc:
      def initialize(collection, path, variables, relation)
        super(collection, path, variables)
        relation.skip_preloading! unless relation.loaded?
        @relation = relation
      end

      def from_collection(collection)
        self.class.new(collection, @path, @variables, @relation)
      end

      def each_with_info
        return super unless block_given?
        preload!
        super
      end

      def preload!
        @relation.preload_associations(@collection)
      end
    end

    class MixedCollectionIterator < CollectionIterator # :nodoc:
      def initialize(collection, paths)
        super(collection)
        @paths = paths
      end

      def each_with_info
        return enum_for(:each_with_info) unless block_given?
        @collection.each_with_index { |o, i| yield(o, @paths[i]) }
      end
    end

    def render_collection_with_partial(collection, partial, context, block)
      iter_vars  = retrieve_variable(partial)

      collection = if collection.respond_to?(:preload_associations)
        PreloadCollectionIterator.new(collection, partial, iter_vars, collection)
      else
        SameCollectionIterator.new(collection, partial, iter_vars)
      end

      template = find_template(partial, @locals.keys + iter_vars)

      layout = if !block && (layout = @options[:layout])
        find_template(layout.to_s, @locals.keys + iter_vars)
      end

      render_collection(collection, context, partial, template, layout, block)
    end

    def render_collection_derive_partial(collection, context, block)
      paths = collection.map { |o| partial_path(o, context) }

      if paths.uniq.length == 1
        # Homogeneous
        render_collection_with_partial(collection, paths.first, context, block)
      else
        if @options[:cached]
          raise NotImplementedError, "render caching requires a template. Please specify a partial when rendering"
        end

        paths.map! { |path| retrieve_variable(path).unshift(path) }
        collection = MixedCollectionIterator.new(collection, paths)
        render_collection(collection, context, nil, nil, nil, block)
      end
    end

    private
      def retrieve_variable(path)
        variable = local_variable(path)
        [variable, :"#{variable}_counter", :"#{variable}_iteration"]
      end

      def render_collection(collection, view, path, template, layout, block)
        identifier = (template && template.identifier) || path
        ActiveSupport::Notifications.instrument(
          "render_collection.reaction_blur",
          identifier: identifier,
          layout: layout && layout.virtual_path,
          count: collection.length
        ) do |payload|
          spacer = if @options.key?(:spacer_template)
            spacer_template = find_template(@options[:spacer_template], @locals.keys)
            build_rendered_template(spacer_template.render(view, @locals), spacer_template)
          else
            RenderedTemplate::EMPTY_SPACER
          end

          collection_body = if template
            cache_collection_render(payload, view, template, collection) do |filtered_collection|
              collection_with_template(view, template, layout, filtered_collection)
            end
          else
            collection_with_template(view, nil, layout, collection)
          end

          return RenderedCollection.empty(@lookup_context.formats.first) if collection_body.empty?

          build_rendered_collection(collection_body, spacer)
        end
      end

      def collection_with_template(view, template, layout, collection)
        locals = @locals
        cache = {}

        partial_iteration = PartialIteration.new(collection.size)

        collection.each_with_info.map do |object, (path, as, counter, iteration)|
          index = partial_iteration.index

          locals[as]        = object
          locals[counter]   = index
          locals[iteration] = partial_iteration

          _template = (cache[path] ||= (template || find_template(path, @locals.keys + [as, counter, iteration])))

          content = _template.render(view, locals, implicit_locals: [counter, iteration])
          content = layout.render(view, locals) { content } if layout
          partial_iteration.iterate!
          build_rendered_template(content, _template)
        end
      end
  end
end
