module Outpost
  module Aggregator
    module JsonInput
      extend ActiveSupport::Concern

      # The default simple JSON for all objects.
      # This catches one-to-one and many-to-one associations.
      # It should be overridden for many-to-many associations.
      def simple_json
        @simple_json ||= {
          "id" => self.respond_to?(:obj_key) ? self.obj_key : self.id
        }
      end

      module ClassMethods
        def accepts_json_input_for(name)
          include InstanceMethodsOnActivation

          # The current collection as simple_json
          define_method "current_#{name}_json" do
            current_json_for(name)
          end

          # The current collection as simple_json and then
          # converted to real JSON.
          define_method "#{name}_json" do
            current_json_for(name).to_json
          end

          define_method "#{name}_json=" do |json|
            process_json_input_for(name.to_s, json)
          end
        end
      end


      module InstanceMethodsOnActivation
        def current_json_for(name)
          Aggregator.array_to_simple_json(self.send(name))
        end

        def process_json_input_for(name, json)
          return if json.empty?
          name = name.to_s
          reflection = self.class.reflect_on_association(name.to_sym)

          json = Array(JSON.parse(json)).sort_by { |c| c["position"].to_i }


          if reflection.collection?
            loaded = []

            json.each do |object_hash|
              if object = Outpost.obj_by_key(object_hash["id"])
                new_object = build_association_for(name, object_hash, object)
                loaded.push(new_object) if new_object
              end
            end

            loaded_json  = Aggregator.array_to_simple_json(loaded)
            current_json = current_json_for(name)

            if current_json != loaded_json
              # This actually opens a DB transaction and saves stuff.
              # This is Rails behavior.
              self.send("#{name}=", loaded)
            end
          else
            object_hash = json.first

            if object_hash.present?
              if object = Outpost.obj_by_key(object_hash["id"])
                build_association_for(name, object_hash, object)
              end
            else
              self.send("#{name}=", nil)
            end
          end

          self.send(name)
        end


        private

        def build_association_for(name, object_hash, object)
          self.send("build_#{name.singularize}_association", object_hash, object)
        end
      end
    end
  end
end