module Recurso
  module Queries
    class Relation

      def initialize(identity, resource, relation_name, all_columns: true, action: :view)
        @identity = identity
        @resource = resource
        @relation = resource.send(relation_name)
        @all_columns = all_columns
        @action = action
      end

      def resources
        @resources ||= join_permissions
          .select("#{@relation.table_name}.#{@all_columns ? :* : :id}")
          .where(coalesce(@action))
          .distinct
      end

      private

      def join_permissions
        @relation.relevant_associations.reduce(@relation) do |result, assoc|
          result.joins(through_join_for(assoc)).joins("
            LEFT OUTER JOIN #{permission_class.table_name} #{assoc.name}_permissions
            ON  #{assoc.name}_permissions.resource_type = '#{assoc.class_name}'
            AND #{assoc.name}_permissions.resource_id   = #{resource_id_for(assoc)}
            AND #{assoc.name}_permissions.#{identity_foreign_key} = #{@identity.id.to_i}
          ")
        end
      end

      def resource_id_for(assoc)
        "#{(assoc.through_reflection || assoc.active_record).table_name}.#{assoc.foreign_key}"
      end

      def through_join_for(assoc)
        return unless through = assoc.through_reflection
        "
          LEFT OUTER JOIN #{through.table_name}
          ON #{through.table_name}.#{through.association_primary_key} = #{resource_id_for(through)}
        "
      end

      def coalesce(action)
        "coalesce(#{level_columns}) IN (#{level_values(action)})"
      end

      def level_columns
        @relation.relevant_associations.map { |assoc| "#{assoc.name}_permissions.level" }.join(',')
      end

      def level_values(action)
        @resource.relevant_levels_for(action).map { |level| permission_class.levels[level] }.join(',')
      end

      def permission_class
        @permission_class ||= Recurso::Config.instance.permission_class_name_for(@identity.class).constantize
      end

      def identity_foreign_key
        @identity_foreign_key ||= Recurso::Config.instance.identity_foreign_key_for(@identity.class)
      end
    end
  end
end