module ActiveRecord
  class Base

    class << self

      # Interprets a polymorphic row from a unified SELECT, returning the appropriate ActiveRecord instance. Overrides ActiveRecord::Base.instantiate_without_callbacks.
      def instantiate_with_polymorphic_checks(record)
        if record['polymorphic_parent_class']
          reflection = record['polymorphic_parent_class'].constantize.reflect_on_association(record['polymorphic_association_id'].to_sym)
#          _logger_debug "Instantiating a polymorphic row for #{record['polymorphic_parent_class']}.reflect_on_association(:#{record['polymorphic_association_id']})"

          # rewrite the record with the right column names
          table_aliases = reflection.options[:table_aliases].dup
          record = Hash[*table_aliases.keys.map {|key| [key, record[table_aliases[key]]] }.flatten]

          # find the real child class
          klass = record["#{self.table_name}.#{reflection.options[:polymorphic_type_key]}"].constantize
          if sti_klass = record["#{klass.table_name}.#{klass.inheritance_column}"]
            klass = klass.class_eval do compute_type(sti_klass) end # in case of namespaced STI models
          end

          # check that the join actually joined to something
          unless (child_id = record["#{self.table_name}.#{reflection.options[:polymorphic_key]}"]) == record["#{klass.table_name}.#{klass.primary_key}"]
            raise ActiveRecord::Associations::PolymorphicError,
              "Referential integrity violation; child <#{klass.name}:#{child_id}> was not found for #{reflection.name.inspect}"
          end

          # eject the join keys
          # XXX not very readable
          record = Hash[*record._select do |column, value|
            column[/^#{klass.table_name}/]
          end.map do |column, value|
            [column[/\.(.*)/, 1], value]
          end.flatten]

          # allocate and assign values
          klass.allocate.tap do |obj|
            obj.instance_variable_set("@attributes", record)
            obj.instance_variable_set("@attributes_cache", Hash.new)

            if obj.respond_to_without_attributes?(:after_find)
              obj.send(:callback, :after_find)
            end

            if obj.respond_to_without_attributes?(:after_initialize)
              obj.send(:callback, :after_initialize)
            end

          end
        else
          instantiate_without_polymorphic_checks(record)
        end
      end

      alias_method_chain :instantiate, :polymorphic_checks
    end

  end
end