module Hanami
  module Model
    # Mapped proxy for ROM relations.
    #
    # It eliminates the need to use #as for repository queries
    #
    # @since 1.0.0
    # @api private
    class MappedRelation < SimpleDelegator
      # Mapper name.
      #
      # With ROM mapping there is a link between the entity class and a generic
      # reference for it. Example: <tt>BookRepository</tt> references <tt>Book</tt>
      # as <tt>:entity</tt>.
      #
      # @since 1.0.0
      # @api private
      MAPPER_NAME = :entity

      # @since 1.0.0
      # @api private
      def self.mapper_name
        MAPPER_NAME
      end

      # @since 1.0.0
      # @api private
      def initialize(relation)
        @relation = relation
        super(relation.as(self.class.mapper_name))
      end

      # Access low level relation's attribute
      #
      # @param attribute [Symbol] the attribute name
      #
      # @return [ROM::SQL::Attribute] the attribute
      #
      # @raise [Hanami::Model::UnknownAttributeError] if the attribute cannot be found
      #
      # @since 1.2.0
      #
      # @example
      #   class UserRepository < Hanami::Repository
      #     def by_matching_name(name)
      #       users
      #         .where(users[:name].ilike(name))
      #         .map_to(User)
      #         .to_a
      #     end
      #   end
      def [](attribute)
        @relation[attribute]
      rescue KeyError => e
        raise UnknownAttributeError.new(e.message)
      end
    end
  end
end