module Scrivito

# @api public
module Associations
  # Searches for CMS objects containing one or more attributes linking to this CMS object.
  #
  # So the search returns the CMS objects in which at least one +html+,
  # +link+, +linklist+, +reference+ or +referencelist+ attribute links to this CMS object.
  #
  # Attributes inside {Scrivito::BasicWidget Widgets} are considered, too.
  #
  # @return [Scrivito::ObjSearchEnumerator]
  # @api public
  def backlinks
    Obj.where(:*, :links_to, self)
  end

  # @api public
  module ClassMethods

    # Specifies a one-to-one association with another class.
    #
    # This method defines a foreign attribute for this class.
    # If the other class contains the foreign attribute, then you should use
    # {Scrivito::Associations::ClassMethods#has_many has_many} instead.
    #
    # This method defines a +reference+ attribute with the given +name+.
    # Only instances of +obj_class+ are valid values for this attribute.
    #
    # @example
    #   class Author < Obj
    #     attribute :first_name, :string
    #     attribute :last_name, :string
    #   end
    #
    #   class Book < Obj
    #     attribute :title, :string
    #     belongs_to :author
    #   end
    #
    #   s_hawking = Author.create(first_name: 'Stephen', last_name: 'Hawking')
    #   history_of_time = Book.create(title: 'A Brief History of Time', author: s_hawking)
    #
    #   history_of_time.author.first_name
    #   # => 'Stephen'
    #
    # @example with an optional +obj_class+
    #   class Book < Obj
    #     belongs_to 'publisher', obj_class: Person
    #   end
    #
    # @param [Symbol, String] name name of the attribute. See
    #   {Scrivito::AttributeContent::ClassMethods#attribute attribute} for details.
    # @param [Class] obj_class (optional) specifies (for use in the UI) the valid class
    #   _of_ _the_ _value_ in this attribute. If no +obj_class+ is given, an +obj_class+ is
    #   derived from the given +name+. For example, from the +name+ +'author'+
    #   the +obj_class+ +Author+ is derived.
    # @return [void]
    # @api public
    def belongs_to(name, obj_class: name)
      klass = to_single_class(obj_class)
      attribute(name, :reference, only: klass)
    end

    # Specifies a one-to-many association.
    #
    # This method defines a foreign attribute for this class.
    # If the other class contains the foreign attribute, then you should use
    # {Scrivito::Associations::ClassMethods#has_many has_many} instead.
    #
    # This method defines a +referencelist+ attribute with the given +name+.
    # Only instances of +obj_class+ are valid values for this attribute.
    #
    # @example
    #   class Author < Obj
    #     attribute :first_name, :string
    #     attribute :last_name, :string
    #   end
    #
    #   class Book < Obj
    #     attribute :title, :string
    #     belongs_to_many :authors
    #   end
    #
    #   s_hawking = Author.create(first_name: 'Stephen' last_name: 'Hawking')
    #   l_hawking = Author.create(first_name: 'Lucy', last_name: 'Hawking')
    #   secret_key_to_the_universe = Book.create(
    #       title: "George's Secret Key to the Universe", authors: [s_hawking, l_hawking])
    #
    #   secret_key_to_the_universe.authors.map(&:first_name)
    #   # => ['Stephen', 'Lucy']
    #
    # @example with an optional +obj_class+
    #   class Book < Obj
    #     belongs_to_many 'reviewers', obj_class: Person
    #   end
    #
    # @param [Symbol, String] name name of the attribute. See
    #   {Scrivito::AttributeContent::ClassMethods#attribute attribute} for details.
    # @param [Class] obj_class (optional) specifies (for use in the UI) the valid class
    #   _of_ _the_ _value_ in this attribute. If no +obj_class+ is given, an +obj_class+
    #   is derived from the given +name+. For example, from the +name+ +'authors'+ the +obj_class+
    #   +Author+ is derived.
    # @return [void]
    # @api public
    def belongs_to_many(name, obj_class: name)
      klass = to_single_class(obj_class)
      attribute(name, :referencelist, only: klass)
    end

    # Specifies a one-to-many or many-to-many association with another class.
    #
    # This method should only be used if the other class contains the foreign attribute.
    # If the current class contains the foreign attribute, then you should use
    # {Scrivito::Associations::ClassMethods#belongs_to belongs_to} or
    # {Scrivito::Associations::ClassMethods#belongs_to_many belongs_to_many} instead.
    #
    # This methods generates a new instance method +<name>+.
    # This newly generated method searches for all +obj_class+ instances,
    # where the +foreign_attribute+ references this instance.
    # This newly generated method returns an
    # {https://ruby-doc.org/core/Enumerable.html +Enumerable+} of {Scrivito::BasicObj BasicObjs}
    # instances.
    #
    # @example
    #   class Book < Obj
    #     attribute :title, :string
    #     belongs_to :author
    #   end
    #
    #   class Author < Obj
    #     attribute :first_name, :string
    #     attribute :last_name, :string
    #     has_many :books
    #   end
    #
    #   s_hawking = Author.create(first_name: 'Stephen', last_name: 'Hawking')
    #   history_of_time = Book.create(title: 'A Brief History of Time', author: s_hawking)
    #   grand_design = Book.create(title: 'The Grand Design', author: s_hawking)
    #
    #   s_hawking.books.to_a
    #   # => [<Book id='abc'>, <Book id='123'>]
    #
    #   s_hawking.books.map(&:title)
    #   # => ['A Brief History of Time', 'The Grand Design']
    #
    # @example with an optional +obj_class+ and +foreign_attribute+
    #   class Book < Obj
    #     belongs_to_many 'reviewers', obj_class: Person
    #   end
    #
    #   class Person < Obj
    #     has_many :reviewed_books, foreign_attribute: 'reviewers', obj_class: Book
    #   end
    #
    #   a_person = Person.all.first
    #   # => <Person id='456'>
    #
    #   a_person.reviewed_books.to_a
    #   # => [<Book id='abc'>, <Book id='123'>]
    #
    # @param [Symbol, String] name name of the search method.
    # @param [Class] obj_class (optional) limit search to instances of +obj_class+.
    #   If no +obj_class+ is given, the +obj_class+ is derived from the given +name+.
    #   For example, from the +name+ +'books'+ the +obj_class+ +Book+ is derived.
    # @param [Symbol, String] foreign_attribute (optional) name of the foreign attribute of the
    #   other class (e.g. as defined by
    #   {Scrivito::Associations::ClassMethods#belongs_to belongs_to} or
    #   {Scrivito::Associations::ClassMethods#belongs_to_many belongs_to_many}).
    #   If no +foreign_attribute+ is given, the foreign attribute is derived from this class.
    #   For example, from the class +Author+ the +foreign_attribute+ +[:author, :authors]+
    #   is derived.
    # @return [void]
    # @api public
    def has_many(name, obj_class: name, foreign_attribute: nil)
      klass = to_single_class(obj_class)
      attributes = to_attribute_names(foreign_attribute)

      define_method(name) do
        klass.where(attributes, :refers_to, self)
      end
    end

    private

    def to_single_class(value)
      return value if value.is_a?(Class)
      value.to_s.camelize.singularize.constantize
    end

    def to_attribute_names(foreign_attribute)
      return [foreign_attribute] if foreign_attribute

      single_attribute = to_s.demodulize.underscore
      [single_attribute, single_attribute.pluralize]
    end
  end
end

end