module DataMapper
  module Associations
    module ManyToMany #:nodoc:
      class Relationship < Associations::OneToMany::Relationship
        extend Chainable

        OPTIONS = superclass::OPTIONS.dup << :through << :via

        # Returns a set of keys that identify the target model
        #
        # @return [DataMapper::PropertySet]
        #   a set of properties that identify the target model
        #
        # @api semipublic
        def child_key
          return @child_key if defined?(@child_key)

          repository_name = child_repository_name || parent_repository_name
          properties      = child_model.properties(repository_name)

          @child_key = if @child_properties
            child_key = properties.values_at(*@child_properties)
            properties.class.new(child_key).freeze
          else
            properties.key
          end
        end

        # @api semipublic
        alias_method :target_key, :child_key

        # Intermediate association for through model
        # relationships
        #
        # Example: for :bugs association in
        #
        # class Software::Engineer
        #   include DataMapper::Resource
        #
        #   has n, :missing_tests
        #   has n, :bugs, :through => :missing_tests
        # end
        #
        # through is :missing_tests
        #
        # TODO: document a case when
        # through option is a model and
        # not an association name
        #
        # @api semipublic
        def through
          return @through if defined?(@through)

          @through = options[:through]

          if @through.kind_of?(Associations::Relationship)
            return @through
          end

          model           = source_model
          repository_name = source_repository_name
          relationships   = model.relationships(repository_name)
          name            = through_relationship_name

          @through = relationships[name] ||
            DataMapper.repository(repository_name) do
              model.has(min..max, name, through_model, one_to_many_options)
            end

          @through.child_key

          @through
        end

        # @api semipublic
        def via
          return @via if defined?(@via)

          @via = options[:via]

          if @via.kind_of?(Associations::Relationship)
            return @via
          end

          name            = self.name
          through         = self.through
          repository_name = through.relative_target_repository_name
          through_model   = through.target_model
          relationships   = through_model.relationships(repository_name)
          singular_name   = DataMapper::Inflector.singularize(name.to_s).to_sym

          @via = relationships[@via] ||
            relationships[name]      ||
            relationships[singular_name]

          @via ||= if anonymous_through_model?
            DataMapper.repository(repository_name) do
              through_model.belongs_to(singular_name, target_model, many_to_one_options)
            end
          else
            raise UnknownRelationshipError, "No relationships named #{name} or #{singular_name} in #{through_model}"
          end

          @via.child_key

          @via
        end

        # @api semipublic
        def links
          return @links if defined?(@links)

          @links = []
          links  = [ through, via ]

          while relationship = links.shift
            if relationship.respond_to?(:links)
              links.unshift(*relationship.links)
            else
              @links << relationship
            end
          end

          @links.freeze
        end

        # Initialize the chain for "many to many" relationships
        #
        # @return [self]
        #
        # @api public
        def finalize
          through
          via
          self
        end

        # @api private
        def source_scope(source)
          { through.inverse => source }
        end

        # @api private
        def query
          # TODO: consider making this a query_for method, so that ManyToMany::Relationship#query only
          # returns the query supplied in the definition
          @many_to_many_query ||= super.merge(:links => links).freeze
        end

        # Eager load the collection using the source as a base
        #
        # @param [Resource, Collection] source
        #   the source to query with
        # @param [Query, Hash] other_query
        #   optional query to restrict the collection
        #
        # @return [ManyToMany::Collection]
        #   the loaded collection for the source
        #
        # @api private
        def eager_load(source, other_query = nil)
          # FIXME: enable SEL for m:m relationships
          source.model.all(query_for(source, other_query))
        end

        private

        # @api private
        def through_model
          namespace, name = through_model_namespace_name

          if namespace.const_defined?(name)
            namespace.const_get(name)
          else
            Model.new(name, namespace) do
              # all properties added to the anonymous through model are keys
              def property(name, type, options = {})
                options[:key] = true
                options.delete(:index)
                super
              end
            end
          end
        end

        # @api private
        def through_model_namespace_name
          target_parts = target_model.base_model.name.split('::')
          source_parts = source_model.base_model.name.split('::')

          name = [ target_parts.pop, source_parts.pop ].sort.join

          namespace = Object

          # find the common namespace between the target_model and source_model
          target_parts.zip(source_parts) do |target_part, source_part|
            break if target_part != source_part
            namespace = namespace.const_get(target_part)
          end

          return namespace, name
        end

        # @api private
        def through_relationship_name
          if anonymous_through_model?
            namespace = through_model_namespace_name.first
            relationship_name = DataMapper::Inflector.underscore(through_model.name.sub(/\A#{namespace.name}::/, '')).tr('/', '_')
            DataMapper::Inflector.pluralize(relationship_name).to_sym
          else
            options[:through]
          end
        end

        # Check if the :through association uses an anonymous model
        #
        # An anonymous model means that DataMapper creates the model
        # in-memory, and sets the relationships to join the source
        # and the target model.
        #
        # @return [Boolean]
        #   true if the through model is anonymous
        #
        # @api private
        def anonymous_through_model?
          options[:through] == Resource
        end

        # @api private
        def nearest_relationship
          return @nearest_relationship if defined?(@nearest_relationship)

          nearest_relationship = self

          while nearest_relationship.respond_to?(:through)
            nearest_relationship = nearest_relationship.through
          end

          @nearest_relationship = nearest_relationship
        end

        # @api private
        def valid_target?(target)
          relationship = via
          source_key   = relationship.source_key
          target_key   = relationship.target_key

          target.kind_of?(target_model) &&
          source_key.valid?(target_key.get(target))
        end

        # @api private
        def valid_source?(source)
          relationship = nearest_relationship
          source_key   = relationship.source_key
          target_key   = relationship.target_key

          source.kind_of?(source_model) &&
          target_key.valid?(source_key.get(source))
        end

        chainable do
          # @api semipublic
          def many_to_one_options
            { :parent_key => target_key.map { |property| property.name } }
          end

          # @api semipublic
          def one_to_many_options
            { :parent_key => source_key.map { |property| property.name } }
          end
        end

        # Returns the inverse relationship class
        #
        # @api private
        def inverse_class
          self.class
        end

        # @api private
        def invert
          inverse_class.new(inverse_name, parent_model, child_model, inverted_options)
        end

        # @api private
        def inverted_options
          links   = self.links.dup
          through = links.pop.inverse

          links.reverse_each do |relationship|
            inverse = relationship.inverse

            through = self.class.new(
              inverse.name,
              inverse.child_model,
              inverse.parent_model,
              inverse.options.merge(:through => through)
            )
          end

          options = self.options

          DataMapper::Ext::Hash.only(options, *OPTIONS - [ :min, :max ]).update(
            :through    => through,
            :child_key  => options[:parent_key],
            :parent_key => options[:child_key],
            :inverse    => self
          )
        end

        # Returns collection class used by this type of
        # relationship
        #
        # @api private
        def collection_class
          ManyToMany::Collection
        end
      end # class Relationship

      class Collection < Associations::OneToMany::Collection
        # Remove every Resource in the m:m Collection from the repository
        #
        # This performs a deletion of each Resource in the Collection from
        # the repository and clears the Collection.
        #
        # @return [Boolean]
        #   true if the resources were successfully destroyed
        #
        # @api public
        def destroy
          assert_source_saved 'The source must be saved before mass-deleting the collection'

          # make sure the records are loaded so they can be found when
          # the intermediaries are removed
          lazy_load

          unless intermediaries.all(via => self).destroy
            return false
          end

          super
        end

        # Remove every Resource in the m:m Collection from the repository, bypassing validation
        #
        # This performs a deletion of each Resource in the Collection from
        # the repository and clears the Collection while skipping
        # validation.
        #
        # @return [Boolean]
        #   true if the resources were successfully destroyed
        #
        # @api public
        def destroy!
          assert_source_saved 'The source must be saved before mass-deleting the collection'

          model      = self.model
          key        = model.key(repository_name)
          conditions = Query.target_conditions(self, key, key)

          unless intermediaries.all(via => self).destroy!
            return false
          end

          unless model.all(:repository => repository, :conditions => conditions).destroy!
            return false
          end

          each do |resource|
            resource.persistence_state = Resource::PersistenceState::Immutable.new(resource)
          end

          clear

          true
        end

        # Return the intermediaries linking the source to the targets
        #
        # @return [Collection]
        #   the intermediary collection
        #
        # @api public
        def intermediaries
          through = self.through
          source  = self.source

          @intermediaries ||= if through.loaded?(source)
            through.get_collection(source)
          else
            reset_intermediaries
          end
        end

        protected

        # Map the resources in the collection to the intermediaries
        #
        # @return [Hash]
        #   the map of resources to their intermediaries
        #
        # @api private
        def intermediary_for
          @intermediary_for ||= {}
        end

        # @api private
        def through
          relationship.through
        end

        # @api private
        def via
          relationship.via
        end

        private

        # @api private
        def _create(attributes, execute_hooks = true)
          via = self.via
          if via.respond_to?(:resource_for)
            resource = super
            if create_intermediary(execute_hooks, resource)
              resource
            end
          else
            if intermediary = create_intermediary(execute_hooks)
              super(attributes.merge(via.inverse => intermediary), execute_hooks)
            end
          end
        end

        # @api private
        def _save(execute_hooks = true)
          via = self.via

          if @removed.any?
            # delete only intermediaries linked to the removed targets
            return false unless intermediaries.all(via => @removed).send(execute_hooks ? :destroy : :destroy!)

            # reset the intermediaries so that it reflects the current state of the datastore
            reset_intermediaries
          end

          loaded_entries = self.loaded_entries

          if via.respond_to?(:resource_for)
            super
            loaded_entries.all? { |resource| create_intermediary(execute_hooks, resource) }
          else
            if loaded_entries.any? && (intermediary = create_intermediary(execute_hooks))
              inverse = via.inverse
              loaded_entries.each { |resource| inverse.set(resource, intermediary) }
            end

            super
          end
        end

        # @api private
        def create_intermediary(execute_hooks, resource = nil)
          intermediary_for = self.intermediary_for

          intermediary_resource = intermediary_for[resource]
          return intermediary_resource if intermediary_resource

          intermediaries = self.intermediaries
          method         = execute_hooks ? :save : :save!

          return unless intermediaries.send(method)

          attributes = {}
          attributes[via] = resource if resource

          intermediary = intermediaries.first_or_new(attributes)
          return unless intermediary.__send__(method)

          # map the resource, even if it is nil, to the intermediary
          intermediary_for[resource] = intermediary
        end

        # @api private
        def reset_intermediaries
          through = self.through
          source  = self.source

          through.set_collection(source, through.collection_for(source))
        end

        # @api private
        def inverse_set(*)
          # do nothing
        end
      end # class Collection
    end # module ManyToMany
  end # module Associations
end # module DataMapper
