module JSONAPIonify::Api
  module Resource::Definitions::Relationships

    def self.extended(klass)
      klass.class_eval do
        extend JSONAPIonify::InheritedAttributes
        inherited_array_attribute :relationship_definitions
      end
    end

    def relates_to_many(name, count_attribute: false, count_hidden: :list, **opts, &block)
      define_relationship(name, Relationship::Many, **opts, &block).tap do
        define_relationship_counter(
          name,
          count_attribute === true ? "#{name.to_s.singularize}_count" : count_attribute.to_s,
          count_hidden
        ) if count_attribute
      end
    end

    def relates_to_one(name, **opts, &block)
      opts[:resource] ||= name.to_s.pluralize.to_sym
      define_relationship(name, Relationship::One, **opts, &block)
    end

    def define_relationship_counter(rel_name, name, hidden)
      attribute name.to_sym, types.Integer, "The number of #{rel_name}.", hidden: hidden do |_, instance, context|
        rel          = context.resource.class.relationship(rel_name)
        rel_context  = rel.new(
          request:           context.request,
          context_overrides: { owner:  instance, fields: {}, params: {} }
        ).exec { |c| c }
        count        = rel_context.collection.uniq.count
        case count
        when Hash
          count.values.reduce(:+)
        when Fixnum
          count
        else
          error :internal_server_error
        end
      end
    end

    def define_relationship(name, klass, **opts, &block)
      const_name = name.to_s.camelcase + 'Relationship'
      remove_const(const_name) if const_defined? const_name
      klass.new(self, name, **opts, &block).tap do |new_relationship|
        relationship_definitions.delete new_relationship
        relationship_definitions << new_relationship
      end
    end

    def relationships
      relationship_definitions
    end

    def relationship(name)
      name       = name.to_sym
      const_name = name.to_s.camelcase + 'Relationship'
      return const_get(const_name, false) if const_defined? const_name
      relationship_definition = relationship_definitions.find { |rel| rel.name == name }
      raise Errors::RelationshipNotFound, "Relationship not found: #{name}" unless relationship_definition
      const_set const_name, relationship_definition.resource_class
    end

  end
end