module GirFFI
  # Specialized kind of Proc to be used for callback arguments.
  # TODO: Create superclass for all actual callback types that does the wrapping for this.
  class Callback < Proc
    # Create Callback from a Proc. Makes sure arguments are properly wrapped,
    # and the callback is stored to prevent garbage collection.
    def self.from namespace, name, prc
      wrap_in_callback_args_mapper(namespace, name, prc).tap do |cb|
        CallbackHelper.store_callback cb
      end
    end

    # TODO: Create actual callback class from the callback info, so no lookup
    # is needed. This class can then also perform the argument mapping.
    def self.wrap_in_callback_args_mapper namespace, name, prc
      return prc if FFI::Function === prc
      return nil if prc.nil?
      info = GObjectIntrospection::IRepository.default.find_by_name namespace, name
      return self.new do |*args|
        prc.call(*map_callback_args(args, info))
      end
    end

    def self.map_callback_args args, info
      args.zip(info.args).map { |arg, inf|
        map_single_callback_arg arg, inf.argument_type }
    end

    # TODO: Use GirFFI::ReturnValue classes for mapping.
    def self.map_single_callback_arg arg, type
      case type.tag
      when :interface
        map_interface_callback_arg arg, type
      when :utf8
        ArgHelper.ptr_to_utf8 arg
      when :void
        map_void_callback_arg arg
      when :array
        subtype = type.param_type(0)
        if subtype.tag == :interface and arg.is_a?(FFI::Pointer)
          map_interface_callback_arg arg, subtype
        else
          raise NotImplementedError
        end
      else
        arg
      end
    end

    def self.map_interface_callback_arg arg, type
      iface = type.interface
      case iface.info_type
      when :object, :interface
        arg.to_object
      when :struct
        klass = GirFFI::Builder.build_class iface
        klass.wrap arg
      else
        arg
      end
    end

    def self.map_void_callback_arg arg
      if arg.null?
        nil
      else
        GirFFI::ArgHelper::OBJECT_STORE[arg.address]
      end
    end

  end
end