proxy.hpp

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/*!
 * \file
 * \brief Implementation of simple mbox proxy.
 *
 * \since
 * v.1.2.0
 */

#pragma once

#include <so_5_extra/error_ranges.hpp>

#include <so_5/mbox.hpp>

namespace so_5 {

namespace extra {

namespace mboxes {

namespace proxy {

namespace errors {

/*!
 * \brief Null pointer to underlying mbox.
 *
 * A proxy-mbox uses underlying mbox and delegates all actions to that mbox.
 * Because of that underlying mbox can't be nullptr.
 *
 * \since
 * v.1.2.0
 */
const int rc_nullptr_as_underlying_mbox =
        ::so_5::extra::errors::mboxes_proxy_errors + 1;

} /* namespace errors */

//
// simple_t
//
/*!
 * \brief A simple proxy that delegates all calls to underlying actual mbox.
 *
 * Sometimes it is necessary to create an own mbox that does
 * some specific task. For example, counts the number of message
 * of some specific type. Something like:
 * \code
 * class my_mbox final : public so_5::abstract_message_box_t
 * {
 *  bool is_appropriate_message_type(
 *      const std::type_index & msg_type ) const { ... }
 *
 *  std::size_t counter_{};
 * ...
 *  void do_deliver_message(
 *          so_5::message_delivery_mode_t delivery_mode,
 *          const std::type_index & msg_type,
 *          const so_5::message_ref_t & message,
 *          unsigned int redirection_deep ) override {
 *      if(is_appropriate_message_type(msg_type))
 *          ++counter_;
 *      ... // Actual message delivery.
 *  }
 * };
 * \endcode
 * But it is hard to create a full implementation of
 * so_5::abstract_message_box_t from the ground up. An existing mbox can be
 * used for doing actual work:
 * \code
 * class my_mbox final : public so_5::abstract_message_box_t
 * {
 *  bool is_appropriate_message_type(
 *      const std::type_index & msg_type ) const { ... }
 *
 *  const so_5::mbox_t mbox_;
 *  std::size_t counter_{};
 * ...
 * public:
 *  my_mbox(so_5::mbox_t mbox) : mbox_{std::move(mbox)} {}
 *  ...
 *  void do_deliver_message(
 *          so_5::message_delivery_mode_t delivery_mode,
 *          const std::type_index & msg_type,
 *          const so_5::message_ref_t & message,
 *          unsigned int redirection_deep ) override {
 *      if(is_appropriate_message_type(msg_type))
 *          ++counter_;
 *      // Use actual mbox for message delivery.
 *      mbox_->do_deliver_message(
 *              delivery_mode, msg_type, message, redirection_deep);
 *  }
 * };
 * \endcode
 * But there is a small problem with this approach: so_5::abstract_message_box_t
 * has a rich interface with a lot of pure virtual methods. It is a boring
 * task to reimplement all of them.
 *
 * In such cases simple_t can be used to reduce amount of developer's work:
 * \code
 * class my_mbox final : public so_5::extra::mboxes::proxy::simple_t
 * {
 *  using base_type = so_5::extra::mboxes::proxy::simple_t;
 *
 *  bool is_appropriate_message_type(
 *      const std::type_index & msg_type ) const { ... }
 *
 *  std::size_t counter_{};
 *
 * public:
 *  my_mbox(so_5::mbox_t mbox) : base_type{std::move(mbox)} {}
 *
 *  void do_deliver_message(
 *          so_5::message_delivery_mode_t delivery_mode,
 *          const std::type_index & msg_type,
 *          const so_5::message_ref_t & message,
 *          unsigned int redirection_deep ) override {
 *      if(is_appropriate_message_type(msg_type))
 *          ++counter_;
 *      // Use actual mbox for message delivery.
 *      base_type::do_deliver_message(
 *              delivery_mode, msg_type, message, redirection_deep);
 *  }
 * }
 * \endcode
 * And that's all.
 *
 * \since
 * v.5.5.23
 */
class simple_t : public ::so_5::abstract_message_box_t
    {
        //! Actual underlying mbox to be used for all calls.
        /*!
         * \attention Should not be nullptr.
         */
        const ::so_5::mbox_t m_underlying_mbox;

        //! Ensure that underlying mbox is not nullptr.
        /*!
         * \throw so_5::exception_t if \a mbox is nullptr.
         */
        ::so_5::mbox_t
        ensure_underlying_mbox_not_null(
            ::so_5::mbox_t mbox )
            {
                if( !mbox )
                    SO_5_THROW_EXCEPTION(
                            errors::rc_nullptr_as_underlying_mbox,
                            "nullptr is used as underlying mbox" );

                return mbox;
            }

    protected :
        //! An accessor to actual mbox.
        /*!
         * This method is intended to be used in derived classes.
         * For example:
         * \code
         * class my_mbox : public so_5::extra::mboxes::proxy::simple_t {
         * public:
         *  void do_deliver_message(
         *          so_5::message_delivery_mode_t delivery_mode,
         *          const std::type_index & msg_type,
         *          const so_5::message_ref_t & message,
         *          unsigned int redirection_deep ) override {
         *      ... // Do some specific stuff.
         *      // Use actual mbox for message delivery.
         *      underlying_mbox().do_deliver_message(
         *              delivery_mode, msg_type, message, redirection_deep);
         *  }
         *  ...
         * };
         * \endcode
         */
        ::so_5::abstract_message_box_t &
        underlying_mbox() const noexcept
            {
                return *m_underlying_mbox;
            }

    public :
        //! Initializing constructor.
        simple_t(
            //! Actual underlying mbox to be used for all operations.
            //! Must not be nullptr.
            ::so_5::mbox_t underlying_mbox )
            :   m_underlying_mbox{
                    ensure_underlying_mbox_not_null( std::move(underlying_mbox) ) }
            {}

        /*!
         * \name Simple implementation of inherited methods.
         * \{
         */
        mbox_id_t
        id() const override
            {
                return underlying_mbox().id();
            }

        void
        subscribe_event_handler(
            const std::type_index & msg_type,
            ::so_5::abstract_message_sink_t & subscriber ) override
            {
                underlying_mbox().subscribe_event_handler( msg_type, subscriber );
            }

        void
        unsubscribe_event_handler(
            const std::type_index & msg_type,
            ::so_5::abstract_message_sink_t & subscriber ) noexcept override
            {
                underlying_mbox().unsubscribe_event_handler( msg_type, subscriber );
            }

        std::string
        query_name() const override
            {
                return underlying_mbox().query_name();
            }

        mbox_type_t
        type() const override
            {
                return underlying_mbox().type();
            }

        void
        do_deliver_message(
            ::so_5::message_delivery_mode_t delivery_mode,
            const std::type_index & msg_type,
            const ::so_5::message_ref_t & message,
            unsigned int redirection_deep ) override
            {
                underlying_mbox().do_deliver_message(
                        delivery_mode,
                        msg_type,
                        message,
                        redirection_deep );
            }

        void
        set_delivery_filter(
            const std::type_index & msg_type,
            const ::so_5::delivery_filter_t & filter,
            ::so_5::abstract_message_sink_t & subscriber ) override
            {
                underlying_mbox().set_delivery_filter(
                        msg_type,
                        filter,
                        subscriber );
            }

        void
        drop_delivery_filter(
            const std::type_index & msg_type,
            ::so_5::abstract_message_sink_t & subscriber ) noexcept override
            {
                underlying_mbox().drop_delivery_filter(
                        msg_type,
                        subscriber );
            }

        so_5::environment_t &
        environment() const noexcept override
            {
                return underlying_mbox().environment();
            }
        /*!
         * \}
         */
    };

} /* namespace proxy */

} /* namespace mboxes */

} /* namespace extra */

} /* namespace so_5 */