fsm.h

/******************************************************************************
The MIT License(MIT)
 
Embedded Template Library.
https://github.com/ETLCPP/etl
https://www.etlcpp.com
 
Copyright(c) 2017 John Wellbelove
 
Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files(the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and / or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions :
 
The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.
 
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.
******************************************************************************/
 
#ifndef ETL_FSM_INCLUDED
#define ETL_FSM_INCLUDED
 
#include "platform.h"
#include "array.h"
#include "error_handler.h"
#include "exception.h"
#include "integral_limits.h"
#include "largest.h"
#include "message_router.h"
#include "nullptr.h"
#include "user_type.h"
#if ETL_USING_CPP11
  #include "tuple.h"
  #include "type_list.h"
#endif
 
#include <stdint.h>
 
#include "private/minmax_push.h"
 
namespace etl
{
  class fsm;
  class hfsm;

#if !defined(ETL_FSM_STATE_ID_TYPE)
  typedef uint_least8_t fsm_state_id_t;
#else
  typedef ETL_FSM_STATE_ID_TYPE fsm_state_id_t;
#endif
 
  // For internal FSM use.
  typedef etl::larger_type<etl::message_id_t>::type fsm_internal_id_t;
 
#if ETL_USING_CPP11 && !defined(ETL_FSM_FORCE_CPP03_IMPLEMENTATION) // For C++11 and above
  template <typename, typename, etl::fsm_state_id_t, typename...>
  class fsm_state;
#else
  #include "private/fsm_fwd_decl_cpp03.h"
#endif
 
  //***************************************************************************
  //***************************************************************************
  class fsm_exception : public etl::exception
  {
  public:
 
    fsm_exception(string_type reason_, string_type file_name_, numeric_type line_number_)
      : etl::exception(reason_, file_name_, line_number_)
    {
    }
  };
 
  //***************************************************************************
  //***************************************************************************
  class fsm_null_state_exception : public etl::fsm_exception
  {
  public:
 
    fsm_null_state_exception(string_type file_name_, numeric_type line_number_)
      : etl::fsm_exception(ETL_ERROR_TEXT("fsm:null state", ETL_FSM_FILE_ID"A"), file_name_, line_number_)
    {
    }
  };
 
  //***************************************************************************
  //***************************************************************************
  class fsm_state_id_exception : public etl::fsm_exception
  {
  public:
 
    fsm_state_id_exception(string_type file_name_, numeric_type line_number_)
      : etl::fsm_exception(ETL_ERROR_TEXT("fsm:state id", ETL_FSM_FILE_ID"B"), file_name_, line_number_)
    {
    }
  };
 
  //***************************************************************************
  //***************************************************************************
  class fsm_state_list_exception : public etl::fsm_exception
  {
  public:
 
    fsm_state_list_exception(string_type file_name_, numeric_type line_number_)
      : etl::fsm_exception(ETL_ERROR_TEXT("fsm:state list", ETL_FSM_FILE_ID"C"), file_name_, line_number_)
    {
    }
  };
 
  //***************************************************************************
  //***************************************************************************
  class fsm_state_list_order_exception : public etl::fsm_exception
  {
  public:
 
    fsm_state_list_order_exception(string_type file_name_, numeric_type line_number_)
      : etl::fsm_exception(ETL_ERROR_TEXT("fsm:state list order", ETL_FSM_FILE_ID"D"), file_name_, line_number_)
    {
    }
  };
 
  //***************************************************************************
  //***************************************************************************
  class fsm_not_started : public etl::fsm_exception
  {
  public:
 
    fsm_not_started(string_type file_name_, numeric_type line_number_)
      : etl::fsm_exception(ETL_ERROR_TEXT("fsm:not started", ETL_FSM_FILE_ID"F"), file_name_, line_number_)
    {
    }
  };
 
  //***************************************************************************
  //***************************************************************************
  class fsm_reentrant_transition_forbidden : public etl::fsm_exception
  {
  public:
 
    fsm_reentrant_transition_forbidden(string_type file_name_, numeric_type line_number_)
      : etl::fsm_exception(ETL_ERROR_TEXT("fsm:reentrant calls to start/receive/etc. forbidden", ETL_FSM_FILE_ID"G"), file_name_, line_number_)
    {
    }
  };
 
  namespace private_fsm
  {
    template <typename T = void>
    class ifsm_state_helper
    {
    public:
 
      // Pass this whenever no state change is desired.
      // The highest unsigned value of fsm_state_id_t.
      static ETL_CONSTANT fsm_state_id_t No_State_Change = etl::integral_limits<fsm_state_id_t>::max;
 
      // Pass this when this event also needs to be passed to the parent.
      static ETL_CONSTANT fsm_state_id_t Pass_To_Parent = No_State_Change - 1U;
 
      // Pass this when this event should trigger a self transition.
      static ETL_CONSTANT fsm_state_id_t Self_Transition = No_State_Change - 2U;
    };
 
    template <typename T>
    ETL_CONSTANT fsm_state_id_t ifsm_state_helper<T>::No_State_Change;
 
    template <typename T>
    ETL_CONSTANT fsm_state_id_t ifsm_state_helper<T>::Pass_To_Parent;
 
    template <typename T>
    ETL_CONSTANT fsm_state_id_t ifsm_state_helper<T>::Self_Transition;
 
#if ETL_USING_CPP11
    // Compile-time: TState::ID must equal its index in the type list (0..N-1)
    template <size_t Id, typename...>
    struct check_ids : etl::true_type
    {
    };
 
    template <size_t Id, typename TState0, typename... TRest>
    struct check_ids<Id, TState0, TRest...>
      : etl::integral_constant< bool, (TState0::STATE_ID == Id) && private_fsm::check_ids<Id + 1, TRest...>::value>
    {
    };
#endif
 
    //***************************************************************************
    //***************************************************************************
    class fsm_reentrancy_guard
    {
    public:
 
      //*******************************************
      //*******************************************
      fsm_reentrancy_guard(bool& transition_guard_flag)
        : is_locked(transition_guard_flag)
      {
        ETL_ASSERT(!is_locked, ETL_ERROR(etl::fsm_reentrant_transition_forbidden));
        is_locked = true;
      }
 
      //*******************************************
      /// Releases lock on reentrancy.
      //*******************************************
      ~fsm_reentrancy_guard() ETL_NOEXCEPT
      {
        is_locked = false;
      }
 
    private:
 
      // Reference to the flag signifying a lock on the state machine.
      bool& is_locked;
 
      // Copy & move semantics disabled since this is a guard.
      fsm_reentrancy_guard(fsm_reentrancy_guard const&) ETL_DELETE;
      fsm_reentrancy_guard& operator=(fsm_reentrancy_guard const&) ETL_DELETE;
#if ETL_USING_CPP11
      fsm_reentrancy_guard(fsm_reentrancy_guard&&) ETL_DELETE;
      fsm_reentrancy_guard& operator=(fsm_reentrancy_guard&&) ETL_DELETE;
#endif
    };
  } // namespace private_fsm
 
  class ifsm_state;
 
#if ETL_USING_CPP11
  //***************************************************************************
  //***************************************************************************
  template <typename... TStates>
  class fsm_state_pack
  {
  public:
 
    friend class etl::fsm;
 
    ETL_STATIC_ASSERT((private_fsm::check_ids<0, TStates...>::value), "State IDs must be 0..N-1 and in order");
    ETL_STATIC_ASSERT(sizeof...(TStates) > 0, "At least one state is required");
    ETL_STATIC_ASSERT(sizeof...(TStates) < private_fsm::ifsm_state_helper<>::No_State_Change,
                      "State IDs mst be less than ifsm_state::No_State_Change");
 
    //*********************************
    // The number of states.
    //*********************************
    static ETL_CONSTEXPR size_t size()
    {
      return sizeof...(TStates);
    }
 
    //*********************************
    //*********************************
    template <typename TState>
    TState& get()
    {
      return etl::get<TState>(storage);
    }
 
    //*********************************
    /// Gets a const reference to the state.
    //*********************************
    template <typename TState>
    const TState& get() const
    {
      return etl::get<TState>(storage);
    }
 
  private:
 
    //*********************************
    //*********************************
    etl::ifsm_state** get_state_list()
    {
      return &states[0];
    }

    etl::tuple<TStates...> storage{};

    etl::ifsm_state* states[sizeof...(TStates)]{&etl::get<TStates>(storage)...};
  };
#endif
 
  //***************************************************************************
  //***************************************************************************
  class ifsm_state : public private_fsm::ifsm_state_helper<>
  {
  public:

    friend class etl::fsm;
    friend class etl::hfsm;
 
    using private_fsm::ifsm_state_helper<>::No_State_Change;
    using private_fsm::ifsm_state_helper<>::Pass_To_Parent;
    using private_fsm::ifsm_state_helper<>::Self_Transition;
 
#if ETL_USING_CPP11 && !defined(ETL_FSM_FORCE_CPP03_IMPLEMENTATION) // For C++11 and above
    template <typename, typename, etl::fsm_state_id_t, typename...>
    friend class fsm_state;
#else
  #include "private/fsm_friend_decl_cpp03.h"
#endif
 
    //*******************************************
    //*******************************************
    etl::fsm_state_id_t get_state_id() const
    {
      return state_id;
    }
 
    //*******************************************
    /// Adds a child to this state.
    /// Only of use when part of an HFSM.
    //*******************************************
    void add_child_state(etl::ifsm_state& state)
    {
      ETL_ASSERT(state.p_parent == ETL_NULLPTR, ETL_ERROR(etl::fsm_null_state_exception));
      state.p_parent = this;
 
      if (p_default_child == ETL_NULLPTR)
      {
        p_default_child = &state;
      }
    }
 
    //*******************************************
    //*******************************************
    template <typename TSize>
    void set_child_states(etl::ifsm_state** state_list, TSize size)
    {
      p_active_child  = ETL_NULLPTR;
      p_default_child = ETL_NULLPTR;
 
      for (TSize i = 0; i < size; ++i)
      {
        ETL_ASSERT(state_list[i] != ETL_NULLPTR, ETL_ERROR(etl::fsm_null_state_exception));
        add_child_state(*state_list[i]);
      }
    }
 
  protected:
 
    //*******************************************
    //*******************************************
    ifsm_state(etl::fsm_state_id_t state_id_)
      : state_id(state_id_)
      , p_context(ETL_NULLPTR)
      , p_parent(ETL_NULLPTR)
      , p_active_child(ETL_NULLPTR)
      , p_default_child(ETL_NULLPTR)
    {
    }
 
    //*******************************************
    //*******************************************
    virtual ~ifsm_state() {}
 
    //*******************************************
    etl::fsm& get_fsm_context() const
    {
      return *p_context;
    }
 
  private:
 
    virtual fsm_state_id_t process_event(const etl::imessage& message) = 0;
 
    virtual fsm_state_id_t on_enter_state()
    {
      return No_State_Change;
    } // By default, do nothing.
    virtual void on_exit_state() {} // By default, do nothing.
 
    //*******************************************
    void set_fsm_context(etl::fsm& context)
    {
      p_context = &context;
    }
 
    // The state id.
    const etl::fsm_state_id_t state_id;
 
    // A pointer to the FSM context.
    etl::fsm* p_context;
 
    // A pointer to the parent.
    ifsm_state* p_parent;
 
    // A pointer to the active child.
    ifsm_state* p_active_child;
 
    // A pointer to the default active child.
    ifsm_state* p_default_child;
 
    // Disabled.
    ifsm_state(const ifsm_state&) ETL_DELETE;
    ifsm_state& operator=(const ifsm_state&) ETL_DELETE;
  };
 
  //***************************************************************************
  //***************************************************************************
  class fsm : public etl::imessage_router
  {
  public:
 
    friend class etl::hfsm;
    using imessage_router::receive;
 
    //*******************************************
    //*******************************************
    fsm(etl::message_router_id_t id)
      : imessage_router(id)
      , p_state(ETL_NULLPTR)
      , state_list(ETL_NULLPTR)
      , number_of_states(0U)
      , is_processing_state_change(false)
    {
    }
 
    //*******************************************
    //*******************************************
    template <typename TSize>
    void set_states(etl::ifsm_state** p_states, TSize size)
    {
      state_list       = p_states;
      number_of_states = etl::fsm_state_id_t(size);
 
      ETL_ASSERT(number_of_states > 0, ETL_ERROR(etl::fsm_state_list_exception));
      ETL_ASSERT(number_of_states < ifsm_state::No_State_Change, ETL_ERROR(etl::fsm_state_list_exception));
 
      for (etl::fsm_state_id_t i = 0; i < size; ++i)
      {
        ETL_ASSERT(state_list[i] != ETL_NULLPTR, ETL_ERROR(etl::fsm_null_state_exception));
        ETL_ASSERT(state_list[i]->get_state_id() == i, ETL_ERROR(etl::fsm_state_list_order_exception));
        state_list[i]->set_fsm_context(*this);
      }
    }
 
#if ETL_USING_CPP11
    //*******************************************
    //*******************************************
    template <typename... TStates>
    void set_states(etl::fsm_state_pack<TStates...>& state_pack)
    {
      state_list       = state_pack.get_state_list();
      number_of_states = etl::fsm_state_id_t(state_pack.size());
 
      for (etl::fsm_state_id_t i = 0; i < number_of_states; ++i)
      {
        state_list[i]->set_fsm_context(*this);
      }
    }
#endif
 
    //*******************************************

    //*******************************************
    virtual void start(bool call_on_enter_state = true)
    {
      private_fsm::fsm_reentrancy_guard transition_lock(is_processing_state_change);
 
      // Can only be started once.
      if (!is_started())
      {
        p_state = state_list[0];
        ETL_ASSERT(p_state != ETL_NULLPTR, ETL_ERROR(etl::fsm_null_state_exception));
 
        if (call_on_enter_state)
        {
          etl::fsm_state_id_t next_state_id;
          etl::ifsm_state*    p_last_state;
 
          do {
            p_last_state  = p_state;
            next_state_id = p_state->on_enter_state();
            if (next_state_id != ifsm_state::No_State_Change)
            {
              ETL_ASSERT(next_state_id < number_of_states, ETL_ERROR(etl::fsm_state_id_exception));
              p_state = state_list[next_state_id];
            }
          } while (p_last_state != p_state);
        }
      }
    }
 
    //*******************************************
    //*******************************************
    void receive(const etl::imessage& message) ETL_OVERRIDE
    {
      private_fsm::fsm_reentrancy_guard transition_lock(is_processing_state_change);
 
      if (is_started())
      {
        etl::fsm_state_id_t next_state_id = p_state->process_event(message);
 
        process_state_change(next_state_id);
      }
      else
      {
        ETL_ASSERT_FAIL(ETL_ERROR(etl::fsm_not_started));
      }
    }
 
    //*******************************************
    //*******************************************
    etl::fsm_state_id_t transition_to(etl::fsm_state_id_t new_state_id)
    {
      private_fsm::fsm_reentrancy_guard transition_lock(is_processing_state_change);
 
      if (is_started())
      {
        return process_state_change(new_state_id);
      }
      else
      {
        return ifsm_state::No_State_Change;
      }
    }
 
    using imessage_router::accepts;
 
    //*******************************************
    //*******************************************
    bool accepts(etl::message_id_t) const ETL_OVERRIDE
    {
      return true;
    }
 
    //*******************************************
    //*******************************************
    etl::fsm_state_id_t get_state_id() const
    {
      ETL_ASSERT(p_state != ETL_NULLPTR, ETL_ERROR(etl::fsm_null_state_exception));
      return p_state->get_state_id();
    }
 
    //*******************************************
    //*******************************************
    ifsm_state& get_state()
    {
      ETL_ASSERT(p_state != ETL_NULLPTR, ETL_ERROR(etl::fsm_null_state_exception));
      return *p_state;
    }
 
    //*******************************************
    //*******************************************
    const ifsm_state& get_state() const
    {
      ETL_ASSERT(p_state != ETL_NULLPTR, ETL_ERROR(etl::fsm_null_state_exception));
      return *p_state;
    }
 
    //*******************************************
    //*******************************************
    bool is_started() const
    {
      return p_state != ETL_NULLPTR;
    }
 
    //*******************************************
    //*******************************************
    virtual void reset(bool call_on_exit_state = false)
    {
      private_fsm::fsm_reentrancy_guard transition_lock(is_processing_state_change);
 
      if (is_started() && call_on_exit_state)
      {
        p_state->on_exit_state();
      }
 
      p_state = ETL_NULLPTR;
    }
 
    //********************************************
    ETL_DEPRECATED
    bool is_null_router() const ETL_OVERRIDE
    {
      return false;
    }
 
    //********************************************
    bool is_producer() const ETL_OVERRIDE
    {
      return true;
    }
 
    //********************************************
    bool is_consumer() const ETL_OVERRIDE
    {
      return true;
    }
 
  private:
 
    //********************************************
    bool have_changed_state(etl::fsm_state_id_t next_state_id) const
    {
      return (next_state_id != p_state->get_state_id()) && (next_state_id != ifsm_state::No_State_Change)
             && (next_state_id != ifsm_state::Self_Transition);
    }
 
    //********************************************
    bool is_self_transition(etl::fsm_state_id_t next_state_id) const
    {
      return (next_state_id == ifsm_state::Self_Transition);
    }
 
    //*******************************************
    //*******************************************
    virtual etl::fsm_state_id_t process_state_change(etl::fsm_state_id_t next_state_id)
    {
      if (is_self_transition(next_state_id))
      {
        p_state->on_exit_state();
        next_state_id = p_state->on_enter_state();
      }
 
      if (have_changed_state(next_state_id))
      {
        ETL_ASSERT_OR_RETURN_VALUE(next_state_id < number_of_states, ETL_ERROR(etl::fsm_state_id_exception), p_state->get_state_id());
        etl::ifsm_state* p_next_state = state_list[next_state_id];
 
        do {
          p_state->on_exit_state();
          p_state = p_next_state;
 
          next_state_id = p_state->on_enter_state();
 
          if (have_changed_state(next_state_id))
          {
            ETL_ASSERT_OR_RETURN_VALUE(next_state_id < number_of_states, ETL_ERROR(etl::fsm_state_id_exception), p_state->get_state_id());
            p_next_state = state_list[next_state_id];
          }
        } while (p_next_state != p_state); // Have we changed state again?
      }
 
      return p_state->get_state_id();
    }
 
    etl::ifsm_state*    p_state;                    
    etl::ifsm_state**   state_list;                 
    etl::fsm_state_id_t number_of_states;           
    bool                is_processing_state_change; 

  };
 
  //*************************************************************************************************
  // For C++11 and above.
  //*************************************************************************************************
#if ETL_USING_CPP11 && !defined(ETL_FSM_FORCE_CPP03_IMPLEMENTATION) // For C++11 and above
  //***************************************************************************
  // The definition for all types.
  //***************************************************************************
  template <typename TContext, typename TDerived, etl::fsm_state_id_t STATE_ID_, typename... TMessageTypes>
  class fsm_state : public ifsm_state
  {
  private:
 
    using message_id_sequence = etl::index_sequence<TMessageTypes::ID...>;
 
  public:
 
    using message_types        = etl::type_list<TMessageTypes...>;
    using sorted_message_types = etl::type_list_sort_t<message_types, etl::compare_message_id_less>;
 
    static_assert(etl::type_list_is_unique<message_types>::value, "All TMessageTypes must be unique");
    static_assert(etl::type_list_all_of<message_types, etl::is_message_type>::value,
                  "All TMessageTypes must satisfy the condition etl::is_message_type");
    static_assert(etl::index_sequence_is_unique<message_id_sequence>::value, "All message IDs must be unique");
 
    static ETL_CONSTANT etl::fsm_state_id_t STATE_ID = STATE_ID_;
 
    fsm_state()
      : ifsm_state(STATE_ID)
    {
    }
 
  protected:
 
    ~fsm_state() {}
 
    TContext& get_fsm_context() const
    {
      return static_cast<TContext&>(ifsm_state::get_fsm_context());
    }
 
  private:
 
    static constexpr size_t            Number_Of_Messages = sizeof...(TMessageTypes);
    static constexpr etl::message_id_t Message_Id_Start   = etl::type_list_type_at_index_t<sorted_message_types, 0>::ID;
 
    static_assert(Number_Of_Messages > 0, "Zero messages");
 
    //**********************************************
    // Checks that the message ids are contiguous.
    //**********************************************
    template <size_t Index, bool Last = (Index + 1U >= Number_Of_Messages)>
    struct contiguous_impl;
 
    template <size_t Index>
    struct contiguous_impl<Index, true> : etl::true_type
    {
    };
 
    template <size_t Index>
    struct contiguous_impl<Index, false>
      : etl::bool_constant< (etl::type_list_type_at_index_t<sorted_message_types, Index>::ID + 1U
                             == etl::type_list_type_at_index_t<sorted_message_types, Index + 1U>::ID)
                            && contiguous_impl<Index + 1U>::value>
    {
    };
 
    // The message ids are contiguous if there are 0 or 1 message types, or if
    // each message id is one greater than the previous message id.
    static constexpr bool Message_Ids_Are_Contiguous = (Number_Of_Messages <= 1U) ? true : contiguous_impl<0U>::value;
 
    using handler_ptr = etl::fsm_state_id_t (*)(TDerived&,
                                                const etl::imessage&); 
    using message_dispatch_table_t = etl::array<handler_ptr,
                                                Number_Of_Messages>; 
    using message_id_table_t = etl::array<etl::message_id_t,
                                          Number_Of_Messages>; 
 
    //********************************************
    etl::fsm_state_id_t process_event(const etl::imessage& message)
    {
      const etl::message_id_t id = message.get_message_id();
 
      // The IDs are sorted, so an ID less than the first is not handled by this
      // router.
      if (id >= Message_Id_Start)
      {
        const size_t index = get_dispatch_index_from_message_id(id);
 
        // If the index is less than Number_Of_Messages, then we have a handler
        // for this message type, so dispatch it.
        if (index < Number_Of_Messages)
        {
          const etl::fsm_state_id_t new_state_id = dispatch(message, index);
 
          if (new_state_id != Pass_To_Parent)
          {
            return new_state_id;
          }
        }
      }
 
  #include "etl/private/diagnostic_array_bounds_push.h"
      // If we get here, then we don't have a handler for this message type, so
      // pass it to the parent if we have one, otherwise call on_event_unknown.
      return (p_parent != nullptr) ? p_parent->process_event(message) : static_cast<TDerived*>(this)->on_event_unknown(message);
  #include "etl/private/diagnostic_pop.h"
    }
 
    //**********************************************
    // Call for a single message type
    //**********************************************
    template <typename TMessage>
    static etl::fsm_state_id_t call_on_event(TDerived& derived, const imessage& msg)
    {
      return derived.on_event(static_cast<const TMessage&>(msg));
    }
 
    //**********************************************
    // Get the handler for a single message type at the index in the sorted
    // type_list. This will be called for each message type to generate the
    // dispatch table.
    //**********************************************
    template <size_t Index>
    static constexpr handler_ptr get_message_handler()
    {
      return &call_on_event< etl::type_list_type_at_index_t<sorted_message_types, Index>>;
    }
 
    //**********************************************
    // Generate the dispatch table at compile time.
    // This will create an array of handler pointers, one for each message type.
    //**********************************************
    template <size_t... Indices>
    static constexpr message_dispatch_table_t make_message_dispatch_table(etl::index_sequence<Indices...>)
    {
      return message_dispatch_table_t{{get_message_handler<Indices>()...}};
    }
 
    //**********************************************
    // Get the message id for a single message type at an index in the sorted
    // type_list. This will be called for each message type to generate the
    // message id table.
    //**********************************************
    template <size_t Index>
    static constexpr etl::message_id_t get_message_id_from_index()
    {
      return etl::type_list_type_at_index_t<sorted_message_types, Index>::ID;
    }
 
    //**********************************************
    // Generate the message id table at compile time.
    // This will create an array of message ids, one for each message type.
    //**********************************************
    template <size_t... Indices>
    static constexpr message_id_table_t make_message_id_table(etl::index_sequence<Indices...>)
    {
      return message_id_table_t{{get_message_id_from_index<Indices>()...}};
    }
 
    //**********************************************
    // Get the dispatch index for a message id.
    // This will be used at runtime to find the handler for a message id.
    // If the message ids are contiguous, we can calculate the index directly.
    // If they are not contiguous, we need to do a binary search. This will
    // return Number_Of_Messages if the message id is not found.
    //**********************************************
    static size_t get_dispatch_index_from_message_id(etl::message_id_t id)
    {
      if ETL_IF_CONSTEXPR (Message_Ids_Are_Contiguous)
      {
        // The IDs are contiguous, so we can calculate the index directly.
        return static_cast<size_t>(id - Message_Id_Start);
      }
      else
      {
        // The IDs are not contiguous, so we need to do a binary search.
        size_t left  = 0;
        size_t right = Number_Of_Messages;
 
        while (left < right)
        {
          size_t mid = (left + right) / 2;
 
          if (message_id_table[mid] == id)
          {
            return mid;
          }
          else if (message_id_table[mid] < id)
          {
            left = mid + 1;
          }
          else
          {
            right = mid;
          }
        }
      }
 
      return Number_Of_Messages; // Not found
    }
 
    //**********************************************
    // Dispatch the message to the appropriate handler based on the index in the
    // dispatch table.
    //**********************************************
    etl::fsm_state_id_t dispatch(const etl::imessage& msg, size_t index)
    {
      return message_dispatch_table[index](static_cast<TDerived&>(*this), msg);
    }
 
    //**********************************************
    // The dispatch table is generated at compile time. The dispatch table
    // contains pointers to the on_receive handlers for each message type.
    //**********************************************
    static ETL_INLINE_VAR constexpr message_dispatch_table_t message_dispatch_table =
      etl::fsm_state<TContext, TDerived, STATE_ID_, TMessageTypes...>::make_message_dispatch_table(
        etl::make_index_sequence< etl::fsm_state<TContext, TDerived, STATE_ID_, TMessageTypes...>::Number_Of_Messages>{});
 
    //**********************************************
    // The message id table is generated at compile time. The message id table
    // contains the corresponding message ids for each message type.
    //**********************************************
    static ETL_INLINE_VAR constexpr message_id_table_t message_id_table =
      etl::fsm_state<TContext, TDerived, STATE_ID_, TMessageTypes...>::make_message_id_table(
        etl::make_index_sequence< etl::fsm_state<TContext, TDerived, STATE_ID_, TMessageTypes...>::Number_Of_Messages>{});
  };
 
  #if ETL_USING_CPP11 && !ETL_USING_CPP17
  template <typename TContext, typename TDerived, etl::fsm_state_id_t STATE_ID_, typename... TMessageTypes>
  constexpr const typename etl::fsm_state< TContext, TDerived, STATE_ID_, TMessageTypes...>::message_dispatch_table_t
    etl::fsm_state<TContext, TDerived, STATE_ID_, TMessageTypes...>::message_dispatch_table;
 
  template <typename TContext, typename TDerived, etl::fsm_state_id_t STATE_ID_, typename... TMessageTypes>
  constexpr const typename etl::fsm_state<TContext, TDerived, STATE_ID_, TMessageTypes...>::message_id_table_t
    etl::fsm_state<TContext, TDerived, STATE_ID_, TMessageTypes...>::message_id_table;
  #endif

  template <typename TContext, typename TDerived, etl::fsm_state_id_t STATE_ID_, typename... TMessageTypes>
  ETL_CONSTANT etl::fsm_state_id_t fsm_state<TContext, TDerived, STATE_ID_, TMessageTypes...>::STATE_ID;
 
  //***************************************************************************
  // The definition for no messages.
  //***************************************************************************
  template <typename TContext, typename TDerived, etl::fsm_state_id_t STATE_ID_>
  class fsm_state<TContext, TDerived, STATE_ID_> : public ifsm_state
  {
  private:
 
    using message_id_sequence = etl::index_sequence<>;
 
  public:
 
    using message_types        = etl::type_list<>;
    using sorted_message_types = etl::type_list<>;
 
    static ETL_CONSTANT etl::fsm_state_id_t STATE_ID = STATE_ID_;
 
    fsm_state()
      : ifsm_state(STATE_ID)
    {
    }
 
  protected:
 
    ~fsm_state() {}
 
    TContext& get_fsm_context() const
    {
      return static_cast<TContext&>(ifsm_state::get_fsm_context());
    }
 
  private:
 
    //********************************************
    etl::fsm_state_id_t process_event(const etl::imessage& message)
    {
      return (p_parent != nullptr) ? p_parent->process_event(message) : static_cast<TDerived*>(this)->on_event_unknown(message);
    }
  };
 
#else
  #include "private/fsm_cpp03.h"
#endif
} // namespace etl
 
#include "private/minmax_pop.h"
 
#endif