/******************************************************************************
The MIT License(MIT)

Embedded Template Library.
https://github.com/ETLCPP/etl
https://www.etlcpp.com

Copyright(c) 2021 Jeremy Overesch, 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
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The above copyright notice and this permission notice shall be included in all
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IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.
******************************************************************************/

#ifndef ETL_HFSM_INCLUDED
#define ETL_HFSM_INCLUDED

#include "fsm.h"

namespace etl
{
  //***************************************************************************
  /// The HFSM class.
  /// Builds on the FSM class by overriding the receive function and adding
  /// state hierarchy walking functions.
  //***************************************************************************
  class hfsm : public etl::fsm
  {
  public:

    //*******************************************
    /// Constructor.
    //*******************************************
    hfsm(etl::message_router_id_t id)
      : fsm(id)
    {
    }

    using fsm::receive;

    //*******************************************
    /// Top level message handler for the HFSM.
    //*******************************************
    void receive(const etl::imessage& message) ETL_OVERRIDE
    {
      etl::fsm_state_id_t next_state_id = p_state->process_event(message);

      if (next_state_id != ifsm_state::No_State_Change)
      {
        ETL_ASSERT(next_state_id < number_of_states, ETL_ERROR(etl::fsm_state_id_exception));
        etl::ifsm_state* p_next_state = state_list[next_state_id];

        // Have we changed state?
        if (p_next_state != p_state)
        {
          etl::ifsm_state* p_root = common_ancestor(p_state, p_next_state);
          do_exits(p_root, p_state);

          p_state = p_next_state;

          next_state_id = do_enters(p_root, p_next_state, true);

          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];
          }
        }
      }
    }

  private:

    //*******************************************
    /// Return the first common ancestor of the two states.
    //*******************************************
    static etl::ifsm_state* common_ancestor(etl::ifsm_state* s1, etl::ifsm_state* s2)
    {
      size_t depth1 = get_depth(s1);
      size_t depth2 = get_depth(s2);

      // Adjust s1 and s2 to the same depth.
      if (depth1 > depth2)
      {
        s1 = adjust_depth(s1, depth1 - depth2);
      }
      else
      {
        s2 = adjust_depth(s2, depth2 - depth1);
      }

      // Now they're aligned to the same depth they can step towards the root together.
      while (s1 != s2)
      {
        s1 = s1->p_parent;
        s2 = s2->p_parent;
      }

      return s1;
    }

    //*******************************************
    /// Find the depth of the state.
    //*******************************************
    static size_t get_depth(etl::ifsm_state* s)
    {
      size_t depth = 0UL;

      while (s != ETL_NULLPTR)
      {
        s = s->p_parent;
        ++depth;
      }

      return depth;
    }

    //*******************************************
    /// Align the depths of the states.
    //*******************************************
    static etl::ifsm_state* adjust_depth(etl::ifsm_state* s, size_t offset)
    {
      while (offset != 0U)
      {
        s = s->p_parent;
        --offset;
      }

      return s;
    }

    //*******************************************
    /// Entering the state.
    //*******************************************
    static etl::fsm_state_id_t do_enters(const etl::ifsm_state* p_root, etl::ifsm_state* p_target, bool activate_default_children)
    {
      ETL_ASSERT(p_target != ETL_NULLPTR, ETL_ERROR(etl::fsm_null_state_exception));

      // We need to go recursively up the tree if the target and root don't match
      if ((p_root != p_target) && (p_target->p_parent != ETL_NULLPTR))
      {
        if (p_target->p_parent != p_root)
        {
          // The parent we're calling shouldn't activate its defaults, or this state will be deactivated.
          do_enters(p_root, p_target->p_parent, false);
        }

        // Set us as our parent's active child
        p_target->p_parent->p_active_child = p_target;
      }

      etl::fsm_state_id_t next_state = p_target->on_enter_state();
      ETL_ASSERT(ifsm_state::No_State_Change == next_state, ETL_ERROR(etl::fsm_state_composite_state_change_forbidden));

      // Activate default child if we need to activate any initial states in an active composite state.
      if (activate_default_children)
      {
        while (p_target->p_default_child != ETL_NULLPTR)
        {
          p_target = p_target->p_default_child;
          p_target->p_parent->p_active_child = p_target;
          next_state = p_target->on_enter_state();
          ETL_ASSERT(ifsm_state::No_State_Change == next_state, ETL_ERROR(etl::fsm_state_composite_state_change_forbidden));
        }

        next_state = p_target->get_state_id();
      }

      return next_state;
    }

    //*******************************************
    /// Exiting the state.
    //*******************************************
    static void do_exits(const etl::ifsm_state* p_root, etl::ifsm_state* p_source)
    {
      etl::ifsm_state* p_current = p_source;

      // Iterate down to the lowest child
      while (p_current->p_active_child != ETL_NULLPTR)
      {
        p_current = p_current->p_active_child;
      }

      // Run exit state on all states up to the root
      while (p_current != p_root)
      {
        p_current->on_exit_state();
        p_current = p_current->p_parent;
      }
    }
  };
}
#endif
