/******************************************************************************
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
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The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

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IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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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)
    {
    }

    //*******************************************
    /// Starts the HFSM.
    /// Can only be called once.
    /// Subsequent calls will do nothing.
    ///\param call_on_enter_state If true will call on_enter_state() for the
    /// first state. Default = true.
    /// If the first state has child states then they will be recursively
    /// entered.
    //*******************************************
    void start(bool call_on_enter_state = true) ETL_OVERRIDE
    {
      private_fsm::fsm_reentrancy_guard transition_lock(is_processing_state_change);

      // Can only be started once.
      if (!is_started())
      {
        etl::ifsm_state* p_first_state = state_list[0];
        ETL_ASSERT(p_first_state != ETL_NULLPTR, ETL_ERROR(etl::fsm_null_state_exception));
        p_state = p_first_state;

        if (call_on_enter_state)
        {
          do_enters_result result = do_enters(ETL_NULLPTR, p_first_state, true);

          if (result.active_state_id != ifsm_state::No_State_Change)
          {
            // If the active_state_id is not No_State_Change, it means that an
            // on_enter changed the target state. Set the state pointer as the
            // active state to use it as the new origin for the transition to
            // the updated target state.
            ETL_ASSERT(result.active_state_id < number_of_states, ETL_ERROR(etl::fsm_state_id_exception));
            p_state = state_list[result.active_state_id];

            process_state_change(result.next_state_id);
          }
          else
          {
            if (have_changed_state(result.next_state_id))
            {
              ETL_ASSERT(result.next_state_id < number_of_states, ETL_ERROR(etl::fsm_state_id_exception));
              p_state = state_list[result.next_state_id];
            }
          }
        }
      }
    }

    //*******************************************
    /// Reset the HFSM to pre-started state.
    ///\param call_on_exit_state If true will call on_exit_state() for the
    /// current state. Default = false.
    //*******************************************
    virtual void reset(bool call_on_exit_state = false) ETL_OVERRIDE
    {
      private_fsm::fsm_reentrancy_guard transition_lock(is_processing_state_change);

      if (is_started() && call_on_exit_state)
      {
        do_exits(ETL_NULLPTR, p_state);
      }

      p_state = ETL_NULLPTR;
    }

  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;
    }

    //*******************************************
    /// Result of a "do_enters()" call
    //*******************************************
    struct do_enters_result
    {
      // State which is presently being targeted as the next state
      etl::fsm_state_id_t next_state_id;
      // State which was active when the on_enter triggered a state change
      etl::fsm_state_id_t active_state_id;
    };

    //*******************************************
    /// Entering the state.
    //*******************************************
    static do_enters_result 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_result result = do_enters(p_root, p_target->p_parent, false);

          // Short circuit the do enters if the parent state decided that a
          // different state should be entered
          if (result.active_state_id != ifsm_state::No_State_Change)
          {
            return result;
          }
        }

        // 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();

      // Short circuit the activation of any child states if the target state
      // changed
      if (next_state != ifsm_state::No_State_Change)
      {
        return {next_state, p_target->get_state_id()};
      }

      // 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();

          // Short circuit the activation of any child states if the target
          // state changed
          if (next_state != ifsm_state::No_State_Change)
          {
            return {next_state, p_target->get_state_id()};
          }
        }

        next_state = p_target->get_state_id();
      }

      // Wrapping No_State_Change in a static_cast gets rid of the "undefined
      // reference" error when compiling on C++11
      return {next_state, static_cast<fsm_state_id_t>(ifsm_state::No_State_Change)};
    }

    //*******************************************
    /// 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;
      }
    }

    //*******************************************
    /// Core function to process a state change.
    //*******************************************
    etl::fsm_state_id_t process_state_change(etl::fsm_state_id_t next_state_id) ETL_OVERRIDE
    {
      if (is_self_transition(next_state_id))
      {
        p_state->on_exit_state();
        next_state_id = p_state->on_enter_state();
      }

      while (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];
        etl::ifsm_state* p_root       = common_ancestor(p_state, p_next_state);

        do_exits(p_root, p_state);

        do_enters_result result = do_enters(p_root, p_next_state, true);
        next_state_id           = result.next_state_id;

        if (result.active_state_id != ifsm_state::No_State_Change)
        {
          // If the active_state_id is not No_State_Change, it means that an
          // on_enter changed the target state. Set the state pointer as the
          // active state to use it as the new origin for the transition to the
          // updated target state.
          ETL_ASSERT(result.active_state_id < number_of_states, ETL_ERROR(etl::fsm_state_id_exception));
          p_state = state_list[result.active_state_id];
          ETL_ASSERT(result.next_state_id < number_of_states, ETL_ERROR(etl::fsm_state_id_exception));
          p_next_state = state_list[result.next_state_id];
        }
        else if (result.next_state_id != ifsm_state::No_State_Change)
        {
          // If the next state is different, means that default children were
          // activated. Assign both p_state and p_next_state to get out of the
          // loop.
          ETL_ASSERT(result.next_state_id < number_of_states, ETL_ERROR(etl::fsm_state_id_exception));
          p_state      = state_list[result.next_state_id];
          p_next_state = state_list[result.next_state_id];
        }
        else
        {
          p_state = p_next_state;
        }
      }

      return p_state->get_state_id();
    }
  };
} // namespace etl
#endif