node-manager.hpp

//
// libsemigroups - C++ library for semigroups and monoids
// Copyright (C) 2019-2025 James D. Mitchell
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program.  If not, see <http://www.gnu.org/licenses/>.
//
 
// This file contains the declaration for a class to manage nodes for
// ToddCoxeterDigraph instances.
 
#ifndef LIBSEMIGROUPS_DETAIL_NODE_MANAGER_HPP_
#define LIBSEMIGROUPS_DETAIL_NODE_MANAGER_HPP_
 
#include <cstddef>      // for size_t
#include <cstdint>      // for uint32_t
#include <numeric>      // for iota
#include <type_traits>  // for true_type
#include <vector>       // for vector
 
#include "libsemigroups/config.hpp"     // for LIBSEMIGROUPS_DEBUG
#include "libsemigroups/constants.hpp"  // for UNDEFINED
#include "libsemigroups/debug.hpp"      // for LIBSEMIGROUPS_ASSERT/DEBUG
#include "libsemigroups/exception.hpp"  // for LISEMIGROUPS_EXCEPTION
#include "libsemigroups/ranges.hpp"
 
namespace libsemigroups {
  namespace detail {
    template <typename NodeType>
    class NodeManager {
     public:
      // NodeManager - typedefs - public

      using node_type = NodeType;
      using Perm      = std::vector<node_type>;

      // NodeManager - constructors + destructor - public
 
      NodeManager();
 
      NodeManager(NodeManager const&) = default;
      NodeManager(NodeManager&&)      = default;
 
      NodeManager& operator=(NodeManager const&) = default;
      NodeManager& operator=(NodeManager&&)      = default;
 
      ~NodeManager();

      // NodeManager - member functions - public
 
      node_type& cursor() {
        return _current;
      }
 
      node_type& lookahead_cursor() {
        return _current_la;
      }

      // std::vector::size is noexcept
      inline size_t node_capacity() const noexcept {
        return _forwd.size();
      }

      inline node_type first_free_node() const noexcept {
        return _first_free_node;
      }

      inline bool has_free_nodes() const noexcept {
        return _first_free_node != UNDEFINED;
      }

      // not noexcept since std::vector::operator[] isn't.
      inline bool is_active_node(node_type c) const {
        LIBSEMIGROUPS_ASSERT(c < _ident.size() || c == UNDEFINED);
        return c != UNDEFINED && _ident[c] == c;
      }

      inline bool is_valid_node(node_type c) const noexcept {
        return c < _forwd.size();
      }

      // not noexcept since std::vector::operator[] isn't.
      inline node_type next_active_node(node_type c) const {
        LIBSEMIGROUPS_ASSERT(is_active_node(c));
        return _forwd[c];
      }
 
      // Note that these iterators are invalidated by any changes to the
      // container, i.e. they can't be used as a substitute for cursors.
      auto cbegin_active_nodes() const {
        return rx::begin(ActiveNodesRange(this));
      }
 
      // Note that these iterators are invalidated by any changes to the
      // container, i.e. they can't be used as a substitute for cursors.
      auto cend_active_nodes() const {
        return rx::end(ActiveNodesRange(this));
      }

      inline size_t number_of_nodes_active() const noexcept {
        return _active;
      }

      inline size_t number_of_nodes_defined() const noexcept {
        return _defined;
      }

      inline size_t number_of_nodes_killed() const noexcept {
        return _nodes_killed;
      }

      NodeManager& growth_factor(float val);

      float growth_factor() const noexcept {
        return _growth_factor;
      }

      // NodeManager - member functions - protected
 
      // not noexcept because free_node isn't, and std::vector::operator[]
      // isn't.
 
      inline void union_nodes(node_type min, node_type max) {
        LIBSEMIGROUPS_ASSERT(is_active_node(min));
        LIBSEMIGROUPS_ASSERT(is_active_node(max));
        LIBSEMIGROUPS_ASSERT(max > min);
        free_node(max);
        // Leave a "forwarding address" so we know what <max> was identified
        // with
        _ident[max] = min;
      }
 
      // not noexcept since std::vector::operator[] isn't.
 
      inline node_type find_node(node_type c) const {
        LIBSEMIGROUPS_ASSERT(is_valid_node(c));
        while (true) {
          node_type d = _ident[c];
          if (d == c) {
            return d;
          }
          node_type e = _ident[d];
          if (d == e) {
            return d;
          }
          _ident[c] = e;
          c         = e;
        }
        LIBSEMIGROUPS_ASSERT(is_active_node(c));
        return c;
      }
 
      void      add_active_nodes(size_t);
      void      add_free_nodes(size_t);
      void      erase_free_nodes();
      node_type new_active_node();
      // TODO rename -> swap_nodes_no_checks
      void switch_nodes(node_type const, node_type const);
      // TODO rename -> permute_nodes_no_checks
      void apply_permutation(Perm p);
 
      // not noexcept since std::vector::operator[] isn't.
      void free_node(node_type const);
 
      void clear();

      // NodeManager - data - protected
 
      constexpr node_type initial_node() const noexcept {
        return _id_node;
      }
 
      static constexpr node_type _id_node = 0;
      node_type                  _current;
      node_type                  _current_la;
 
     private:
      struct ActiveNodesRange {
        using output_type = node_type;
 
        NodeManager const* _node_manager;
        output_type        _current;
 
        ActiveNodesRange() : _node_manager(nullptr), _current(UNDEFINED) {}
 
        explicit ActiveNodesRange(NodeManager const* nm)
            : _node_manager(nm), _current(nm->initial_node()) {}
 
        output_type get() const noexcept {
          return _current;
        }
 
        void next() noexcept {
          _current = _node_manager->next_active_node(_current);
        }
 
        bool at_end() const noexcept {
          return _node_manager == nullptr
                 || _current == _node_manager->first_free_node();
        }
 
        size_t size_hint() const noexcept {
          return _node_manager->number_of_nodes_active();
        }
 
        static constexpr bool is_finite     = true;
        static constexpr bool is_idempotent = true;
      };
 
     public:
      ActiveNodesRange active_nodes() const {
        return ActiveNodesRange(this);
      }
 
     private:
      // NodeManager - member functions - private

      // NodeManager - data - private
 
      // Stats
      size_t _active;
      size_t _defined;
      size_t _nodes_killed;
 
      // Settings
      float _growth_factor;
 
      // Data
      std::vector<node_type>         _bckwd;
      node_type                      _first_free_node;
      std::vector<node_type>         _forwd;
      mutable std::vector<node_type> _ident;
      node_type                      _last_active_node;
 
#ifdef LIBSEMIGROUPS_DEBUG
 
     protected:
      // NodeManager - member functions (debug only) - protected
      void debug_validate_forwd_bckwd() const;
#endif
    };
 
  }  // namespace detail
}  // namespace libsemigroups
 
#ifndef LIBSEMIGROUPS_PARSED_BY_DOXYGEN
// TODO replace uint32_t by Node
template <>
struct rx::is_input_range<
    typename libsemigroups::detail::NodeManager<uint32_t>::ActiveNodesRange>
    : std::true_type {};
#endif
#include "node-manager.tpp"
 
#endif  // LIBSEMIGROUPS_DETAIL_NODE_MANAGER_HPP_