EntityMap.h

// Copyright (C) 2025 Jørgen S. Dokken and Joseph P. Dean
//
// This file is part of DOLFINx (https://www.fenicsproject.org)
//
// SPDX-License-Identifier:    LGPL-3.0-or-later
 
#pragma once
 
#include "Topology.h"
#include <concepts>
#include <dolfinx/common/IndexMap.h>
#include <span>
#include <vector>
 
namespace dolfinx::mesh
{
class EntityMap
{
public:
  template <typename U>
    requires std::is_convertible_v<std::remove_cvref_t<U>,
                                   std::vector<std::int32_t>>
  EntityMap(std::shared_ptr<const Topology> topology,
            std::shared_ptr<const Topology> sub_topology, int dim,
            U&& sub_topology_to_topology)
      : _dim(dim), _topology(topology),
        _sub_topology_to_topology(std::forward<U>(sub_topology_to_topology)),
        _sub_topology(sub_topology)
  {
    auto e_imap = sub_topology->index_map(_dim);
    if (!e_imap)
    {
      throw std::runtime_error(
          "No index map for entities, call `Topology::create_entities("
          + std::to_string(_dim) + ")");
    }
 
    std::size_t num_ents = e_imap->size_local() + e_imap->num_ghosts();
    if (num_ents != _sub_topology_to_topology.size())
    {
      throw std::runtime_error(
          "Size mismatch between `sub_topology_to_topology` and index map.");
    }
  }

  EntityMap(const EntityMap& map) = default;

  EntityMap(EntityMap&& map) = default;
 
  // Destructor
  ~EntityMap() = default;

  std::size_t dim() const;

  std::shared_ptr<const Topology> topology() const;

  std::shared_ptr<const Topology> sub_topology() const;

  std::vector<std::int32_t>
  sub_topology_to_topology(std::span<const std::int32_t> entities,
                           bool inverse) const;
 
private:
  // Dimension of the entities
  std::size_t _dim;
 
  // A topology
  std::shared_ptr<const Topology> _topology;
 
  // A list of `_dim`-dimensional entities in _topology, where
  // `_sub_topology_to_topology[i]` is the index in `_topology` of the
  // `i`th entity in `_sub_topology`
  std::vector<std::int32_t> _sub_topology_to_topology;
 
  // A second topology, consisting of a subset of entities in
  // `_topology`
  std::shared_ptr<const Topology> _sub_topology;
};
} // namespace dolfinx::mesh