io.hpp

#pragma once
 
#include <functional>
#include <iostream>
#include <optional>
#include <string>
 
#include <mshio/mshio.h>
#include <wmtk/Types.hpp>
 
#include "Logger.hpp"
 
namespace wmtk {
 
class MshData
{
public:
    template <typename Fn>
    void add_edge_vertices(size_t num_vertices, const Fn& get_vertex_cb)
    {
        add_vertices<1>(num_vertices, get_vertex_cb);
    }
 
    template <typename Fn>
    void add_face_vertices(size_t num_vertices, const Fn& get_vertex_cb)
    {
        add_vertices<2>(num_vertices, get_vertex_cb);
    }
 
    template <typename Fn>
    void add_tet_vertices(size_t num_vertices, const Fn& get_vertex_cb)
    {
        add_vertices<3>(num_vertices, get_vertex_cb);
    }
 
    void add_empty_vertices(int dim)
    {
        if (dim < 1 || dim > 3) {
            log_and_throw_error("Only 1,2,3D elements are supported!");
        }
 
        if (m_spec.nodes.entity_blocks.empty()) {
            log_and_throw_error("First vertex block cannot be empty.");
        }
 
        mshio::NodeBlock block;
        block.num_nodes_in_block = 0;
        block.entity_dim = dim;
        block.entity_tag = (int)m_spec.nodes.num_entity_blocks + 1;
 
        m_spec.nodes.num_entity_blocks += 1;
        m_spec.nodes.entity_blocks.push_back(std::move(block));
    }
 
    void add_edge_vertices() { add_empty_vertices(1); }
    void add_face_vertices() { add_empty_vertices(2); }
    void add_tet_vertices() { add_empty_vertices(3); }
 
    template <typename Fn>
    void add_edges(size_t num_edges, const Fn& get_edge_cb)
    {
        add_simplex_elements<1>(num_edges, get_edge_cb);
    }
 
    template <typename Fn>
    void add_faces(size_t num_faces, const Fn& get_face_cb)
    {
        add_simplex_elements<2>(num_faces, get_face_cb);
    }
 
    template <typename Fn>
    void add_tets(size_t num_tets, const Fn& get_tet_cb)
    {
        add_simplex_elements<3>(num_tets, get_tet_cb);
    }
 
    template <int NUM_FIELDS, typename Fn>
    void add_edge_vertex_attribute(const std::string& name, const Fn& get_attribute_cb)
    {
        add_vertex_attribute<NUM_FIELDS, 1>(name, get_attribute_cb);
    }
 
    template <int NUM_FIELDS, typename Fn>
    void add_face_vertex_attribute(const std::string& name, const Fn& get_attribute_cb)
    {
        add_vertex_attribute<NUM_FIELDS, 2>(name, get_attribute_cb);
    }
 
    template <int NUM_FIELDS, typename Fn>
    void add_tet_vertex_attribute(const std::string& name, const Fn& get_attribute_cb)
    {
        add_vertex_attribute<NUM_FIELDS, 3>(name, get_attribute_cb);
    }
 
    template <int NUM_FIELDS, typename Fn>
    void add_edge_attribute(const std::string& name, const Fn& get_attribute_cb)
    {
        add_element_attribute<NUM_FIELDS, 1>(name, get_attribute_cb);
    }
 
    template <int NUM_FIELDS, typename Fn>
    void add_face_attribute(const std::string& name, const Fn& get_attribute_cb)
    {
        add_element_attribute<NUM_FIELDS, 2>(name, get_attribute_cb);
    }
 
    template <int NUM_FIELDS, typename Fn>
    void add_tet_attribute(const std::string& name, const Fn& get_attribute_cb)
    {
        add_element_attribute<NUM_FIELDS, 3>(name, get_attribute_cb);
    }
 
    void add_physical_group(const std::string& name)
    {
        auto& entities = m_spec.entities;
 
        const auto& vertex_block = m_spec.nodes.entity_blocks.back();
        const int tag = vertex_block.entity_tag;
        const int dim = vertex_block.entity_dim;
 
        double min_x = std::numeric_limits<double>::max();
        double min_y = std::numeric_limits<double>::max();
        double min_z = std::numeric_limits<double>::max();
        double max_x = std::numeric_limits<double>::lowest();
        double max_y = std::numeric_limits<double>::lowest();
        double max_z = std::numeric_limits<double>::lowest();
        for (size_t i = 0; i < vertex_block.num_nodes_in_block; ++i) {
            min_x = std::min(vertex_block.data[3 * i + 0], min_x);
            min_y = std::min(vertex_block.data[3 * i + 1], min_y);
            min_z = std::min(vertex_block.data[3 * i + 2], min_z);
            max_x = std::max(vertex_block.data[3 * i + 0], max_x);
            max_y = std::max(vertex_block.data[3 * i + 1], max_y);
            max_z = std::max(vertex_block.data[3 * i + 2], max_z);
        }
 
        mshio::PhysicalGroup ph;
        ph.dim = dim;
        ph.tag = tag;
        ph.name = name;
        m_spec.physical_groups.emplace_back(ph);
 
        switch (dim) {
        case 0: {
            mshio::PointEntity e{tag, min_x, min_y, min_z};
            e.physical_group_tags.push_back(tag);
            entities.points.push_back(e);
            break;
        }
        case 1: {
            mshio::CurveEntity e{tag, min_x, min_y, min_z, max_x, max_y, max_z};
            e.physical_group_tags.push_back(tag);
            entities.curves.push_back(e);
            break;
        }
        case 2: {
            mshio::SurfaceEntity e{tag, min_x, min_y, min_z, max_x, max_y, max_z};
            e.physical_group_tags.push_back(tag);
            entities.surfaces.push_back(e);
            break;
        }
        case 3: {
            mshio::VolumeEntity e{tag, min_x, min_y, min_z, max_x, max_y, max_z};
            e.physical_group_tags.push_back(tag);
            entities.volumes.push_back(e);
            break;
        }
        default: log_and_throw_error("Entity of dim {} cannot be written to .msh.");
        }
    }
 
    inline size_t get_num_edge_vertices() const { return get_num_vertices(1); }
 
    inline size_t get_num_face_vertices() const { return get_num_vertices(2); }
 
    inline size_t get_num_tet_vertices() const { return get_num_vertices(3); }
 
    inline size_t get_num_edges() const { return get_num_simplex_elements(1); }
 
    inline size_t get_num_faces() const { return get_num_simplex_elements(2); }
 
    inline size_t get_num_tets() const { return get_num_simplex_elements(3); }
 
    template <typename Fn>
    void extract_tet_vertices(Fn&& set_vertex_cb) const
    {
        return extract_vertices(3, std::forward<Fn>(set_vertex_cb));
    }
 
    template <typename Fn>
    void extract_face_vertices(Fn&& set_vertex_cb) const
    {
        return extract_vertices(2, std::forward<Fn>(set_vertex_cb));
    }
 
    template <typename Fn>
    void extract_edge_vertices(Fn&& set_vertex_cb) const
    {
        extract_vertices(1, std::forward<Fn>(set_vertex_cb));
    }
 
    template <typename Fn>
    void extract_edges(Fn&& set_edge_cb) const
    {
        extract_simplex_elements<1>(std::forward<Fn>(set_edge_cb));
    }
 
    template <typename Fn>
    void extract_faces(Fn&& set_face_cb) const
    {
        extract_simplex_elements<2>(std::forward<Fn>(set_face_cb));
    }
 
    template <typename Fn>
    void extract_tets(Fn&& set_tet_cb) const
    {
        extract_simplex_elements<3>(std::forward<Fn>(set_tet_cb));
    }
 
    std::vector<std::string> get_edge_vertex_attribute_names() const
    {
        return get_vertex_attribute_names<1>();
    }
 
    std::vector<std::string> get_face_vertex_attribute_names() const
    {
        return get_vertex_attribute_names<2>();
    }
 
    std::vector<std::string> get_tet_vertex_attribute_names() const
    {
        return get_vertex_attribute_names<3>();
    }
 
    std::vector<std::string> get_edge_attribute_names() const
    {
        return get_element_attribute_names<1>();
    }
 
    std::vector<std::string> get_face_attribute_names() const
    {
        return get_element_attribute_names<2>();
    }
 
    std::vector<std::string> get_tet_attribute_names() const
    {
        return get_element_attribute_names<3>();
    }
 
    std::vector<std::string> get_all_element_attribute_names() const
    {
        std::vector<std::string> attr_names;
        attr_names.reserve(m_spec.element_data.size());
        for (const auto& data : m_spec.element_data) {
            attr_names.push_back(data.header.string_tags.front());
        }
        return attr_names;
    }
 
    template <typename Fn>
    void extract_edge_vertex_attribute(const std::string& attr_name, Fn&& set_attr)
    {
        extract_vertex_attribute<1>(attr_name, std::forward<Fn>(set_attr));
    }
 
    template <typename Fn>
    void extract_face_vertex_attribute(const std::string& attr_name, Fn&& set_attr)
    {
        extract_vertex_attribute<2>(attr_name, std::forward<Fn>(set_attr));
    }
 
    template <typename Fn>
    void extract_tet_vertex_attribute(const std::string& attr_name, Fn&& set_attr)
    {
        extract_vertex_attribute<3>(attr_name, std::forward<Fn>(set_attr));
    }
 
    template <typename Fn>
    void extract_edge_attribute(const std::string& attr_name, Fn&& set_attr)
    {
        extract_element_attribute<1>(attr_name, std::forward<Fn>(set_attr));
    }
 
    template <typename Fn>
    void extract_face_attribute(const std::string& attr_name, Fn&& set_attr)
    {
        extract_element_attribute<2>(attr_name, std::forward<Fn>(set_attr));
    }
 
    template <typename Fn>
    void extract_tet_attribute(const std::string& attr_name, Fn&& set_attr)
    {
        extract_element_attribute<3>(attr_name, std::forward<Fn>(set_attr));
    }
 
    std::optional<mshio::PhysicalGroup> get_physical_group_by_name(const std::string& name)
    {
        for (const mshio::PhysicalGroup& ph : m_spec.physical_groups) {
            if (ph.name == name) {
                return ph;
            }
        }
        return {};
    }
 
    void get_VF(const int& dim, const int& tag, MatrixXd& V, MatrixXi& F)
    {
        assert(dim > 0 && tag > 0);
 
        const size_t n_V = get_num_vertices(dim, tag);
        const size_t n_F = get_num_simplex_elements(dim, tag);
 
        if (n_V > 0) {
            V.resize(n_V, 3);
            extract_vertices(dim, tag, [&V](size_t i, double x, double y, double z) {
                V.row(i) = Vector3d(x, y, z);
            });
        }
        if (n_F > 0) {
            F.resize(n_F, dim + 1);
            switch (dim) {
            case 1:
                extract_simplex_elements<1>([&F](size_t i, size_t v0, size_t v1) {
                    F.row(i) = Vector2i((int)v0, (int)v1);
                });
                break;
            case 2:
                extract_simplex_elements<2>([&F](size_t i, size_t v0, size_t v1, size_t v2) {
                    F.row(i) = Vector3i((int)v0, (int)v1, (int)v2);
                });
                break;
            case 3:
                extract_simplex_elements<3>(
                    [&F](size_t i, size_t v0, size_t v1, size_t v2, size_t v3) {
                        F.row(i) = Vector4i((int)v0, (int)v1, (int)v2, (int)v3);
                    });
                break;
            default: log_and_throw_error("Cannot extract elements for dimension {}", dim);
            }
        }
    }
 
    void save(const std::string& filename, bool binary = true)
    {
        m_spec.mesh_format.file_type = binary;
        mshio::validate_spec(m_spec);
        mshio::save_msh(filename, m_spec);
    }
 
    void save(std::ostream& out, bool binary = true)
    {
        m_spec.mesh_format.file_type = binary;
        mshio::validate_spec(m_spec);
        mshio::save_msh(out, m_spec);
    }
 
    void load(const std::string& filename) { m_spec = mshio::load_msh(filename); }
 
    void load(std::istream& in) { m_spec = mshio::load_msh(in); }
 
private:
    template <int DIM, typename Fn>
    void add_vertices(size_t num_vertices, const Fn& get_vertex_cb)
    {
        static_assert(DIM >= 1 && DIM <= 3, "Only 1,2,3D elements are supported!");
        if (num_vertices == 0) {
            logger().trace("Adding empty vertex block.");
        }
        mshio::NodeBlock block;
        block.num_nodes_in_block = num_vertices;
        block.tags.reserve(num_vertices);
        block.data.reserve(num_vertices * 3);
        block.entity_dim = DIM;
        block.entity_tag = (int)m_spec.nodes.num_entity_blocks + 1;
 
        const size_t tag_offset = m_spec.nodes.max_node_tag;
        for (size_t i = 0; i < num_vertices; i++) {
            const auto& v = get_vertex_cb(i);
            block.tags.push_back(tag_offset + i + 1);
            block.data.push_back(v[0]);
            block.data.push_back(v[1]);
            block.data.push_back(v[2]);
        }
 
        m_spec.nodes.num_entity_blocks += 1;
        m_spec.nodes.num_nodes += num_vertices;
        m_spec.nodes.min_node_tag = 1;
        m_spec.nodes.max_node_tag += num_vertices;
        m_spec.nodes.entity_blocks.push_back(std::move(block));
    }
 
    template <int DIM, typename Fn>
    void add_simplex_elements(size_t num_elements, const Fn& get_element_cb)
    {
        static_assert(
            DIM == 1 || DIM == 2 || DIM == 3,
            "Only 1,2,3D simplex elements are supported");
        if (num_elements == 0) return;
 
        if (m_spec.nodes.num_nodes == 0) {
            log_and_throw_error("Please add a vertex block before adding elements.");
        }
        const auto& vertex_block = m_spec.nodes.entity_blocks.back();
        // assert(!vertex_block.tags.empty());
        if (vertex_block.entity_dim != DIM) {
            log_and_throw_error(
                "It seems the last added vertex block has different dimension "
                "than the elements you want to add.");
        }
 
        mshio::ElementBlock block;
        block.entity_dim = DIM;
        block.entity_tag = vertex_block.entity_tag;
        if constexpr (DIM == 1) {
            block.element_type = 1; // 2-node line.
        } else if constexpr (DIM == 2) {
            block.element_type = 2; // 3-node triangle.
        } else {
            block.element_type = 4; // 4-node tet.
        }
        block.num_elements_in_block = num_elements;
 
        const size_t vertex_offset =
            vertex_block.num_nodes_in_block == 0 ? 0 : vertex_block.tags.front() - 1;
        if (vertex_offset == 0) {
            logger().trace(
                "Do not offset vertex IDs for this element block as vertex block was empty");
        }
 
        const size_t tag_offset = m_spec.elements.max_element_tag;
        block.data.reserve(num_elements * (DIM + 2));
        for (size_t i = 0; i < num_elements; i++) {
            const auto& e = get_element_cb(i);
            block.data.push_back(tag_offset + i + 1); // element tag.
            for (size_t j = 0; j <= DIM; j++) {
                block.data.push_back(vertex_offset + e[j] + 1);
            }
        }
 
        m_spec.elements.num_entity_blocks++;
        m_spec.elements.num_elements += num_elements;
        m_spec.elements.min_element_tag = 1;
        m_spec.elements.max_element_tag += num_elements;
        m_spec.elements.entity_blocks.push_back(std::move(block));
    }
 
    template <int NUM_FIELDS, int ELEMENT_DIM, typename Fn>
    void add_vertex_attribute(const std::string& name, const Fn& get_attribute_cb)
    {
        static_assert(
            NUM_FIELDS == 1 || NUM_FIELDS == 3 || NUM_FIELDS == 9,
            "Only scalar, vector and tensor fields are supported as attribute!");
        if (m_spec.nodes.entity_blocks.empty()) {
            throw std::runtime_error("Please add vertices before adding vertex attributes.");
        }
        const auto& vertex_block = m_spec.nodes.entity_blocks.back();
        const size_t num_vertices = vertex_block.num_nodes_in_block;
        assert(num_vertices != 0);
 
        if (vertex_block.entity_dim != ELEMENT_DIM) {
            throw std::runtime_error(
                "It seems the last added vertex block has different dimension "
                "from the vertex attribute you want to add.");
        }
 
        mshio::Data data;
        data.header.string_tags = {name};
        data.header.real_tags = {0.0};
        data.header.int_tags = {0, NUM_FIELDS, int(num_vertices), 0, ELEMENT_DIM};
 
        data.entries.resize(num_vertices);
        for (size_t i = 0; i < num_vertices; i++) {
            auto& entry = data.entries[i];
            entry.tag = vertex_block.tags[i];
            entry.data.reserve(NUM_FIELDS);
            const auto& attr = get_attribute_cb(i);
            if constexpr (NUM_FIELDS == 1) {
                entry.data.push_back(attr);
            } else {
                for (size_t j = 0; j < NUM_FIELDS; j++) {
                    entry.data.push_back(attr[j]);
                }
            }
        }
 
        m_spec.node_data.push_back(std::move(data));
    }
 
    template <int NUM_FIELDS, int ELEMENT_DIM, typename Fn>
    void add_element_attribute(const std::string& name, const Fn& get_attribute_cb)
    {
        static_assert(
            NUM_FIELDS == 1 || NUM_FIELDS == 3 || NUM_FIELDS == 9,
            "Only scalar, vector and tensor fields are supported as attribute!");
        if (m_spec.elements.entity_blocks.empty()) {
            throw std::runtime_error("Please add elements before adding element attributes!");
        }
        const auto& elem_block = m_spec.elements.entity_blocks.back();
        if (elem_block.entity_dim != ELEMENT_DIM) {
            throw std::runtime_error(
                "It seems the last added element block has different dimension "
                "than the element attribute you want to add.");
        }
        const size_t num_elements = elem_block.num_elements_in_block;
 
        mshio::Data data;
        data.header.string_tags = {name};
        data.header.real_tags = {0.0};
        data.header.int_tags = {0, NUM_FIELDS, int(num_elements), 0, ELEMENT_DIM};
 
        data.entries.resize(num_elements);
        for (size_t i = 0; i < num_elements; i++) {
            auto& entry = data.entries[i];
            entry.tag = elem_block.data[i * (ELEMENT_DIM + 2)];
            entry.data.reserve(NUM_FIELDS);
            const auto& attr = get_attribute_cb(i);
            if constexpr (NUM_FIELDS == 1) {
                entry.data.push_back(attr);
            } else {
                for (size_t j = 0; j < NUM_FIELDS; j++) {
                    entry.data.push_back(attr[j]);
                }
            }
        }
 
        m_spec.element_data.push_back(std::move(data));
    }
 
    const mshio::NodeBlock* get_vertex_block(const int dim) const
    {
        for (const auto& block : m_spec.nodes.entity_blocks) {
            if (block.entity_dim == dim) {
                return &block;
            }
        }
        return nullptr;
    }
 
    const mshio::NodeBlock* get_vertex_block(const int dim, const int tag) const
    {
        for (const auto& block : m_spec.nodes.entity_blocks) {
            if (block.entity_dim == dim && block.entity_tag == tag) {
                return &block;
            }
        }
        return nullptr;
    }
 
    const mshio::ElementBlock* get_simplex_element_block(const int dim) const
    {
        for (const auto& block : m_spec.elements.entity_blocks) {
            if (block.entity_dim == dim) {
                return &block;
            }
        }
        return nullptr;
    }
 
    const mshio::ElementBlock* get_simplex_element_block(const int dim, const int tag) const
    {
        for (const auto& block : m_spec.elements.entity_blocks) {
            if (block.entity_dim == dim && block.entity_tag == tag) {
                return &block;
            }
        }
        return nullptr;
    }
 
    size_t get_num_vertices(const int dim) const
    {
        const auto* block = get_vertex_block(dim);
        if (block != nullptr) {
            return block->num_nodes_in_block;
        } else {
            return 0;
        }
    }
 
    size_t get_num_vertices(const int dim, const int tag) const
    {
        const auto* block = get_vertex_block(dim, tag);
        if (block != nullptr) {
            return block->num_nodes_in_block;
        } else {
            return 0;
        }
    }
 
    size_t get_num_simplex_elements(const int dim) const
    {
        const auto* block = get_simplex_element_block(dim);
        if (block != nullptr) {
            return block->num_elements_in_block;
        } else {
            return 0;
        }
    }
 
    size_t get_num_simplex_elements(const int dim, const int tag) const
    {
        const auto* block = get_simplex_element_block(dim, tag);
        if (block != nullptr) {
            return block->num_elements_in_block;
        } else {
            return 0;
        }
    }
 
    template <typename Fn>
    void extract_vertices(const int dim, Fn&& set_vertex_cb) const
    {
        const auto* block = get_vertex_block(dim);
        if (block == nullptr) return;
 
        const size_t num_vertices = block->num_nodes_in_block;
        if (num_vertices == 0) return;
 
        const size_t tag_offset = block->tags.front();
        for (size_t i = 0; i < num_vertices; i++) {
            size_t tag = block->tags[i] - tag_offset;
            set_vertex_cb(tag, block->data[i * 3], block->data[i * 3 + 1], block->data[i * 3 + 2]);
        }
    }
 
    template <typename Fn>
    void extract_vertices(const int dim, const int tag, Fn&& set_vertex_cb) const
    {
        const auto* block = get_vertex_block(dim, tag);
        if (block == nullptr) return;
 
        const size_t num_vertices = block->num_nodes_in_block;
        if (num_vertices == 0) return;
 
        const size_t tag_offset = block->tags.front();
        for (size_t i = 0; i < num_vertices; i++) {
            size_t tag = block->tags[i] - tag_offset;
            set_vertex_cb(tag, block->data[i * 3], block->data[i * 3 + 1], block->data[i * 3 + 2]);
        }
    }
 
    template <int DIM, typename Fn>
    void extract_simplex_elements(Fn&& set_element_cb) const
    {
        const auto* vertex_block = get_vertex_block(DIM);
        const auto* element_block = get_simplex_element_block(DIM);
        if (element_block == nullptr) return;
        assert(vertex_block != nullptr);
 
        const size_t num_elements = element_block->num_elements_in_block;
        if (num_elements == 0) return;
        assert(vertex_block->num_nodes_in_block != 0);
 
        const size_t vert_tag_offset = vertex_block->tags.front();
        const size_t elem_tag_offset = element_block->data.front();
        for (size_t i = 0; i < num_elements; i++) {
            const size_t tag = element_block->data[i * (DIM + 2)] - elem_tag_offset;
            assert(tag < num_elements);
            const auto* element = element_block->data.data() + i * (DIM + 2) + 1;
 
            if constexpr (DIM == 1) {
                set_element_cb(tag, element[0] - vert_tag_offset, element[1] - vert_tag_offset);
            } else if constexpr (DIM == 2) {
                set_element_cb(
                    tag,
                    element[0] - vert_tag_offset,
                    element[1] - vert_tag_offset,
                    element[2] - vert_tag_offset);
            } else if constexpr (DIM == 3) {
                set_element_cb(
                    tag,
                    element[0] - vert_tag_offset,
                    element[1] - vert_tag_offset,
                    element[2] - vert_tag_offset,
                    element[3] - vert_tag_offset);
            }
        }
    }
 
    template <int DIM>
    std::vector<std::string> get_vertex_attribute_names() const
    {
        std::vector<std::string> attr_names;
        attr_names.reserve(m_spec.node_data.size());
        for (const auto& data : m_spec.node_data) {
            const auto& int_tags = data.header.int_tags;
            if (int_tags.size() >= 5 && int_tags[4] == DIM) {
                attr_names.push_back(data.header.string_tags.front());
            }
        }
        return attr_names;
    }
 
    template <int DIM>
    std::vector<std::string> get_element_attribute_names() const
    {
        std::vector<std::string> attr_names;
        attr_names.reserve(m_spec.element_data.size());
        for (const auto& data : m_spec.element_data) {
            const auto& int_tags = data.header.int_tags;
            if (int_tags.size() >= 5 && int_tags[4] == DIM) {
                attr_names.push_back(data.header.string_tags.front());
            }
        }
        return attr_names;
    }
 
    template <int DIM, typename Fn>
    void extract_vertex_attribute(const std::string& attr_name, Fn&& set_attr)
    {
        const auto* vertex_block = get_vertex_block(DIM);
        const size_t tag_offset = vertex_block->tags.front();
        for (const auto& data : m_spec.node_data) {
            if (data.header.string_tags.front() != attr_name) continue;
            if (data.header.int_tags.size() >= 5 && data.header.int_tags[4] != DIM) {
                log_and_throw_error("Attribute " + attr_name + " is of the wrong DIM.");
            }
 
            for (const auto& entry : data.entries) {
                const size_t tag = entry.tag - tag_offset;
                assert(tag < vertex_block->num_nodes_in_block);
                set_attr(tag, entry.data);
            }
        }
    }
 
    template <int DIM, typename Fn>
    void extract_element_attribute(const std::string& attr_name, Fn&& set_attr)
    {
        const auto* element_block = get_simplex_element_block(DIM);
        const size_t tag_offset = element_block->data.front();
        for (const auto& data : m_spec.element_data) {
            if (data.header.string_tags.front() != attr_name) continue;
            if (data.header.int_tags.size() >= 5 && data.header.int_tags[4] != DIM) {
                throw std::runtime_error("Attribute " + attr_name + " is of the wrong DIM.");
            }
 
            for (const mshio::DataEntry& entry : data.entries) {
                const size_t tag = entry.tag - tag_offset;
                assert(tag < element_block->num_elements_in_block);
                set_attr(tag, entry.data);
            }
        }
    }
 
 
public:
    mshio::MshSpec m_spec;
};
 
} // namespace wmtk