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__title__ = "FreeCAD Fenics XML mesh writer"
__author__ = "Johannes Hartung"
__url__ = "https://www.freecad.org"

## @package exportFenicsXML
#  \ingroup FEM
#  \brief FreeCAD Fenics Mesh XML writer for FEM workbench


from xml.etree import ElementTree as ET  # parsing xml files and exporting

from FreeCAD import Console

from .importToolsFem import get_FemMeshObjectDimension
from .importToolsFem import get_FemMeshObjectElementTypes
from .importToolsFem import get_MaxDimElementFromList


def write_fenics_mesh_xml(fem_mesh_obj, outputfile):
    """
        For the export, we only have to use the highest dimensional entities and their
        vertices to be exported.
        For second order elements, we have to delete the mid element nodes.
    """

    # TODO: check for second order elements
    # (reduce element order would be ok - all elements have at least the first
    # necessary nodes)

    FreeCAD_to_Fenics_dict = {
        "Triangle": "triangle",
        "Tetra": "tetrahedron",
        "Hexa": "hexahedron",
        "Edge": "interval",
        "Node": "point",
        "Quadrangle": "quadrilateral",

        "Polygon": "unknown", "Polyhedron": "unknown",
        "Prism": "unknown", "Pyramid": "unknown",
    }

    XML_Number_of_Nodes_dict = {
        "point": 1,
        "interval": 2,
        "triangle": 3,
        "quadrilateral": 4,
        "tetrahedron": 4,
        "hexahedron": 8
    }

    Console.PrintMessage(f"Converting {fem_mesh_obj.Label} to fenics XML File\n")
    Console.PrintMessage(f"Dimension of mesh: {get_FemMeshObjectDimension(fem_mesh_obj)}\n")

    elements_in_mesh = get_FemMeshObjectElementTypes(fem_mesh_obj)
    Console.PrintMessage(f"Elements appearing in mesh: {str(elements_in_mesh)}\n")
    celltype_in_mesh = get_MaxDimElementFromList(elements_in_mesh)
    (num_cells, cellname_fc, dim_cell) = celltype_in_mesh
    cellname_fenics = FreeCAD_to_Fenics_dict[cellname_fc]
    num_verts_cell = XML_Number_of_Nodes_dict[cellname_fenics]
    Console.PrintMessage(f"Celltype in mesh -> {str(celltype_in_mesh)} " +
                         f"and its Fenics name: {cellname_fenics}\n")

    root = ET.Element("dolfin", dolfin="http://fenicsproject.org")
    meshchild = ET.SubElement(root, "mesh", celltype=cellname_fenics, dim=str(dim_cell))
    vertices = ET.SubElement(meshchild, "vertices", size=str(fem_mesh_obj.FemMesh.NodeCount))

    for (nodeind, fc_vec) in list(fem_mesh_obj.FemMesh.Nodes.items()):
        ET.SubElement(
            vertices, "vertex", index=str(nodeind - 1),
            # FC starts from 1, fenics starts from 0 to size-1
            x=str(fc_vec[0]), y=str(fc_vec[1]), z=str(fc_vec[2]))

    cells = ET.SubElement(meshchild, "cells", size=str(num_cells))
    if dim_cell == 3:
        fc_cells = fem_mesh_obj.FemMesh.Volumes
    elif dim_cell == 2:
        fc_cells = fem_mesh_obj.FemMesh.Faces
    elif dim_cell == 1:
        fc_cells = fem_mesh_obj.FemMesh.Edges
    else:
        fc_cells = ()

    for (fen_ind, fc_volume_ind) in enumerate(fc_cells):
        # FC starts after all other entities, fenics start from 0 to size-1
        nodeindices = fem_mesh_obj.FemMesh.getElementNodes(fc_volume_ind)

        cell_args = {}
        for (vi, ni) in enumerate(nodeindices):
            if vi < num_verts_cell:  # XML only supports first order meshs
                cell_args["v" + str(vi)] = str(ni - 1)
        # generate as many v entries in dict as nodes are listed in cell
        # works only for first order elements

        ET.SubElement(cells, cellname_fenics, index=str(fen_ind), **cell_args)

    # ET.SubElement(meshchild, "data")
    # removed to eliminate warning from meshio

    fp = open(outputfile, "wb")
    fp.write(ET.tostring(root))
    # xml core functionality does not support pretty printing
    # so the output file looks quite ugly
    fp.close()