Add overwrite NBLOCK (#11)

* add append feature

* add docs

mapdl_archive/archive.py

@@ -3,6 +3,7 @@
 import logging
 import os
 import pathlib
+import shutil
 
 import numpy as np
 from pyvista import CellType, UnstructuredGrid
@@ -226,6 +227,61 @@ def plot(self, *args, **kwargs):
         kwargs.setdefault("show_edges", True)
         return self.grid.plot(*args, **kwargs)
 
+    @property
+    def _nblock_start(self) -> int:
+        """Return the start of the node block in the original file."""
+        return self._raw["nblock_start"]
+
+    @property
+    def _nblock_end(self) -> int:
+        """Return the end of the node block in the original file."""
+        return self._raw["nblock_end"]
+
+    def overwrite_nblock(self, filename, node_id, pos, angles=None, sig_digits=13):
+        """Write out an archive file to disk while replacing its NBLOCK.
+
+        Parameters
+        ----------
+        filename : str or file handle
+            Filename to write node block to.
+        node_id : numpy.ndarray
+            ANSYS node numbers.
+        pos : np.ndarray
+            Array of node coordinates.
+        angles : numpy.ndarray, optional
+            Writes the node angles for each node when included.
+        sig_digits : int, default: 13
+            Number of significant digits to use when writing the nodes. Must be
+            greater than 0.
+
+        Examples
+        --------
+        Write a new archive file that overwrites the NBLOCK with random nodes
+        and reuse the existing node numbers.
+
+        >>> import numpy as np
+        >>> import mapdl_archive
+        >>> archive = mapdl_archive.Archive(examples.hexarchivefile)
+        >>> new_nodes = np.random.random(archive.nodes.shape)
+        >>> archive.overwrite_nblock("new_archive.cdb", archive.nnum, new_nodes)
+
+        """
+        with open(self._filename, "rb") as src_file, open(filename, "wb") as dest_file:
+            # Copy the beginning of the file up to _nblock_start
+            dest_file.write(src_file.read(self._nblock_start))
+
+        # Write new nblock
+        write_nblock(
+            filename, node_id, pos, angles=angles, mode="a", sig_digits=sig_digits
+        )
+
+        # Copy the rest of the original file
+        with open(self._filename, "rb") as src_file, open(filename, "ab") as dest_file:
+            src_file.seek(self._nblock_end)
+            dest_file.seek(0, io.SEEK_END)
+
+            shutil.copyfileobj(src_file, dest_file)
+
 
 def save_as_archive(
     filename,

mapdl_archive/cython/_reader.pyx

@@ -94,7 +94,7 @@ def read(filename, read_parameters=False, debug=False, read_eblock=True):
     cdef int [::1] nnum = np.empty(0, ctypes.c_int)
     cdef double [:, ::1] nodes = np.empty((0, 0))
     cdef int d_size[3]
-    cdef int f_size, nfields
+    cdef int f_size, nfields, nblock_start, nblock_end, _start
 
     # EBLOCK
     cdef int nelem = 0
@@ -314,6 +314,7 @@ def read(filename, read_parameters=False, debug=False, read_eblock=True):
 
         elif first_char == 'N' or first_char == 'n':
             ungetc(first_char, cfile);  # Put the character back into the stream
+            _start = ftell(cfile)  # used for NBLOCK
             fgets(line, sizeof(line), cfile)
 
             if debug:
@@ -328,6 +329,9 @@ def read(filename, read_parameters=False, debug=False, read_eblock=True):
                 if debug:
                     print('reading NBLOCK due to ', line.decode())
 
+                # Before reading NBLOCK, save where the nblock started
+                nblock_start = _start
+
                 # Get size of NBLOCK
                 nnodes = int(line[line.rfind(b',') + 1:])
                 nnum = np.empty(nnodes, dtype=ctypes.c_int)
@@ -343,6 +347,10 @@ def read(filename, read_parameters=False, debug=False, read_eblock=True):
                 nnodes_read = read_nblock_cfile(cfile, &nnum[0], &nodes[0, 0], nnodes, d_size, f_size)
                 nodes_read = True
 
+                # read final line
+                fgets(line, sizeof(line), cfile)
+                nblock_end = ftell(cfile)
+
                 if nnodes_read != nnodes:
                     nnodes = nnodes_read
                     nodes = nodes[:nnodes]
@@ -465,16 +473,18 @@ def read(filename, read_parameters=False, debug=False, read_eblock=True):
 
     return {
         'rnum': np.asarray(rnum),
-            'rdat': rdat,
-            'ekey': np.asarray(elem_type, ctypes.c_int),
-            'nnum': np.asarray(nnum),
-            'nodes': np.asarray(nodes),
-            'elem': np.array(elem[:elem_sz]),
-            'elem_off': np.array(elem_off),
-            'node_comps': node_comps,
-            'elem_comps': elem_comps,
-            'keyopt': keyopt,
-            'parameters': parameters
+        'rdat': rdat,
+        'ekey': np.asarray(elem_type, ctypes.c_int),
+        'nnum': np.asarray(nnum),
+        'nodes': np.asarray(nodes),
+        'elem': np.array(elem[:elem_sz]),
+        'elem_off': np.array(elem_off),
+        'node_comps': node_comps,
+        'elem_comps': elem_comps,
+        'keyopt': keyopt,
+        'parameters': parameters,
+        'nblock_start': nblock_start,
+        'nblock_end': nblock_end,
     }
 
 

tests/test_archive.py

@@ -131,6 +131,9 @@ def test_archive_init(hex_archive):
     assert isinstance(hex_archive._raw, dict)
     assert isinstance(hex_archive.grid, pv.UnstructuredGrid)
 
+    assert hex_archive._nblock_start > 0
+    assert hex_archive._nblock_end > hex_archive._nblock_start
+
 
 def test_parse_vtk(hex_archive):
     grid = hex_archive.grid
@@ -545,6 +548,31 @@ def test_etblock():
     assert archive.n_elem == 1
 
 
+def test_overwrite_nblock(tmpdir, hex_archive):
+    # ensure that we capture the entire NBLOCK
+    with open(hex_archive._filename, "rb") as fid:
+        fid.seek(hex_archive._nblock_start)
+        nblock_txt = fid.read(
+            hex_archive._nblock_end - hex_archive._nblock_start
+        ).decode()
+
+    assert nblock_txt.startswith("NBLOCK")
+    assert nblock_txt.splitlines()[-1].endswith("-1,")
+
+    filename = str(tmpdir.mkdir("tmpdir").join("tmp.cdb"))
+    nodes = np.random.random(hex_archive.nodes.shape)
+    hex_archive.overwrite_nblock(
+        filename,
+        hex_archive.nnum,
+        nodes,
+    )
+
+    archive_new = Archive(filename)
+    assert np.allclose(nodes, archive_new.grid.points)
+    assert np.allclose(hex_archive.nnum, archive_new.nnum)
+    assert np.allclose(hex_archive.grid.cells.size, archive_new.grid.cells.size)
+
+
 class TestPathlibFilename:
     def test_pathlib_filename_property(self, pathlib_archive):
         assert isinstance(pathlib_archive.pathlib_filename, pathlib.Path)