import numpy as np
import os
from mpi4py import MPI
from tacs import TACS

# Load structural mesh from BDF file
mesh = TACS.MeshLoader(comm, bdf_filename)

# Set constitutive properties
density = 1.0
E = 1.0e6
nu = 0.3
shear_correction = 5.0/6.0
yield_stress = 1.0
thickness = 0.1

# Loop over components of the mesh
for i in range(mesh.getNumComponents()):
    stiff = TACS.Elasticity3D(density, E, nu, shear_correction, yield_stress, thickness)
    elem = TACS.LinearElasticity3D(stiff)
    mesh.setElement(i, elem)

# Create TACS assembler object
assembler = TACS.Assembler(mesh)

# Create KS function and get design variable values
ks_func = TACS.KSFailure(assembler, ks_weight)
ks_func.setKSFailureType(TACS.MAX_FAILURE)

# Get node locations and create forces
Xpts = mesh.getNodes()
forces = np.zeros(3*Xpts.shape[0])

# Set up and solve analysis problem
ans = assembler.createVec()
res = assembler.createVec()
mat = assembler.createFEMat()
ans.set(0.0)
assembler.zeroVariables()
assembler.assembleJacobian(1.0, 0.0, 0.0, res, mat)
mat.factor()
mat.applyBCs(res)
mat.solve(res, ans)

# Evaluate function and solve for adjoint variables
ks_func.setFunction(ans)
adjoint = ks_func.createDesignVec()
ks_func.evalConstr(adjoint)

# Compute total derivative with respect to material design variables and nodal locations
ks_func.addAdjoint(1.0, adjoint)
ks_func.addOutput(1.0, adjoint)

# Create random direction for perturbation
perturb = np.random.rand(3*Xpts.shape[0])

# Compute total derivative with respect to nodal locations
ks_func.addOutput(-1.0, perturb)

# Set complex step and compute perturbed solution
perturbed_ans = assembler.createVec()
perturbed_ans.axpy(1e-30, perturb)
perturbed_ans.axpy(1.0, ans)

# Evaluate function for perturbed solution and compute projected derivative
ks_func.setFunction(perturbed_ans)
ks_func.evalConstr(adjoint)

# Output results for visualization
TACS.writeTACSAdjointToVTK("output.vtk", mesh, adjoint)