#!/usr/bin/env python
# Copyright 2014-2019 The PySCF Developers. All Rights Reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
#
# Author: Qiming Sun <osirpt.sun@gmail.com>
#

'''
Non-relativistic unrestricted Kohn-Sham for periodic systems at a single k-point

See Also:
    pyscf.pbc.dft.krks.py : Non-relativistic Restricted Kohn-Sham for periodic
                            systems with k-point sampling
'''


import numpy
import pyscf.dft
from pyscf import lib
from pyscf.pbc.scf import uhf as pbcuhf
from pyscf.lib import logger
from pyscf.dft import uks as mol_uks
from pyscf.pbc.dft import gen_grid
from pyscf.pbc.dft import rks
from pyscf.pbc.dft import multigrid
from pyscf import __config__

get_rho = rks.get_rho

def get_veff(ks, cell=None, dm=None, dm_last=0, vhf_last=0, hermi=1,
             kpt=None, kpts_band=None):
    '''Coulomb + XC functional for UKS.  See pyscf/pbc/dft/uks.py
    :func:`get_veff` fore more details.
    '''
    if cell is None: cell = ks.cell
    if dm is None: dm = ks.make_rdm1()
    if kpt is None: kpt = ks.kpt
    t0 = (logger.process_clock(), logger.perf_counter())

    ni = ks._numint
    hybrid = ni.libxc.is_hybrid_xc(ks.xc)

    if not hybrid and isinstance(ks.with_df, multigrid.MultiGridFFTDF):
        if ks.do_nlc():
            raise NotImplementedError(f'MultiGrid for NLC functional {ks.xc} + {ks.nlc}')
        n, exc, vxc = multigrid.nr_uks(ks.with_df, ks.xc, dm, hermi,
                                       kpt.reshape(1,3), kpts_band,
                                       with_j=True, return_j=False)
        logger.info(ks, 'nelec by numeric integration = %s', n)
        t0 = logger.timer(ks, 'vxc', *t0)
        return vxc

    if not isinstance(dm, numpy.ndarray):
        dm = numpy.asarray(dm)
    if dm.ndim == 2:  # RHF DM
        dm = numpy.asarray((dm*.5,dm*.5))

    # ndim = 3 : dm.shape = ([alpha,beta], nao, nao)
    ground_state = (dm.ndim == 3 and dm.shape[0] == 2 and kpts_band is None)
    ks.initialize_grids(cell, dm, kpt, ground_state)

    if hermi == 2:  # because rho = 0
        n, exc, vxc = (0,0), 0, 0
    else:
        max_memory = ks.max_memory - lib.current_memory()[0]
        n, exc, vxc = ni.nr_uks(cell, ks.grids, ks.xc, dm, 0, hermi,
                                kpt, kpts_band, max_memory=max_memory)
        if ks.do_nlc():
            if ni.libxc.is_nlc(ks.xc):
                xc = ks.xc
            else:
                assert ni.libxc.is_nlc(ks.nlc)
                xc = ks.nlc
            n, enlc, vnlc = ni.nr_nlc_vxc(cell, ks.nlcgrids, xc, dm[0]+dm[1],
                                          0, hermi, kpt, max_memory=max_memory)
            exc += enlc
            vxc += vnlc
        logger.info(ks, 'nelec by numeric integration = %s', n)
        t0 = logger.timer(ks, 'vxc', *t0)

    if not hybrid:
        vj = ks.get_j(cell, dm[0]+dm[1], hermi, kpt, kpts_band)
        vxc += vj
    else:
        omega, alpha, hyb = ni.rsh_and_hybrid_coeff(ks.xc, spin=cell.spin)
        if getattr(ks.with_df, '_j_only', False):  # for GDF and MDF
            logger.warn(ks, 'df.j_only cannot be used with hybrid functional')
            ks.with_df._j_only = False
            # Rebuild df object due to the change of parameter _j_only
            if ks.with_df._cderi is not None:
                ks.with_df.build()
        if omega == 0:
            vj, vk = ks.get_jk(cell, dm, hermi, kpt, kpts_band)
            vk *= hyb
        elif alpha == 0: # LR=0, only SR exchange
            vj = ks.get_j(cell, dm, hermi, kpt, kpts_band)
            vk = ks.get_k(cell, dm, hermi, kpt, kpts_band, omega=-omega)
            vk *= hyb
        elif hyb == 0: # SR=0, only LR exchange
            vj = ks.get_j(cell, dm, hermi, kpt, kpts_band)
            vk = ks.get_k(cell, dm, hermi, kpt, kpts_band, omega=omega)
            vk *= alpha
        else: # SR and LR exchange with different ratios
            vj, vk = ks.get_jk(cell, dm, hermi, kpt, kpts_band)
            vk *= hyb
            vklr = ks.get_k(cell, dm, hermi, kpt, kpts_band, omega=omega)
            vklr *= (alpha - hyb)
            vk += vklr
        vj = vj[0] + vj[1]
        vxc += vj - vk

        if ground_state:
            exc -=(numpy.einsum('ij,ji', dm[0], vk[0]) +
                   numpy.einsum('ij,ji', dm[1], vk[1])).real * .5

    if ground_state:
        ecoul = numpy.einsum('ij,ji', dm[0]+dm[1], vj).real * .5
    else:
        ecoul = None

    vxc = lib.tag_array(vxc, ecoul=ecoul, exc=exc, vj=None, vk=None)
    return vxc


class UKS(rks.KohnShamDFT, pbcuhf.UHF):
    '''UKS class adapted for PBCs.

    This is a literal duplication of the molecular UKS class with some `mol`
    variables replaced by `cell`.
    '''

    get_rho = get_rho
    get_vsap = mol_uks.UKS.get_vsap
    init_guess_by_vsap = mol_uks.UKS.init_guess_by_vsap
    get_veff = get_veff
    energy_elec = pyscf.dft.uks.energy_elec

    def __init__(self, cell, kpt=numpy.zeros(3), xc='LDA,VWN',
                 exxdiv=getattr(__config__, 'pbc_scf_SCF_exxdiv', 'ewald')):
        pbcuhf.UHF.__init__(self, cell, kpt, exxdiv=exxdiv)
        rks.KohnShamDFT.__init__(self, xc)

    def dump_flags(self, verbose=None):
        pbcuhf.UHF.dump_flags(self, verbose)
        rks.KohnShamDFT.dump_flags(self, verbose)
        return self

    def to_hf(self):
        '''Convert to UHF object.'''
        from pyscf.pbc import scf
        return self._transfer_attrs_(scf.UHF(self.cell, self.kpt))

    to_gpu = lib.to_gpu


if __name__ == '__main__':
    from pyscf.pbc import gto
    cell = gto.Cell()
    cell.unit = 'A'
    cell.atom = 'C 0.,  0.,  0.; C 0.8917,  0.8917,  0.8917'
    cell.a = '''0.      1.7834  1.7834
                1.7834  0.      1.7834
                1.7834  1.7834  0.    '''

    cell.basis = 'gth-szv'
    cell.pseudo = 'gth-pade'
    cell.verbose = 7
    cell.output = '/dev/null'
    cell.build()
    mf = UKS(cell)
    print(mf.kernel())
