gurobi.py

from ctypes.util import find_library
import logging
from sys import maxsize, platform
from typing import List, Tuple
from os.path import isfile
import os.path
from glob import glob
import re
from os import environ
import numbers
from cffi import FFI
import importlib.util
import pathlib
from mip.exceptions import (
    ParameterNotAvailable,
    SolutionNotAvailable,
    ProgrammingError,
    InterfacingError,
)
from mip import (
    Model,
    Column,
    Var,
    LinExpr,
    Constr,
    Solver,
    VConstrList,
    VVarList,
    xsum,
    MAXIMIZE,
    MINIMIZE,
    CONTINUOUS,
    INTEGER,
    BINARY,
    OptimizationStatus,
    EQUAL,
    LESS_OR_EQUAL,
    GREATER_OR_EQUAL,
    SearchEmphasis,
    LP_Method,
)
from mip.lists import EmptyVarSol, EmptyRowSol
import mip

logger = logging.getLogger(__name__)

ffi = FFI()
CData = ffi.CData
os_is_64_bit = maxsize > 2**32
INF = float("inf")
MAX_NAME_SIZE = 512  # for variables and constraints

lib_path = None
has_gurobi = False

if "GUROBI_HOME" in environ:
    if platform.lower().startswith("win"):
        lib_path_dir = os.path.join(os.environ["GUROBI_HOME"], "bin", "*")
        pattern = r"gurobi([0-9]{2,3}).dll"

    else:
        lib_path_dir = os.path.join(os.environ["GUROBI_HOME"], "lib", "*")
        pattern = r"libgurobi([0-9]{2,3})[.].*"

    for libfile in glob(lib_path_dir):
        match = re.match(pattern, os.path.basename(libfile))
        if match:
            lib_path = libfile

            # checking gurobi version
            major_ver = match.group(1)[:-1]
            minor_ver = match.group(1)[-1]
            break

if lib_path is None:
    for major_ver in reversed(range(6, 11)):
        for minor_ver in reversed(range(0, 11)):
            lib_path = find_library("gurobi{}{}".format(major_ver, minor_ver))
            if lib_path is not None:
                break
        if lib_path is not None:
            break

# Check for gurobi through pip installation
if lib_path is None:
    gurobipy_spec = importlib.util.find_spec("gurobipy")
    if gurobipy_spec:
        parent_path = pathlib.Path(gurobipy_spec.origin).parent
        if platform.lower().startswith("win"):
            extension = ".dll"
        else:
            extension = ".so"
        lib_path = str(next(parent_path.glob(f"*{extension}")))


if lib_path is None:
    has_gurobi = False
else:
    has_gurobi = True
    grblib = ffi.dlopen(lib_path)

    ffi.cdef(
        """
        typedef struct _GRBmodel GRBmodel;
        typedef struct _GRBenv GRBenv;

        typedef int(*gurobi_callback)(GRBmodel *model, void *cbdata,
                                    int where, void *usrdata);


        GRBenv *GRBgetenv(GRBmodel *model);

        int GRBloadenv(GRBenv **envP, const char *logfilename);

        int GRBnewmodel(GRBenv *env, GRBmodel **modelP,
            const char *Pname, int numvars,
            double *obj, double *lb, double *ub, char *vtype,
            char **varnames);

        void GRBfreeenv(GRBenv *env);

        int GRBfreemodel(GRBmodel *model);

        int GRBgetintattr(GRBmodel *model, const char *attrname, int *valueP);

        int GRBsetintattr(GRBmodel *model, const char *attrname, int newvalue);

        int GRBgetintattrelement(GRBmodel *model, const char *attrname,
            int element, int *valueP);

        int GRBsetintattrelement(GRBmodel *model, const char *attrname,
            int element, int newvalue);

        int GRBgetdblattr(GRBmodel *model, const char *attrname,
            double *valueP);

        int GRBsetdblattr(GRBmodel *model, const char *attrname,
            double newvalue);

        int GRBgetdblattrarray(GRBmodel *model, const char *attrname,
            int first, int len, double *values);

        int GRBsetdblattrarray(GRBmodel *model, const char *attrname,
            int first, int len, double *newvalues);

        int GRBsetdblattrlist(GRBmodel *model, const char *attrname,
            int len, int *ind, double *newvalues);

        int GRBgetdblattrelement(GRBmodel *model, const char *attrname,
            int element, double *valueP);

        int GRBsetdblattrelement(GRBmodel *model, const char *attrname,
            int element, double newvalue);

        int GRBgetcharattrarray(GRBmodel *model, const char *attrname,
                    int first, int len, char *values);

        int GRBsetcharattrarray(GRBmodel *model, const char *attrname,
            int first, int len, char *newvalues);

        int GRBgetcharattrelement(GRBmodel *model, const char *attrname,
                                int element, char *valueP);
        int GRBsetcharattrelement(GRBmodel *model, const char *attrname,
                                int element, char newvalue);

        int GRBgetstrattrelement(GRBmodel *model, const char *attrname,
                            int element, char **valueP);

        int GRBgetstrattr (GRBmodel *model, const char *attrname,
            char **valueP);

        int GRBsetstrattr (GRBmodel *model, const char *attrname,
            const char *newvalue);

        int GRBgetintparam(GRBenv *env, const char *paramname, int *valueP);

        int GRBsetintparam(GRBenv *env, const char *paramname, int value);

        int GRBgetdblparam(GRBenv *env, const char *paramname, double *valueP);

        int GRBsetdblparam(GRBenv *env, const char *paramname, double value);

        int GRBsetobjectiven(GRBmodel *model, int index,
                        int priority, double weight,
                        double abstol, double reltol, const char *name,
                        double constant, int lnz, int *lind, double *lval);

        int GRBaddvar(GRBmodel *model, int numnz, int *vind, double *vval,
                    double obj, double lb, double ub, char vtype,
                    const char *varname);

        int GRBaddconstr(GRBmodel *model, int numnz, int *cind, double *cval,
            char sense, double rhs, const char *constrname);

        int GRBaddsos(GRBmodel *model,
            int numsos, int nummembers, int *types,
                int *beg, int *ind, double *weight);

        int GRBgetconstrs(GRBmodel *model, int *numnzP, int *cbeg,
                int *cind, double *cval, int start, int len);

        int GRBgetvars(GRBmodel *model, int *numnzP, int *vbeg, int *vind,
            double *vval, int start, int len);

        int GRBgetvarbyname(GRBmodel *model, const char *name, int *indexP);

        int GRBgetconstrbyname(GRBmodel *model, const char *name, int *indexP);

        int GRBoptimize(GRBmodel *model);

        int GRBupdatemodel(GRBmodel *model);

        int GRBwrite(GRBmodel *model, const char *filename);

        int GRBreadmodel(GRBenv *env, const char *filename, GRBmodel **modelP);

        int GRBread(GRBmodel *model, const char *filename);

        int GRBdelvars(GRBmodel *model, int numdel, int *ind );

        int GRBsetcharattrlist(GRBmodel *model, const char *attrname,
            int len, int *ind, char *newvalues);

        int GRBsetcallbackfunc(GRBmodel *model,
                    gurobi_callback grbcb,
                    void  *usrdata);

        int GRBcbget(void *cbdata, int where, int what, void *resultP);

        int GRBcbsetparam(void *cbdata, const char *paramname,
            const char *newvalue);

        int GRBcbsolution(void *cbdata, const double *solution,
            double *objvalP);

        int GRBcbcut(void *cbdata, int cutlen, const int *cutind,
            const double *cutval,
            char cutsense, double cutrhs);

        int GRBcblazy(void *cbdata, int lazylen, const int *lazyind,
            const double *lazyval, char lazysense, double lazyrhs);

        int GRBdelconstrs (GRBmodel *model, int numdel, int *ind);

        int	GRBreset (GRBmodel *model, int clearall);
    """
    )

    GRBloadenv = grblib.GRBloadenv
    GRBnewmodel = grblib.GRBnewmodel
    GRBfreeenv = grblib.GRBfreeenv
    GRBfreemodel = grblib.GRBfreemodel
    GRBaddvar = grblib.GRBaddvar
    GRBaddconstr = grblib.GRBaddconstr
    GRBaddsos = grblib.GRBaddsos
    GRBoptimize = grblib.GRBoptimize
    GRBgetvarbyname = grblib.GRBgetvarbyname
    GRBsetdblattrarray = grblib.GRBsetdblattrarray
    GRBsetcharattrlist = grblib.GRBsetcharattrlist
    GRBsetdblattrlist = grblib.GRBsetdblattrlist
    GRBwrite = grblib.GRBwrite
    GRBreadmodel = grblib.GRBreadmodel
    GRBread = grblib.GRBread
    GRBgetconstrbyname = grblib.GRBgetconstrbyname
    GRBupdatemodel = grblib.GRBupdatemodel
    GRBgetcharattrelement = grblib.GRBgetcharattrelement
    GRBgetconstrs = grblib.GRBgetconstrs
    GRBgetdblattrelement = grblib.GRBgetdblattrelement
    GRBgetvars = grblib.GRBgetvars
    GRBsetcharattrelement = grblib.GRBsetcharattrelement
    GRBsetdblattrelement = grblib.GRBsetdblattrelement
    GRBsetintattr = grblib.GRBsetintattr
    GRBsetintattrelement = grblib.GRBsetintattrelement
    GRBgetintattrelement = grblib.GRBgetintattrelement
    GRBsetdblattr = grblib.GRBsetdblattr
    GRBgetintattr = grblib.GRBgetintattr
    GRBgetintparam = grblib.GRBgetintparam
    GRBsetintparam = grblib.GRBsetintparam
    GRBgetdblattr = grblib.GRBgetdblattr
    GRBsetdblparam = grblib.GRBsetdblparam
    GRBgetdblparam = grblib.GRBgetdblparam
    GRBgetstrattrelement = grblib.GRBgetstrattrelement
    GRBcbget = grblib.GRBcbget
    GRBcbsetparam = grblib.GRBcbsetparam
    GRBcbsolution = grblib.GRBcbsolution
    GRBcbcut = grblib.GRBcbcut
    GRBcblazy = grblib.GRBcblazy
    GRBsetcallbackfunc = grblib.GRBsetcallbackfunc
    GRBdelvars = grblib.GRBdelvars
    GRBdelconstrs = grblib.GRBdelconstrs
    GRBgetenv = grblib.GRBgetenv
    GRBgetstrattr = grblib.GRBgetstrattr
    GRBsetstrattr = grblib.GRBsetstrattr
    GRBgetdblattrarray = grblib.GRBgetdblattrarray
    GRBreset = grblib.GRBreset

    GRB_CB_MIPSOL = 4
    GRB_CB_MIPNODE = 5

    GRB_CB_PRE_COLDEL = 1000
    GRB_CB_PRE_ROWDEL = 1001
    GRB_CB_PRE_SENCHG = 1002
    GRB_CB_PRE_BNDCHG = 1003
    GRB_CB_PRE_COECHG = 1004

    GRB_CB_SPX_ITRCNT = 2000
    GRB_CB_SPX_OBJVAL = 2001
    GRB_CB_SPX_PRIMINF = 2002
    GRB_CB_SPX_DUALINF = 2003
    GRB_CB_SPX_ISPERT = 2004

    GRB_CB_MIP_OBJBST = 3000
    GRB_CB_MIP_OBJBND = 3001
    GRB_CB_MIP_NODCNT = 3002
    GRB_CB_MIP_SOLCNT = 3003
    GRB_CB_MIP_CUTCNT = 3004
    GRB_CB_MIP_NODLFT = 3005
    GRB_CB_MIP_ITRCNT = 3006

    GRB_CB_MIPSOL_SOL = 4001
    GRB_CB_MIPSOL_OBJ = 4002
    GRB_CB_MIPSOL_OBJBST = 4003
    GRB_CB_MIPSOL_OBJBND = 4004
    GRB_CB_MIPSOL_NODCNT = 4005
    GRB_CB_MIPSOL_SOLCNT = 4006

    GRB_CB_MIPNODE_STATUS = 5001
    GRB_CB_MIPNODE_REL = 5002
    GRB_CB_MIPNODE_OBJBST = 5003
    GRB_CB_MIPNODE_OBJBND = 5004
    GRB_CB_MIPNODE_NODCNT = 5005
    GRB_CB_MIPNODE_SOLCNT = 5006

    GRB_CB_MSG_STRING = 6001
    GRB_CB_RUNTIME = 6002
    GRB_OPTIMAL = 2


class SolverGurobi(Solver):
    def __init__(self, model: Model, name: str, sense: str, modelp: CData = ffi.NULL):
        """modelp should be informed if a model should not be created,
        but only allow access to an existing one"""
        if not has_gurobi:
            raise FileNotFoundError(
                """Gurobi not found. Plase check if the
            Gurobi dynamic loadable library is reachable or define
            the environment variable GUROBI_HOME indicating the gurobi
            installation path.
            """
            )

        super().__init__(model, name, sense)

        # setting class members to default values
        self._log = ""
        self._env = ffi.NULL
        self._model = ffi.NULL
        self._callback = None
        self._ownsModel = True
        self._venv_loaded = False
        self._nlazy = 0

        if modelp == ffi.NULL:
            self._ownsModel = True
            self._env = ffi.new("GRBenv **")

            # creating Gurobi environment
            st = GRBloadenv(self._env, "".encode("utf-8"))
            if st != 0:
                raise InterfacingError(
                    "Gurobi environment could not be loaded, check your license."
                )
            self._env = self._env[0]

            # creating Gurobi model
            self._model = ffi.new("GRBmodel **")
            st = GRBnewmodel(
                self._env,
                self._model,
                name.encode("utf-8"),
                0,
                ffi.NULL,
                ffi.NULL,
                ffi.NULL,
                ffi.NULL,
                ffi.NULL,
            )
            if st != 0:
                raise InterfacingError("Could not create Gurobi model")
            self._model = self._model[0]

            # setting objective sense
            if sense == MAXIMIZE:
                self.set_int_attr("ModelSense", -1)
            else:
                self.set_int_attr("ModelSense", 1)
        else:
            self._ownsModel = False
            self._model = modelp
            self._env = GRBgetenv(self._model)

        self._venv_loaded = True
        # default number of threads
        self.__threads = 0

        # fine grained control of what is changed
        # for selective call on model.update
        self.__n_cols_buffer = 0
        self.__n_int_buffer = 0
        self.__n_rows_buffer = 0
        self.__n_modified_cols = 0
        self.__n_modified_rows = 0
        self.__updated = True
        self.__name_space = ffi.new("char[{}]".format(MAX_NAME_SIZE))
        self.__log = []

        # where solution will be stored
        self.__x = EmptyVarSol(model)
        self.__rc = EmptyVarSol(model)
        self.__pi = EmptyRowSol(model)
        self.__obj_val = None

    def __clear_sol(self):
        model = self.model
        self.__x = EmptyVarSol(model)
        self.__rc = EmptyVarSol(model)
        self.__pi = EmptyRowSol(model)
        self.__obj_val = None

    def __del__(self):
        # freeing Gurobi model and environment
        if self._ownsModel:
            if self._model:
                GRBfreemodel(self._model)
            if self._env and self._venv_loaded:
                GRBfreeenv(self._env)

    def add_var(
        self,
        obj: float = 0,
        lb: float = 0,
        ub: float = INF,
        var_type: str = CONTINUOUS,
        column: Column = None,
        name: str = "",
    ):
        # collecting column data
        nz = 0 if column is None else len(column.constrs)
        if nz:
            self.flush_rows()
            vind = ffi.new("int[]", [c.idx for c in column.constrs])
            vval = ffi.new("double[]", [column.coeffs[i] for i in range(nz)])
        else:
            vind = ffi.NULL
            vval = ffi.NULL

        # variable type
        vtype = var_type.encode("utf-8")

        st = GRBaddvar(
            self._model,
            nz,
            vind,
            vval,
            obj,
            lb,
            ub,
            vtype,
            name.encode("utf-8"),
        )
        if st != 0:
            raise ParameterNotAvailable(
                "Error adding variable {} to model.".format(name)
            )

        self.__n_cols_buffer += 1
        if vtype == BINARY or vtype == INTEGER:
            self.__n_int_buffer += 1

    def add_cut(self, lin_expr: LinExpr):
        # added in SolverGurobiCB

        return

    def add_constr(self, lin_expr: LinExpr, name: str = ""):
        # collecting linear expression data
        nz = len(lin_expr.expr)
        cind = ffi.new("int[]", [var.idx for var in lin_expr.expr.keys()])
        cval = ffi.new("double[]", [coef for coef in lin_expr.expr.values()])

        # constraint sense and rhs
        sense = lin_expr.sense.encode("utf-8")
        rhs = -lin_expr.const

        if not name:
            name = "r({})".format(self.num_rows())

        st = GRBaddconstr(self._model, nz, cind, cval, sense, rhs, name.encode("utf-8"))
        if st != 0:
            raise ParameterNotAvailable(
                "Error adding constraint {} to the model".format(name)
            )
        self.__n_rows_buffer += 1

    def add_lazy_constr(self: "Solver", lin_expr: "LinExpr"):
        self.flush_rows()
        self.set_int_param("LazyConstraints", 1)
        self._nlazy += 1
        self.add_constr(lin_expr, "lz({})".format(self._nlazy))
        self.set_int_attr_element("Lazy", self.num_rows() - 1, 3)

    def add_sos(self, sos: List[Tuple["Var", float]], sos_type: int):
        self.flush_cols()
        types = ffi.new("int[]", [sos_type])
        beg = ffi.new("int[]", [0, len(sos)])
        idx = ffi.new("int[]", [v.idx for (v, f) in sos])
        w = ffi.new("double[]", [f for (v, f) in sos])
        st = GRBaddsos(self._model, 1, len(sos), types, beg, idx, w)
        if st != 0:
            raise ParameterNotAvailable("Error adding SOS to the model")

    def get_objective_bound(self) -> float:
        return self.get_dbl_attr("ObjBound")

    def get_objective(self) -> LinExpr:
        self.flush_cols()
        attr = "Obj".encode("utf-8")
        # st = GRBsetdblattrarray(self._model, attr,
        #                         0, num_vars, zeros)
        obj = ffi.new("double[]", [0.0 for i in range(self.num_cols())])

        st = GRBgetdblattrarray(self._model, attr, 0, self.num_cols(), obj)
        if st != 0:
            raise ParameterNotAvailable("Error getting objective function")
        obj_expr = xsum(
            obj[i] * self.model.vars[i]
            for i in range(self.num_cols())
            if abs(obj[i]) > 1e-20
        )
        obj_expr.add_const(self.get_objective_const())
        obj_expr.sense = self.get_objective_sense()
        return obj_expr

    def get_objective_const(self) -> float:
        return self.get_dbl_attr("ObjCon")

    def relax(self):
        self.flush_cols()
        idxv = [var.idx for var in self.model.vars if var.var_type in [BINARY, INTEGER]]

        n = len(idxv)
        idxs = ffi.new("int[]", idxv)

        cont_char = CONTINUOUS.encode("utf-8")
        ccont = ffi.new("char[]", [cont_char for i in range(n)])

        attr = "VType".encode("utf-8")
        GRBsetcharattrlist(self._model, attr, n, idxs, ccont)
        self.__updated = False
        self.update()

    def get_max_seconds(self) -> float:
        return self.get_dbl_param("TimeLimit")

    def set_max_seconds(self, max_seconds: float):
        self.set_dbl_param("TimeLimit", max_seconds)

    def get_max_solutions(self) -> int:
        return self.get_int_param("SolutionLimit")

    def set_max_solutions(self, max_solutions: int):
        self.set_int_param("SolutionLimit", max_solutions)

    def get_max_nodes(self) -> int:
        rdbl = self.get_dbl_param("NodeLimit")
        rint = min(maxsize, int(rdbl))
        return rint

    def set_max_nodes(self, max_nodes: int):
        self.set_dbl_param("NodeLimit", float(max_nodes))

    def set_num_threads(self, threads: int):
        self.__threads = threads

    def optimize(self, relax: bool = False) -> OptimizationStatus:

        # todo add branch_selector and incumbent_updater callbacks
        @ffi.callback(
            """
        int (GRBmodel *, void *, int, void *)
        """
        )
        def callback(
            p_model: CData, p_cbdata: CData, where: int, p_usrdata: CData
        ) -> int:

            if self.model.store_search_progress_log:
                if where == 3:
                    res = ffi.new("double *")
                    st = GRBcbget(p_cbdata, where, GRB_CB_MIP_OBJBND, res)
                    if st == 0:
                        obj_bound = res[0]
                        st = GRBcbget(p_cbdata, where, GRB_CB_MIP_OBJBST, res)
                        if st == 0:
                            obj_best = res[0]
                            st = GRBcbget(p_cbdata, where, GRB_CB_RUNTIME, res)
                            if st == 0:
                                sec = res[0]
                                log = self.__log
                                if not log:
                                    log.append((sec, (obj_bound, obj_best)))
                                else:
                                    difl = abs(obj_bound - log[-1][1][0])
                                    difu = abs(obj_best - log[-1][1][1])
                                    if difl >= 1e-6 or difu >= 1e-6:
                                        logger.info(
                                            ">>>>>>> {} {}".format(obj_bound, obj_best)
                                        )
                                    log.append((sec, (obj_bound, obj_best)))

            # adding cuts or lazy constraints
            if self.model.cuts_generator and where == GRB_CB_MIPNODE:
                st = ffi.new("int *")
                st[0] = 0

                error = GRBcbget(p_cbdata, where, GRB_CB_MIPNODE_STATUS, st)
                if error:
                    raise ParameterNotAvailable("Could not get gurobi status")
                if st[0] != GRB_OPTIMAL:
                    return 0

                mgc = ModelGurobiCB(p_model, p_cbdata, where)
                self.model.cuts_generator.generate_constrs(mgc)
                return 0

            # adding lazy constraints
            if self.model.lazy_constrs_generator and where == GRB_CB_MIPSOL:
                mgc = ModelGurobiCB(p_model, p_cbdata, where)
                self.model.lazy_constrs_generator.generate_constrs(mgc)

            return 0

        self.update()
        if (
            self.model.cuts_generator is not None
            or self.model.lazy_constrs_generator is not None
            or self.model.store_search_progress_log
        ):
            GRBsetcallbackfunc(self._model, callback, ffi.NULL)
            if self.model.lazy_constrs_generator:
                self.set_int_param("LazyConstraints", 1)

        if self.__threads >= 1:
            self.set_int_param("Threads", self.__threads)

        if self.model.cuts != -1:
            self.set_int_param("Cuts", self.model.cuts)

        if self.model.clique != -1:
            self.set_int_param("CliqueCuts", self.model.clique)

        if self.model.cut_passes != -1:
            self.set_int_param("CutPasses", self.model.cut_passes)

        if self.model.preprocess != -1:
            self.set_int_param("Presolve", self.model.preprocess)

        if self.model.integer_tol >= 0.0:
            self.set_dbl_param("IntFeasTol", self.model.integer_tol)
        if self.model.infeas_tol >= 0.0:
            self.set_dbl_param("FeasibilityTol", self.model.infeas_tol)
        if self.model.opt_tol >= 0.0:
            self.set_dbl_param("OptimalityTol", self.model.opt_tol)

        if self.model.lp_method == LP_Method.PRIMAL:
            self.set_int_param("Method", 0)
        elif self.model.lp_method == LP_Method.DUAL:
            self.set_int_param("Method", 1)
        elif self.model.lp_method == LP_Method.BARRIER:
            self.set_int_param("Method", 2)
        elif self.model.lp_method == LP_Method.BARRIERNOCROSS:
            self.set_int_param("Method", 2)
            self.set_int_param("Crossover", 0)
        else:
            self.set_int_param("Method", 3)

        self.set_int_param("Seed", self.model.seed)
        self.set_int_param("PoolSolutions", self.model.sol_pool_size)

        self.set_mip_gap(self.model.max_mip_gap)
        self.set_mip_gap_abs(self.model.max_mip_gap_abs)

        # executing Gurobi to solve the formulation
        self.__clear_sol()

        # if solve only LP relax, saving var types
        int_vars = []
        if relax:
            int_vars = [
                (v, v.var_type)
                for v in self.model.vars
                if v.var_type in [BINARY, INTEGER]
            ]
            for v, _ in int_vars:
                v.var_type = CONTINUOUS
            self.update()

        status = GRBoptimize(self._model)
        if int_vars:
            for v, vt in int_vars:
                v.var_type = vt
            self.update()

        if status != 0:
            if status == 10009:
                raise InterfacingError(
                    "gurobi found but license not accepted, please check it"
                )
            if status == 10001:
                raise MemoryError("out of memory error")

            raise InterfacingError("Gurobi error {} while optimizing.".format(status))

        status = self.get_int_attr("Status")
        # checking status for MIP optimization which
        # finished before the search to be
        # concluded (time, iteration limit...)
        if (self.num_int() + self.get_int_attr("NumSOS")) and (not relax):
            if status in [8, 9, 10, 11, 13]:
                nsols = self.get_int_attr("SolCount")
                if nsols >= 1:
                    self.__x = ffi.new("double[{}]".format(self.num_cols()))
                    self.__obj_val = self.get_dbl_attr("ObjVal")

                    attr = "X".encode("utf-8")
                    st = GRBgetdblattrarray(
                        self._model, attr, 0, self.num_cols(), self.__x
                    )
                    if st:
                        raise ParameterNotAvailable("Error querying Gurobi solution")

                    return OptimizationStatus.FEASIBLE

                return OptimizationStatus.NO_SOLUTION_FOUND

        if status == 1:  # LOADED
            return OptimizationStatus.LOADED
        if status == 2:  # OPTIMAL
            if isinstance(self.__x, EmptyVarSol):
                self.__obj_val = self.get_dbl_attr("ObjVal")

                self.__x = ffi.new("double[{}]".format(self.num_cols()))
                attr = "X".encode("utf-8")
                st = GRBgetdblattrarray(self._model, attr, 0, self.num_cols(), self.__x)
                if st:
                    raise ParameterNotAvailable("Error quering Gurobi solution")

                if (self.num_int() + self.get_int_attr("NumSOS")) == 0 or (relax):
                    self.__pi = ffi.new("double[{}]".format(self.num_rows()))
                    attr = "Pi".encode("utf-8")
                    st = GRBgetdblattrarray(
                        self._model, attr, 0, self.num_rows(), self.__pi
                    )
                    if st:
                        raise ParameterNotAvailable("Error quering Gurobi solution")

                    self.__rc = ffi.new("double[{}]".format(self.num_cols()))
                    attr = "RC".encode("utf-8")
                    st = GRBgetdblattrarray(
                        self._model, attr, 0, self.num_cols(), self.__rc
                    )
                    if st:
                        raise ParameterNotAvailable("Error quering Gurobi solution")

            return OptimizationStatus.OPTIMAL
        if status == 3:  # INFEASIBLE
            return OptimizationStatus.INFEASIBLE
        if status == 4:  # INF_OR_UNBD
            # Special case by gurobi, where an additional run has to be made
            # to determine infeasibility or unbounded problem
            # For this run dual reductions must be disabled
            # See gurobi support article online - How do I resolve the error "Model is infeasible or unbounded"?
            # self.set_int_param("DualReductions", 0)
            # GRBoptimize(self._model)
            # return OptimizationStatus.INFEASIBLE if self.get_int_attr("Status") == 3 else OptimizationStatus.UNBOUNDED
            return OptimizationStatus.INF_OR_UNBD
        if status == 5:  # UNBOUNDED
            return OptimizationStatus.UNBOUNDED
        if status == 6:  # CUTOFF
            return OptimizationStatus.CUTOFF
        if status == 7:  # ITERATION_LIMIT
            return OptimizationStatus.OTHER
        if status == 8:  # NODE_LIMIT
            return OptimizationStatus.OTHER
        if status == 9:  # TIME_LIMIT
            return OptimizationStatus.OTHER
        if status == 10:  # SOLUTION_LIMIT
            return OptimizationStatus.FEASIBLE
        if status == 11:  # INTERRUPTED
            return OptimizationStatus.OTHER
        if status == 12:  # NUMERIC
            return OptimizationStatus.OTHER
        if status == 13:  # SUBOPTIMAL
            return OptimizationStatus.FEASIBLE
        if status == 14:  # INPROGRESS
            return OptimizationStatus.OTHER
        if status == 15:  # USER_OBJ_LIMIT
            return OptimizationStatus.FEASIBLE

        self._updated = True
        return status

    def get_objective_sense(self) -> str:
        isense = self.get_int_attr("ModelSense")
        if isense == 1:
            return MINIMIZE
        elif isense == -1:
            return MAXIMIZE
        else:
            raise ValueError("Unknown sense")

    def set_objective_sense(self, sense: str):
        if sense.strip().upper() == MAXIMIZE.strip().upper():
            self.set_int_attr("ModelSense", -1)
        elif sense.strip().upper() == MINIMIZE.strip().upper():
            self.set_int_attr("ModelSense", 1)
        else:
            raise ValueError(
                "Unknown sense: {}, use {} or {}".format(sense, MAXIMIZE, MINIMIZE)
            )
        self.__updated = False

    def get_num_solutions(self) -> int:
        return self.get_int_attr("SolCount")

    def var_get_xi(self, var: Var, i: int) -> float:
        self.set_int_param("SolutionNumber", i)
        return self.get_dbl_attr_element("Xn", var.idx)

    def var_get_index(self, name: str) -> int:
        self.update()
        idx = ffi.new("int *")
        st = GRBgetvarbyname(self._model, name.encode("utf-8"), idx)
        if st:
            raise ParameterNotAvailable("Error calling GRBgetvarbyname")
        return idx[0]

    def get_objective_value_i(self, i: int) -> float:
        self.set_int_param("SolutionNumber", i)
        return self.get_dbl_attr("PoolObjVal")

    def get_objective_value(self) -> float:
        return self.__obj_val

    def get_log(self) -> List[Tuple[float, Tuple[float, float]]]:
        return self.__log

    def set_processing_limits(
        self: "Solver",
        max_time: numbers.Real = mip.INF,
        max_nodes: int = mip.INT_MAX,
        max_sol: int = mip.INT_MAX,
        max_seconds_same_incumbent: float = mip.INF,
        max_nodes_same_incumbent: int = mip.INT_MAX,
    ):
        # todo: Set limits even when they are 'inf'
        if max_time != INF:
            self.set_dbl_param("TimeLimit", max_time)
        if max_nodes != INF:
            self.set_dbl_param("NodeLimit", max_nodes)
        if max_sol != INF:
            self.set_int_param("SolutionLimit", max_sol)

    def set_objective(self, lin_expr: LinExpr, sense: str = "") -> None:
        self.flush_cols()
        # collecting linear expression data
        nz = len(lin_expr.expr)
        cind = ffi.new("int[]", [var.idx for var in lin_expr.expr.keys()])
        cval = ffi.new("double[]", [coef for coef in lin_expr.expr.values()])

        # objective function constant
        const = lin_expr.const

        # resetting objective function
        num_vars = self.num_cols()
        zeros = ffi.new("double[]", [0.0 for i in range(num_vars)])

        attr = "Obj".encode("utf-8")
        st = GRBsetdblattrarray(self._model, attr, 0, num_vars, zeros)

        if st != 0:
            raise ParameterNotAvailable(
                "Could not set gurobi double attribute array Obj"
            )

        # setting objective sense
        if MAXIMIZE in (lin_expr.sense, sense):
            self.set_int_attr("ModelSense", -1)
        elif MINIMIZE in (lin_expr.sense, sense):
            self.set_int_attr("ModelSense", 1)

        # setting objective function
        self.set_dbl_attr("ObjCon", const)
        error = GRBsetdblattrlist(self._model, attr, nz, cind, cval)
        if error != 0:
            raise ParameterNotAvailable("Error modifying attribute Obj")
        self.__n_modified_cols += 1

    def set_objective_const(self, const: float) -> None:
        self.set_dbl_attr("ObjCon", const)
        self.__updated = False

    def set_start(self, start: List[Tuple[Var, float]]) -> None:
        # collecting data
        nz = len(start)
        cind = ffi.new("int[]", [el[0].idx for el in start])
        cval = ffi.new("double[]", [el[1] for el in start])

        st = GRBsetdblattrlist(self._model, "Start".encode("utf-8"), nz, cind, cval)
        if st != 0:
            raise ParameterNotAvailable("Error modifying attribute Start")
        self.__updated = False

    def flush_cols(self):
        """should be called in methods that require updated column
        information, e.g. when adding a new constraint"""
        if self.__n_cols_buffer or self.__n_modified_cols:
            self.update()

    def flush_rows(self):
        """should be called in methods that require updated row
        information, e.g. when adding a new column"""
        if self.__n_rows_buffer or self.__n_modified_rows:
            self.update()

    def write(self, file_path: str) -> None:
        # writing formulation to output file
        self.update()
        st = GRBwrite(self._model, file_path.encode("utf-8"))
        if st != 0:
            raise InterfacingError("Could not write gurobi model.")

    def read(self, file_path: str) -> None:
        if not isfile(file_path):
            raise FileNotFoundError("File {} does not exist".format(file_path))

        lfile = file_path.lower()

        MEXTS = [".mps.gz", ".mps.bz2", ".lp.gz", ".lp.bz2", ".lp", ".mps"]
        is_model = False
        for ext in MEXTS:
            if lfile.endswith(ext):
                is_model = True
                break

        if is_model:
            GRBfreemodel(self._model)
            self._model = ffi.new("GRBmodel **")
            st = GRBreadmodel(self._env, file_path.encode("utf-8"), self._model)
            if st != 0:
                raise InterfacingError(
                    "Could not read model {}, check contents".format(file_path)
                )
            self._model = self._model[0]
        else:
            error = GRBread(self._model, file_path.encode("utf-8"))
            if error:
                raise IOError("Error loading %s" % file_path)

    def num_cols(self) -> int:
        return self.get_int_attr("NumVars") + self.__n_cols_buffer

    def num_int(self) -> int:
        return self.get_int_attr("NumIntVars") + self.__n_int_buffer

    def num_rows(self) -> int:
        return self.get_int_attr("NumConstrs") + self.__n_rows_buffer

    def num_nz(self) -> int:
        self.flush_rows()
        return self.get_int_attr("NumNZs")

    def get_cutoff(self) -> float:
        return self.get_dbl_param("Cutoff")

    def set_cutoff(self, cutoff: float):
        self.set_dbl_param("Cutoff", cutoff)

    def get_mip_gap_abs(self) -> float:
        return self.get_dbl_param("MIPGapAbs")

    def set_mip_gap_abs(self, allowable_gap: float):
        self.set_dbl_param("MIPGapAbs", allowable_gap)

    def get_mip_gap(self) -> float:
        return self.get_dbl_param("MIPGap")

    def set_mip_gap(self, allowable_ratio_gap: float):
        self.set_dbl_param("MIPGap", allowable_ratio_gap)

    def get_verbose(self) -> int:
        return self.get_int_param("OutputFlag")

    def set_verbose(self, verbose: int):
        self.set_int_param("OutputFlag", verbose)

    def constr_get_expr(self, constr: Constr) -> LinExpr:
        self.flush_rows()

        nnz = ffi.new("int *")
        # obtaining number of non-zeros
        st = GRBgetconstrs(self._model, nnz, ffi.NULL, ffi.NULL, ffi.NULL, constr.idx, 1)
        if st != 0:
            raise ParameterNotAvailable(
                "Could not get info for constraint {}".format(constr.idx)
            )
        nz = nnz[0]

        # creating arrays to hold indices and coefficients
        cbeg = ffi.new("int[2]")
        cind = ffi.new("int[{}]".format(nz))
        cval = ffi.new("double[{}]".format(nz))

        # obtaining variables and coefficients
        st = GRBgetconstrs(self._model, nnz, cbeg, cind, cval, constr.idx, 1)
        if st != 0:
            raise ParameterNotAvailable("Could not query constraint contents")

        # obtaining sense and rhs
        c_sense = ffi.new("char *")
        rhs = ffi.new("double *")
        st = GRBgetcharattrelement(
            self._model, "Sense".encode("utf-8"), constr.idx, c_sense
        )
        if st != 0:
            raise ParameterNotAvailable(
                "Could not query sense for constraint {}".format(constr.idx)
            )
        st = GRBgetdblattrelement(self._model, "RHS".encode("utf-8"), constr.idx, rhs)
        if st != 0:
            raise ParameterNotAvailable(
                "Could not query RHS for constraint {}".format(constr.idx)
            )

        ssense = c_sense[0].decode("utf-8")
        # translating sense
        sense = ""
        if ssense == "<":
            sense = LESS_OR_EQUAL
        elif ssense == ">":
            sense = GREATER_OR_EQUAL
        elif ssense == "=":
            sense = EQUAL

        expr = LinExpr(const=-rhs[0], sense=sense)
        for i in range(nz):
            expr.add_var(self.model.vars[cind[i]], cval[i])

        return expr

    def constr_get_rhs(self, idx: int) -> float:
        GRBupdatemodel(self._model)
        return self.get_dbl_attr_element("RHS", idx)

    def constr_set_rhs(self, idx: int, rhs: float):
        self.set_dbl_attr_element("RHS", idx, rhs)

    def constr_get_name(self, idx: int) -> str:
        self.flush_rows()
        return self.get_str_attr_element("ConstrName", idx)

    def constr_set_expr(self, constr: Constr, value: LinExpr) -> LinExpr:
        raise NotImplementedError("Gurobi functionality currently unavailable")

    def constr_get_slack(self, constr: "Constr") -> float:
        return self.get_dbl_attr_element("Slack", constr.idx)

    def constr_get_pi(self, constr: "Constr") -> float:
        return self.__pi[constr.idx]

    def constr_get_index(self, name: str) -> int:
        GRBupdatemodel(self._model)
        idx = ffi.new("int *")
        st = GRBgetconstrbyname(self._model, name.encode("utf-8"), idx)
        if st != 0:
            raise ParameterNotAvailable("Error calling GRBgetconstrbyname")
        return idx[0]

    def remove_constrs(self, constrsList: List[int]):
        idx = ffi.new("int[]", constrsList)
        st = GRBdelconstrs(self._model, len(constrsList), idx)
        if st != 0:
            raise ParameterNotAvailable("Error calling GRBdelconstrs")
        self.__n_modified_rows += len(constrsList)

    # Variable-related getters/setters\

    def var_get_branch_priority(self: "Solver", var: "mip.Var") -> numbers.Real:
        self.flush_cols()
        return self.get_int_attr_element("BranchPriority", var.idx)

    def var_set_branch_priority(self: "Solver", var: "mip.Var", value: numbers.Real):
        self.set_int_attr_element("BranchPriority", var.idx, value)

    def var_get_lb(self, var: Var) -> float:
        self.flush_cols()
        return self.get_dbl_attr_element("LB", var.idx)

    def var_set_lb(self, var: Var, value: float) -> None:
        self.set_dbl_attr_element("LB", var.idx, value)
        self.__n_modified_cols += 1

    def var_get_ub(self, var: Var) -> float:
        self.flush_cols()
        return self.get_dbl_attr_element("UB", var.idx)

    def var_set_ub(self, var: Var, value: float) -> None:
        self.set_dbl_attr_element("UB", var.idx, value)
        self.__n_modified_cols += 1

    def var_get_obj(self, var: Var) -> float:
        self.flush_cols()
        return self.get_dbl_attr_element("Obj", var.idx)

    def var_set_obj(self, var: Var, value: float) -> None:
        self.set_dbl_attr_element("Obj", var.idx, value)
        self.__n_modified_cols += 1

    def var_get_var_type(self, var: Var) -> str:
        self.flush_cols()
        res = ffi.new("char *")
        st = GRBgetcharattrelement(self._model, "VType".encode("utf-8"), var.idx, res)
        if st != 0:
            raise ParameterNotAvailable("Error querying variable type in gurobi")

        vt = res[0].decode("utf-8")

        if vt == "B":
            return BINARY
        elif vt == "C":
            return CONTINUOUS
        elif vt == "I":
            return INTEGER

        raise ValueError("Gurobi: invalid variable type returned...")

    def var_set_var_type(self, var: Var, value: str) -> None:
        self.set_char_attr_element("VType", var.idx, value)
        self._updated = False

    def var_get_column(self, var: Var) -> Column:
        self.update()

        nnz = ffi.new("int*")

        # obtaining number of non-zeros
        error = GRBgetvars(self._model, nnz, ffi.NULL, ffi.NULL, ffi.NULL, var.idx, 1)
        if error != 0:
            raise ParameterNotAvailable("Error querying gurobi model information")

        nz = nnz[0]

        # creating arrays to hold indices and coefficients
        cbeg = ffi.new("int[2]")
        cind = ffi.new("int[{}]".format(nz))
        cval = ffi.new("double[{}]".format(nz))

        # obtaining variables and coefficients
        error = GRBgetvars(self._model, nnz, cbeg, cind, cval, var.idx, 1)
        if error != 0:
            raise ParameterNotAvailable("Error querying gurobi model information")

        constr = [self.model.constrs[cind[i]] for i in range(nz)]
        coefs = [float(cval[i]) for i in range(nz)]

        return Column(constr, coefs)

    def var_set_column(self, var: Var, value: Column):
        raise NotImplementedError("Gurobi functionality currently unavailable")

    def var_get_rc(self, var: Var) -> float:
        return self.__rc[var.idx]

    def var_get_x(self, var: Var) -> float:
        return self.__x[var.idx]

    def var_get_name(self, idx: int) -> str:
        self.flush_cols()
        return self.get_str_attr_element("VarName", idx)

    def remove_vars(self, varsList: List[int]):
        idx = ffi.new("int[]", varsList)
        st = GRBdelvars(self._model, len(varsList), idx)
        if st != 0:
            raise ParameterNotAvailable("Error calling GRBdelvars")
        self.__n_modified_cols += len(varsList)

    def get_emphasis(self) -> SearchEmphasis:
        fc = self.get_int_param("MIPFocus")
        if fc == 1:
            return SearchEmphasis.FEASIBILITY
        if fc in (2, 3):
            return SearchEmphasis.OPTIMALITY

        return 0

    def set_emphasis(self, emph: SearchEmphasis):
        if emph == SearchEmphasis.FEASIBILITY:
            self.set_int_param("MIPFocus", 1)
        elif emph == SearchEmphasis.OPTIMALITY:
            self.set_int_param("MIPFocus", 2)
        else:
            self.set_int_param("MIPFocus", 0)

    def update(self):
        if (
            self.__n_cols_buffer
            + self.__n_int_buffer
            + self.__n_rows_buffer
            + self.__n_modified_cols
            + self.__n_modified_rows
        ) == 0 and self.__updated:
            return
        GRBupdatemodel(self._model)
        self.__n_cols_buffer = 0
        self.__n_int_buffer = 0
        self.__n_rows_buffer = 0
        self.__n_modified_cols = 0
        self.__n_modified_rows = 0
        self.__updated = True

    def set_char_attr_element(self, name: str, index: int, value: str):
        if len(value) != 1:
            raise ValueError("Expected value of length 1, got {}".format(len(value)))
        error = GRBsetcharattrelement(
            self._model, name.encode("utf-8"), index, value.encode("utf-8")
        )
        if error != 0:
            raise ParameterNotAvailable(
                "Error setting gurobi char attr element {} index {} to value {}".format(
                    name, index, value
                )
            )

    def get_dbl_attr_element(self, name: str, index: int) -> float:
        res = ffi.new("double *")
        error = GRBgetdblattrelement(self._model, name.encode("utf-8"), index, res)
        if error != 0:
            raise ParameterNotAvailable(
                "Error get grb double attr element {} index {}".format(name, index)
            )
        return res[0]

    def set_dbl_attr_element(self, name: str, index: int, value: float):
        error = GRBsetdblattrelement(self._model, name.encode("utf-8"), index, value)
        if error != 0:
            raise ParameterNotAvailable(
                "Error modifying dbl attribute {} for element {} to value {}".format(
                    name, index, value
                )
            )

    def get_int_attr_element(self, name: str, index: int) -> float:
        res = ffi.new("int *")
        error = GRBgetintattrelement(self._model, name.encode("utf-8"), index, res)
        if error != 0:
            raise ParameterNotAvailable(
                "Error get grb double attr element {} index {}".format(name, index)
            )
        return res[0]

    def set_int_attr_element(self, name: str, index: int, value: int):
        error = GRBsetintattrelement(self._model, name.encode("utf-8"), index, value)
        if error != 0:
            raise ParameterNotAvailable(
                "Error modifying int attribute {} for element {} to value {}".format(
                    name, index, value
                )
            )

    def set_int_attr(self, name: str, value: int):
        error = GRBsetintattr(self._model, name.encode("utf-8"), value)
        if error != 0:
            raise ParameterNotAvailable(
                "Error modifying int attribute {} to {}".format(name, value)
            )
        GRBupdatemodel(self._model)

    def set_dbl_attr(self, name: str, value: float):
        error = GRBsetdblattr(self._model, name.encode("utf-8"), value)
        if error != 0:
            raise ParameterNotAvailable(
                "Error modifying double attribute {} to {}".format(name, value)
            )
        GRBupdatemodel(self._model)

    def get_int_attr(self, name: str) -> int:
        res = ffi.new("int *")
        error = GRBgetintattr(self._model, name.encode("utf-8"), res)
        if error != 0:
            raise ParameterNotAvailable("Error getting int attribute {}".format(name))
        return res[0]

    def get_int_param(self, name: str) -> int:
        res = ffi.new("int *")
        env = GRBgetenv(self._model)
        error = GRBgetintparam(env, name.encode("utf-8"), res)
        if error != 0:
            raise ParameterNotAvailable(
                "Error getting gurobi integer parameter {}".format(name)
            )
        return res[0]

    def set_int_param(self, name: str, value: int):
        env = GRBgetenv(self._model)
        error = GRBsetintparam(env, name.encode("utf-8"), value)
        if error != 0:
            raise ParameterNotAvailable(
                "Error mofifying int parameter {} to value {}".format(name, value)
            )
        GRBupdatemodel(self._model)

    def get_dbl_attr(self, attr: str) -> float:
        res = ffi.new("double *")
        error = GRBgetdblattr(self._model, attr.encode("utf-8"), res)
        if error != 0:
            raise ParameterNotAvailable(
                "Error getting gurobi double attribute {}".format(attr)
            )
        return res[0]

    def set_dbl_param(self, param: str, value: float):
        env = GRBgetenv(self._model)
        error = GRBsetdblparam(env, param.encode("utf-8"), float(value))
        if error != 0:
            raise ParameterNotAvailable(
                "Error setting gurobi double param {}  to {}".format(param, value)
            )

    def get_dbl_param(self, param: str) -> float:
        res = ffi.new("double *")
        env = GRBgetenv(self._model)
        error = GRBgetdblparam(env, param.encode("utf-8"), res)
        if error != 0:
            raise ParameterNotAvailable(
                "Error getting gurobi double parameter {}".format(param)
            )
        return res[0]

    def get_str_attr_element(self, attr: str, index: int) -> str:
        vName = ffi.new("char **")
        error = GRBgetstrattrelement(self._model, attr.encode("utf-8"), index, vName)
        if error != 0:
            raise ParameterNotAvailable(
                "Error getting str attribute {} index {}".format(attr, index)
            )
        return ffi.string(vName[0]).decode("utf-8")

    def get_problem_name(self) -> str:
        vName = ffi.new("char **")
        error = GRBgetstrattr(self._model, "ModelName".encode("utf-8"), vName)
        if error != 0:
            raise ParameterNotAvailable("Error getting problem name from gurobi")
        return ffi.string(vName[0]).decode("utf-8")

    def set_problem_name(self, name: str):
        error = GRBsetstrattr(
            self._model, "ModelName".encode("utf-8"), name.encode("utf-8")
        )

        if error != 0:
            raise ParameterNotAvailable("Error setting problem name in Gurobi")
        GRBupdatemodel(self._model)

    def get_pump_passes(self) -> int:
        return self.get_int_param("PumpPasses")

    def set_pump_passes(self, passes: int):
        self.set_int_param("PumpPasses", passes)

    def reset(self):
        self.__x = EmptyVarSol(self.model)
        self.__rc = EmptyVarSol(self.model)
        self.__pi = EmptyRowSol(self.model)
        self.__obj_val = None
        error = GRBreset(self._model, 0)
        if error != 0:
            raise ParameterNotAvailable("Error resetting gurobi model")


class SolverGurobiCB(SolverGurobi):
    """Just like previous solver, but aware that
    running in the callback, so some methods
    should be different (e.g. to get the frac sol)"""

    def __init__(
        self,
        model: Model,
        grb_model: CData = ffi.NULL,
        cb_data: CData = ffi.NULL,
        where: int = -1,
    ):
        # TODO: Replace with exceptions with meaningful text.
        assert grb_model != ffi.NULL
        assert cb_data != ffi.NULL

        super().__init__(model, "", "", modelp=grb_model)

        self._cb_data = cb_data
        self._objconst = 0.0
        self._model = grb_model
        self._env = GRBgetenv(self._model)
        self._status = OptimizationStatus.LOADED
        self._obj_value = INF
        self._best_bound = INF
        self._status = OptimizationStatus.LOADED
        self._where = where

        if where not in [GRB_CB_MIPSOL, GRB_CB_MIPNODE]:
            return

        self.__relaxed = False
        gstatus = ffi.new("int *")
        if where == GRB_CB_MIPNODE:
            res = GRBcbget(cb_data, where, GRB_CB_MIPNODE_STATUS, gstatus)
            if res != 0:
                raise ParameterNotAvailable("Error getting status")
            if gstatus[0] == GRB_OPTIMAL:
                self._status = OptimizationStatus.OPTIMAL
                ires = ffi.new("int *")
                st = GRBgetintattr(grb_model, "NumVars".encode("utf-8"), ires)
                if st != 0:
                    raise ParameterNotAvailable("Could not query number of variables")
                ncols = ires[0]
                self._cb_sol = ffi.new("double[{}]".format(ncols))
                res = GRBcbget(cb_data, where, GRB_CB_MIPNODE_REL, self._cb_sol)
                if res != 0:
                    raise ParameterNotAvailable("Error getting fractional solution")
            else:
                self._cb_sol = ffi.NULL
        elif where == GRB_CB_MIPSOL:
            self._status = OptimizationStatus.FEASIBLE
            ires = ffi.new("int *")
            st = GRBgetintattr(grb_model, "NumVars".encode("utf-8"), ires)
            if st != 0:
                raise ParameterNotAvailable(
                    "Could not query number of variables in Gurobi callback"
                )
            ncols = ires[0]

            self._cb_sol = ffi.new("double[{}]".format(ncols))
            res = GRBcbget(cb_data, where, GRB_CB_MIPSOL_SOL, self._cb_sol)
            if res != 0:
                raise ParameterNotAvailable(
                    "Error getting integer solution in gurobi callback"
                )
            objp = ffi.new("double *")
            res = GRBcbget(cb_data, where, GRB_CB_MIPSOL_OBJ, objp)
            if res != 0:
                raise ParameterNotAvailable("Error getting solution obj in Gurobi")
            self._obj_value = objp[0]

        else:
            self._cb_sol = ffi.NULL

    def add_cut(self, lin_expr: "LinExpr"):
        numnz = len(lin_expr.expr)

        cind = ffi.new("int[]", [var.idx for var in lin_expr.expr.keys()])
        cval = ffi.new("double[]", [coef for coef in lin_expr.expr.values()])

        # constraint sense and rhs
        sense = lin_expr.sense.encode("utf-8")
        rhs = -lin_expr.const

        if self._where == GRB_CB_MIPNODE:
            GRBcbcut(self._cb_data, numnz, cind, cval, sense, rhs)
        elif self._where == GRB_CB_MIPSOL:
            GRBcblazy(self._cb_data, numnz, cind, cval, sense, rhs)

    def add_constr(self, lin_expr: "LinExpr", name: str = ""):
        # collecting linear expression data
        nz = len(lin_expr.expr)
        cind = ffi.new("int[]", [var.idx for var in lin_expr.expr.keys()])
        cval = ffi.new("double[]", [coef for coef in lin_expr.expr.values()])

        # constraint sense and rhs
        sense = lin_expr.sense.encode("utf-8")
        rhs = -lin_expr.const

        if self._where == GRB_CB_MIPSOL:
            res = GRBcblazy(self._cb_data, nz, cind, cval, sense, rhs)
            if res != 0:
                raise ParameterNotAvailable("Error adding lazy constraint in Gurobi.")
        elif self._where == GRB_CB_MIPNODE:
            res = GRBcbcut(self._cb_data, nz, cind, cval, sense, rhs)
            if res != 0:
                raise ParameterNotAvailable("Error adding lazy constraint in Gurobi.")

    def add_lazy_constr(self, lin_expr: "LinExpr"):
        if self._where == GRB_CB_MIPSOL:
            # collecting linear expression data
            nz = len(lin_expr.expr)
            cind = ffi.new("int[]", [var.idx for var in lin_expr.expr.keys()])
            cval = ffi.new("double[]", [coef for coef in lin_expr.expr.values()])

            # constraint sense and rhs
            sense = lin_expr.sense.encode("utf-8")
            rhs = -lin_expr.const

            res = GRBcblazy(self._cb_data, nz, cind, cval, sense, rhs)
            if res != 0:
                raise ParameterNotAvailable("Error adding lazy constraint in Gurobi.")
        elif self._where == GRB_CB_MIPNODE:
            # collecting linear expression data
            nz = len(lin_expr.expr)
            cind = ffi.new("int[]", [var.idx for var in lin_expr.expr.keys()])
            cval = ffi.new("double[]", [coef for coef in lin_expr.expr.values()])

            # constraint sense and rhs
            sense = lin_expr.sense.encode("utf-8")
            rhs = -lin_expr.const

            res = GRBcbcut(self._cb_data, nz, cind, cval, sense, rhs)
            if res != 0:
                raise ParameterNotAvailable("Error adding cutting plane in Gurobi.")
        else:
            raise ProgrammingError(
                "Calling add_lazy_constr in unknown callback location"
            )

    def get_status(self):
        return self._status

    def var_get_x(self, var: Var):
        if self._cb_sol == ffi.NULL:
            raise SolutionNotAvailable("Solution not available")

        return self._cb_sol[var.idx]

    def __del__(self):
        return


class ModelGurobiCB(Model):
    def __init__(
        self,
        grb_model: CData = ffi.NULL,
        cb_data: CData = ffi.NULL,
        where: int = -1,
    ):
        # initializing variables with default values
        self.solver_name = "gurobicb"

        self.solver = SolverGurobiCB(self, grb_model, cb_data, where)

        # list of constraints and variables
        self.constrs = VConstrList(self)
        self.vars = VVarList(self)
        self._status = self.solver.get_status()

        # initializing additional control variables
        self.__cuts = -1
        self.__cut_passes = -1
        self.__clique = -1
        self.__preprocess = -1
        self.__constrs_generator = None
        self.__lazy_constrs_generator = None
        self.__start = None
        self.__threads = 0
        self.__n_cols = 0
        self.__n_rows = 0
        self.__gap = INF
        self.__store_search_progress_log = False
        self.where = where

    def add_constr(self, lin_expr: LinExpr, name: str = "") -> "Constr":
        if self.where == GRB_CB_MIPNODE:
            self.add_cut(lin_expr)
            return None

        self.add_lazy_constr(lin_expr)
        return None