"""
Copyright, the CVXPY authors

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.
"""
import time
from distutils.version import StrictVersion

import cvxpy.settings as s
from cvxpy.reductions.solution import Solution, failure_solution
from cvxpy.reductions.solvers import utilities
from cvxpy.reductions.solvers.conic_solvers import scs_conif
from cvxpy.reductions.solvers.conic_solvers.conic_solver import ConicSolver


class DIFFCP(scs_conif.SCS):
    """An interface for the DIFFCP solver, a differentiable wrapper of SCS and ECOS.
    """
    # Map of DIFFCP status to CVXPY status.
    STATUS_MAP = {"Solved": s.OPTIMAL,
                  "Solved/Inaccurate": s.OPTIMAL_INACCURATE,
                  "Unbounded": s.UNBOUNDED,
                  "Unbounded/Inaccurate": s.UNBOUNDED_INACCURATE,
                  "Infeasible": s.INFEASIBLE,
                  "Infeasible/Inaccurate": s.INFEASIBLE_INACCURATE,
                  "Failure": s.SOLVER_ERROR,
                  "Indeterminate": s.SOLVER_ERROR,
                  "Interrupted": s.SOLVER_ERROR}

    def name(self):
        """The name of the solver.
        """
        return s.DIFFCP

    def import_solver(self) -> None:
        """Imports the solver.
        """
        import diffcp
        patch_version = int(diffcp.__version__.split(".")[2])
        if patch_version < 15:
            raise ImportError("diffcp >= 1.0.15 is required")

    def apply(self, problem):
        problem, data, inv_data = self._prepare_data_and_inv_data(problem)

        # Apply parameter values.
        # Obtain A, b such that Ax + s = b, s \in cones.
        #
        # Keep zeros in A that are affected by parameters
        c, d, A, b = problem.apply_parameters(keep_zeros=True)
        data[s.C] = c
        inv_data[s.OFFSET] = d
        data[s.A] = -A
        data[s.B] = b
        return data, inv_data

    def invert(self, solution, inverse_data):
        """Returns the solution to the original problem given the inverse_data.
        """
        attr = {}
        if solution["solve_method"] == s.SCS:
            import scs
            if StrictVersion(scs.__version__) < StrictVersion('3.0.0'):
                status = scs_conif.SCS.STATUS_MAP[solution["info"]["statusVal"]]
                attr[s.SOLVE_TIME] = solution["info"]["solveTime"]
                attr[s.SETUP_TIME] = solution["info"]["setupTime"]
            else:
                status = scs_conif.SCS.STATUS_MAP[solution["info"]["status_val"]]
                attr[s.SOLVE_TIME] = solution["info"]["solve_time"]
                attr[s.SETUP_TIME] = solution["info"]["setup_time"]
        elif solution["solve_method"] == s.ECOS:
            status = self.STATUS_MAP[solution["info"]["status"]]
            attr[s.SOLVE_TIME] = solution["info"]["solveTime"]
            attr[s.SETUP_TIME] = solution["info"]["setupTime"]

        attr[s.NUM_ITERS] = solution["info"]["iter"]
        attr[s.EXTRA_STATS] = solution

        if status in s.SOLUTION_PRESENT:
            primal_val = solution["info"]["pobj"]
            opt_val = primal_val + inverse_data[s.OFFSET]
            # TODO expand primal and dual variables from lower triangular to full.
            # TODO but this makes map from solution to variables not a slice.
            primal_vars = {
                inverse_data[DIFFCP.VAR_ID]: solution["x"]
            }
            eq_dual_vars = utilities.get_dual_values(
                solution["y"][:inverse_data[ConicSolver.DIMS].zero],
                self.extract_dual_value,
                inverse_data[DIFFCP.EQ_CONSTR]
            )
            ineq_dual_vars = utilities.get_dual_values(
                solution["y"][inverse_data[ConicSolver.DIMS].zero:],
                self.extract_dual_value,
                inverse_data[DIFFCP.NEQ_CONSTR]
            )
            dual_vars = {}
            dual_vars.update(eq_dual_vars)
            dual_vars.update(ineq_dual_vars)
            return Solution(status, opt_val, primal_vars, dual_vars, attr)
        else:
            return failure_solution(status, attr)

    def solve_via_data(self, data, warm_start: bool, verbose: bool, solver_opts,
                       solver_cache=None):
        """Returns the result of the call to the solver.

        Parameters
        ----------
        data : dict
            Data generated via an apply call.
        warm_start : Bool
            Whether to warm_start diffcp.
        verbose : Bool
            Control the verbosity.
        solver_opts : dict
            SCS-specific solver options.

        Returns
        -------
        The result returned by a call to scs.solve().
        """
        import diffcp
        A = data[s.A]
        b = data[s.B]
        c = data[s.C]
        cones = scs_conif.dims_to_solver_dict(data[ConicSolver.DIMS])

        solver_opts["solve_method"] = solver_opts.get("solve_method", s.SCS)
        warm_start_tuple = None

        if solver_opts["solve_method"] == s.SCS:
            import scs
            if StrictVersion(scs.__version__) < StrictVersion('3.0.0'):
                # Default to eps = 1e-4 instead of 1e-3.
                solver_opts["eps"] = solver_opts.get("eps", 1e-4)
            else:
                solver_opts['eps_abs'] = solver_opts.get('eps_abs', 1e-5)
                solver_opts['eps_rel'] = solver_opts.get('eps_rel', 1e-5)

            if warm_start and solver_cache is not None and \
                    self.name() in solver_cache:
                warm_start_tuple = (solver_cache[self.name()]["x"],
                                    solver_cache[self.name()]["y"],
                                    solver_cache[self.name()]["s"])

        start = time.time()
        results = diffcp.solve_and_derivative_internal(
            A, b, c, cones, verbose=verbose,
            warm_start=warm_start_tuple,
            raise_on_error=False,
            **solver_opts)
        end = time.time()
        results["TOT_TIME"] = end - start
        results["solve_method"] = solver_opts["solve_method"]

        if solver_cache is not None:
            solver_cache[self.name()] = results
        return results
