# This code is part of Qiskit.
#
# (C) Copyright IBM 2022.
#
# This code is licensed under the Apache License, Version 2.0. You may
# obtain a copy of this license in the LICENSE.txt file in the root directory
# of this source tree or at http://www.apache.org/licenses/LICENSE-2.0.
#
# Any modifications or derivative works of this code must retain this
# copyright notice, and modified files need to carry a notice indicating
# that they have been altered from the originals.

"""Simulator options."""

from dataclasses import dataclass
from typing import TYPE_CHECKING, List, Optional, Union

from qiskit.exceptions import MissingOptionalLibraryError
from qiskit.providers import BackendV1, BackendV2
from qiskit.utils import optionals

from qiskit.transpiler import CouplingMap

from .utils import _flexible

if TYPE_CHECKING:
    import qiskit_aer


@_flexible
@dataclass()
class SimulatorOptions:
    """Simulator options.

    For best practice in simulating a backend make sure to pass the
    basis gates and coupling map of that backend.

    Args:
        noise_model: Noise model for the simulator.

        seed_simulator: Random seed to control sampling.

        coupling_map: Directed coupling map to target in mapping. If
            the coupling map is symmetric, both directions need to be specified.
            Each entry in the list specifies a directed two-qubit interactions,
            e.g: ``[[0, 1], [0, 3], [1, 2], [1, 5], [2, 5], [4, 1], [5, 3]]``

        basis_gates: List of basis gate names to unroll to. For example,
            ``['u1', 'u2', 'u3', 'cx']``. If ``None``, do not unroll.
    """

    noise_model: Optional[Union[dict, "qiskit_aer.noise.noise_model.NoiseModel"]] = None
    seed_simulator: Optional[int] = None
    coupling_map: Optional[Union[List[List[int]], "CouplingMap"]] = None
    basis_gates: Optional[List[str]] = None

    def set_backend(self, backend: Union[BackendV1, BackendV2]) -> None:
        """Set backend for simulation.
        This method changes noise_model, coupling_map, basis_gates according to given backend.

        Args:
            backend: backend to be set.
        """
        if not optionals.HAS_AER:
            raise MissingOptionalLibraryError(
                "qiskit-aer", "Aer provider", "pip install qiskit-aer"
            )

        from qiskit_aer.noise import NoiseModel  # pylint:disable=import-outside-toplevel

        self.noise_model = NoiseModel.from_backend(backend)

        if isinstance(backend, BackendV1):
            self.coupling_map = backend.configuration().coupling_map
            self.basis_gates = backend.configuration().basis_gates
        elif isinstance(backend, BackendV2):
            self.coupling_map = backend.coupling_map
            self.basis_gates = backend.operation_names