# -*- coding: utf-8 -*-

# This code is part of Qiskit.
#
# (C) Copyright IBM 2017.
#
# 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.

"""This module implements the abstract base class for backend modules.

To create add-on backend modules subclass the Backend class in this module.
Doing so requires that the required backend interface is implemented.
"""
from abc import ABC, abstractmethod

from qiskit.version import __version__
from .models import BackendStatus


class BaseBackend(ABC):
    """Base class for backends."""

    @abstractmethod
    def __init__(self, configuration, provider=None):
        """Base class for backends.

        This method should initialize the module and its configuration, and
        raise an exception if a component of the module is
        not available.

        Args:
            configuration (BackendConfiguration): backend configuration
            provider (BaseProvider): provider responsible for this backend

        Raises:
            FileNotFoundError if backend executable is not available.
            QiskitError: if there is no name in the configuration
        """
        self._configuration = configuration
        self._provider = provider

    @abstractmethod
    def run(self, qobj):
        """Run a Qobj on the the backend."""
        pass

    def configuration(self):
        """Return the backend configuration.

        Returns:
            BackendConfiguration: the configuration for the backend.
        """
        return self._configuration

    def properties(self):
        """Return backend properties.

        Returns:
            BackendProperties: the configuration for the backend. If the backend
            does not support properties, it returns ``None``.
        """
        return None

    def provider(self):
        """Return the backend Provider.

        Returns:
            BaseProvider: the Provider responsible for the backend.
        """
        return self._provider

    def status(self):
        """Return backend status.

        Returns:
            BackendStatus: the status of the backend.
        """
        return BackendStatus(backend_name=self.name(),
                             backend_version=__version__,
                             operational=True,
                             pending_jobs=0,
                             status_msg='')

    def name(self):
        """Return backend name.

        Returns:
            str: the name of the backend.
        """
        return self._configuration.backend_name

    def __str__(self):
        return self.name()

    def __repr__(self):
        """Official string representation of a Backend.

        Note that, by Qiskit convention, it is consciously *not* a fully valid
        Python expression. Subclasses should provide 'a string of the form
        <...some useful description...>'. [0]

        [0] https://docs.python.org/3/reference/datamodel.html#object.__repr__
        """
        return "<{}('{}') from {}()>".format(self.__class__.__name__,
                                             self.name(),
                                             self._provider)
