# Copyright 2024 Aegiq Ltd.
#
# 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.


from typing import Any

from multimethod import multimethod

from lightworks.emulator.utils import BackendError
from lightworks.sdk.tasks import Batch, Task

from .permanent import PermanentBackend
from .slos import SLOSBackend


class Backend:
    """
    Provide central location for selecting and interacting with different
    simulation backends.

    Args:

        backend (str) : A string detailing the backend which is to be used.

    """

    def __init__(self, backend: str) -> None:
        self.backend = backend

    def run(self, task: Task | Batch) -> dict[Any, Any] | list[dict[Any, Any]]:
        """
        Runs the provided task on the current backend.

        Args:

            task (Task|Batch) : A task or batch to run.

        Returns:

            dict: A dictionary like results object containing details of the
                calculated values from a task. If a batch is run then this will
                be a list of results in the same order the task were added to
                the batch.

        """
        if not isinstance(task, Task | Batch):
            raise TypeError("Object to run on the backend must be a task.")
        return self._run(task)

    @multimethod
    def _run(self, task: Task) -> dict[Any, Any]:
        if task.__class__.__name__ not in self.__backend.compatible_tasks:
            msg = (
                "Selected backend not compatible with task, supported tasks for"
                f"the backend are: {', '.join(self.__backend.compatible_tasks)}"
                "."
            )
            raise BackendError(msg)
        return self.__backend.run(task)

    @_run.register
    def _run_batch(self, task: Batch) -> list[dict[Any, Any]]:
        return [self._run(t) for t in task]

    @property
    def backend(self) -> str:
        """
        Returns the name of the currently selected backend.
        """
        return self.__backend.name

    @backend.setter
    def backend(self, value: str) -> None:
        backends = {"permanent": PermanentBackend, "slos": SLOSBackend}
        if value not in backends:
            msg = (
                "Backend name not recognised, valid options are: "
                f"{', '.join(backends.keys())}."
            )
            raise ValueError(msg)
        self.__backend = backends[value]()  # initialise backend

    def __str__(self) -> str:
        return self.backend

    def __repr__(self) -> str:
        return f"lightworks.emulator.Backend('{self.backend}')"
