# Copyright (c) Microsoft Corporation.
# Licensed under the MIT License.

from collections import Counter
import logging
from typing import Any, Dict, List, Optional, Tuple, Union
from uuid import uuid4

from qiskit import QuantumCircuit
from qiskit.providers import Options
from qiskit.transpiler.target import Target
from .... import TargetProfile
from .. import OutputSemantics
from ..execution import DetaultExecutor
from ..jobs import QsSimJob
from .backend_base import BackendBase
from .compilation import Compilation
from .errors import Errors

logger = logging.getLogger(__name__)


class QSharpBackend(BackendBase):
    """
    A virtual backend for running Qiskit circuits using the Q# simulator.
    """

    # This init is included for the docstring
    # pylint: disable=useless-parent-delegation
    def __init__(
        self,
        target: Optional[Target] = None,
        qiskit_pass_options: Optional[Dict[str, Any]] = None,
        transpile_options: Optional[Dict[str, Any]] = None,
        qasm_export_options: Optional[Dict[str, Any]] = None,
        skip_transpilation: bool = False,
        **fields,
    ):
        """
        Parameters:
            target (Target): The target to use for the backend.
            qiskit_pass_options (Dict): Options for the Qiskit passes.
            transpile_options (Dict): Options for the transpiler.
            qasm_export_options (Dict): Options for the QASM3 exporter.
            **options: Additional options for the execution.
              - name (str): The name of the circuit. This is used as the entry point for the program.
                  The circuit name will be used if not specified.
              - target_profile (TargetProfile): The target profile to use for the compilation.
              - output_semantics (OutputSemantics, optional): The output semantics for the compilation. Defaults to `Qiskit`.
              - shots (int): The number of shots to run the program for. Defaults to `1024`.
              - seed (int): The seed to use for the random number generator. Defaults to `None`.
              - search_path (str): The path to search for imports. Defaults to '.'.
              - output_fn (Callable[[Output], None]): A callback function to
                  receive the output of the circuit. Defaults to `None`.
              - executor(ThreadPoolExecutor or other Executor):
                  The executor to be used to submit the job. Defaults to SynchronousExecutor.
        """

        super().__init__(
            target,
            qiskit_pass_options,
            transpile_options,
            qasm_export_options,
            skip_transpilation,
            **fields,
        )

    @classmethod
    def _default_options(cls):
        return Options(
            name="program",
            params=None,
            search_path=".",
            shots=1024,
            seed=None,
            output_fn=None,
            target_profile=TargetProfile.Unrestricted,
            output_semantics=OutputSemantics.Qiskit,
            executor=DetaultExecutor(),
        )

    def run(
        self,
        run_input: Union[QuantumCircuit, List[QuantumCircuit]],
        **options,
    ) -> QsSimJob:
        """
        Runs the given QuantumCircuit using the Q# simulator.

        Args:
            run_input (QuantumCircuit): The QuantumCircuit to be executed.
            **options: Additional options for the execution. Defaults to backend config values.
              - name (str): The name of the circuit. This is used as the entry point for the program.
                  The circuit name will be used if not specified.
              - params (Optional[str]): The entry expression to use for the program. Defaults to None.
              - target_profile (TargetProfile): The target profile to use for the compilation.
              - output_semantics (OutputSemantics, optional): The output semantics for the compilation.
              - shots (int): The number of shots to run the program for. Defaults to 1024.
              - seed (int): The seed to use for the random number generator. Defaults to None.
              - search_path (str): The path to search for imports. Defaults to '.'.
              - output_fn (Callable[[Output], None]): A callback function to
                  receive the output of the circuit.
              - executor(ThreadPoolExecutor or other Executor):
                  The executor to be used to submit the job.
        Returns:
            QSharpJob: The simulation job

        :raises QSharpError: If there is an error evaluating the source code.
        :raises QasmError: If there is an error generating, parsing, or compiling QASM.
        :raises ValueError: If the run_input is not a QuantumCircuit
            or List[QuantumCircuit].
        """

        run_input = self._validate_quantum_circuits(run_input)
        return self._run(run_input, **options)

    def _execute(self, programs: List[Compilation], **input_params) -> Dict[str, Any]:
        exec_results: List[Tuple[Compilation, Dict[str, Any]]] = [
            (
                program,
                _run_qasm(program.qasm, vars(self.options).copy(), **input_params),
            )
            for program in programs
        ]
        job_results = []

        shots = input_params.get("shots")
        if shots is None:
            raise ValueError(str(Errors.MISSING_NUMBER_OF_SHOTS))

        for program, exec_result in exec_results:
            results = [self._shot_to_bitstring(result) for result in exec_result]

            counts = Counter(results)
            counts_dict = dict(counts)
            probabilities = {
                bitstring: (count / shots) for bitstring, count in counts_dict.items()
            }

            job_result = {
                "data": {"counts": counts_dict, "probabilities": probabilities},
                "success": True,
                "header": {
                    "metadata": {"qasm": program.qasm},
                    "name": program.circuit.name,
                    "compilation_time_taken": program.time_taken,
                },
                "shots": shots,
            }
            job_results.append(job_result)

        # All of these fields are required by the Result object
        result_dict = {
            "results": job_results,
            "qobj_id": str(uuid4()),
            "success": True,
        }

        return result_dict


def _run_qasm(
    qasm: str,
    default_options: Options,
    **options,
) -> Any:
    """
    Runs the supplied OpenQASM 3 program.
    Gates defined by stdgates.inc will be overridden with definitions
    from the Q# compiler.

    Any gates, such as matrix unitaries, that are not able to be
    transpiled will result in an error.

    Parameters:
    source (str): The input OpenQASM 3 string to be processed.
        **options: Additional keyword arguments to pass to the execution. Defaults to backend config values.
        - target_profile (TargetProfile): The target profile to use for the compilation.
        - output_semantics (OutputSemantics, optional): The output semantics for the compilation.
        - name (str): The name of the circuit. This is used as the entry point for the program. Defaults to 'program'.
        - search_path (str): The optional search path for resolving qasm imports.
        - shots (int): The number of shots to run the program for. Defaults to 1.
        - seed (int): The seed to use for the random number generator.
        - output_fn (Optional[Callable[[Output], None]]): A callback function that will be called with each output. Defaults to None.

    :returns values: A result or runtime errors.

    :raises QSharpError: If there is an error evaluating the source code.
    :raises QasmError: If there is an error generating, parsing, or compiling QASM.
    """

    from ...._native import run_qasm_program, Output  # type: ignore
    from ...._fs import read_file, list_directory, resolve
    from ...._http import fetch_github

    def callback(output: Output) -> None:
        print(output)

    output_fn = options.pop("output_fn", callback)

    def value_or_default(key: str) -> Any:
        return options.pop(key, default_options[key])

    # when passing the args into the rust layer, any kwargs with None values
    # will cause an error, so we need to filter them out.
    args = {}
    if name := value_or_default("name"):
        args["name"] = name

    if target_profile := value_or_default("target_profile"):
        args["target_profile"] = target_profile
    if output_semantics := value_or_default("output_semantics"):
        args["output_semantics"] = output_semantics

    if search_path := value_or_default("search_path"):
        args["search_path"] = search_path
    if shots := value_or_default("shots"):
        args["shots"] = shots
    if seed := value_or_default("seed"):
        args["seed"] = seed

    return run_qasm_program(
        qasm,
        output_fn,
        None,
        None,
        None,
        read_file,
        list_directory,
        resolve,
        fetch_github,
        **args,
    )
