"""passbook policy engine"""
from multiprocessing import Pipe, set_start_method
from multiprocessing.connection import Connection
from typing import List, Optional

from django.core.cache import cache
from django.http import HttpRequest
from elasticapm import capture_span
from structlog import get_logger

from passbook.core.models import User
from passbook.policies.models import Policy, PolicyBinding, PolicyBindingModel
from passbook.policies.process import PolicyProcess, cache_key
from passbook.policies.types import PolicyRequest, PolicyResult

LOGGER = get_logger()
# This is only really needed for macOS, because Python 3.8 changed the default to spawn
# spawn causes issues with objects that aren't picklable, and also the django setup
set_start_method("fork")


class PolicyProcessInfo:
    """Dataclass to hold all information and communication channels to a process"""

    process: PolicyProcess
    connection: Connection
    result: Optional[PolicyResult]
    binding: PolicyBinding

    def __init__(
        self, process: PolicyProcess, connection: Connection, binding: PolicyBinding
    ):
        self.process = process
        self.connection = connection
        self.binding = binding
        self.result = None


class PolicyEngine:
    """Orchestrate policy checking, launch tasks and return result"""

    use_cache: bool = True
    request: PolicyRequest

    __pbm: PolicyBindingModel
    __cached_policies: List[PolicyResult]
    __processes: List[PolicyProcessInfo]

    def __init__(
        self, pbm: PolicyBindingModel, user: User, request: HttpRequest = None
    ):
        if not isinstance(pbm, PolicyBindingModel):
            raise ValueError(f"{pbm} is not instance of PolicyBindingModel")
        self.__pbm = pbm
        self.request = PolicyRequest(user)
        if request:
            self.request.http_request = request
        self.__cached_policies = []
        self.__processes = []

    def _iter_bindings(self) -> List[PolicyBinding]:
        """Make sure all Policies are their respective classes"""
        return PolicyBinding.objects.filter(target=self.__pbm, enabled=True).order_by(
            "order"
        )

    def _check_policy_type(self, policy: Policy):
        """Check policy type, make sure it's not the root class as that has no logic implemented"""
        # policy_type = type(policy)
        if policy.__class__ == Policy:
            raise TypeError(f"Policy '{policy}' is root type")

    @capture_span(name="PolicyEngine", span_type="policy.engine.build")
    def build(self) -> "PolicyEngine":
        """Build task group"""
        for binding in self._iter_bindings():
            self._check_policy_type(binding.policy)
            key = cache_key(binding, self.request)
            cached_policy = cache.get(key, None)
            if cached_policy and self.use_cache:
                LOGGER.debug(
                    "P_ENG: Taking result from cache",
                    policy=binding.policy,
                    cache_key=key,
                )
                self.__cached_policies.append(cached_policy)
                continue
            LOGGER.debug("P_ENG: Evaluating policy", policy=binding.policy)
            our_end, task_end = Pipe(False)
            task = PolicyProcess(binding, self.request, task_end)
            LOGGER.debug("P_ENG: Starting Process", policy=binding.policy)
            task.start()
            self.__processes.append(
                PolicyProcessInfo(process=task, connection=our_end, binding=binding)
            )
        # If all policies are cached, we have an empty list here.
        for proc_info in self.__processes:
            proc_info.process.join(proc_info.binding.timeout)
            # Only call .recv() if no result is saved, otherwise we just deadlock here
            if not proc_info.result:
                proc_info.result = proc_info.connection.recv()
        return self

    @property
    def result(self) -> PolicyResult:
        """Get policy-checking result"""
        messages: List[str] = []
        process_results: List[PolicyResult] = [
            x.result for x in self.__processes if x.result
        ]
        for result in process_results + self.__cached_policies:
            LOGGER.debug(
                "P_ENG: result", passing=result.passing, messages=result.messages
            )
            if result.messages:
                messages += result.messages
            if not result.passing:
                return PolicyResult(False, *messages)
        return PolicyResult(True, *messages)

    @property
    def passing(self) -> bool:
        """Only get true/false if user passes"""
        return self.result.passing