"""A registry that maps identifiers of mission planners to the instances
themselves. Other extensions that provide mission planning services need to
register themselves in the mission planner registry so their services can
be used by clients.
"""

from contextlib import contextmanager
from functools import partial
from typing import Iterator

from flockwave.server.model import default_id_generator
from flockwave.server.registries.base import RegistryBase
from flockwave.server.registries.objects import ObjectRegistryProxy
from flockwave.server.types import Disposer
from flockwave.server.utils.validation import cached_validator_for

from .model import Mission, MissionType

__all__ = ("MissionRegistry", "MissionTypeRegistry")


class MissionTypeRegistry(RegistryBase[MissionType]):
    """A registry that maps identifiers of mission types to the mission classes
    themselves. Other extensions that provide missions or mission planning
    services need to register themselves in the mission type registry so their
    services can be used by clients.
    """

    def add(self, id: str, type: MissionType) -> Disposer:
        """Registers a mission type in the registry.

        Parameters:
            id: the identifier of the mission type
            type: the mission type to register

        Returns:
            a disposer function that can be called to deregister the mission type
        """
        if id in self._entries:
            raise KeyError(f"Mission planner ID already taken: {id}")
        self._entries[id] = type
        return partial(self._entries.__delitem__, id)

    @contextmanager
    def use(self, id: str, type: MissionType) -> Iterator[MissionType]:
        """Adds a new mission type, hands control back to the caller in a
        context, and then removes the mission type when the caller exits the
        context.

        Parameters:
            id: the identifier of the mission type
            type: the mission type to register

        Yields:
            MissionType: the mission type that was added
        """
        disposer = self.add(id, type)
        try:
            yield type
        finally:
            disposer()


class MissionRegistry(ObjectRegistryProxy[Mission]):
    """Registry that maps mission identifiers to the state objects of the
    missions themselves.

    This registry is a view into the global object registry of the application
    such that it enumerates only the missions in the object registry.

    It is assumed that missions are registered in the global object registry
    only via this proxy object, never directly.
    """

    _mission_type_registry: MissionTypeRegistry
    """Registry that associates string identifiers of mission types to the
    corresponding MissionType_ objects.
    """

    def __init__(
        self,
        mission_type_registry: MissionTypeRegistry,
    ):
        """Constructor.

        Parameters:
            mission_type_registry: registry that associates string identifiers
                of mission types to the corresponding MissionType_ objects
        """
        super().__init__()
        self._mission_type_registry = mission_type_registry

    def create(self, type: str) -> Mission:
        """Creates a new mission, adds it to the registry and returns the
        corresponding state object.

        Parameters:
            type: the identifier of the type of the mission

        Raises:
            KeyError: if the given mission type is not registered
            RuntimeError: if the object registry was not assigned to the
                mission registry yet
        """
        if self._object_registry is None:
            raise RuntimeError(
                "object registry has not been assigned to mission registry yet"
            )
        mission_type = self._mission_type_registry.find_by_id(type)

        while True:
            mission_id = default_id_generator()
            if mission_id not in self._object_registry:
                break

        mission: Mission = mission_type.create_mission()
        mission._id = mission_id
        mission.type = type

        schema = mission_type.get_parameter_schema()
        if schema:
            try:
                validator = cached_validator_for(schema)
            except Exception as ex:
                raise RuntimeError(f"Mission parameter schema error: {ex}") from None
            mission.parameter_validator = validator
        else:
            mission.parameter_validator = None

        return self._add(mission)