"""Permission handlers for the impress core app."""
from django.core import exceptions

from rest_framework import permissions

ACTION_FOR_METHOD_TO_PERMISSION = {
    "versions_detail": {"DELETE": "versions_destroy", "GET": "versions_retrieve"}
}


class IsAuthenticated(permissions.BasePermission):
    """
    Allows access only to authenticated users. Alternative method checking the presence
    of the auth token to avoid hitting the database.
    """

    def has_permission(self, request, view):
        return bool(request.auth) or request.user.is_authenticated


class IsAuthenticatedOrSafe(IsAuthenticated):
    """Allows access to authenticated users (or anonymous users but only on safe methods)."""

    def has_permission(self, request, view):
        if request.method in permissions.SAFE_METHODS:
            return True
        return super().has_permission(request, view)


class IsSelf(IsAuthenticated):
    """
    Allows access only to authenticated users. Alternative method checking the presence
    of the auth token to avoid hitting the database.
    """

    def has_object_permission(self, request, view, obj):
        """Write permissions are only allowed to the user itself."""
        return obj == request.user


class IsOwnedOrPublic(IsAuthenticated):
    """
    Allows access to authenticated users only for objects that are owned or not related
    to any user via the "owner" field.
    """

    def has_object_permission(self, request, view, obj):
        """Unsafe permissions are only allowed for the owner of the object."""
        if obj.owner == request.user:
            return True

        if request.method in permissions.SAFE_METHODS and obj.owner is None:
            return True

        try:
            return obj.user == request.user
        except exceptions.ObjectDoesNotExist:
            return False


class AccessPermission(permissions.BasePermission):
    """Permission class for access objects."""

    def has_object_permission(self, request, view, obj):
        """Check permission for a given object."""
        abilities = obj.get_abilities(request.user)
        action = view.action
        try:
            action = ACTION_FOR_METHOD_TO_PERMISSION[view.action][request.method]
        except KeyError:
            pass
        return abilities.get(action, False)