from typing import cast

from mypy.checker import TypeChecker
from mypy.nodes import MemberExpr, TypeInfo
from mypy.plugin import AttributeContext, FunctionContext
from mypy.types import Instance
from mypy.types import Type as MypyType
from mypy.types import TypeType

from mypy_django_plugin.django.context import DjangoContext
from mypy_django_plugin.lib import helpers


def get_user_model_hook(ctx: FunctionContext, django_context: DjangoContext) -> MypyType:
    auth_user_model = django_context.settings.AUTH_USER_MODEL
    model_cls = django_context.apps_registry.get_model(auth_user_model)
    model_cls_fullname = helpers.get_class_fullname(model_cls)

    model_info = helpers.lookup_fully_qualified_generic(model_cls_fullname,
                                                        helpers.get_typechecker_api(ctx).modules)
    assert isinstance(model_info, TypeInfo)

    return TypeType(Instance(model_info, []))


def get_type_of_settings_attribute(ctx: AttributeContext, django_context: DjangoContext) -> MypyType:
    assert isinstance(ctx.context, MemberExpr)
    setting_name = ctx.context.name
    if not hasattr(django_context.settings, setting_name):
        ctx.api.fail(f"'Settings' object has no attribute {setting_name!r}", ctx.context)
        return ctx.default_attr_type

    typechecker_api = helpers.get_typechecker_api(ctx)

    # first look for the setting in the project settings file, then global settings
    settings_module = typechecker_api.modules.get(django_context.django_settings_module)
    global_settings_module = typechecker_api.modules.get('django.conf.global_settings')
    for module in [settings_module, global_settings_module]:
        if module is not None:
            sym = module.names.get(setting_name)
            if sym is not None and sym.type is not None:
                return sym.type

    # if by any reason it isn't present there, get type from django settings
    value = getattr(django_context.settings, setting_name)
    value_fullname = helpers.get_class_fullname(value.__class__)

    value_info = helpers.lookup_fully_qualified_typeinfo(typechecker_api, value_fullname)
    if value_info is None:
        return ctx.default_attr_type

    return Instance(value_info, [])