# -*- coding: utf-8 -*-
from __future__ import unicode_literals

import inspect
import types
from itertools import chain

from django.apps import apps
from django.core.checks import Error, Tags, register


@register(Tags.models)
def check_all_models(app_configs=None, **kwargs):
    errors = []
    if app_configs is None:
        models = apps.get_models()
    else:
        models = chain.from_iterable(app_config.get_models() for app_config in app_configs)
    for model in models:
        if not inspect.ismethod(model.check):
            errors.append(
                Error(
                    "The '%s.check()' class method is currently overridden by %r."
                    % (model.__name__, model.check),
                    obj=model,
                    id='models.E020'
                )
            )
        else:
            errors.extend(model.check(**kwargs))
    return errors


@register(Tags.models, Tags.signals)
def check_model_signals(app_configs=None, **kwargs):
    """
    Ensure lazily referenced model signals senders are installed.
    """
    # Avoid circular import
    from django.db import models

    errors = []
    for name in dir(models.signals):
        obj = getattr(models.signals, name)
        if isinstance(obj, models.signals.ModelSignal):
            for reference, receivers in obj.unresolved_references.items():
                for receiver, _, _ in receivers:
                    # The receiver is either a function or an instance of class
                    # defining a `__call__` method.
                    if isinstance(receiver, types.FunctionType):
                        description = "The '%s' function" % receiver.__name__
                    else:
                        description = "An instance of the '%s' class" % receiver.__class__.__name__
                    errors.append(
                        Error(
                            "%s was connected to the '%s' signal "
                            "with a lazy reference to the '%s' sender, "
                            "which has not been installed." % (
                                description, name, '.'.join(reference)
                            ),
                            obj=receiver.__module__,
                            id='signals.E001'
                        )
                    )
    return errors