from io import StringIO

from django.apps import apps
from django.core import management
from django.db import migrations
from django.db.models import signals
from django.test import TransactionTestCase, override_settings

APP_CONFIG = apps.get_app_config('migrate_signals')
SIGNAL_ARGS = ['app_config', 'verbosity', 'interactive', 'using', 'plan', 'apps']
MIGRATE_DATABASE = 'default'
MIGRATE_VERBOSITY = 1
MIGRATE_INTERACTIVE = False


class Receiver:
    def __init__(self, signal):
        self.call_counter = 0
        self.call_args = None
        signal.connect(self, sender=APP_CONFIG)

    def __call__(self, signal, sender, **kwargs):
        self.call_counter += 1
        self.call_args = kwargs


class OneTimeReceiver:
    """
    Special receiver for handle the fact that test runner calls migrate for
    several databases and several times for some of them.
    """

    def __init__(self, signal):
        self.signal = signal
        self.call_counter = 0
        self.call_args = None
        self.signal.connect(self, sender=APP_CONFIG)

    def __call__(self, signal, sender, **kwargs):
        # Although test runner calls migrate for several databases,
        # testing for only one of them is quite sufficient.
        if kwargs['using'] == MIGRATE_DATABASE:
            self.call_counter += 1
            self.call_args = kwargs
            # we need to test only one call of migrate
            self.signal.disconnect(self, sender=APP_CONFIG)


# We connect receiver here and not in unit test code because we need to
# connect receiver before test runner creates database.  That is, sequence of
# actions would be:
#
#   1. Test runner imports this module.
#   2. We connect receiver.
#   3. Test runner calls migrate for create default database.
#   4. Test runner execute our unit test code.
pre_migrate_receiver = OneTimeReceiver(signals.pre_migrate)
post_migrate_receiver = OneTimeReceiver(signals.post_migrate)


class MigrateSignalTests(TransactionTestCase):

    available_apps = ['migrate_signals']

    def test_call_time(self):
        self.assertEqual(pre_migrate_receiver.call_counter, 1)
        self.assertEqual(post_migrate_receiver.call_counter, 1)

    def test_args(self):
        pre_migrate_receiver = Receiver(signals.pre_migrate)
        post_migrate_receiver = Receiver(signals.post_migrate)
        management.call_command(
            'migrate', database=MIGRATE_DATABASE, verbosity=MIGRATE_VERBOSITY,
            interactive=MIGRATE_INTERACTIVE, stdout=StringIO(),
        )

        for receiver in [pre_migrate_receiver, post_migrate_receiver]:
            args = receiver.call_args
            self.assertEqual(receiver.call_counter, 1)
            self.assertEqual(set(args), set(SIGNAL_ARGS))
            self.assertEqual(args['app_config'], APP_CONFIG)
            self.assertEqual(args['verbosity'], MIGRATE_VERBOSITY)
            self.assertEqual(args['interactive'], MIGRATE_INTERACTIVE)
            self.assertEqual(args['using'], 'default')
            self.assertEqual(args['plan'], [])
            self.assertIsInstance(args['apps'], migrations.state.StateApps)

    @override_settings(MIGRATION_MODULES={'migrate_signals': 'migrate_signals.custom_migrations'})
    def test_migrations_only(self):
        """
        If all apps have migrations, migration signals should be sent.
        """
        pre_migrate_receiver = Receiver(signals.pre_migrate)
        post_migrate_receiver = Receiver(signals.post_migrate)
        stdout = StringIO()
        management.call_command(
            'migrate', database=MIGRATE_DATABASE, verbosity=MIGRATE_VERBOSITY,
            interactive=MIGRATE_INTERACTIVE, stdout=stdout,
        )
        for receiver in [pre_migrate_receiver, post_migrate_receiver]:
            args = receiver.call_args
            self.assertEqual(receiver.call_counter, 1)
            self.assertEqual(set(args), set(SIGNAL_ARGS))
            self.assertEqual(args['app_config'], APP_CONFIG)
            self.assertEqual(args['verbosity'], MIGRATE_VERBOSITY)
            self.assertEqual(args['interactive'], MIGRATE_INTERACTIVE)
            self.assertEqual(args['using'], 'default')
            self.assertIsInstance(args['plan'][0][0], migrations.Migration)
            # The migration isn't applied backward.
            self.assertFalse(args['plan'][0][1])
            self.assertIsInstance(args['apps'], migrations.state.StateApps)
        self.assertEqual(pre_migrate_receiver.call_args['apps'].get_models(), [])
        self.assertEqual(
            [model._meta.label for model in post_migrate_receiver.call_args['apps'].get_models()],
            ['migrate_signals.Signal']
        )
        # Migrating with an empty plan.
        pre_migrate_receiver = Receiver(signals.pre_migrate)
        post_migrate_receiver = Receiver(signals.post_migrate)
        management.call_command(
            'migrate', database=MIGRATE_DATABASE, verbosity=MIGRATE_VERBOSITY,
            interactive=MIGRATE_INTERACTIVE, stdout=stdout,
        )
        self.assertEqual(
            [model._meta.label for model in pre_migrate_receiver.call_args['apps'].get_models()],
            ['migrate_signals.Signal']
        )
        self.assertEqual(
            [model._meta.label for model in post_migrate_receiver.call_args['apps'].get_models()],
            ['migrate_signals.Signal']
        )
