from __future__ import unicode_literals
from collections import OrderedDict
import copy

from django.apps import AppConfig
from django.apps.registry import Apps, apps as global_apps
from django.db import models
from django.db.models.options import DEFAULT_NAMES, normalize_together
from django.db.models.fields.related import do_pending_lookups
from django.db.models.fields.proxy import OrderWrt
from django.conf import settings
from django.utils import six
from django.utils.encoding import force_text, smart_text
from django.utils.functional import cached_property
from django.utils.module_loading import import_string
from django.utils.version import get_docs_version


class InvalidBasesError(ValueError):
    pass


class ProjectState(object):
    """
    Represents the entire project's overall state.
    This is the item that is passed around - we do it here rather than at the
    app level so that cross-app FKs/etc. resolve properly.
    """

    def __init__(self, models=None, real_apps=None):
        self.models = models or {}
        # Apps to include from main registry, usually unmigrated ones
        self.real_apps = real_apps or []

    def add_model(self, model_state):
        app_label, model_name = model_state.app_label, model_state.name_lower
        self.models[(app_label, model_name)] = model_state
        if 'apps' in self.__dict__:  # hasattr would cache the property
            self.reload_model(app_label, model_name)

    def remove_model(self, app_label, model_name):
        del self.models[app_label, model_name]
        if 'apps' in self.__dict__:  # hasattr would cache the property
            self.apps.unregister_model(app_label, model_name)

    def reload_model(self, app_label, model_name):
        if 'apps' in self.__dict__:  # hasattr would cache the property
            # Get relations before reloading the models, as _meta.apps may change
            try:
                related_old = {
                    f.related_model for f in
                    self.apps.get_model(app_label, model_name)._meta.related_objects
                }
            except LookupError:
                related_old = set()
            self._reload_one_model(app_label, model_name)
            # Reload models if there are relations
            model = self.apps.get_model(app_label, model_name)
            related_m2m = {f.related_model for f in model._meta.many_to_many}
            for rel_model in related_old.union(related_m2m):
                self._reload_one_model(rel_model._meta.app_label, rel_model._meta.model_name)
            if related_m2m:
                # Re-render this model after related models have been reloaded
                self._reload_one_model(app_label, model_name)

    def _reload_one_model(self, app_label, model_name):
        self.apps.unregister_model(app_label, model_name)
        self.models[app_label, model_name].render(self.apps)

    def clone(self):
        "Returns an exact copy of this ProjectState"
        new_state = ProjectState(
            models={k: v.clone() for k, v in self.models.items()},
            real_apps=self.real_apps,
        )
        if 'apps' in self.__dict__:
            new_state.apps = self.apps.clone()
        return new_state

    @cached_property
    def apps(self):
        return StateApps(self.real_apps, self.models)

    @property
    def concrete_apps(self):
        self.apps = StateApps(self.real_apps, self.models, ignore_swappable=True)
        return self.apps

    @classmethod
    def from_apps(cls, apps):
        "Takes in an Apps and returns a ProjectState matching it"
        app_models = {}
        for model in apps.get_models(include_swapped=True):
            model_state = ModelState.from_model(model)
            app_models[(model_state.app_label, model_state.name_lower)] = model_state
        return cls(app_models)

    def __eq__(self, other):
        if set(self.models.keys()) != set(other.models.keys()):
            return False
        if set(self.real_apps) != set(other.real_apps):
            return False
        return all(model == other.models[key] for key, model in self.models.items())

    def __ne__(self, other):
        return not (self == other)


class AppConfigStub(AppConfig):
    """
    Stubs a Django AppConfig. Only provides a label, and a dict of models.
    """
    # Not used, but required by AppConfig.__init__
    path = ''

    def __init__(self, label):
        self.label = label
        # App-label and app-name are not the same thing, so technically passing
        # in the label here is wrong. In practice, migrations don't care about
        # the app name, but we need something unique, and the label works fine.
        super(AppConfigStub, self).__init__(label, None)

    def import_models(self, all_models):
        self.models = all_models


class StateApps(Apps):
    """
    Subclass of the global Apps registry class to better handle dynamic model
    additions and removals.
    """
    def __init__(self, real_apps, models, ignore_swappable=False):
        # Any apps in self.real_apps should have all their models included
        # in the render. We don't use the original model instances as there
        # are some variables that refer to the Apps object.
        # FKs/M2Ms from real apps are also not included as they just
        # mess things up with partial states (due to lack of dependencies)
        real_models = []
        for app_label in real_apps:
            app = global_apps.get_app_config(app_label)
            for model in app.get_models():
                real_models.append(ModelState.from_model(model, exclude_rels=True))
        # Populate the app registry with a stub for each application.
        app_labels = {model_state.app_label for model_state in models.values()}
        app_configs = [AppConfigStub(label) for label in sorted(real_apps + list(app_labels))]
        super(StateApps, self).__init__(app_configs)

        # We keep trying to render the models in a loop, ignoring invalid
        # base errors, until the size of the unrendered models doesn't
        # decrease by at least one, meaning there's a base dependency loop/
        # missing base.
        unrendered_models = list(models.values()) + real_models
        while unrendered_models:
            new_unrendered_models = []
            for model in unrendered_models:
                try:
                    model.render(self)
                except InvalidBasesError:
                    new_unrendered_models.append(model)
            if len(new_unrendered_models) == len(unrendered_models):
                raise InvalidBasesError(
                    "Cannot resolve bases for %r\nThis can happen if you are inheriting models from an "
                    "app with migrations (e.g. contrib.auth)\n in an app with no migrations; see "
                    "https://docs.djangoproject.com/en/%s/topics/migrations/#dependencies "
                    "for more" % (new_unrendered_models, get_docs_version())
                )
            unrendered_models = new_unrendered_models

        # If there are some lookups left, see if we can first resolve them
        # ourselves - sometimes fields are added after class_prepared is sent
        for lookup_model, operations in self._pending_lookups.items():
            try:
                model = self.get_model(lookup_model[0], lookup_model[1])
            except LookupError:
                app_label = "%s.%s" % (lookup_model[0], lookup_model[1])
                if app_label == settings.AUTH_USER_MODEL and ignore_swappable:
                    continue
                # Raise an error with a best-effort helpful message
                # (only for the first issue). Error message should look like:
                # "ValueError: Lookup failed for model referenced by
                # field migrations.Book.author: migrations.Author"
                msg = "Lookup failed for model referenced by field {field}: {model[0]}.{model[1]}"
                raise ValueError(msg.format(field=operations[0][1], model=lookup_model))
            else:
                do_pending_lookups(model)

    def clone(self):
        """
        Return a clone of this registry, mainly used by the migration framework.
        """
        clone = StateApps([], {})
        clone.all_models = copy.deepcopy(self.all_models)
        clone.app_configs = copy.deepcopy(self.app_configs)
        return clone

    def register_model(self, app_label, model):
        self.all_models[app_label][model._meta.model_name] = model
        if app_label not in self.app_configs:
            self.app_configs[app_label] = AppConfigStub(app_label)
            self.app_configs[app_label].models = OrderedDict()
        self.app_configs[app_label].models[model._meta.model_name] = model
        self.clear_cache()

    def unregister_model(self, app_label, model_name):
        try:
            del self.all_models[app_label][model_name]
            del self.app_configs[app_label].models[model_name]
        except KeyError:
            pass
        self.clear_cache()


class ModelState(object):
    """
    Represents a Django Model. We don't use the actual Model class
    as it's not designed to have its options changed - instead, we
    mutate this one and then render it into a Model as required.

    Note that while you are allowed to mutate .fields, you are not allowed
    to mutate the Field instances inside there themselves - you must instead
    assign new ones, as these are not detached during a clone.
    """

    def __init__(self, app_label, name, fields, options=None, bases=None, managers=None):
        self.app_label = app_label