from __future__ import unicode_literals

import copy
from collections import OrderedDict
from contextlib import contextmanager

from django.apps import AppConfig
from django.apps.registry import Apps, apps as global_apps
from django.conf import settings
from django.db import models
from django.db.models.fields.proxy import OrderWrt
from django.db.models.fields.related import RECURSIVE_RELATIONSHIP_CONSTANT
from django.db.models.options import DEFAULT_NAMES, normalize_together
from django.db.models.utils import make_model_tuple
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

from .exceptions import InvalidBasesError


def _get_app_label_and_model_name(model, app_label=''):
    if isinstance(model, six.string_types):
        split = model.split('.', 1)
        return (tuple(split) if len(split) == 2 else (app_label, split[0]))
    else:
        return model._meta.app_label, model._meta.model_name


def get_related_models_recursive(model):
    """
    Returns all models that have a direct or indirect relationship
    to the given model.

    Relationships are either defined by explicit relational fields, like
    ForeignKey, ManyToManyField or OneToOneField, or by inheriting from another
    model (a superclass is related to its subclasses, but not vice versa). Note,
    however, that a model inheriting from a concrete model is also related to
    its superclass through the implicit *_ptr OneToOneField on the subclass.
    """
    def _related_models(m):
        return [
            f.related_model for f in m._meta.get_fields(include_parents=True, include_hidden=True)
            if f.is_relation and f.related_model is not None and not isinstance(f.related_model, six.string_types)
        ] + [
            subclass for subclass in m.__subclasses__()
            if issubclass(subclass, models.Model)
        ]

    seen = set()
    queue = _related_models(model)
    for rel_mod in queue:
        rel_app_label, rel_model_name = rel_mod._meta.app_label, rel_mod._meta.model_name
        if (rel_app_label, rel_model_name) in seen:
            continue
        seen.add((rel_app_label, rel_model_name))
        queue.extend(_related_models(rel_mod))
    return seen - {(model._meta.app_label, model._meta.model_name)}


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)
            # Need to do this explicitly since unregister_model() doesn't clear
            # the cache automatically (#24513)
            self.apps.clear_cache()

    def reload_model(self, app_label, model_name):
        if 'apps' in self.__dict__:  # hasattr would cache the property
            try:
                old_model = self.apps.get_model(app_label, model_name)
            except LookupError:
                related_models = set()
            else:
                # Get all relations to and from the old model before reloading,
                # as _meta.apps may change
                related_models = get_related_models_recursive(old_model)

            # Get all outgoing references from the model to be rendered
            model_state = self.models[(app_label, model_name)]
            # Directly related models are the models pointed to by ForeignKeys,
            # OneToOneFields, and ManyToManyFields.
            direct_related_models = set()
            for name, field in model_state.fields:
                if field.is_relation:
                    if field.remote_field.model == RECURSIVE_RELATIONSHIP_CONSTANT:
                        continue
                    rel_app_label, rel_model_name = _get_app_label_and_model_name(field.related_model, app_label)
                    direct_related_models.add((rel_app_label, rel_model_name.lower()))

            # For all direct related models recursively get all related models.
            related_models.update(direct_related_models)
            for rel_app_label, rel_model_name in direct_related_models:
                try:
                    rel_model = self.apps.get_model(rel_app_label, rel_model_name)
                except LookupError:
                    pass
                else:
                    related_models.update(get_related_models_recursive(rel_model))

            # Include the model itself
            related_models.add((app_label, model_name))

            # Unregister all related models
            with self.apps.bulk_update():
                for rel_app_label, rel_model_name in related_models:
                    self.apps.unregister_model(rel_app_label, rel_model_name)

            states_to_be_rendered = []
            # Gather all models states of those models that will be rerendered.
            # This includes:
            # 1. All related models of unmigrated apps
            for model_state in self.apps.real_models:
                if (model_state.app_label, model_state.name_lower) in related_models:
                    states_to_be_rendered.append(model_state)

            # 2. All related models of migrated apps
            for rel_app_label, rel_model_name in related_models:
                try:
                    model_state = self.models[rel_app_label, rel_model_name]
                except KeyError:
                    pass
                else:
                    states_to_be_rendered.append(model_state)

            # Render all models
            self.apps.render_multiple(states_to_be_rendered)

    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)
        self.real_models = []
        for app_label in real_apps:
            app = global_apps.get_app_config(app_label)
            for model in app.get_models():
                self.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)

        self.render_multiple(list(models.values()) + self.real_models)

        # There shouldn't be any operations pending at this point.
        pending_models = set(self._pending_operations)
        if ignore_swappable:
            pending_models -= {make_model_tuple(settings.AUTH_USER_MODEL)}
        if pending_models:
            raise ValueError(self._pending_models_error(pending_models))

    def _pending_models_error(self, pending_models):
        """
        Almost all internal uses of lazy operations are to resolve string model
        references in related fields. We can extract the fields from those
        operations and use them to provide a nicer error message.

        This will work for any function passed to lazy_related_operation() that
        has a keyword argument called 'field'.
        """
        def extract_field(operation):
            # operation is annotated with the field in
            # apps.registry.Apps.lazy_model_operation().
            return getattr(operation, 'field', None)

        def extract_field_names(operations):
            return (str(field) for field in map(extract_field, operations) if field)

        get_ops = self._pending_operations.__getitem__
        # Ordered list of pairs of the form
        # ((app_label, model_name), [field_name_1, field_name_2, ...])
        models_fields = sorted(
            (model_key, sorted(extract_field_names(get_ops(model_key))))
            for model_key in pending_models
        )

        def model_text(model_key, fields):
            field_list = ", ".join(fields)
            field_text = " (referred to by fields: %s)" % field_list if fields else ""
            return ("%s.%s" % model_key) + field_text

        msg = "Unhandled pending operations for models:"
        return "\n  ".join([msg] + [model_text(*i) for i in models_fields])

    @contextmanager
    def bulk_update(self):
        # Avoid clearing each model's cache for each change. Instead, clear
        # all caches when we're finished updating the model instances.
        ready = self.ready
        self.ready = False
        try:
            yield
        finally:
            self.ready = ready
            self.clear_cache()

    def render_multiple(self, model_states):
        # 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.
        if not model_states:
            return
        # Prevent that all model caches are expired for each render.
        with self.bulk_update():
            unrendered_models = model_states
            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

    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)
        # No need to actually clone them, they'll never change
        clone.real_models = self.real_models
        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.do_pending_operations(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


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.
    """