from __future__ import unicode_literals

import copy
import importlib
import threading
import uuid
import warnings

import django
import six
from django.apps import apps
from django.conf import settings
from django.contrib import admin
from django.contrib.auth import get_user_model
from django.core.exceptions import ObjectDoesNotExist
from django.db import models
from django.db.models import Q
from django.db.models.fields.proxy import OrderWrt
from django.forms.models import model_to_dict
from django.urls import reverse
from django.utils.text import format_lazy
from django.utils.timezone import now
from simple_history import utils
from . import exceptions
from .manager import HistoryDescriptor
from .signals import post_create_historical_record, pre_create_historical_record

if django.VERSION < (2,):
    from django.utils.translation import ugettext_lazy as _
    from django.utils.encoding import smart_text as smart_str
    from django.utils.encoding import python_2_unicode_compatible
else:
    from django.utils.translation import gettext_lazy as _
    from django.utils.encoding import smart_str

registered_models = {}


def _default_get_user(request, **kwargs):
    try:
        return request.user
    except AttributeError:
        return None


def _history_user_getter(historical_instance):
    if historical_instance.history_user_id is None:
        return None
    User = get_user_model()
    try:
        return User.objects.get(pk=historical_instance.history_user_id)
    except User.DoesNotExist:
        return None


def _history_user_setter(historical_instance, user):
    if user is not None:
        historical_instance.history_user_id = user.pk


class HistoricalRecords(object):
    thread = threading.local()

    def __init__(
        self,
        verbose_name=None,
        bases=(models.Model,),
        user_related_name="+",
        table_name=None,
        inherit=False,
        excluded_fields=None,
        history_id_field=None,
        history_change_reason_field=None,
        user_model=None,
        get_user=_default_get_user,
        cascade_delete_history=False,
        custom_model_name=None,
        app=None,
        history_user_id_field=None,
        history_user_getter=_history_user_getter,
        history_user_setter=_history_user_setter,
        related_name=None,
        use_base_model_db=False,
    ):
        self.user_set_verbose_name = verbose_name
        self.user_related_name = user_related_name
        self.table_name = table_name
        self.inherit = inherit
        self.history_id_field = history_id_field
        self.history_change_reason_field = history_change_reason_field
        self.user_model = user_model
        self.get_user = get_user
        self.cascade_delete_history = cascade_delete_history
        self.custom_model_name = custom_model_name
        self.app = app
        self.user_id_field = history_user_id_field
        self.user_getter = history_user_getter
        self.user_setter = history_user_setter
        self.related_name = related_name
        self.use_base_model_db = use_base_model_db

        if excluded_fields is None:
            excluded_fields = []
        self.excluded_fields = excluded_fields
        try:
            if isinstance(bases, six.string_types):
                raise TypeError
            self.bases = (HistoricalChanges,) + tuple(bases)
        except TypeError:
            raise TypeError("The `bases` option must be a list or a tuple.")

    def contribute_to_class(self, cls, name):
        self.manager_name = name
        self.module = cls.__module__
        self.cls = cls
        models.signals.class_prepared.connect(self.finalize, weak=False)
        self.add_extra_methods(cls)

        if cls._meta.abstract and not self.inherit:
            msg = (
                "HistoricalRecords added to abstract model ({}) without "
                "inherit=True".format(self.cls.__name__)
            )
            warnings.warn(msg, UserWarning)

    def add_extra_methods(self, cls):
        def save_without_historical_record(self, *args, **kwargs):
            """
            Save model without saving a historical record

            Make sure you know what you're doing before you use this method.
            """
            self.skip_history_when_saving = True
            try:
                ret = self.save(*args, **kwargs)
            finally:
                del self.skip_history_when_saving
            return ret

        setattr(cls, "save_without_historical_record", save_without_historical_record)

    def finalize(self, sender, **kwargs):
        inherited = False
        if self.cls is not sender:  # set in concrete
            inherited = self.inherit and issubclass(sender, self.cls)
            if not inherited:
                return  # set in abstract

        if hasattr(sender._meta, "simple_history_manager_attribute"):
            raise exceptions.MultipleRegistrationsError(
                "{}.{} registered multiple times for history tracking.".format(
                    sender._meta.app_label, sender._meta.object_name
                )
            )
        history_model = self.create_history_model(sender, inherited)
        if inherited:
            # Make sure history model is in same module as concrete model
            module = importlib.import_module(history_model.__module__)
        else:
            module = importlib.import_module(self.module)
        setattr(module, history_model.__name__, history_model)

        # The HistoricalRecords object will be discarded,
        # so the signal handlers can't use weak references.
        models.signals.post_save.connect(self.post_save, sender=sender, weak=False)
        models.signals.post_delete.connect(self.post_delete, sender=sender, weak=False)

        descriptor = HistoryDescriptor(history_model)
        setattr(sender, self.manager_name, descriptor)
        sender._meta.simple_history_manager_attribute = self.manager_name

    def get_history_model_name(self, model):
        if not self.custom_model_name:
            return "Historical{}".format(model._meta.object_name)
        # Must be trying to use a custom history model name
        if callable(self.custom_model_name):
            name = self.custom_model_name(model._meta.object_name)
        else:
            #  simple string
            name = self.custom_model_name
        # Desired class name cannot be same as the model it is tracking
        if not (
            name.lower() == model._meta.object_name.lower()
            and model.__module__ == self.module
        ):
            return name
        raise ValueError(
            "The 'custom_model_name' option '{}' evaluates to a name that is the same "
            "as the model it is tracking. This is not permitted.".format(
                self.custom_model_name
            )
        )

    def create_history_model(self, model, inherited):
        """
        Creates a historical model to associate with the model provided.
        """
        attrs = {
            "__module__": self.module,
            "_history_excluded_fields": self.excluded_fields,
        }

        app_module = "%s.models" % model._meta.app_label

        if inherited:
            # inherited use models module
            attrs["__module__"] = model.__module__
        elif model.__module__ != self.module:
            # registered under different app
            attrs["__module__"] = self.module
        elif app_module != self.module:
            # Abuse an internal API because the app registry is loading.
            app = apps.app_configs[model._meta.app_label]
            models_module = app.name
            attrs["__module__"] = models_module

        fields = self.copy_fields(model)
        attrs.update(fields)
        attrs.update(self.get_extra_fields(model, fields))
        # type in python2 wants str as a first argument
        attrs.update(Meta=type(str("Meta"), (), self.get_meta_options(model)))
        if self.table_name is not None:
            attrs["Meta"].db_table = self.table_name

        # Set as the default then check for overrides
        name = self.get_history_model_name(model)

        registered_models[model._meta.db_table] = model
        history_model = type(str(name), self.bases, attrs)
        return (
            python_2_unicode_compatible(history_model)
            if django.VERSION < (2,)
            else history_model
        )

    def fields_included(self, model):
        fields = []
        for field in model._meta.fields:
            if field.name not in self.excluded_fields:
                fields.append(field)
        return fields

    def copy_fields(self, model):
        """
        Creates copies of the model's original fields, returning
        a dictionary mapping field name to copied field object.
        """
        fields = {}
        for field in self.fields_included(model):
            field = copy.copy(field)
            field.remote_field = copy.copy(field.remote_field)
            if isinstance(field, OrderWrt):
                # OrderWrt is a proxy field, switch to a plain IntegerField
                field.__class__ = models.IntegerField
            if isinstance(field, models.ForeignKey):
                old_field = field
                old_swappable = old_field.swappable
                old_field.swappable = False
                try:
                    _name, _path, args, field_args = old_field.deconstruct()
                finally:
                    old_field.swappable = old_swappable
                if getattr(old_field, "one_to_one", False) or isinstance(
                    old_field, models.OneToOneField
                ):
                    FieldType = models.ForeignKey
                else:
                    FieldType = type(old_field)

                # If field_args['to'] is 'self' then we have a case where the object
                # has a foreign key to itself. If we pass the historical record's
                # field to = 'self', the foreign key will point to an historical
                # record rather than the base record. We can use old_field.model here.
                if field_args.get("to", None) == "self":
                    field_args["to"] = old_field.model

                # Override certain arguments passed when creating the field
                # so that they work for the historical field.
                field_args.update(
                    db_constraint=False,
                    related_name="+",
                    null=True,
                    blank=True,
                    primary_key=False,
                    db_index=True,
                    serialize=True,
                    unique=False,
                    on_delete=models.DO_NOTHING,
                )
                field = FieldType(*args, **field_args)
                field.name = old_field.name
            else:
                transform_field(field)
            fields[field.name] = field
        return fields

    def _get_history_change_reason_field(self):
        if self.history_change_reason_field:
            # User specific field from init
            history_change_reason_field = self.history_change_reason_field
        elif getattr(
            settings, "SIMPLE_HISTORY_HISTORY_CHANGE_REASON_USE_TEXT_FIELD", False
        ):
            # Use text field with no max length, not enforced by DB anyways
            history_change_reason_field = models.TextField(null=True)
        else:
            # Current default, with max length
            history_change_reason_field = models.CharField(max_length=100, null=True)

        return history_change_reason_field

    def _get_history_id_field(self):
        if self.history_id_field:
            history_id_field = self.history_id_field
            history_id_field.primary_key = True
            history_id_field.editable = False
        elif getattr(settings, "SIMPLE_HISTORY_HISTORY_ID_USE_UUID", False):
            history_id_field = models.UUIDField(
                primary_key=True, default=uuid.uuid4, editable=False
            )
        else:
            history_id_field = models.AutoField(primary_key=True)

        return history_id_field

    def _get_history_user_fields(self):
        if self.user_id_field is not None:
            # Tracking user using explicit id rather than Django ForeignKey
            history_user_fields = {
                "history_user": property(self.user_getter, self.user_setter),
                "history_user_id": self.user_id_field,
            }
        else:
            user_model = self.user_model or getattr(
                settings, "AUTH_USER_MODEL", "auth.User"
            )

            history_user_fields = {
                "history_user": models.ForeignKey(
                    user_model,
                    null=True,
                    related_name=self.user_related_name,
                    on_delete=models.SET_NULL,
                )
            }

        return history_user_fields

    def _get_history_related_field(self, model):
        if self.related_name:
            if self.manager_name == self.related_name:
                raise exceptions.RelatedNameConflictError(
                    "The related name must not be called like the history manager."
                )
            return {
                "history_relation": models.ForeignKey(
                    model,
                    on_delete=models.DO_NOTHING,
                    related_name=self.related_name,
                    db_constraint=False,
                )
            }
        else:
            return {}

    def get_extra_fields(self, model, fields):
        """Return dict of extra fields added to the historical record model"""

        def revert_url(self):
            """URL for this change in the default admin site."""
            opts = model._meta
            app_label, model_name = opts.app_label, opts.model_name
            return reverse(
                "%s:%s_%s_simple_history" % (admin.site.name, app_label, model_name),
                args=[getattr(self, opts.pk.attname), self.history_id],
            )

        def get_instance(self):
            attrs = {
                field.attname: getattr(self, field.attname) for field in fields.values()
            }
            if self._history_excluded_fields:
                excluded_attnames = [
                    model._meta.get_field(field).attname
                    for field in self._history_excluded_fields
                ]
                try:
                    values = (
                        model.objects.filter(pk=getattr(self, model._meta.pk.attname))
                        .values(*excluded_attnames)
                        .get()
                    )
                except ObjectDoesNotExist:
                    pass
                else:
                    attrs.update(values)
            return model(**attrs)

        def get_next_record(self):
            """
            Get the next history record for the instance. `None` if last.
            """
            history = utils.get_history_manager_for_model(self.instance)
            return (
                history.filter(Q(history_date__gt=self.history_date))
                .order_by("history_date")
                .first()
            )

        def get_prev_record(self):
            """
            Get the previous history record for the instance. `None` if first.
            """
            history = utils.get_history_manager_for_model(self.instance)
            return (
                history.filter(Q(history_date__lt=self.history_date))
                .order_by("history_date")
                .last()
            )

        extra_fields = {
            "history_id": self._get_history_id_field(),
            "history_date": models.DateTimeField(),
            "history_change_reason": self._get_history_change_reason_field(),
            "history_type": models.CharField(
                max_length=1,
                choices=(("+", _("Created")), ("~", _("Changed")), ("-", _("Deleted"))),
            ),
            "history_object": HistoricalObjectDescriptor(
                model, self.fields_included(model)
            ),
            "instance": property(get_instance),
            "instance_type": model,
            "next_record": property(get_next_record),
            "prev_record": property(get_prev_record),
            "revert_url": revert_url,
            "__str__": lambda self: "{} as of {}".format(
                self.history_object, self.history_date
            ),
        }

        extra_fields.update(self._get_history_related_field(model))
        extra_fields.update(self._get_history_user_fields())

        return extra_fields

    def get_meta_options(self, model):
        """
        Returns a dictionary of fields that will be added to
        the Meta inner class of the historical record model.
        """
        meta_fields = {
            "ordering": ("-history_date", "-history_id"),
            "get_latest_by": "history_date",
        }
        if self.user_set_verbose_name:
            name = self.user_set_verbose_name
        else:
            name = format_lazy("historical {}", smart_str(model._meta.verbose_name))
        meta_fields["verbose_name"] = name
        if self.app:
            meta_fields["app_label"] = self.app
        return meta_fields

    def post_save(self, instance, created, using=None, **kwargs):
        if not created and hasattr(instance, "skip_history_when_saving"):
            return
        if not kwargs.get("raw", False):
            self.create_historical_record(instance, created and "+" or "~", using=using)

    def post_delete(self, instance, using=None, **kwargs):
        if self.cascade_delete_history:
            manager = getattr(instance, self.manager_name)
            manager.using(using).all().delete()
        else:
            self.create_historical_record(instance, "-", using=using)

    def create_historical_record(self, instance, history_type, using=None):
        using = using if self.use_base_model_db else None
        history_date = getattr(instance, "_history_date", now())
        history_user = self.get_history_user(instance)
        history_change_reason = getattr(instance, "changeReason", None)
        manager = getattr(instance, self.manager_name)

        attrs = {}
        for field in self.fields_included(instance):
            attrs[field.attname] = getattr(instance, field.attname)

        relation_field = getattr(manager.model, "history_relation", None)
        if relation_field is not None:
            attrs["history_relation"] = instance

        history_instance = manager.model(
            history_date=history_date,
            history_type=history_type,
            history_user=history_user,
            history_change_reason=history_change_reason,
            **attrs
        )

        pre_create_historical_record.send(
            sender=manager.model,
            instance=instance,
            history_date=history_date,
            history_user=history_user,
            history_change_reason=history_change_reason,
            history_instance=history_instance,
            using=using,
        )

        history_instance.save(using=using)

        post_create_historical_record.send(
            sender=manager.model,
            instance=instance,
            history_instance=history_instance,
            history_date=history_date,
            history_user=history_user,
            history_change_reason=history_change_reason,
            using=using,
        )

    def get_history_user(self, instance):
        """Get the modifying user from instance or middleware."""
        try:
            return instance._history_user
        except AttributeError:
            request = None
            try:
                if self.thread.request.user.is_authenticated:
                    request = self.thread.request
            except AttributeError:
                pass

        return self.get_user(instance=instance, request=request)


def transform_field(field):
    """Customize field appropriately for use in historical model"""
    field.name = field.attname
    if isinstance(field, models.BigAutoField):
        field.__class__ = models.BigIntegerField
    elif isinstance(field, models.AutoField):
        field.__class__ = models.IntegerField

    elif isinstance(field, models.FileField):
        # Don't copy file, just path.
        field.__class__ = models.TextField

    # Historical instance shouldn't change create/update timestamps
    field.auto_now = False
    field.auto_now_add = False

    if field.primary_key or field.unique:
        # Unique fields can no longer be guaranteed unique,
        # but they should still be indexed for faster lookups.
        field.primary_key = False
        field._unique = False
        field.db_index = True
        field.serialize = True


class HistoricalObjectDescriptor(object):
    def __init__(self, model, fields_included):
        self.model = model
        self.fields_included = fields_included

    def __get__(self, instance, owner):
        values = {f.attname: getattr(instance, f.attname) for f in self.fields_included}
        return self.model(**values)


class HistoricalChanges(object):
    def diff_against(self, old_history):
        if not isinstance(old_history, type(self)):
            raise TypeError(
                ("unsupported type(s) for diffing: " "'{}' and '{}'").format(
                    type(self), type(old_history)
                )
            )

        changes = []
        changed_fields = []
        old_values = model_to_dict(old_history.instance)
        current_values = model_to_dict(self.instance)
        for field, new_value in current_values.items():
            if field in old_values:
                old_value = old_values[field]
                if old_value != new_value:
                    change = ModelChange(field, old_value, new_value)
                    changes.append(change)
                    changed_fields.append(field)

        return ModelDelta(changes, changed_fields, old_history, self)


class ModelChange(object):
    def __init__(self, field_name, old_value, new_value):
        self.field = field_name
        self.old = old_value
        self.new = new_value


class ModelDelta(object):
    def __init__(self, changes, changed_fields, old_record, new_record):
        self.changes = changes
        self.changed_fields = changed_fields
        self.old_record = old_record
        self.new_record = new_record