import json
from collections import OrderedDict
from datetime import date

from django import forms
from django.contrib.auth.models import User
from django.contrib.contenttypes.fields import GenericForeignKey
from django.contrib.contenttypes.models import ContentType
from django.contrib.postgres.fields import JSONField
from django.core.validators import ValidationError
from django.db import models
from django.http import HttpResponse
from django.template import Template, Context
from django.urls import reverse
from django.utils.text import slugify
from rest_framework.utils.encoders import JSONEncoder
from taggit.models import TagBase, GenericTaggedItemBase

from utilities.fields import ColorField
from utilities.forms import CSVChoiceField, DatePicker, LaxURLField, StaticSelect2, add_blank_choice
from utilities.utils import deepmerge, render_jinja2
from .choices import *
from .constants import *
from .querysets import ConfigContextQuerySet
from .utils import FunctionalityQueryset


__all__ = (
    'ConfigContext',
    'ConfigContextModel',
    'CustomField',
    'CustomFieldChoice',
    'CustomFieldModel',
    'CustomFieldValue',
    'CustomLink',
    'ExportTemplate',
    'Graph',
    'ImageAttachment',
    'ObjectChange',
    'ReportResult',
    'Script',
    'Tag',
    'TaggedItem',
    'Webhook',
)


#
# Webhooks
#

class Webhook(models.Model):
    """
    A Webhook defines a request that will be sent to a remote application when an object is created, updated, and/or
    delete in NetBox. The request will contain a representation of the object, which the remote application can act on.
    Each Webhook can be limited to firing only on certain actions or certain object types.
    """
    obj_type = models.ManyToManyField(
        to=ContentType,
        related_name='webhooks',
        verbose_name='Object types',
        limit_choices_to=FunctionalityQueryset('webhooks'),
        help_text="The object(s) to which this Webhook applies."
    )
    name = models.CharField(
        max_length=150,
        unique=True
    )
    type_create = models.BooleanField(
        default=False,
        help_text="Call this webhook when a matching object is created."
    )
    type_update = models.BooleanField(
        default=False,
        help_text="Call this webhook when a matching object is updated."
    )
    type_delete = models.BooleanField(
        default=False,
        help_text="Call this webhook when a matching object is deleted."
    )
    payload_url = models.CharField(
        max_length=500,
        verbose_name='URL',
        help_text="A POST will be sent to this URL when the webhook is called."
    )
    enabled = models.BooleanField(
        default=True
    )
    http_method = models.CharField(
        max_length=30,
        choices=WebhookHttpMethodChoices,
        default=WebhookHttpMethodChoices.METHOD_POST,
        verbose_name='HTTP method'
    )
    http_content_type = models.CharField(
        max_length=100,
        default=HTTP_CONTENT_TYPE_JSON,
        verbose_name='HTTP content type',
        help_text='The complete list of official content types is available '
                  '<a href="https://www.iana.org/assignments/media-types/media-types.xhtml">here</a>.'
    )
    additional_headers = models.TextField(
        blank=True,
        help_text="User-supplied HTTP headers to be sent with the request in addition to the HTTP content type. "
                  "Headers should be defined in the format <code>Name: Value</code>. Jinja2 template processing is "
                  "support with the same context as the request body (below)."
    )
    body_template = models.TextField(
        blank=True,
        help_text='Jinja2 template for a custom request body. If blank, a JSON object representing the change will be '
                  'included. Available context data includes: <code>event</code>, <code>model</code>, '
                  '<code>timestamp</code>, <code>username</code>, <code>request_id</code>, and <code>data</code>.'
    )
    secret = models.CharField(
        max_length=255,
        blank=True,
        help_text="When provided, the request will include a 'X-Hook-Signature' "
                  "header containing a HMAC hex digest of the payload body using "
                  "the secret as the key. The secret is not transmitted in "
                  "the request."
    )
    ssl_verification = models.BooleanField(
        default=True,
        verbose_name='SSL verification',
        help_text="Enable SSL certificate verification. Disable with caution!"
    )
    ca_file_path = models.CharField(
        max_length=4096,
        null=True,
        blank=True,
        verbose_name='CA File Path',
        help_text='The specific CA certificate file to use for SSL verification. '
                  'Leave blank to use the system defaults.'
    )

    class Meta:
        ordering = ('name',)
        unique_together = ('payload_url', 'type_create', 'type_update', 'type_delete',)

    def __str__(self):
        return self.name

    def clean(self):
        if not self.type_create and not self.type_delete and not self.type_update:
            raise ValidationError(
                "You must select at least one type: create, update, and/or delete."
            )

        if not self.ssl_verification and self.ca_file_path:
            raise ValidationError({
                'ca_file_path': 'Do not specify a CA certificate file if SSL verification is disabled.'
            })

    def render_headers(self, context):
        """
        Render additional_headers and return a dict of Header: Value pairs.
        """
        if not self.additional_headers:
            return {}
        ret = {}
        data = render_jinja2(self.additional_headers, context)
        for line in data.splitlines():
            header, value = line.split(':')
            ret[header.strip()] = value.strip()
        return ret

    def render_body(self, context):
        """
        Render the body template, if defined. Otherwise, jump the context as a JSON object.
        """
        if self.body_template:
            return render_jinja2(self.body_template, context)
        else:
            return json.dumps(context, cls=JSONEncoder)


#
# Custom fields
#

class CustomFieldModel(models.Model):
    _cf = None

    class Meta:
        abstract = True

    def cache_custom_fields(self):
        """
        Cache all custom field values for this instance
        """
        self._cf = {
            field.name: value for field, value in self.get_custom_fields().items()
        }

    @property
    def cf(self):
        """
        Name-based CustomFieldValue accessor for use in templates
        """
        if self._cf is None:
            self.cache_custom_fields()
        return self._cf

    def get_custom_fields(self):
        """
        Return a dictionary of custom fields for a single object in the form {<field>: value}.
        """

        # Find all custom fields applicable to this type of object
        content_type = ContentType.objects.get_for_model(self)
        fields = CustomField.objects.filter(obj_type=content_type)

        # If the object exists, populate its custom fields with values
        if hasattr(self, 'pk'):
            values = self.custom_field_values.all()
            values_dict = {cfv.field_id: cfv.value for cfv in values}
            return OrderedDict([(field, values_dict.get(field.pk)) for field in fields])
        else:
            return OrderedDict([(field, None) for field in fields])


class CustomField(models.Model):
    obj_type = models.ManyToManyField(
        to=ContentType,
        related_name='custom_fields',
        verbose_name='Object(s)',
        limit_choices_to=FunctionalityQueryset('custom_fields'),
        help_text='The object(s) to which this field applies.'
    )
    type = models.CharField(
        max_length=50,
        choices=CustomFieldTypeChoices,
        default=CustomFieldTypeChoices.TYPE_TEXT
    )
    name = models.CharField(
        max_length=50,
        unique=True
    )
    label = models.CharField(
        max_length=50,
        blank=True,
        help_text='Name of the field as displayed to users (if not provided, '
                  'the field\'s name will be used)'
    )
    description = models.CharField(
        max_length=100,
        blank=True
    )
    required = models.BooleanField(
        default=False,
        help_text='If true, this field is required when creating new objects '
                  'or editing an existing object.'
    )
    filter_logic = models.CharField(
        max_length=50,
        choices=CustomFieldFilterLogicChoices,
        default=CustomFieldFilterLogicChoices.FILTER_LOOSE,
        help_text='Loose matches any instance of a given string; exact '
                  'matches the entire field.'
    )
    default = models.CharField(
        max_length=100,
        blank=True,
        help_text='Default value for the field. Use "true" or "false" for booleans.'
    )
    weight = models.PositiveSmallIntegerField(
        default=100,
        help_text='Fields with higher weights appear lower in a form.'
    )

    class Meta:
        ordering = ['weight', 'name']

    def __str__(self):
        return self.label or self.name.replace('_', ' ').capitalize()

    def serialize_value(self, value):
        """
        Serialize the given value to a string suitable for storage as a CustomFieldValue
        """
        if value is None:
            return ''
        if self.type == CustomFieldTypeChoices.TYPE_BOOLEAN:
            return str(int(bool(value)))
        if self.type == CustomFieldTypeChoices.TYPE_DATE:
            # Could be date/datetime object or string
            try:
                return value.strftime('%Y-%m-%d')
            except AttributeError:
                return value
        if self.type == CustomFieldTypeChoices.TYPE_SELECT:
            # Could be ModelChoiceField or TypedChoiceField
            return str(value.id) if hasattr(value, 'id') else str(value)
        return value

    def deserialize_value(self, serialized_value):
        """
        Convert a string into the object it represents depending on the type of field
        """
        if serialized_value == '':
            return None
        if self.type == CustomFieldTypeChoices.TYPE_INTEGER:
            return int(serialized_value)
        if self.type == CustomFieldTypeChoices.TYPE_BOOLEAN:
            return bool(int(serialized_value))
        if self.type == CustomFieldTypeChoices.TYPE_DATE:
            # Read date as YYYY-MM-DD
            return date(*[int(n) for n in serialized_value.split('-')])
        if self.type == CustomFieldTypeChoices.TYPE_SELECT:
            return self.choices.get(pk=int(serialized_value))
        return serialized_value

    def to_form_field(self, set_initial=True, enforce_required=True, for_csv_import=False):
        """
        Return a form field suitable for setting a CustomField's value for an object.

        set_initial: Set initial date for the field. This should be False when generating a field for bulk editing.
        enforce_required: Honor the value of CustomField.required. Set to False for filtering/bulk editing.
        for_csv_import: Return a form field suitable for bulk import of objects in CSV format.
        """
        initial = self.default if set_initial else None
        required = self.required if enforce_required else False

        # Integer
        if self.type == CustomFieldTypeChoices.TYPE_INTEGER:
            field = forms.IntegerField(required=required, initial=initial)

        # Boolean
        elif self.type == CustomFieldTypeChoices.TYPE_BOOLEAN:
            choices = (
                (None, '---------'),
                (1, 'True'),
                (0, 'False'),
            )
            if initial is not None and initial.lower() in ['true', 'yes', '1']:
                initial = 1
            elif initial is not None and initial.lower() in ['false', 'no', '0']:
                initial = 0
            else:
                initial = None
            field = forms.NullBooleanField(
                required=required, initial=initial, widget=StaticSelect2(choices=choices)
            )

        # Date
        elif self.type == CustomFieldTypeChoices.TYPE_DATE:
            field = forms.DateField(required=required, initial=initial, widget=DatePicker())

        # Select
        elif self.type == CustomFieldTypeChoices.TYPE_SELECT:
            choices = [(cfc.pk, cfc.value) for cfc in self.choices.all()]

            if not required:
                choices = add_blank_choice(choices)

            # Set the initial value to the PK of the default choice, if any
            if set_initial:
                default_choice = self.choices.filter(value=self.default).first()
                if default_choice:
                    initial = default_choice.pk

            field_class = CSVChoiceField if for_csv_import else forms.ChoiceField
            field = field_class(
                choices=choices, required=required, initial=initial, widget=StaticSelect2()
            )

        # URL
        elif self.type == CustomFieldTypeChoices.TYPE_URL:
            field = LaxURLField(required=required, initial=initial)

        # Text
        else:
            field = forms.CharField(max_length=255, required=required, initial=initial)

        field.model = self
        field.label = self.label if self.label else self.name.replace('_', ' ').capitalize()
        if self.description:
            field.help_text = self.description

        return field


class CustomFieldValue(models.Model):
    field = models.ForeignKey(
        to='extras.CustomField',
        on_delete=models.CASCADE,
        related_name='values'
    )
    obj_type = models.ForeignKey(
        to=ContentType,
        on_delete=models.PROTECT,
        related_name='+'
    )
    obj_id = models.PositiveIntegerField()
    obj = GenericForeignKey(
        ct_field='obj_type',
        fk_field='obj_id'
    )
    serialized_value = models.CharField(
        max_length=255
    )

    class Meta:
        ordering = ('obj_type', 'obj_id', 'pk')  # (obj_type, obj_id) may be non-unique
        unique_together = ('field', 'obj_type', 'obj_id')

    def __str__(self):
        return '{} {}'.format(self.obj, self.field)

    @property
    def value(self):
        return self.field.deserialize_value(self.serialized_value)

    @value.setter
    def value(self, value):
        self.serialized_value = self.field.serialize_value(value)

    def save(self, *args, **kwargs):
        # Delete this object if it no longer has a value to store
        if self.pk and self.value is None:
            self.delete()
        else:
            super().save(*args, **kwargs)


class CustomFieldChoice(models.Model):
    field = models.ForeignKey(
        to='extras.CustomField',
        on_delete=models.CASCADE,
        related_name='choices',
        limit_choices_to={'type': CustomFieldTypeChoices.TYPE_SELECT}
    )
    value = models.CharField(
        max_length=100
    )
    weight = models.PositiveSmallIntegerField(
        default=100,
        help_text='Higher weights appear lower in the list'
    )

    class Meta:
        ordering = ['field', 'weight', 'value']
        unique_together = ['field', 'value']

    def __str__(self):
        return self.value

    def clean(self):
        if self.field.type != CustomFieldTypeChoices.TYPE_SELECT:
            raise ValidationError("Custom field choices can only be assigned to selection fields.")

    def delete(self, using=None, keep_parents=False):
        # When deleting a CustomFieldChoice, delete all CustomFieldValues which point to it
        pk = self.pk
        super().delete(using, keep_parents)
        CustomFieldValue.objects.filter(
            field__type=CustomFieldTypeChoices.TYPE_SELECT,
            serialized_value=str(pk)
        ).delete()


#
# Custom links
#

class CustomLink(models.Model):
    """
    A custom link to an external representation of a NetBox object. The link text and URL fields accept Jinja2 template
    code to be rendered with an object as context.
    """
    content_type = models.ForeignKey(
        to=ContentType,
        on_delete=models.CASCADE,
        limit_choices_to=FunctionalityQueryset('custom_links')
    )
    name = models.CharField(
        max_length=100,
        unique=True
    )
    text = models.CharField(
        max_length=500,
        help_text="Jinja2 template code for link text"
    )
    url = models.CharField(
        max_length=500,
        verbose_name='URL',
        help_text="Jinja2 template code for link URL"
    )
    weight = models.PositiveSmallIntegerField(
        default=100
    )
    group_name = models.CharField(
        max_length=50,
        blank=True,
        help_text="Links with the same group will appear as a dropdown menu"
    )
    button_class = models.CharField(
        max_length=30,
        choices=CustomLinkButtonClassChoices,
        default=CustomLinkButtonClassChoices.CLASS_DEFAULT,
        help_text="The class of the first link in a group will be used for the dropdown button"
    )
    new_window = models.BooleanField(
        help_text="Force link to open in a new window"
    )

    class Meta:
        ordering = ['group_name', 'weight', 'name']

    def __str__(self):
        return self.name


#
# Graphs
#

class Graph(models.Model):
    type = models.ForeignKey(
        to=ContentType,
        on_delete=models.CASCADE,
        limit_choices_to=FunctionalityQueryset('graphs')
    )
    weight = models.PositiveSmallIntegerField(
        default=1000
    )
    name = models.CharField(
        max_length=100,
        verbose_name='Name'
    )
    template_language = models.CharField(
        max_length=50,
        choices=TemplateLanguageChoices,
        default=TemplateLanguageChoices.LANGUAGE_JINJA2
    )
    source = models.CharField(
        max_length=500,
        verbose_name='Source URL'
    )
    link = models.URLField(
        blank=True,
        verbose_name='Link URL'
    )

    class Meta:
        ordering = ('type', 'weight', 'name', 'pk')  # (type, weight, name) may be non-unique

    def __str__(self):
        return self.name

    def embed_url(self, obj):
        context = {'obj': obj}

        # TODO: Remove in v2.8
        if self.template_language == TemplateLanguageChoices.LANGUAGE_DJANGO:
            template = Template(self.source)
            return template.render(Context(context))

        elif self.template_language == TemplateLanguageChoices.LANGUAGE_JINJA2:
            return render_jinja2(self.source, context)

    def embed_link(self, obj):
        if self.link is None:
            return ''

        context = {'obj': obj}

        # TODO: Remove in v2.8
        if self.template_language == TemplateLanguageChoices.LANGUAGE_DJANGO:
            template = Template(self.link)
            return template.render(Context(context))

        elif self.template_language == TemplateLanguageChoices.LANGUAGE_JINJA2:
            return render_jinja2(self.link, context)


#
# Export templates
#

class ExportTemplate(models.Model):
    content_type = models.ForeignKey(
        to=ContentType,
        on_delete=models.CASCADE,
        limit_choices_to=FunctionalityQueryset('export_templates')
    )
    name = models.CharField(
        max_length=100
    )
    description = models.CharField(
        max_length=200,
        blank=True
    )
    template_language = models.CharField(
        max_length=50,
        choices=TemplateLanguageChoices,
        default=TemplateLanguageChoices.LANGUAGE_JINJA2
    )
    template_code = models.TextField(
        help_text='The list of objects being exported is passed as a context variable named <code>queryset</code>.'
    )
    mime_type = models.CharField(
        max_length=50,
        blank=True,
        verbose_name='MIME type',
        help_text='Defaults to <code>text/plain</code>'
    )
    file_extension = models.CharField(
        max_length=15,
        blank=True,
        help_text='Extension to append to the rendered filename'
    )

    class Meta:
        ordering = ['content_type', 'name']
        unique_together = [
            ['content_type', 'name']
        ]

    def __str__(self):
        return '{}: {}'.format(self.content_type, self.name)

    def render(self, queryset):
        """
        Render the contents of the template.
        """
        context = {
            'queryset': queryset
        }

        if self.template_language == TemplateLanguageChoices.LANGUAGE_DJANGO:
            template = Template(self.template_code)
            output = template.render(Context(context))

        elif self.template_language == TemplateLanguageChoices.LANGUAGE_JINJA2:
            output = render_jinja2(self.template_code, context)

        else:
            return None

        # Replace CRLF-style line terminators
        output = output.replace('\r\n', '\n')

        return output

    def render_to_response(self, queryset):
        """
        Render the template to an HTTP response, delivered as a named file attachment
        """
        output = self.render(queryset)
        mime_type = 'text/plain' if not self.mime_type else self.mime_type

        # Build the response
        response = HttpResponse(output, content_type=mime_type)
        filename = 'netbox_{}{}'.format(
            queryset.model._meta.verbose_name_plural,
            '.{}'.format(self.file_extension) if self.file_extension else ''
        )
        response['Content-Disposition'] = 'attachment; filename="{}"'.format(filename)

        return response


#
# Image attachments
#

def image_upload(instance, filename):

    path = 'image-attachments/'

    # Rename the file to the provided name, if any. Attempt to preserve the file extension.
    extension = filename.rsplit('.')[-1].lower()
    if instance.name and extension in ['bmp', 'gif', 'jpeg', 'jpg', 'png']:
        filename = '.'.join([instance.name, extension])
    elif instance.name:
        filename = instance.name

    return '{}{}_{}_{}'.format(path, instance.content_type.name, instance.object_id, filename)


class ImageAttachment(models.Model):
    """
    An uploaded image which is associated with an object.
    """
    content_type = models.ForeignKey(
        to=ContentType,
        on_delete=models.CASCADE
    )
    object_id = models.PositiveIntegerField()
    parent = GenericForeignKey(
        ct_field='content_type',
        fk_field='object_id'
    )
    image = models.ImageField(
        upload_to=image_upload,
        height_field='image_height',
        width_field='image_width'
    )
    image_height = models.PositiveSmallIntegerField()
    image_width = models.PositiveSmallIntegerField()
    name = models.CharField(
        max_length=50,
        blank=True
    )
    created = models.DateTimeField(
        auto_now_add=True
    )

    class Meta:
        ordering = ('name', 'pk')  # name may be non-unique

    def __str__(self):
        if self.name:
            return self.name
        filename = self.image.name.rsplit('/', 1)[-1]
        return filename.split('_', 2)[2]

    def delete(self, *args, **kwargs):

        _name = self.image.name

        super().delete(*args, **kwargs)

        # Delete file from disk
        self.image.delete(save=False)

        # Deleting the file erases its name. We restore the image's filename here in case we still need to reference it
        # before the request finishes. (For example, to display a message indicating the ImageAttachment was deleted.)
        self.image.name = _name

    @property
    def size(self):
        """
        Wrapper around `image.size` to suppress an OSError in case the file is inaccessible. Also opportunistically
        catch other exceptions that we know other storage back-ends to throw.
        """
        expected_exceptions = [OSError]

        try:
            from botocore.exceptions import ClientError
            expected_exceptions.append(ClientError)
        except ImportError:
            pass

        try:
            return self.image.size
        except tuple(expected_exceptions):
            return None


#
# Config contexts
#

class ConfigContext(models.Model):
    """
    A ConfigContext represents a set of arbitrary data available to any Device or VirtualMachine matching its assigned
    qualifiers (region, site, etc.). For example, the data stored in a ConfigContext assigned to site A and tenant B
    will be available to a Device in site A assigned to tenant B. Data is stored in JSON format.
    """
    name = models.CharField(
        max_length=100,
        unique=True
    )
    weight = models.PositiveSmallIntegerField(
        default=1000
    )
    description = models.CharField(
        max_length=100,
        blank=True
    )
    is_active = models.BooleanField(
        default=True,
    )
    regions = models.ManyToManyField(
        to='dcim.Region',
        related_name='+',
        blank=True
    )
    sites = models.ManyToManyField(
        to='dcim.Site',
        related_name='+',
        blank=True
    )
    roles = models.ManyToManyField(
        to='dcim.DeviceRole',
        related_name='+',
        blank=True
    )
    platforms = models.ManyToManyField(
        to='dcim.Platform',
        related_name='+',
        blank=True
    )
    cluster_groups = models.ManyToManyField(
        to='virtualization.ClusterGroup',
        related_name='+',
        blank=True
    )
    clusters = models.ManyToManyField(
        to='virtualization.Cluster',
        related_name='+',
        blank=True
    )
    tenant_groups = models.ManyToManyField(
        to='tenancy.TenantGroup',
        related_name='+',
        blank=True
    )
    tenants = models.ManyToManyField(
        to='tenancy.Tenant',
        related_name='+',
        blank=True
    )
    tags = models.ManyToManyField(
        to='extras.Tag',
        related_name='+',
        blank=True
    )
    data = JSONField()

    objects = ConfigContextQuerySet.as_manager()

    class Meta:
        ordering = ['weight', 'name']

    def __str__(self):
        return self.name

    def get_absolute_url(self):
        return reverse('extras:configcontext', kwargs={'pk': self.pk})

    def clean(self):

        # Verify that JSON data is provided as an object
        if type(self.data) is not dict:
            raise ValidationError(
                {'data': 'JSON data must be in object form. Example: {"foo": 123}'}
            )


class ConfigContextModel(models.Model):
    """
    A model which includes local configuration context data. This local data will override any inherited data from
    ConfigContexts.
    """
    local_context_data = JSONField(
        blank=True,
        null=True,
    )

    class Meta:
        abstract = True

    def get_config_context(self):
        """
        Return the rendered configuration context for a device or VM.
        """

        # Compile all config data, overwriting lower-weight values with higher-weight values where a collision occurs
        data = OrderedDict()
        for context in ConfigContext.objects.get_for_object(self):
            data = deepmerge(data, context.data)

        # If the object has local config context data defined, merge it last
        if self.local_context_data:
            data = deepmerge(data, self.local_context_data)

        return data

    def clean(self):

        super().clean()

        # Verify that JSON data is provided as an object
        if self.local_context_data and type(self.local_context_data) is not dict:
            raise ValidationError(
                {'local_context_data': 'JSON data must be in object form. Example: {"foo": 123}'}
            )


#
# Custom scripts
#

class Script(models.Model):
    """
    Dummy model used to generate permissions for custom scripts. Does not exist in the database.
    """
    class Meta:
        managed = False
        permissions = (
            ('run_script', 'Can run script'),
        )


#
# Report results
#

class ReportResult(models.Model):
    """
    This model stores the results from running a user-defined report.
    """
    report = models.CharField(
        max_length=255,
        unique=True
    )
    created = models.DateTimeField(
        auto_now_add=True
    )
    user = models.ForeignKey(
        to=User,
        on_delete=models.SET_NULL,
        related_name='+',
        blank=True,
        null=True
    )
    failed = models.BooleanField()
    data = JSONField()

    class Meta:
        ordering = ['report']

    def __str__(self):
        return "{} {} at {}".format(
            self.report,
            "passed" if not self.failed else "failed",
            self.created
        )


#
# Change logging
#

class ObjectChange(models.Model):
    """
    Record a change to an object and the user account associated with that change. A change record may optionally
    indicate an object related to the one being changed. For example, a change to an interface may also indicate the
    parent device. This will ensure changes made to component models appear in the parent model's changelog.
    """
    time = models.DateTimeField(
        auto_now_add=True,
        editable=False,
        db_index=True
    )
    user = models.ForeignKey(
        to=User,
        on_delete=models.SET_NULL,
        related_name='changes',
        blank=True,
        null=True
    )
    user_name = models.CharField(
        max_length=150,
        editable=False
    )
    request_id = models.UUIDField(
        editable=False
    )
    action = models.CharField(
        max_length=50,
        choices=ObjectChangeActionChoices
    )
    changed_object_type = models.ForeignKey(
        to=ContentType,
        on_delete=models.PROTECT,
        related_name='+'
    )
    changed_object_id = models.PositiveIntegerField()
    changed_object = GenericForeignKey(
        ct_field='changed_object_type',
        fk_field='changed_object_id'
    )
    related_object_type = models.ForeignKey(
        to=ContentType,
        on_delete=models.PROTECT,
        related_name='+',
        blank=True,
        null=True
    )
    related_object_id = models.PositiveIntegerField(
        blank=True,
        null=True
    )
    related_object = GenericForeignKey(
        ct_field='related_object_type',
        fk_field='related_object_id'
    )
    object_repr = models.CharField(
        max_length=200,
        editable=False
    )
    object_data = JSONField(
        editable=False
    )

    csv_headers = [
        'time', 'user', 'user_name', 'request_id', 'action', 'changed_object_type', 'changed_object_id',
        'related_object_type', 'related_object_id', 'object_repr', 'object_data',
    ]

    class Meta:
        ordering = ['-time']

    def __str__(self):
        return '{} {} {} by {}'.format(
            self.changed_object_type,
            self.object_repr,
            self.get_action_display().lower(),
            self.user_name
        )

    def save(self, *args, **kwargs):

        # Record the user's name and the object's representation as static strings
        if not self.user_name:
            self.user_name = self.user.username
        if not self.object_repr:
            self.object_repr = str(self.changed_object)

        return super().save(*args, **kwargs)

    def get_absolute_url(self):
        return reverse('extras:objectchange', args=[self.pk])

    def to_csv(self):
        return (
            self.time,
            self.user,
            self.user_name,
            self.request_id,
            self.get_action_display(),
            self.changed_object_type,
            self.changed_object_id,
            self.related_object_type,
            self.related_object_id,
            self.object_repr,
            self.object_data,
        )


#
# Tags
#

# TODO: figure out a way around this circular import for ObjectChange
from utilities.models import ChangeLoggedModel  # noqa: E402


class Tag(TagBase, ChangeLoggedModel):
    color = ColorField(
        default='9e9e9e'
    )
    comments = models.TextField(
        blank=True,
        default=''
    )

    def get_absolute_url(self):
        return reverse('extras:tag', args=[self.slug])

    def slugify(self, tag, i=None):
        # Allow Unicode in Tag slugs (avoids empty slugs for Tags with all-Unicode names)
        slug = slugify(tag, allow_unicode=True)
        if i is not None:
            slug += "_%d" % i
        return slug


class TaggedItem(GenericTaggedItemBase):
    tag = models.ForeignKey(
        to=Tag,
        related_name="%(app_label)s_%(class)s_items",
        on_delete=models.CASCADE
    )

    class Meta:
        index_together = (
            ("content_type", "object_id")
        )