django-helpdesk/helpdesk/models.py

"""
django-helpdesk - A Django powered ticket tracker for small enterprise.

(c) Copyright 2008 Jutda. All Rights Reserved. See LICENSE for details.

models.py - Model (and hence database) definitions. This is the core of the
            helpdesk structure.
"""


from .lib import convert_value
from .templated_email import send_templated_mail
from .validators import validate_file_extension
from .webhooks import send_new_ticket_webhook
import datetime
from django.conf import settings
from django.contrib.auth import get_user_model
from django.contrib.auth.models import Permission
from django.contrib.contenttypes.models import ContentType
from django.core.exceptions import ObjectDoesNotExist, ValidationError
from django.db import models
from django.utils import timezone
from django.utils.safestring import mark_safe
from django.utils.translation import gettext, gettext_lazy as _
from helpdesk import settings as helpdesk_settings
from io import StringIO
from markdown import markdown
from markdown.extensions import Extension
import mimetypes
import os
import re
from rest_framework import serializers
import uuid


def format_time_spent(time_spent):
    if time_spent:
        time_spent = "{0:02d}h:{1:02d}m".format(
            time_spent.seconds // 3600,
            time_spent.seconds % 3600 // 60
        )
    else:
        time_spent = ""
    return time_spent


class EscapeHtml(Extension):
    def extendMarkdown(self, md):
        md.preprocessors.deregister('html_block')
        md.inlinePatterns.deregister('html')


def get_markdown(text):
    if not text:
        return ""

    pattern = r'([\[\s\S\]]*?)\(([\s\S]*?):([\s\S]*?)\)'
    # Regex check
    if re.match(pattern, text):
        # get get value of group regex
        scheme = re.search(pattern, text, re.IGNORECASE).group(2)
        # scheme check
        if scheme in helpdesk_settings.ALLOWED_URL_SCHEMES:
            replacement = '\\1(\\2:\\3)'
        else:
            replacement = '\\1(\\3)'

        text = re.sub(pattern, replacement, text, flags=re.IGNORECASE)

    return mark_safe(
        markdown(
            text,
            extensions=[
                EscapeHtml(), 'markdown.extensions.nl2br',
                'markdown.extensions.fenced_code'
            ]
        )
    )


class Queue(models.Model):
    """
    A queue is a collection of tickets into what would generally be business
    areas or departments.

    For example, a company may have a queue for each Product they provide, or
    a queue for each of Accounts, Pre-Sales, and Support.

    """

    title = models.CharField(
        _('Title'),
        max_length=100,
    )

    slug = models.SlugField(
        _('Slug'),
        max_length=50,
        unique=True,
        help_text=_('This slug is used when building ticket ID\'s. Once set, '
                    'try not to change it or e-mailing may get messy.'),
    )

    email_address = models.EmailField(
        _('E-Mail Address'),
        blank=True,
        null=True,
        help_text=_('All outgoing e-mails for this queue will use this e-mail '
                    'address. If you use IMAP or POP3, this should be the e-mail '
                    'address for that mailbox.'),
    )

    locale = models.CharField(
        _('Locale'),
        max_length=10,
        blank=True,
        null=True,
        help_text=_('Locale of this queue. All correspondence in this '
                    'queue will be in this language.'),
    )

    allow_public_submission = models.BooleanField(
        _('Allow Public Submission?'),
        blank=True,
        default=False,
        help_text=_(
            'Should this queue be listed on the public submission form?'),
    )

    allow_email_submission = models.BooleanField(
        _('Allow E-Mail Submission?'),
        blank=True,
        default=False,
        help_text=_('Do you want to poll the e-mail box below for new '
                    'tickets?'),
    )

    escalate_days = models.IntegerField(
        _('Escalation Days'),
        blank=True,
        null=True,
        help_text=_('For tickets which are not held, how often do you wish to '
                    'increase their priority? Set to 0 for no escalation.'),
    )

    new_ticket_cc = models.CharField(
        _('New Ticket CC Address'),
        blank=True,
        null=True,
        max_length=200,
        help_text=_('If an e-mail address is entered here, then it will '
                    'receive notification of all new tickets created for this queue. '
                    'Enter a comma between multiple e-mail addresses.'),
    )

    updated_ticket_cc = models.CharField(
        _('Updated Ticket CC Address'),
        blank=True,
        null=True,
        max_length=200,
        help_text=_('If an e-mail address is entered here, then it will '
                    'receive notification of all activity (new tickets, closed '
                    'tickets, updates, reassignments, etc) for this queue. Separate '
                    'multiple addresses with a comma.'),
    )

    enable_notifications_on_email_events = models.BooleanField(
        _('Notify contacts when email updates arrive'),
        blank=True,
        default=False,
        help_text=_('When an email arrives to either create a ticket or to '
                    'interact with an existing discussion. Should email notifications be sent ? '
                    'Note: the new_ticket_cc and updated_ticket_cc work independently of this feature'),
    )

    email_box_type = models.CharField(
        _('E-Mail Box Type'),
        max_length=5,
        choices=(('pop3', _('POP 3')),
                 ('imap', _('IMAP')),
                 ('oauth', _('IMAP OAUTH')),
                 ('local', _('Local Directory'))),
        blank=True,
        null=True,
        help_text=_('E-Mail server type for creating tickets automatically '
                    'from a mailbox - both POP3 and IMAP are supported, as well as '
                    'reading from a local directory.'),
    )

    email_box_host = models.CharField(
        _('E-Mail Hostname'),
        max_length=200,
        blank=True,
        null=True,
        help_text=_('Your e-mail server address - either the domain name or '
                    'IP address. May be "localhost".'),
    )

    email_box_port = models.IntegerField(
        _('E-Mail Port'),
        blank=True,
        null=True,
        help_text=_('Port number to use for accessing e-mail. Default for '
                    'POP3 is "110", and for IMAP is "143". This may differ on some '
                    'servers. Leave it blank to use the defaults.'),
    )

    email_box_ssl = models.BooleanField(
        _('Use SSL for E-Mail?'),
        blank=True,
        default=False,
        help_text=_('Whether to use SSL for IMAP or POP3 - the default ports '
                    'when using SSL are 993 for IMAP and 995 for POP3.'),
    )

    email_box_user = models.CharField(
        _('E-Mail Username'),
        max_length=200,
        blank=True,
        null=True,
        help_text=_('Username for accessing this mailbox.'),
    )

    email_box_pass = models.CharField(
        _('E-Mail Password'),
        max_length=200,
        blank=True,
        null=True,
        help_text=_('Password for the above username'),
    )

    email_box_imap_folder = models.CharField(
        _('IMAP Folder'),
        max_length=100,
        blank=True,
        null=True,
        help_text=_('If using IMAP, what folder do you wish to fetch messages '
                    'from? This allows you to use one IMAP account for multiple '
                    'queues, by filtering messages on your IMAP server into separate '
                    'folders. Default: INBOX.'),
    )

    email_box_local_dir = models.CharField(
        _('E-Mail Local Directory'),
        max_length=200,
        blank=True,
        null=True,
        help_text=_('If using a local directory, what directory path do you '
                    'wish to poll for new email? '
                    'Example: /var/lib/mail/helpdesk/'),
    )

    permission_name = models.CharField(
        _('Django auth permission name'),
        max_length=72,  # based on prepare_permission_name() pre-pending chars to slug
        blank=True,
        null=True,
        editable=False,
        help_text=_('Name used in the django.contrib.auth permission system'),
    )

    email_box_interval = models.IntegerField(
        _('E-Mail Check Interval'),
        help_text=_(
            'How often do you wish to check this mailbox? (in Minutes)'),
        blank=True,
        null=True,
        default='5',
    )

    email_box_last_check = models.DateTimeField(
        blank=True,
        null=True,
        editable=False,
        # This is updated by management/commands/get_mail.py.
    )

    socks_proxy_type = models.CharField(
        _('Socks Proxy Type'),
        max_length=8,
        choices=(('socks4', _('SOCKS4')), ('socks5', _('SOCKS5'))),
        blank=True,
        null=True,
        help_text=_(
            'SOCKS4 or SOCKS5 allows you to proxy your connections through a SOCKS server.'),
    )

    socks_proxy_host = models.GenericIPAddressField(
        _('Socks Proxy Host'),
        blank=True,
        null=True,
        help_text=_('Socks proxy IP address. Default: 127.0.0.1'),
    )

    socks_proxy_port = models.IntegerField(
        _('Socks Proxy Port'),
        blank=True,
        null=True,
        help_text=_(
            'Socks proxy port number. Default: 9150 (default TOR port)'),
    )

    logging_type = models.CharField(
        _('Logging Type'),
        max_length=5,
        choices=(
            ('none', _('None')),
            ('debug', _('Debug')),
            ('info', _('Information')),
            ('warn', _('Warning')),
            ('error', _('Error')),
            ('crit', _('Critical'))
        ),
        blank=True,
        null=True,
        help_text=_('Set the default logging level. All messages at that '
                    'level or above will be logged to the directory set '
                    'below. If no level is set, logging will be disabled.'),
    )

    logging_dir = models.CharField(
        _('Logging Directory'),
        max_length=200,
        blank=True,
        null=True,
        help_text=_('If logging is enabled, what directory should we use to '
                    'store log files for this queue? '
                    'The standard logging mechanims are used if no directory is set'),
    )

    default_owner = models.ForeignKey(
        settings.AUTH_USER_MODEL,
        on_delete=models.SET_NULL,
        related_name='default_owner',
        blank=True,
        null=True,
        verbose_name=_('Default owner'),
    )

    dedicated_time = models.DurationField(
        help_text=_("Time to be spent on this Queue in total"),
        blank=True, null=True
    )

    def __str__(self):
        return "%s" % self.title

    class Meta:
        ordering = ('title',)
        verbose_name = _('Queue')
        verbose_name_plural = _('Queues')

    def _from_address(self):
        """
        Short property to provide a sender address in SMTP format,
        eg 'Name <email>'. We do this so we can put a simple error message
        in the sender name field, so hopefully the admin can see and fix it.
        """
        if not self.email_address:
            # must check if given in format "Foo <foo@example.com>"
            default_email = re.match(
                ".*<(?P<email>.*@*.)>", settings.DEFAULT_FROM_EMAIL)
            if default_email is not None:
                # already in the right format, so just include it here
                return u'NO QUEUE EMAIL ADDRESS DEFINED %s' % settings.DEFAULT_FROM_EMAIL
            else:
                return u'NO QUEUE EMAIL ADDRESS DEFINED <%s>' % settings.DEFAULT_FROM_EMAIL
        else:
            return u'%s <%s>' % (self.title, self.email_address)
    from_address = property(_from_address)

    @property
    def time_spent(self):
        """Return back total time spent on the ticket. This is calculated value
        based on total sum from all FollowUps
        """
        total = datetime.timedelta(0)
        for val in self.ticket_set.all():
            if val.time_spent:
                total = total + val.time_spent
        return total

    @property
    def time_spent_formated(self):
        return format_time_spent(self.time_spent)

    def prepare_permission_name(self):
        """Prepare internally the codename for the permission and store it in permission_name.
        :return: The codename that can be used to create a new Permission object.
        """
        # Prepare the permission associated to this Queue
        basename = "queue_access_%s" % self.slug
        self.permission_name = "helpdesk.%s" % basename
        return basename

    def save(self, *args, **kwargs):
        if self.email_box_type == 'imap' and not self.email_box_imap_folder:
            self.email_box_imap_folder = 'INBOX'

        if self.socks_proxy_type:
            if not self.socks_proxy_host:
                self.socks_proxy_host = '127.0.0.1'
            if not self.socks_proxy_port:
                self.socks_proxy_port = 9150
        else:
            self.socks_proxy_host = None
            self.socks_proxy_port = None

        if not self.email_box_port:
            if self.email_box_type == 'imap' and self.email_box_ssl:
                self.email_box_port = 993
            elif self.email_box_type == 'imap' and not self.email_box_ssl:
                self.email_box_port = 143
            elif self.email_box_type == 'pop3' and self.email_box_ssl:
                self.email_box_port = 995
            elif self.email_box_type == 'pop3' and not self.email_box_ssl:
                self.email_box_port = 110

        if not self.id:
            # Prepare the permission codename and the permission
            # (even if they are not needed with the current configuration)
            basename = self.prepare_permission_name()

            Permission.objects.create(
                name=_("Permission for queue: ") + self.title,
                content_type=ContentType.objects.get_for_model(self.__class__),
                codename=basename,
            )

        super(Queue, self).save(*args, **kwargs)

    def delete(self, *args, **kwargs):
        permission_name = self.permission_name
        super(Queue, self).delete(*args, **kwargs)

        # once the Queue is safely deleted, remove the permission (if exists)
        if permission_name:
            try:
                p = Permission.objects.get(codename=permission_name[9:])
                p.delete()
            except ObjectDoesNotExist:
                pass


def mk_secret():
    return str(uuid.uuid4())


class Ticket(models.Model):
    """
    To allow a ticket to be entered as quickly as possible, only the
    bare minimum fields are required. These basically allow us to
    sort and manage the ticket. The user can always go back and
    enter more information later.

    A good example of this is when a customer is on the phone, and
    you want to give them a ticket ID as quickly as possible. You can
    enter some basic info, save the ticket, give the customer the ID
    and get off the phone, then add in further detail at a later time
    (once the customer is not on the line).

    Note that assigned_to is optional - unassigned tickets are displayed on
    the dashboard to prompt users to take ownership of them.
    """

    OPEN_STATUS = helpdesk_settings.OPEN_STATUS
    REOPENED_STATUS = helpdesk_settings.REOPENED_STATUS
    RESOLVED_STATUS = helpdesk_settings.RESOLVED_STATUS
    CLOSED_STATUS = helpdesk_settings.CLOSED_STATUS
    DUPLICATE_STATUS = helpdesk_settings.DUPLICATE_STATUS

    STATUS_CHOICES = helpdesk_settings.TICKET_STATUS_CHOICES
    OPEN_STATUSES = helpdesk_settings.TICKET_OPEN_STATUSES

    PRIORITY_CHOICES = helpdesk_settings.TICKET_PRIORITY_CHOICES

    title = models.CharField(
        _('Title'),
        max_length=200,
    )

    queue = models.ForeignKey(
        Queue,
        on_delete=models.CASCADE,
        verbose_name=_('Queue'),
    )

    created = models.DateTimeField(
        _('Created'),
        blank=True,
        help_text=_('Date this ticket was first created'),
    )

    modified = models.DateTimeField(
        _('Modified'),
        blank=True,
        help_text=_('Date this ticket was most recently changed.'),
    )

    submitter_email = models.EmailField(
        _('Submitter E-Mail'),
        blank=True,
        null=True,
        help_text=_('The submitter will receive an email for all public '
                    'follow-ups left for this task.'),
    )

    assigned_to = models.ForeignKey(
        settings.AUTH_USER_MODEL,
        on_delete=models.CASCADE,
        related_name='assigned_to',
        blank=True,
        null=True,
        verbose_name=_('Assigned to'),
    )

    status = models.IntegerField(
        _('Status'),
        choices=STATUS_CHOICES,
        default=OPEN_STATUS,
    )

    on_hold = models.BooleanField(
        _('On Hold'),
        blank=True,
        default=False,
        help_text=_(
            'If a ticket is on hold, it will not automatically be escalated.'),
    )

    description = models.TextField(
        _('Description'),
        blank=True,
        null=True,
        help_text=_('The content of the customers query.'),
    )

    resolution = models.TextField(
        _('Resolution'),
        blank=True,
        null=True,
        help_text=_('The resolution provided to the customer by our staff.'),
    )

    priority = models.IntegerField(
        _('Priority'),
        choices=PRIORITY_CHOICES,
        default=3,
        blank=3,
        help_text=_('1 = Highest Priority, 5 = Low Priority'),
    )

    due_date = models.DateTimeField(
        _('Due on'),
        blank=True,
        null=True,
    )

    last_escalation = models.DateTimeField(
        blank=True,
        null=True,
        editable=False,
        help_text=_('The date this ticket was last escalated - updated '
                    'automatically by management/commands/escalate_tickets.py.'),
    )

    secret_key = models.CharField(
        _("Secret key needed for viewing/editing ticket by non-logged in users"),
        max_length=36,
        default=mk_secret,
    )

    kbitem = models.ForeignKey(
        "KBItem",
        blank=True,
        null=True,
        on_delete=models.CASCADE,
        verbose_name=_(
            'Knowledge base item the user was viewing when they created this ticket.'),
    )

    merged_to = models.ForeignKey(
        'self',
        verbose_name=_('merged to'),
        related_name='merged_tickets',
        on_delete=models.CASCADE,
        null=True,
        blank=True
    )

    @property
    def time_spent(self):
        """Return back total time spent on the ticket. This is calculated value
        based on total sum from all FollowUps
        """
        total = datetime.timedelta(0)
        for val in self.followup_set.all():
            if val.time_spent:
                total = total + val.time_spent
        return total

    @property
    def time_spent_formated(self):
        return format_time_spent(self.time_spent)

    def send(self, roles, dont_send_to=None, **kwargs):
        """
        Send notifications to everyone interested in this ticket.

        The the roles argument is a dictionary mapping from roles to (template, context) pairs.
        If a role is not present in the dictionary, users of that type will not receive the notification.

        The following roles exist:

          - 'submitter'
          - 'new_ticket_cc'
          - 'ticket_cc'
          - 'assigned_to'

        Here is an example roles dictionary:

        {
            'submitter': (template_name, context),
            'assigned_to': (template_name2, context),
        }

        **kwargs are passed to send_templated_mail defined in templated_email.py

        returns the set of email addresses the notification was delivered to.

        """
        recipients = set()

        if dont_send_to is not None:
            recipients.update(dont_send_to)

        recipients.add(self.queue.email_address)

        def should_receive(email):
            return email and email not in recipients

        def send(role, recipient):
            if recipient and recipient not in recipients and role in roles:
                template, context = roles[role]
                send_templated_mail(
                    template, context, recipient, sender=self.queue.from_address, **kwargs)
                recipients.add(recipient)

        send('submitter', self.submitter_email)
        send('ticket_cc', self.queue.updated_ticket_cc)
        send('new_ticket_cc', self.queue.new_ticket_cc)
        if self.assigned_to:
            send('assigned_to', self.assigned_to.email)
        if self.queue.enable_notifications_on_email_events:
            for cc in self.ticketcc_set.all():
                send('ticket_cc', cc.email_address)
        if "new_ticket_cc" in roles:
            send_new_ticket_webhook(self)
        return recipients

    def _get_assigned_to(self):
        """ Custom property to allow us to easily print 'Unassigned' if a
        ticket has no owner, or the users name if it's assigned. If the user
        has a full name configured, we use that, otherwise their username. """
        if not self.assigned_to:
            return _('Unassigned')
        else:
            if self.assigned_to.get_full_name():
                return self.assigned_to.get_full_name()
            else:
                return self.assigned_to.get_username()
    get_assigned_to = property(_get_assigned_to)

    def _get_ticket(self):
        """ A user-friendly ticket ID, which is a combination of ticket ID
        and queue slug. This is generally used in e-mail subjects. """

        return u"[%s]" % self.ticket_for_url
    ticket = property(_get_ticket)

    def _get_ticket_for_url(self):
        """ A URL-friendly ticket ID, used in links. """
        return u"%s-%s" % (self.queue.slug, self.id)
    ticket_for_url = property(_get_ticket_for_url)

    def _get_priority_css_class(self):
        """
        Return the boostrap class corresponding to the priority.
        """
        if self.priority == 2:
            return "warning"
        elif self.priority == 1:
            return "danger"
        elif self.priority == 5:
            return "success"
        else:
            return ""
    get_priority_css_class = property(_get_priority_css_class)

    def _get_status(self):
        """
        Displays the ticket status, with an "On Hold" message if needed.
        """
        held_msg = ''
        if self.on_hold:
            held_msg = _(' - On Hold')
        dep_msg = ''
        if not self.can_be_resolved:
            dep_msg = _(' - Open dependencies')
        return u'%s%s%s' % (self.get_status_display(), held_msg, dep_msg)
    get_status = property(_get_status)

    def _get_ticket_url(self):
        """
        Returns a publicly-viewable URL for this ticket, used when giving
        a URL to the submitter of a ticket.
        """
        from django.contrib.sites.models import Site
        from django.core.exceptions import ImproperlyConfigured
        from django.urls import reverse
        try:
            site = Site.objects.get_current()
        except ImproperlyConfigured:
            site = Site(domain='configure-django-sites.com')
        if helpdesk_settings.HELPDESK_USE_HTTPS_IN_EMAIL_LINK:
            protocol = 'https'
        else:
            protocol = 'http'
        return u"%s://%s%s?ticket=%s&email=%s&key=%s" % (
            protocol,
            site.domain,
            reverse('helpdesk:public_view'),
            self.ticket_for_url,
            self.submitter_email,
            self.secret_key
        )
    ticket_url = property(_get_ticket_url)

    def _get_staff_url(self):
        """
        Returns a staff-only URL for this ticket, used when giving a URL to
        a staff member (in emails etc)
        """
        from django.contrib.sites.models import Site
        from django.core.exceptions import ImproperlyConfigured
        from django.urls import reverse
        try:
            site = Site.objects.get_current()
        except ImproperlyConfigured:
            site = Site(domain='configure-django-sites.com')
        if helpdesk_settings.HELPDESK_USE_HTTPS_IN_EMAIL_LINK:
            protocol = 'https'
        else:
            protocol = 'http'
        return u"%s://%s%s" % (
            protocol,
            site.domain,
            reverse('helpdesk:view',
                    args=[self.id])
        )
    staff_url = property(_get_staff_url)

    def _can_be_resolved(self):
        """
        Returns a boolean.
        True = any dependencies are resolved
        False = There are non-resolved dependencies
        """
        return TicketDependency.objects.filter(ticket=self).filter(
            depends_on__status__in=Ticket.OPEN_STATUSES).count() == 0
    can_be_resolved = property(_can_be_resolved)

    def get_submitter_userprofile(self):
        User = get_user_model()
        try:
            return User.objects.get(email=self.submitter_email)
        except (User.DoesNotExist, User.MultipleObjectsReturned):
            return None

    class Meta:
        get_latest_by = "created"
        ordering = ('id',)
        verbose_name = _('Ticket')
        verbose_name_plural = _('Tickets')

    def __str__(self):
        return '%s %s' % (self.id, self.title)

    def get_absolute_url(self):
        from django.urls import reverse
        return reverse('helpdesk:view', args=(self.id,))

    def save(self, *args, **kwargs):
        if not self.id:
            # This is a new ticket as no ID yet exists.
            self.created = timezone.now()

        if not self.priority:
            self.priority = 3

        self.modified = timezone.now()

        if len(self.title) > 200:
            self.title = self.title[:197] + "..."

        super(Ticket, self).save(*args, **kwargs)

    @staticmethod
    def queue_and_id_from_query(query):
        # Apply the opposite logic here compared to self._get_ticket_for_url
        # Ensure that queues with '-' in them will work
        parts = query.split('-')
        queue = '-'.join(parts[0:-1])
        return queue, parts[-1]

    def get_markdown(self):
        return get_markdown(self.description)

    @property
    def get_resolution_markdown(self):
        return get_markdown(self.resolution)

    def add_email_to_ticketcc_if_not_in(self, email=None, user=None, ticketcc=None):
        """
        Check that given email/user_email/ticketcc_email is not already present on the ticket
        (submitter email, assigned to, or in ticket CCs) and add it to a new ticket CC,
        or move the given one

        :param str email:
        :param User user:
        :param TicketCC ticketcc:
        :rtype: TicketCC|None
        """
        if ticketcc:
            email = ticketcc.display
        elif user:
            if user.email:
                email = user.email
            else:
                # Ignore if user has no email address
                return
        elif not email:
            raise ValueError(
                'You must provide at least one parameter to get the email from')

        # Prepare all emails already into the ticket
        ticket_emails = [x.display for x in self.ticketcc_set.all()]
        if self.submitter_email:
            ticket_emails.append(self.submitter_email)
        if self.assigned_to and self.assigned_to.email:
            ticket_emails.append(self.assigned_to.email)

        # Check that email is not already part of the ticket
        if email not in ticket_emails:
            if ticketcc:
                ticketcc.ticket = self
                ticketcc.save(update_fields=['ticket'])
            elif user:
                ticketcc = self.ticketcc_set.create(user=user)
            else:
                ticketcc = self.ticketcc_set.create(email=email)
            return ticketcc

    def set_custom_field_values(self):
        for field in CustomField.objects.all():
            try:
                value = self.ticketcustomfieldvalue_set.get(field=field).value
            except TicketCustomFieldValue.DoesNotExist:
                value = None
            setattr(self, 'custom_%s' % field.name, value)

    def save_custom_field_values(self, data):
        for field, value in data.items():
            if field.startswith('custom_'):
                field_name = field.replace('custom_', '', 1)
                customfield = CustomField.objects.get(name=field_name)
                cfv, created = self.ticketcustomfieldvalue_set.get_or_create(
                    field=customfield,
                    defaults={'value': convert_value(value)}
                )
                if not created:
                    cfv.value = convert_value(value)
                    cfv.save()


class FollowUpManager(models.Manager):

    def private_followups(self):
        return self.filter(public=False)

    def public_followups(self):
        return self.filter(public=True)


class FollowUp(models.Model):
    """
    A FollowUp is a comment and/or change to a ticket. We keep a simple
    title, the comment entered by the user, and the new status of a ticket
    to enable easy flagging of details on the view-ticket page.

    The title is automatically generated at save-time, based on what action
    the user took.

    Tickets that aren't public are never shown to or e-mailed to the submitter,
    although all staff can see them.
    """

    ticket = models.ForeignKey(
        Ticket,
        on_delete=models.CASCADE,
        verbose_name=_('Ticket'),
    )

    date = models.DateTimeField(
        _('Date'),
        default=timezone.now
    )

    title = models.CharField(
        _('Title'),
        max_length=200,
        blank=True,
        null=True,
    )

    comment = models.TextField(
        _('Comment'),
        blank=True,
        null=True,
    )

    public = models.BooleanField(
        _('Public'),
        blank=True,
        default=False,
        help_text=_(
            'Public tickets are viewable by the submitter and all '
            'staff, but non-public tickets can only be seen by staff.'
        ),
    )

    user = models.ForeignKey(
        settings.AUTH_USER_MODEL,
        on_delete=models.CASCADE,
        blank=True,
        null=True,
        verbose_name=_('User'),
    )

    new_status = models.IntegerField(
        _('New Status'),
        choices=Ticket.STATUS_CHOICES,
        blank=True,
        null=True,
        help_text=_('If the status was changed, what was it changed to?'),
    )

    message_id = models.CharField(
        _('E-Mail ID'),
        max_length=256,
        blank=True,
        null=True,
        help_text=_("The Message ID of the submitter's email."),
        editable=False,
    )

    objects = FollowUpManager()

    time_spent = models.DurationField(
        help_text=_("Time spent on this follow up"),
        blank=True, null=True
    )

    class Meta:
        ordering = ('date',)
        verbose_name = _('Follow-up')
        verbose_name_plural = _('Follow-ups')

    def __str__(self):
        return '%s' % self.title

    def get_absolute_url(self):
        return u"%s#followup%s" % (self.ticket.get_absolute_url(), self.id)

    def save(self, *args, **kwargs):
        t = self.ticket
        t.modified = timezone.now()
        t.save()
        super(FollowUp, self).save(*args, **kwargs)

    def get_markdown(self):
        return get_markdown(self.comment)

    @property
    def time_spent_formated(self):
        return format_time_spent(self.time_spent)


class TicketChange(models.Model):
    """
    For each FollowUp, any changes to the parent ticket (eg Title, Priority,
    etc) are tracked here for display purposes.
    """

    followup = models.ForeignKey(
        FollowUp,
        on_delete=models.CASCADE,
        verbose_name=_('Follow-up'),
    )

    field = models.CharField(
        _('Field'),
        max_length=100,
    )

    old_value = models.TextField(
        _('Old Value'),
        blank=True,
        null=True,
    )

    new_value = models.TextField(
        _('New Value'),
        blank=True,
        null=True,
    )

    def __str__(self):
        out = '%s ' % self.field
        if not self.new_value:
            out += gettext('removed')
        elif not self.old_value:
            out += gettext('set to %s') % self.new_value
        else:
            out += gettext('changed from "%(old_value)s" to "%(new_value)s"') % {
                'old_value': self.old_value,
                'new_value': self.new_value
            }
        return out

    class Meta:
        verbose_name = _('Ticket change')
        verbose_name_plural = _('Ticket changes')


def attachment_path(instance, filename):
    """Just bridge"""
    return instance.attachment_path(filename)


class Attachment(models.Model):
    """
    Represents a file attached to a follow-up. This could come from an e-mail
    attachment, or it could be uploaded via the web interface.
    """

    file = models.FileField(
        _('File'),
        upload_to=attachment_path,
        max_length=1000,
        validators=[validate_file_extension]
    )

    filename = models.CharField(
        _('Filename'),
        blank=True,
        max_length=1000,
    )

    mime_type = models.CharField(
        _('MIME Type'),
        blank=True,
        max_length=255,
    )

    size = models.IntegerField(
        _('Size'),
        blank=True,
        help_text=_('Size of this file in bytes'),
    )

    def __str__(self):
        return '%s' % self.filename

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

        if not self.size:
            self.size = self.get_size()

        if not self.filename:
            self.filename = self.get_filename()

        if not self.mime_type:
            self.mime_type = \
                mimetypes.guess_type(self.filename, strict=False)[0] or \
                'application/octet-stream'

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

    def get_filename(self):
        return str(self.file)

    def get_size(self):
        return self.file.file.size

    def attachment_path(self, filename):
        """Provide a file path that will help prevent files being overwritten, by
        putting attachments in a folder off attachments for ticket/followup_id/.
        """
        assert NotImplementedError(
            "This method is to be implemented by Attachment classes"
        )

    class Meta:
        ordering = ('filename',)
        verbose_name = _('Attachment')
        verbose_name_plural = _('Attachments')
        abstract = True


class FollowUpAttachment(Attachment):

    followup = models.ForeignKey(
        FollowUp,
        on_delete=models.CASCADE,
        verbose_name=_('Follow-up'),
    )

    def attachment_path(self, filename):

        path = 'helpdesk/attachments/{ticket_for_url}-{secret_key}/{id_}'.format(
            ticket_for_url=self.followup.ticket.ticket_for_url,
            secret_key=self.followup.ticket.secret_key,
            id_=self.followup.id)
        att_path = os.path.join(settings.MEDIA_ROOT, path)
        if settings.DEFAULT_FILE_STORAGE == "django.core.files.storage.FileSystemStorage":
            if not os.path.exists(att_path):
                os.makedirs(att_path, helpdesk_settings.HELPDESK_ATTACHMENT_DIR_PERMS)
        return os.path.join(path, filename)


class KBIAttachment(Attachment):

    kbitem = models.ForeignKey(
        "KBItem",
        on_delete=models.CASCADE,
        verbose_name=_('Knowledge base item'),
    )

    def attachment_path(self, filename):

        path = 'helpdesk/attachments/kb/{category}/{kbi}'.format(
            category=self.kbitem.category,
            kbi=self.kbitem.id)
        att_path = os.path.join(settings.MEDIA_ROOT, path)
        if settings.DEFAULT_FILE_STORAGE == "django.core.files.storage.FileSystemStorage":
            if not os.path.exists(att_path):
                os.makedirs(att_path, helpdesk_settings.HELPDESK_ATTACHMENT_DIR_PERMS)
        return os.path.join(path, filename)


class PreSetReply(models.Model):
    """
    We can allow the admin to define a number of pre-set replies, used to
    simplify the sending of updates and resolutions. These are basically Django
    templates with a limited context - however if you wanted to get crafy it would
    be easy to write a reply that displays ALL updates in hierarchical order etc
    with use of for loops over {{ ticket.followup_set.all }} and friends.

    When replying to a ticket, the user can select any reply set for the current
    queue, and the body text is fetched via AJAX.
    """
    class Meta:
        ordering = ('name',)
        verbose_name = _('Pre-set reply')
        verbose_name_plural = _('Pre-set replies')

    queues = models.ManyToManyField(
        Queue,
        blank=True,
        help_text=_('Leave blank to allow this reply to be used for all '
                    'queues, or select those queues you wish to limit this reply to.'),
    )

    name = models.CharField(
        _('Name'),
        max_length=100,
        help_text=_('Only used to assist users with selecting a reply - not '
                    'shown to the user.'),
    )

    body = models.TextField(
        _('Body'),
        help_text=_('Context available: {{ ticket }} - ticket object (eg '
                    '{{ ticket.title }}); {{ queue }} - The queue; and {{ user }} '
                    '- the current user.'),
    )

    def __str__(self):
        return '%s' % self.name


class EscalationExclusion(models.Model):
    """
    An 'EscalationExclusion' lets us define a date on which escalation should
    not happen, for example a weekend or public holiday.

    You may also have a queue that is only used on one day per week.

    To create these on a regular basis, check out the README file for an
    example cronjob that runs 'create_escalation_exclusions.py'.
    """

    queues = models.ManyToManyField(
        Queue,
        blank=True,
        help_text=_('Leave blank for this exclusion to be applied to all queues, '
                    'or select those queues you wish to exclude with this entry.'),
    )

    name = models.CharField(
        _('Name'),
        max_length=100,
    )

    date = models.DateField(
        _('Date'),
        help_text=_('Date on which escalation should not happen'),
    )

    def __str__(self):
        return '%s' % self.name

    class Meta:
        verbose_name = _('Escalation exclusion')
        verbose_name_plural = _('Escalation exclusions')


class EmailTemplate(models.Model):
    """
    Since these are more likely to be changed than other templates, we store
    them in the database.

    This means that an admin can change email templates without having to have
    access to the filesystem.
    """

    template_name = models.CharField(
        _('Template Name'),
        max_length=100,
    )

    subject = models.CharField(
        _('Subject'),
        max_length=100,
        help_text=_('This will be prefixed with "[ticket.ticket] ticket.title"'
                    '. We recommend something simple such as "(Updated") or "(Closed)"'
                    ' - the same context is available as in plain_text, below.'),
    )

    heading = models.CharField(
        _('Heading'),
        max_length=100,
        help_text=_('In HTML e-mails, this will be the heading at the top of '
                    'the email - the same context is available as in plain_text, '
                    'below.'),
    )

    plain_text = models.TextField(
        _('Plain Text'),
        help_text=_('The context available to you includes {{ ticket }}, '
                    '{{ queue }}, and depending on the time of the call: '
                    '{{ resolution }} or {{ comment }}.'),
    )

    html = models.TextField(
        _('HTML'),
        help_text=_(
            'The same context is available here as in plain_text, above.'),
    )

    locale = models.CharField(
        _('Locale'),
        max_length=10,
        blank=True,
        null=True,
        help_text=_('Locale of this template.'),
    )

    def __str__(self):
        return '%s' % self.template_name

    class Meta:
        ordering = ('template_name', 'locale')
        verbose_name = _('e-mail template')
        verbose_name_plural = _('e-mail templates')


class KBCategory(models.Model):
    """
    Lets help users help themselves: the Knowledge Base is a categorised
    listing of questions & answers.
    """

    name = models.CharField(
        _('Name of the category'),
        max_length=100,
    )

    title = models.CharField(
        _('Title on knowledgebase page'),
        max_length=100,
    )

    slug = models.SlugField(
        _('Slug'),
    )

    description = models.TextField(
        _('Description'),
    )

    queue = models.ForeignKey(
        Queue,
        blank=True,
        null=True,
        on_delete=models.CASCADE,
        verbose_name=_(
            'Default queue when creating a ticket after viewing this category.'),
    )

    public = models.BooleanField(
        default=True,
        verbose_name=_("Is KBCategory publicly visible?")
    )

    def __str__(self):
        return '%s' % self.name

    class Meta:
        ordering = ('title',)
        verbose_name = _('Knowledge base category')
        verbose_name_plural = _('Knowledge base categories')

    def get_absolute_url(self):
        from django.urls import reverse
        return reverse('helpdesk:kb_category', kwargs={'slug': self.slug})


class KBItem(models.Model):
    """
    An item within the knowledgebase. Very straightforward question/answer
    style system.
    """
    voted_by = models.ManyToManyField(
        settings.AUTH_USER_MODEL,
        related_name='votes',
    )
    downvoted_by = models.ManyToManyField(
        settings.AUTH_USER_MODEL,
        related_name='downvotes',
    )
    category = models.ForeignKey(
        KBCategory,
        on_delete=models.CASCADE,
        verbose_name=_('Category'),
    )

    title = models.CharField(
        _('Title'),
        max_length=100,
    )

    question = models.TextField(
        _('Question'),
    )

    answer = models.TextField(
        _('Answer'),
    )

    votes = models.IntegerField(
        _('Votes'),
        help_text=_('Total number of votes cast for this item'),
        default=0,
    )

    recommendations = models.IntegerField(
        _('Positive Votes'),
        help_text=_('Number of votes for this item which were POSITIVE.'),
        default=0,
    )

    last_updated = models.DateTimeField(
        _('Last Updated'),
        help_text=_(
            'The date on which this question was most recently changed.'),
        blank=True,
    )

    team = models.ForeignKey(
        helpdesk_settings.HELPDESK_TEAMS_MODEL,
        on_delete=models.CASCADE,
        verbose_name=_('Team'),
        blank=True,
        null=True,
    )

    order = models.PositiveIntegerField(
        _('Order'),
        blank=True,
        null=True,
    )

    enabled = models.BooleanField(
        _('Enabled to display to users'),
        default=True,
    )

    def save(self, *args, **kwargs):
        if not self.last_updated:
            self.last_updated = timezone.now()
        return super(KBItem, self).save(*args, **kwargs)

    def get_team(self):
        return helpdesk_settings.HELPDESK_KBITEM_TEAM_GETTER(self)

    def _score(self):
        """ Return a score out of 10 or Unrated if no votes """
        if self.votes > 0:
            return (self.recommendations / self.votes) * 10
        else:
            return _('Unrated')
    score = property(_score)

    def __str__(self):
        return '%s: %s' % (self.category.title, self.title)

    class Meta:
        ordering = ('order', 'title',)
        verbose_name = _('Knowledge base item')
        verbose_name_plural = _('Knowledge base items')

    def get_absolute_url(self):
        from django.urls import reverse
        return str(reverse('helpdesk:kb_category', args=(self.category.slug,))) + "?kbitem=" + str(self.pk)

    def query_url(self):
        from django.urls import reverse
        return str(reverse('helpdesk:list')) + "?kbitem=" + str(self.pk)

    def num_open_tickets(self):
        return Ticket.objects.filter(kbitem=self, status__in=(1, 2)).count()

    def unassigned_tickets(self):
        return Ticket.objects.filter(kbitem=self, status__in=(1, 2), assigned_to__isnull=True)

    def get_markdown(self):
        return get_markdown(self.answer)


class SavedSearch(models.Model):
    """
    Allow a user to save a ticket search, eg their filtering and sorting
    options, and optionally share it with other users. This lets people
    easily create a set of commonly-used filters, such as:
        * My tickets waiting on me
        * My tickets waiting on submitter
        * My tickets in 'Priority Support' queue with priority of 1
        * All tickets containing the word 'billing'.
         etc...
    """
    user = models.ForeignKey(
        settings.AUTH_USER_MODEL,
        on_delete=models.CASCADE,
        verbose_name=_('User'),
    )

    title = models.CharField(
        _('Query Name'),
        max_length=100,
        help_text=_('User-provided name for this query'),
    )

    shared = models.BooleanField(
        _('Shared With Other Users?'),
        blank=True,
        default=False,
        help_text=_('Should other users see this query?'),
    )

    query = models.TextField(
        _('Search Query'),
        help_text=_('Pickled query object. Be wary changing this.'),
    )

    def __str__(self):
        if self.shared:
            return '%s (*)' % self.title
        else:
            return '%s' % self.title

    class Meta:
        verbose_name = _('Saved search')
        verbose_name_plural = _('Saved searches')


def get_default_setting(setting):
    from helpdesk.settings import DEFAULT_USER_SETTINGS
    return DEFAULT_USER_SETTINGS[setting]


def login_view_ticketlist_default():
    return get_default_setting('login_view_ticketlist')


def email_on_ticket_change_default():
    return get_default_setting('email_on_ticket_change')


def email_on_ticket_assign_default():
    return get_default_setting('email_on_ticket_assign')


def tickets_per_page_default():
    return get_default_setting('tickets_per_page')


def use_email_as_submitter_default():
    return get_default_setting('use_email_as_submitter')


class UserSettings(models.Model):
    """
    A bunch of user-specific settings that we want to be able to define, such
    as notification preferences and other things that should probably be
    configurable.
    """
    PAGE_SIZES = ((10, '10'), (25, '25'), (50, '50'), (100, '100'))

    user = models.OneToOneField(
        settings.AUTH_USER_MODEL,
        on_delete=models.CASCADE,
        related_name="usersettings_helpdesk")

    settings_pickled = models.TextField(
        _('DEPRECATED! Settings Dictionary DEPRECATED!'),
        help_text=_('DEPRECATED! This is a base64-encoded representation of a pickled Python dictionary. '
                    'Do not change this field via the admin.'),
        blank=True,
        null=True,
    )

    login_view_ticketlist = models.BooleanField(
        verbose_name=_('Show Ticket List on Login?'),
        help_text=_(
            'Display the ticket list upon login? Otherwise, the dashboard is shown.'),
        default=login_view_ticketlist_default,
    )

    email_on_ticket_change = models.BooleanField(
        verbose_name=_('E-mail me on ticket change?'),
        help_text=_(
            'If you\'re the ticket owner and the ticket is changed via the web by somebody else,'
            'do you want to receive an e-mail?'
        ),
        default=email_on_ticket_change_default,
    )

    email_on_ticket_assign = models.BooleanField(
        verbose_name=_('E-mail me when assigned a ticket?'),
        help_text=_(
            'If you are assigned a ticket via the web, do you want to receive an e-mail?'),
        default=email_on_ticket_assign_default,
    )

    tickets_per_page = models.IntegerField(
        verbose_name=_('Number of tickets to show per page'),
        help_text=_(
            'How many tickets do you want to see on the Ticket List page?'),
        default=tickets_per_page_default,
        choices=PAGE_SIZES,
    )

    use_email_as_submitter = models.BooleanField(
        verbose_name=_('Use my e-mail address when submitting tickets?'),
        help_text=_('When you submit a ticket, do you want to automatically '
                    'use your e-mail address as the submitter address? You '
                    'can type a different e-mail address when entering the '
                    'ticket if needed, this option only changes the default.'),
        default=use_email_as_submitter_default,
    )

    def __str__(self):
        return 'Preferences for %s' % self.user

    class Meta:
        verbose_name = _('User Setting')
        verbose_name_plural = _('User Settings')


def create_usersettings(sender, instance, created, **kwargs):
    """
    Helper function to create UserSettings instances as
    required, eg when we first create the UserSettings database
    table via 'syncdb' or when we save a new user.

    If we end up with users with no UserSettings, then we get horrible
    'DoesNotExist: UserSettings matching query does not exist.' errors.
    """
    if created:
        UserSettings.objects.create(user=instance)


models.signals.post_save.connect(
    create_usersettings, sender=settings.AUTH_USER_MODEL)


class IgnoreEmail(models.Model):
    """
    This model lets us easily ignore e-mails from certain senders when
    processing IMAP and POP3 mailboxes, eg mails from postmaster or from
    known trouble-makers.
    """
    class Meta:
        verbose_name = _('Ignored e-mail address')
        verbose_name_plural = _('Ignored e-mail addresses')

    queues = models.ManyToManyField(
        Queue,
        blank=True,
        help_text=_('Leave blank for this e-mail to be ignored on all queues, '
                    'or select those queues you wish to ignore this e-mail for.'),
    )

    name = models.CharField(
        _('Name'),
        max_length=100,
    )

    date = models.DateField(
        _('Date'),
        help_text=_('Date on which this e-mail address was added'),
        blank=True,
        editable=False
    )

    email_address = models.CharField(
        _('E-Mail Address'),
        max_length=150,
        help_text=_('Enter a full e-mail address, or portions with '
                    'wildcards, eg *@domain.com or postmaster@*.'),
    )

    keep_in_mailbox = models.BooleanField(
        _('Save Emails in Mailbox?'),
        blank=True,
        default=False,
        help_text=_('Do you want to save emails from this address in the mailbox? '
                    'If this is unticked, emails from this address will be deleted.'),
    )

    def __str__(self):
        return '%s' % self.name

    def save(self, *args, **kwargs):
        if not self.date:
            self.date = timezone.now()
        return super(IgnoreEmail, self).save(*args, **kwargs)

    def queue_list(self):
        """Return a list of the queues this IgnoreEmail applies to.
        If this IgnoreEmail applies to ALL queues, return '*'.
        """
        queues = self.queues.all().order_by('title')
        if len(queues) == 0:
            return '*'
        else:
            return ', '.join([str(q) for q in queues])

    def test(self, email):
        """
        Possible situations:
            1. Username & Domain both match
            2. Username is wildcard, domain matches
            3. Username matches, domain is wildcard
            4. username & domain are both wildcards
            5. Other (no match)

            1-4 return True, 5 returns False.
        """

        own_parts = self.email_address.split("@")
        email_parts = email.split("@")

        if self.email_address == email or \
                own_parts[0] == "*" and own_parts[1] == email_parts[1] or \
                own_parts[1] == "*" and own_parts[0] == email_parts[0] or \
                own_parts[0] == "*" and own_parts[1] == "*":
            return True
        else:
            return False


class TicketCC(models.Model):
    """
    Often, there are people who wish to follow a ticket who aren't the
    person who originally submitted it. This model provides a way for those
    people to follow a ticket.

    In this circumstance, a 'person' could be either an e-mail address or
    an existing system user.
    """

    ticket = models.ForeignKey(
        Ticket,
        on_delete=models.CASCADE,
        verbose_name=_('Ticket'),
    )

    user = models.ForeignKey(
        settings.AUTH_USER_MODEL,
        on_delete=models.CASCADE,
        blank=True,
        null=True,
        help_text=_('User who wishes to receive updates for this ticket.'),
        verbose_name=_('User'),
    )

    email = models.EmailField(
        _('E-Mail Address'),
        blank=True,
        null=True,
        help_text=_('For non-user followers, enter their e-mail address'),
    )

    can_view = models.BooleanField(
        _('Can View Ticket?'),
        blank=True,
        default=False,
        help_text=_('Can this CC login to view the ticket details?'),
    )

    can_update = models.BooleanField(
        _('Can Update Ticket?'),
        blank=True,
        default=False,
        help_text=_('Can this CC login and update the ticket?'),
    )

    def _email_address(self):
        if self.user and self.user.email is not None:
            return self.user.email
        else:
            return self.email
    email_address = property(_email_address)

    def _display(self):
        if self.user:
            return self.user
        else:
            return self.email
    display = property(_display)

    def __str__(self):
        return '%s for %s' % (self.display, self.ticket.title)

    def clean(self):
        if self.user and not self.user.email:
            raise ValidationError('User has no email address')


class CustomFieldManager(models.Manager):

    def get_queryset(self):
        return super(CustomFieldManager, self).get_queryset().order_by('ordering')


class CustomField(models.Model):
    """
    Definitions for custom fields that are glued onto each ticket.
    """

    name = models.SlugField(
        _('Field Name'),
        help_text=_('As used in the database and behind the scenes. '
                    'Must be unique and consist of only lowercase letters with no punctuation.'),
        unique=True,
    )

    label = models.CharField(
        _('Label'),
        max_length=30,
        help_text=_('The display label for this field'),
    )

    help_text = models.TextField(
        _('Help Text'),
        help_text=_('Shown to the user when editing the ticket'),
        blank=True,
        null=True
    )

    DATA_TYPE_CHOICES = (
        ('varchar', _('Character (single line)')),
        ('text', _('Text (multi-line)')),
        ('integer', _('Integer')),
        ('decimal', _('Decimal')),
        ('list', _('List')),
        ('boolean', _('Boolean (checkbox yes/no)')),
        ('date', _('Date')),
        ('time', _('Time')),
        ('datetime', _('Date & Time')),
        ('email', _('E-Mail Address')),
        ('url', _('URL')),
        ('ipaddress', _('IP Address')),
        ('slug', _('Slug')),
    )

    data_type = models.CharField(
        _('Data Type'),
        max_length=100,
        help_text=_('Allows you to restrict the data entered into this field'),
        choices=DATA_TYPE_CHOICES,
    )

    max_length = models.IntegerField(
        _('Maximum Length (characters)'),
        blank=True,
        null=True,
    )

    decimal_places = models.IntegerField(
        _('Decimal Places'),
        help_text=_('Only used for decimal fields'),
        blank=True,
        null=True,
    )

    empty_selection_list = models.BooleanField(
        _('Add empty first choice to List?'),
        default=False,
        help_text=_('Only for List: adds an empty first entry to the choices list, '
                    'which enforces that the user makes an active choice.'),
    )

    list_values = models.TextField(
        _('List Values'),
        help_text=_('For list fields only. Enter one option per line.'),
        blank=True,
        null=True,
    )

    ordering = models.IntegerField(
        _('Ordering'),
        help_text=_(
            'Lower numbers are displayed first; higher numbers are listed later'),
        blank=True,
        null=True,
    )

    def _choices_as_array(self):
        valuebuffer = StringIO(self.list_values)
        choices = [[item.strip(), item.strip()]
                   for item in valuebuffer.readlines()]
        valuebuffer.close()
        return choices
    choices_as_array = property(_choices_as_array)

    required = models.BooleanField(
        _('Required?'),
        help_text=_('Does the user have to enter a value for this field?'),
        default=False,
    )

    staff_only = models.BooleanField(
        _('Staff Only?'),
        help_text=_('If this is ticked, then the public submission form '
                    'will NOT show this field'),
        default=False,
    )

    objects = CustomFieldManager()

    def __str__(self):
        return '%s' % self.name

    class Meta:
        verbose_name = _('Custom field')
        verbose_name_plural = _('Custom fields')

    def get_choices(self):
        if not self.data_type == 'list':
            return None
        choices = self.choices_as_array
        if self.empty_selection_list:
            choices.insert(0, ('', '---------'))
        return choices

    def build_api_field(self):
        customfield_to_api_field_dict = {
            'varchar': serializers.CharField,
            'text': serializers.CharField,
            'integer': serializers.IntegerField,
            'decimal': serializers.DecimalField,
            'list': serializers.ChoiceField,
            'boolean': serializers.BooleanField,
            'date': serializers.DateField,
            'time': serializers.TimeField,
            'datetime': serializers.DateTimeField,
            'email': serializers.EmailField,
            'url': serializers.URLField,
            'ipaddress': serializers.IPAddressField,
            'slug': serializers.SlugField,
        }

        # Prepare attributes for each types
        attributes = {
            'label': self.label,
            'help_text': self.help_text,
            'required': self.required,
        }
        if self.data_type in ('varchar', 'text'):
            attributes['max_length'] = self.max_length
            if self.data_type == 'text':
                attributes['style'] = {'base_template': 'textarea.html'}
        elif self.data_type == 'decimal':
            attributes['decimal_places'] = self.decimal_places
            attributes['max_digits'] = self.max_length
        elif self.data_type == 'list':
            attributes['choices'] = self.get_choices()

        try:
            return customfield_to_api_field_dict[self.data_type](**attributes)
        except KeyError:
            raise NameError("Unrecognized data_type %s" % self.data_type)


class TicketCustomFieldValue(models.Model):
    ticket = models.ForeignKey(
        Ticket,
        on_delete=models.CASCADE,
        verbose_name=_('Ticket'),
    )

    field = models.ForeignKey(
        CustomField,
        on_delete=models.CASCADE,
        verbose_name=_('Field'),
    )

    value = models.TextField(blank=True, null=True)

    def __str__(self):
        return '%s / %s' % (self.ticket, self.field)

    @property
    def default_value(self) -> str:
        return _("Not defined")

    class Meta:
        unique_together = (('ticket', 'field'),)
        verbose_name = _('Ticket custom field value')
        verbose_name_plural = _('Ticket custom field values')


class TicketDependency(models.Model):
    """
    The ticket identified by `ticket` cannot be resolved until the ticket in `depends_on` has been resolved.
    To help enforce this, a helper function `can_be_resolved` on each Ticket instance checks that
    these have all been resolved.
    """
    class Meta:
        unique_together = (('ticket', 'depends_on'),)
        verbose_name = _('Ticket dependency')
        verbose_name_plural = _('Ticket dependencies')

    ticket = models.ForeignKey(
        Ticket,
        on_delete=models.CASCADE,
        verbose_name=_('Ticket'),
        related_name='ticketdependency',
    )

    depends_on = models.ForeignKey(
        Ticket,
        on_delete=models.CASCADE,
        verbose_name=_('Depends On Ticket'),
        related_name='depends_on',
    )

    def __str__(self):
        return '%s / %s' % (self.ticket, self.depends_on)


def is_a_list_without_empty_element(task_list):
    if not isinstance(task_list, list):
        raise ValidationError(f'{task_list} is not a list')
    for task in task_list:
        if not isinstance(task, str):
            raise ValidationError(f'{task} is not a string')
        if task.strip() == '':
            raise ValidationError('A task cannot be an empty string')


class ChecklistTemplate(models.Model):
    name = models.CharField(
        verbose_name=_('Name'),
        max_length=100
    )
    task_list = models.JSONField(verbose_name=_('Task List'), validators=[is_a_list_without_empty_element])

    class Meta:
        verbose_name = _('Checklist Template')
        verbose_name_plural = _('Checklist Templates')

    def __str__(self):
        return self.name


class Checklist(models.Model):
    ticket = models.ForeignKey(
        Ticket,
        on_delete=models.CASCADE,
        verbose_name=_('Ticket'),
        related_name='checklists',
    )
    name = models.CharField(
        verbose_name=_('Name'),
        max_length=100
    )

    class Meta:
        verbose_name = _('Checklist')
        verbose_name_plural = _('Checklists')

    def __str__(self):
        return self.name

    def create_tasks_from_template(self, template):
        for position, task in enumerate(template.task_list):
            self.tasks.create(description=task, position=position)


class ChecklistTaskQuerySet(models.QuerySet):
    def todo(self):
        return self.filter(completion_date__isnull=True)

    def completed(self):
        return self.filter(completion_date__isnull=False)


class ChecklistTask(models.Model):
    checklist = models.ForeignKey(
        Checklist,
        on_delete=models.CASCADE,
        verbose_name=_('Checklist'),
        related_name='tasks',
    )
    description = models.CharField(
        verbose_name=_('Description'),
        max_length=250
    )
    completion_date = models.DateTimeField(
        verbose_name=_('Completion Date'),
        null=True,
        blank=True
    )
    position = models.PositiveSmallIntegerField(
        verbose_name=_('Position'),
        db_index=True
    )

    objects = ChecklistTaskQuerySet.as_manager()

    class Meta:
        verbose_name = _('Checklist Task')
        verbose_name_plural = _('Checklist Tasks')
        ordering = ('position',)

    def __str__(self):
        return self.description