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import json
import string

from django.contrib.contenttypes.fields import GenericRelation
from django.core.exceptions import ValidationError
from django.core.validators import RegexValidator
from django.db import models
from django.urls import reverse
from django.utils.safestring import mark_safe
from django.utils.text import slugify
from djiffy.models import Canvas, Manifest
from sortedm2m.fields import SortedManyToManyField
from unidecode import unidecode

from derrida.common.models import DateRange, Named, Notable
from derrida.common.utils import absolutize_url
from derrida.footnotes.models import Footnote
from derrida.people.models import Person
from derrida.places.models import Place

class WorkCount(models.Model):
    '''Mix-in for models related to works; adds work count property and link to
    associated works'''
    class Meta:
        abstract = True

    def work_count(self):
        Return number of associated :class:`derrida.books.models.Works` for
        a given object as an HTML snippet for the Django admin.
        base_url = reverse('admin:books_work_changelist')
        return mark_safe('<a href="%s?%ss__id__exact=%s">%s</a>' % (
    work_count.short_description = '# works'
    # NOTE: possible to use a count field for admin ordering!
    # see
    # book_count.admin_order_field = 'work__count'

class InstanceCount(models.Model):
    '''Mix-in for models related to books; adds book count property and link to
    associated books'''
    class Meta:
        abstract = True

    def instance_count(self):
        Return a count of associated :class:`derrida.books.models.Instance` for
        object as an HTML snippet for the Django admin.
        base_url = reverse('admin:books_instance_changelist')
        return mark_safe('<a href="%s?%ss__id__exact=%s">%s</a>' % (
    instance_count.short_description = '# instances'

class Subject(Named, Notable, WorkCount):
    '''Subject categorization for books'''
    #: optional uri
    uri = models.URLField(blank=True, null=True)

class Language(Named, Notable, WorkCount, InstanceCount):
    '''Language that a book is written in or a language included in a book'''
    #: optional uri
    uri = models.URLField(blank=True, null=True)
    code = models.CharField(blank=True, null=True, max_length=3,
        help_text='two or three letter language code from ISO 639')

class Publisher(Named, Notable, InstanceCount):
    '''Publisher of a book'''

class OwningInstitution(Named, Notable, InstanceCount):
    '''Institution that owns the extant copy of a book'''
    #: short name (optioal)
    short_name = models.CharField(max_length=255, blank=True,
        help_text='Optional short name for admin display')
    #: contact information
    contact_info = models.TextField()
    #: :class:`~derrida.places.models.Place`
    place = models.ForeignKey(Place)

    def __str__(self):
        return self.short_name or

class Journal(Named, Notable):
    '''List of associated journals for items published as journal articles'''

class Work(Notable):
    '''A platonic work.  Stores common information about multiple
    instances, copies, or editions of the same work.  Aggregates one
    or more :class:`Instance` objects.'''
    #: primary title
    primary_title = models.TextField()
    #: short title
    short_title = models.CharField(max_length=255)
    #: original publication date
    year = models.IntegerField(blank=True, null=True,
        help_text='Original publication date')
    # NOTE: this is inteneded for a generic linked data URI;
    # finding aid URL should be tracked on Instance rather than Work
    #: optional URI
    uri = models.URLField('URI', blank=True, help_text='Linked data URI',
    #: relation to :class:`Person` authors
    authors = models.ManyToManyField(Person, blank=True)
    #: :class:`Subject` related through :class:`WorkSubject`
    subjects = models.ManyToManyField(Subject, through='WorkSubject')
    #: :class:`Language` related through :class:`WorkLanguage`
    languages = models.ManyToManyField(Language, through='WorkLanguage')

    class Meta:
        ordering = ['primary_title']
        verbose_name = 'Derrida library work'

    def __str__(self):
        return '%s (%s)' % (self.short_title, self.year or 'n.d.')

    def author_names(self):
        '''Display author names; convenience access for display in admin'''
        # NOTE: possibly might want to use last names here
        return ', '.join(str(auth) for auth in self.authors.all())
    author_names.short_description = 'Authors'
    author_names.admin_order_field = 'authors__authorized_name'

    def instance_count(self):
        Return count of :class:`` associated with
        :class:`Work` formatted as an HTML snippet for the Django admin.
        base_url = reverse('admin:books_instance_changelist')
        return mark_safe('<a href="%s?%ss__id__exact=%s">%s</a>' % (
    instance_count.short_description = '# instances'

class InstanceQuerySet(models.QuerySet):
    '''Custom :class:`~django.db.models.QuerySet` for :class:`Instance` to
    make it easy to find all instances that have a digital

    def with_digital_eds(self):
        Return :class:`derrida.books.models.Instance` queryset filtered by
        having a digital edition.
        return self.exclude(digital_edition__isnull=True)

class Instance(Notable):
    '''A single instance of a :class:`Work` - i.e., a specific copy or edition
    or translation.  Can also include books that appear as sections
    of a collected works.'''

    #: :class:`Work` this instance belongs to
    work = models.ForeignKey(Work)
    #: alternate title (optional)
    alternate_title = models.CharField(blank=True, max_length=255)
    #: :class:`Publisher` (optional)
    publisher = models.ForeignKey(Publisher, blank=True, null=True)
    #: publication :class:`~derrida.places.models.Place` (optional, sorted many to many)
    pub_place = SortedManyToManyField(Place,
        verbose_name='Place(s) of Publication', blank=True)
    #: Zotero identifier
    zotero_id = models.CharField(max_length=8, default='', blank=True)
    # identifying slug for use in get_absolute_url, indexed for speed
    slug = models.SlugField(max_length=255,
                                'To auto-generate a valid slug for a new '
                                'instance, choose a work then click '
                                '"Save and Continue Editing" in the lower '
                                'right. Editing slugs of previously saved '
                                'instances should be done with caution, '
                                'as this may break permanent links.'

    #: item is extant
    is_extant = models.BooleanField(help_text='Extant in PUL JD', default=False)
    #: item is annotated
    is_annotated = models.BooleanField(default=False)
    #: item is translated
    is_translation = models.BooleanField(default=False)
    #: description of item dimensions (optional)
    dimensions = models.CharField(max_length=255, blank=True)
    #: copyright year
    copyright_year = models.PositiveIntegerField(blank=True, null=True)
    #: related :class:`Journal` for a journal article
    journal = models.ForeignKey(Journal, blank=True, null=True)
    print_date_help_text = 'Date as YYYY-MM-DD, YYYY-MM, or YYYY format. Use' \
        + ' print date day/month/year known flags to indicate' \
        + ' that the information is not known.'
    #: print date
    print_date = models.DateField('Print Date',
        blank=True, null=True, help_text=print_date_help_text)
    #: print date day is known
    print_date_day_known = models.BooleanField(default=False)
    #: print date month is known
    print_date_month_known = models.BooleanField(default=False)
    #: print date year is known
    print_date_year_known = models.BooleanField(default=True)
    #: finding aid URL
    uri = models.URLField('URI', blank=True, default='',
        help_text='Finding Aid URL for items in PUL Derrida Library')
    # item has a dedication
    has_dedication = models.BooleanField(default=False)
    # item has insertiosn
    has_insertions = models.BooleanField(default=False)
    # page range: using character fields to support non-numeric pages, e.g.
    # roman numerals for introductory pages; using two fields to support
    # sorting within a volume of collected works.
    #: start page for book section or journal article
    start_page = models.CharField(max_length=20, blank=True, null=True)
    #: end page for book section or journal article
    end_page = models.CharField(max_length=20, blank=True, null=True)
    #: optional label to distinguish multiple copies of the same work
    copy = models.CharField(max_length=1, blank=True,
        help_text='Label to distinguish multiple copies of the same edition',
            message='Please set a capital letter from A-Z.'

    #: :class:`Language` this item is written in;
    # uses :class:`InstanceLanguage` to indicate primary language
    languages = models.ManyToManyField(Language, through='InstanceLanguage')

    #: :class:`Instance` that collects this item, for book section
    collected_in = models.ForeignKey('self', related_name='collected_set',
        on_delete=models.SET_NULL, blank=True, null=True,
        help_text='Larger work instance that collects or includes this item')
    # work instances are connected to owning institutions via the Catalogue
    # model; mapping as a many-to-many with a through
    # model in case we want to access owning instutions directly

    #: :class:`OwningInstitution`; connected through :class:`InstanceCatalogue`
    owning_institutions = models.ManyToManyField(OwningInstitution,

    #: :class:`DerridaWork` this item is cited in
    cited_in = models.ManyToManyField('DerridaWork',
        help_text='Derrida works that cite this edition or instance',

    #: digital edition via IIIF as instance of :class:`djiffy.models.Manifest`
    digital_edition = models.OneToOneField(Manifest, blank=True, null=True,
        help_text='Digitized edition of this book, if available')

    #: flag to suppress content page images, to comply with copyright
    #: owner take-down request
    suppress_all_images = models.BooleanField(default=False,
        help_text='''Suppress large image display for all annotated pages
        in this volume, to comply with copyright take-down requests.
        (Overview images, insertions, and thumbnails will still display.)''')
    #: specific page images to be suppressed, to comply with copyright
    #: owner take-down request
    suppressed_images = models.ManyToManyField(Canvas, blank=True,
        help_text='''Suppress large image for specific annotated images to comply
        with copyright take-down requests.''')

    # proof-of-concept generic relation to footnotes
    #: generic relation to :class:~`derrida.footnotes.models.Footnote`
    footnotes = GenericRelation(Footnote)

    objects = InstanceQuerySet.as_manager()

    class Meta:
        ordering = ['alternate_title', 'work__primary_title'] ## ??
        verbose_name = 'Derrida library work instance'
        unique_together = (("work", "copyright_year", "copy"),)

    def save(self, *args, **kwargs):
        if not self.slug:
            self.slug = self.generate_safe_slug()
        super(Instance, self).save(*args, **kwargs)

    def clean(self):
        # Don't allow both journal and collected work
        if self.journal and self.collected_in:
            raise ValidationError('Cannot belong to both a journal and a collection')

    def __str__(self):
        return '%s (%s%s)' % (self.display_title(),
                              self.copyright_year or 'n.d.',
                              ' %s' % self.copy if self.copy else '')

    def get_absolute_url(self):
        '''URL for this :class:`Instance` on the website.'''
        return reverse('books:detail', kwargs={'slug': self.slug})

    def get_uri(self):
        '''public URI for this instance to be used as an identifier'''
        return absolutize_url(reverse('books:instance', args=[]))

    def generate_base_slug(self):
        '''Generate a slug based on first author, work title, and year.
        Not guaranteed to be unique if there are multiple copies of
        the same instance/edition of a work.

        :rtype str: String in the format ``lastname-title-of-work-year``
        # get the first author, if there is one
        author =
        if author:
            # use the last name of the first author
            author = author.authorized_name.split(',')[0]
            # otherwise, set it to an empty string
            author = ''
        # truncate the title to first several words of the title
        title = ' '.join([:9])
        # use copyright year if available, with fallback to work year if
        year = self.copyright_year or or ''
        # # return a slug (not unique for multiple copies of same instance)
        return slugify('%s %s %s' % (unidecode(author), unidecode(title), year))

    def generate_safe_slug(self):
        '''Generate a unique slug.  Checks for duplicates and calculates
        an appropriate copy letter if needed.

        :rtype str: String in the format `lastname-title-of-work-year-copy`

        # base slug, without any copy letter
        base_slug = self.generate_base_slug()
        if self.copy:
            slug = '-'.join([base_slug, self.copy])
            slug = base_slug

        # check for any copies with the same base slug
        duplicates = Instance.objects.filter(
        # exclude current record if it has already been saved
            duplicates = duplicates.exclude(
        # any new copies should start with 'B' since 'A' is implicit in already
        # saved slug for original
        new_copy_letter = 'B'
        # check for duplicates
        if duplicates.exists():
            # get the list of matching slugs
            slugs = duplicates.values_list('slug', flat=True)
            # if slug with specified copy is already unique, use that without
            # further processing
            if not slug in slugs:
                return slug

            # otherwise, calculate the appropriate copy letter to use

            # collect copy suffixes from the slugs
            # (trailing single uppercase letters only)
            letters = [ltr for slug in slugs
                       for ltr in slug.rsplit('-', 1)[1]
                       if len(ltr) == 1 and ltr in string.ascii_uppercase]

            # if existing copies letters are found, increment from the
            # highest one (already sorted properly from queryset return)
            if letters:
                next_copy = chr(ord(letters[0]) + 1)
                # otherwise, default next copy is B (first is assumed to be A)
                next_copy = 'B'
            slug = '-'.join([base_slug, next_copy])
            # also store the new copy letter as instance copy
            self.copy = next_copy

        return slug

    def display_title(self):
        '''display title - alternate title or work short title'''
        return self.alternate_title or or '[no title]'
    display_title.short_description = 'Title'

    def is_digitized(self):
        '''boolean indicator if there is an associated digital edition'''
        return bool(self.digital_edition) or \
            bool(self.collected_in and self.collected_in.digital_edition)
    # technically sorts on the foreign key, but that effectively filters
    # instances with/without digital additions
    is_digitized.admin_order_field = 'digital_edition'
    is_digitized.boolean = True

    def primary_language(self):
        '''Primary :class:`Language` for this work instance.  Use only
        language or primary language for the instance if available; falls
        back to only or primary language for the associated work.'''

        langs = self.languages.all()
        # if instance has only one language, use that
        # (whether or not marked as primary)
        if langs.exists():
            # if more than one, filter to just primary
            if langs.count() > 1:
                langs = langs.filter(instancelanguage__is_primary=True)

        # otherwise, return language for the work
        if not langs and
            langs =
            # filter by primary if more than one
            if langs.count() > 1:
                langs = langs.filter(worklanguage__is_primary=True)

        if langs:
            return langs.first()

    def location(self):
        '''Location in Derrida's library (currently only available for
        digitized books).'''
        # NOTE: PUL digital editions from the Finding Aid include the
        # location in the item title
        if self.is_digitized():
            # Split manifest label on dashes; at most we want the first two
            location_parts = self.digital_edition.label.split(' - ')[:2]
            # some volumes include a "Gift Books" notation we don't care about
            if location_parts[-1].startswith('Gift Books'):
                location_parts = location_parts[:-1]
            return ', '.join(location_parts)

    def item_type(self):
        '''item type: book, book section, or journal article'''
        if self.journal:
            return 'Journal Article'
        if self.collected_in:
            return 'Book Section'
        return 'Book'

    def author_names(self):
        '''Display Work author names; convenience access for display in admin'''
    author_names.short_description = 'Authors'
    author_names.admin_order_field = 'work__authors__authorized_name'

    def catalogue_call_numbers(self):
        '''Convenience access to catalogue call numbers, for display in admin'''
        return ', '.join([c.call_number for c in self.instancecatalogue_set.all()
                          if c.call_number])
    catalogue_call_numbers.short_description = 'Call Numbers'
    catalogue_call_numbers.admin_order_field = 'catalogue__call_number'

    def print_year(self):
        '''Year from :attr:`print_date` if year is known'''
        if self.print_date and self.print_date_year_known:
            return self.print_date.year

    def year(self):
        '''year for indexing and display; :attr:`print_date` if known,
        otherwise :attr:`copyright_year`'''
        return self.print_year() or self.copyright_year

    def images(self):
        '''Queryset containing all :class:`djiffy.models.Canvas` objects
        associated with the digital edition for this item.'''
        if self.digital_edition:
            return self.digital_edition.canvases.all()
        return Canvas.objects.none()

    #: terms in an image label that indicate a canvas should be
    #: considered an overview image (e.g., cover & outside views)
    overview_labels = ['cover', 'spine', 'back', 'edge', 'view']

    def overview_images(self):
        '''Overview images for this book - cover, spine, etc.
        Filtered based on canvas label naming conventions.'''
        label_query = models.Q()
        for overview_label in self.overview_labels:
            label_query |= models.Q(label__icontains=overview_label)
        return self.images().filter(label_query) \

    def annotated_pages(self):
        '''Annotated pages for this book. Filtered based on the presence
        of a documented :class:`~derrida.interventions.models.Intervention`
        in the database.'''
        return self.images().filter(intervention__isnull=False).distinct()

    def insertion_images(self):
        '''Insertion images for this book.
        Filtered based on canvas label naming conventions.'''
        # NOTE: using Insertion because of possible case-sensitive
        # search on mysql even when icontains is used
        return self.images().filter(label__icontains='Insertion')

    def allow_canvas_detail(cls, canvas):
        '''Check if canvas detail view is allowed.  Allows insertion images,
        overview images, and pages with documented interventions.'''
        return any([
            'insertion' in canvas.label.lower(),
            any(label in canvas.label.lower()
                for label in cls.overview_labels),

    def allow_canvas_large_image(self, canvas):
        '''Check if canvas large image view is allowed.  Always allows
        insertion images and overview images; other pages with documented
        interventions are allowed as long as they are not suppressed,
        either via :attr:`suppress_all_images` or specific
        # insertion & overview always allowed
        if any(['insertion' in canvas.label.lower(),
                any(label in canvas.label.lower()
                    for label in self.overview_labels)]):
            # allow
            return True
        # if all other images are suppressed, deny without checking further
        if self.suppress_all_images:
            return False
        # if image has interventions, check if it is suppressed
        if canvas.intervention_set.exists():
            # deny if suppressed, otherwise allow
            return canvas not in self.suppressed_images.all()

    def related_instances(self):
        '''Find related works; for now, this means works by the
        same author.  For a work that collects item, include
        work by any book section authors.'''
        authors = list(
        if self.collected_set.exists():
            for instance in self.collected_set.all():

        return Instance.objects.filter(work__authors__in=authors) \
                       .exclude( \

    #: map local :attr:`item_type` to equivalent zotero template name
    zotero_template_by_itemtype = {
        'Book': 'book',
        'Book Section': 'bookSection',
        'Journal Article': 'journalArticle'

    def as_zotero_item(self, library):
        '''Serialize the instance as an item suitable for export to a Zotero
        library. Requires a :class:`pyzotero.zotero.Zotero` instance for API
        calls to retrieve item type templates and creator types.'''
        # get the item template/creator types based on item type

        # retrieve appropriate item and creator templates based on item type
        zotero_template = self.zotero_template_by_itemtype[self.item_type]
        template = library.item_template(zotero_template)
        creator_types = library.item_creator_types(zotero_template)

        # set common properties
        # zotero id, if set (API will reject if it's set to an empty string)
        if self.zotero_id:
            template['key'] = self.zotero_id

        # use local instance URI for zotero url, for compatibility
        # with other data exports
        template['url'] = self.get_uri()

        # metadata
        template['title'] = self.alternate_title or
        template['shortTitle'] =
        template['date'] = self.copyright_year
        template['publisher'] = if self.publisher else ''
        # place is not valid for journal articles
        if self.pub_place.count() and not self.item_type == 'Journal Article':
            template['place'] = '; '.join([ for place in self.pub_place.all()])

        # no series, volume, or edition information stored in db

        # author
        template['creators'] = [] # clear out the default one first
        for author in # authors come from work
                'creatorType': 'author',
                'firstName': author.firstname,
                'lastName': author.lastname

        # other creators
        # create a lookup dict of zotero's "localized" creator type names
        # for matching on local creator_type names
        type_names = {c['localized']: c['creatorType'] for c in creator_types}
        author = CreatorType.objects.get(name='Author')
        # all creators that are not authors
        for creator in self.instancecreator_set.exclude(creator_type=author):
            # match on localized name, because we use it
            if in type_names:
                    # lookup on localized name and send the "type name"
                    'creatorType': type_names[],
                    'firstName': creator.person.firstname,
                    'lastName': creator.person.lastname
        # add to collections based on derrida works that cited this item;
        # use collection zotero id from DerridaWork
        template['collections'] = [derrida_work.zotero_id for derrida_work in \

        # page range; only stored for book sections and journal articles
        if self.start_page and self.end_page:
            template['pages'] = '-'.join((self.start_page, self.end_page))

        # convert boolean fields to tags
        tags = []
        for attr in ['is_extant', 'is_annotated', 'is_translation',
                     'has_dedication', 'has_insertions', 'digital_edition']:
            if getattr(self, attr):
                # use attribute name as tag
                # strip "is_" and convert underscores to spaces
                tags.append(attr.replace('is_', '').replace('_', ' '))
        # zotero template requires a list of dictionaries
        template['tags'] = [{'tag': tagval} for tagval in tags]

        # try to use primary language, otherwise pick first language
        language = self.languages.filter(instancelanguage__is_primary=True).first()
        if not language and self.languages.exists():
            language = self.languages.first()
        template['language'] = language.code if language else ''

        # use finding aids URL as archive location
        if self.uri and 'princeton' in self.uri:
            template['archiveLocation'] = self.uri

            # if we have a princeton URI,
            # use catalogue for location in archive / library catalog
            # set archive based on catalogue information (i.e., PUL)
            # NOTE: only applying to items with princeton urls, because
            # import seems to have associated all items with princeton
            # as owning institution, whether they are extant or not
            current_catalog = self.instancecatalogue_set.filter(is_current=True).first()
            if current_catalog:
                template['archive'] =

        # item-type specific metadata
        if self.item_type == 'Book Section':
            # title of the book this work appears in
            template['bookTitle'] = self.collected_in.display_title()
            # publication information stored on the book, but don't override
            # if anything was set on the book section
            book_metadata = self.collected_in.as_zotero_item(library)
            for field in ['date', 'publisher', 'place', 'language',
                          'archive', 'archiveLocation']:
                if not template.get(field, None) and field in book_metadata:
                    template[field] = book_metadata[field]

        if self.item_type == 'Journal Article':
            template['publicationTitle'] =

        # add notes to abstract field
        notes = []
        # include copy information, if present, to indicate multiple copies
        if self.copy:
            notes.append('Copy {}'.format(self.copy))
        # include total reference count
        if self.reference_set.exists():
            # in future, this should be reference count *per* derrida work
            ref_count = self.reference_set.count()
            notes.append('{} reference{}'.format(
                ref_count, 's' if ref_count != 1 else ''))
        # number of pages with annotations documented
        annotated_page_count = self.annotated_pages().count()
        if annotated_page_count:
            notes.append('{} page{} with documented annotations'.format(
                annotated_page_count, 's' if annotated_page_count != 1 else ''))
        if notes:
            template['abstractNote'] = '\n'.join(notes)

        return template

class WorkSubject(Notable):
    '''Through-model for work-subject relationship, to allow designating
    a particular subject as primary or adding notes.'''
    #: :class:`Subject`
    subject = models.ForeignKey(Subject)
    #: :class:`Work`
    work = models.ForeignKey(Work)
    #: boolean flag indicating if this subject is primary for this work
    is_primary = models.BooleanField(default=False)

    class Meta:
        unique_together = ('subject', 'work')
        verbose_name = 'Subject'

    def __str__(self):
        return '%s %s%s' % (, self.subject,
            ' (primary)' if self.is_primary else '')

class WorkLanguage(Notable):
    '''Through-model for work-language relationship, to allow designating
    one language as primary or adding notes.'''
    #: :class:`Language`
    language = models.ForeignKey(Language)
    #: :class:`Work`
    work = models.ForeignKey(Work)
    #: boolean flag indicating if this language is primary for this work
    is_primary = models.BooleanField()

    class Meta:
        unique_together = ('work', 'language')
        verbose_name = 'Language'

    def __str__(self):
        return '%s %s%s' % (, self.language,
            ' (primary)' if self.is_primary else '')

class InstanceLanguage(Notable):
    '''Through-model for instance-language relationship, to allow designating
    one language as primary or adding notes.'''
    #: :class:`Language`
    language = models.ForeignKey(Language)
    #: :class:`Instance`
    instance = models.ForeignKey(Instance)
    #: boolean flag indicating if this language is primary for this instance
    is_primary = models.BooleanField()

    class Meta:
        unique_together = ('instance', 'language')
        verbose_name = 'Language'

    def __str__(self):
        return '%s %s%s' % (self.instance, self.language,
            ' (primary)' if self.is_primary else '')

class InstanceCatalogue(Notable, DateRange):
    '''Location of a work instance  in the real world, associating it with an
    owning instutition.'''
    institution = models.ForeignKey(OwningInstitution)
    instance = models.ForeignKey(Instance)
    is_current = models.BooleanField()
    # using char instead of int because assuming  call numbers may contain
    # strings as well as numbers
    call_number = models.CharField(max_length=255, blank=True, null=True,
        help_text='Used for Derrida shelf mark')

    class Meta:
        verbose_name = 'Catalogue'

    def __str__(self):
        dates = ''
        if self.dates:
            dates = ' (%s)' % self.dates
        return '%s / %s%s' % (self.instance, self.institution, dates)

class CreatorType(Named, Notable):
    '''Type of creator role a person can have to a book - author,
    editor, translator, etc.'''
    uri = models.URLField(blank=True, null=True)

class InstanceCreator(Notable):
    creator_type = models.ForeignKey(CreatorType)
    # technically should disallow author here, but can clean that up later
    person = models.ForeignKey(Person)
    instance = models.ForeignKey(Instance)

    def __str__(self):
        return '%s %s %s' % (self.person, self.creator_type, self.instance)

class PersonBookRelationshipType(Named, Notable):
    '''Type of non-annotation relationship assocating a person
    with a book.'''
    uri = models.URLField(blank=True, null=True)

class PersonBook(Notable, DateRange):
    '''Interactions or connections between books and people other than
    person = models.ForeignKey(Person)
    book = models.ForeignKey(Instance)
    relationship_type = models.ForeignKey(PersonBookRelationshipType)

    class Meta:
        verbose_name = 'Person/Book Interaction'

    def __str__(self):
        dates = ''
        if self.dates:
            dates = ' (%s)' % self.dates
        return '%s - %s%s' % (self.person,, dates)

# New citationality model
class DerridaWork(Notable):
    '''This models the reference copy used to identify all citations, not
    part of Derrida's library'''
    #: short title
    short_title = models.CharField(max_length=255)
    #: full citation
    full_citation = models.TextField()
    #: boolean indicator for primary work
    is_primary = models.BooleanField()
    #: slug for use in URLs
    slug = models.SlugField(
        help_text='slug for use in URLs (changing after creation will break URLs)')
    #: zotero collection ID for use in populating library
    zotero_id = models.CharField(max_length=8, default='', blank=True)

    def __str__(self):
        return self.short_title

class DerridaWorkSection(models.Model):
    '''Sections of a :class:`DerridaWork` (e.g. chapters). Used to look at
    :class:`Reference` by sections of the work.'''
    name = models.CharField(max_length=255)
    derridawork = models.ForeignKey(DerridaWork)
    order = models.PositiveIntegerField('Order')
    start_page = models.IntegerField(blank=True, null=True,
       help_text='Sections with no pages will be treated as headers.')
    end_page = models.IntegerField(blank=True, null=True)

    class Meta:
        ordering = ['derridawork', 'order']

    def __str__(self):

class ReferenceType(Named, Notable):
    '''Type of reference, i.e. citation, quotation, footnotes, epigraph.'''

class ReferenceQuerySet(models.QuerySet):
    '''Custom :class:`~django.db.models.QuerySet` for :class:`Reference`.'''

    def order_by_source_page(self):
        '''Order by page in derrida work (attr:`Reference.derridawork_page`)'''
        return self.order_by('derridawork_page')

    def order_by_author(self):
        '''Order by author of cited work'''
        return self.order_by('instance__work__authors__authorized_name')

    def summary_values(self, include_author=False):
        '''Return a values list of summary information for display or
        visualization.  Currently used for histogram visualization.
        Author of cited work is aliased to `author`.

        :param include_author: optionally include author information;
            off by default, since this creates repeated records for
            references to multi-author works
        extra_fields = {}
        if include_author:
            extra_fields['author'] = models.F('instance__work__authors__authorized_name')

        return self.values(
            'id', 'instance__slug', 'derridawork__slug',
            'derridawork_page', 'derridawork_pageloc', **extra_fields)

class Reference(models.Model):
    '''Reference to a book from a work by Derrida.  Can be a citation,
    quotation, or other kind of reference.'''
    #: :class:`Instance` that is referenced
    instance = models.ForeignKey(Instance, blank=True, null=True)
    #: :class:`DerridaWork` that references the item
    derridawork = models.ForeignKey(DerridaWork)
    #: page in the Derrida work.
    derridawork_page = models.IntegerField()
    #: location/identifier on the page
    derridawork_pageloc = models.CharField(max_length=2)
    #: page in the referenced item
    book_page = models.CharField(max_length=255, blank=True)
    #: :class:`ReferenceType`
    reference_type = models.ForeignKey(ReferenceType)
    #: anchor text
    anchor_text = models.TextField(blank=True)
    #: ManyToManyField to :class:`djiffy.models.Canvas`
    canvases = models.ManyToManyField(Canvas, blank=True,
        help_text="Scanned images from Derrida's Library | ")
    #: ManyToManyField to :class:`derrida.interventions.Intervention`
    interventions = models.ManyToManyField('interventions.Intervention',
        blank=True)  # Lazy reference to avoid a circular import

    objects = ReferenceQuerySet.as_manager()

    class Meta:
        ordering = ['derridawork', 'derridawork_page', 'derridawork_pageloc']

    def __str__(self):
        return "%s, %s%s: %s, %s, %s" % (
            # instance is technically optional...
            self.instance.display_title() if self.instance else '[no instance]',

    def get_absolute_url(self):
        '''URL for this reference on the site'''
        # NOTE: currently view is html snippet for loading via ajax only
        return reverse('books:reference', kwargs={
            'derridawork_slug': self.derridawork.slug,
            'page': self.derridawork_page,
            'pageloc': self.derridawork_pageloc

    def get_uri(self):
        '''public URI for this instance to be used as an identifier'''
        return absolutize_url(self.get_absolute_url())

    def anchor_text_snippet(self):
        '''Anchor text snippet, for admin display'''
        snippet = self.anchor_text[:100]
        if len(self.anchor_text) > 100:
            return ''.join([snippet, ' ...'])
        return snippet
    anchor_text_snippet.short_description = 'Anchor Text'
    anchor_text.admin_order_field = 'anchor_text'

    def instance_slug(self):
        '''Slug for the work instance used to display this reference.
        For a reference to a book section, returns the slug
        for the book that collects it.

    def instance_url(self):
        '''absolute url for the work instance where this reference
        is displayed; uses :attr:`instance_slug`'''
        return reverse('books:detail', args=[self.instance_slug])

    def book(self):
        '''The "book" this reference is associated with; for a book section,
        this is the work instance the section is collected in; for all other
        cases, it is the work instance associated with this reference.
        return self.instance.collected_in or self.instance

    def instance_ids_with_digital_editions():
        '''Used as a convenience method to provide a readonly field in the
        admin change form for :class:`Reference` with a list of JSON formatted
        primary keys. This is used by jQuery in the :class:`Reference`
        change_form and reference inlines on the :class:`Instance`change_form
        to disable the autocomplete fields when there is or is not a digital
        edition. See ``sitemedia/js/reference-instance-canvas-toggle.js`` for
        this logic.

        :rtype: JSON formatted string of :class:`Instance` primary keys
        with_digital_eds = Instance.objects.with_digital_eds()
        # Flatten to just the primary keys
        ids = with_digital_eds.values_list('id', flat=True).order_by('id')
        # Return serialized JSON
        return json.dumps(list(ids))