regluit/core/bookloader.py

"""
external library imports
"""
import json
import logging
import re
import requests
from django.core.files.base import ContentFile
from django.core.files.storage import default_storage
from regluit.core.validation import test_file

from datetime import timedelta
from xml.etree import ElementTree
from urlparse import (urljoin, urlparse)


# django imports

from django.conf import settings
from django.core.files.base import ContentFile
from django_comments.models import Comment
from django.db import IntegrityError
from django.forms import ValidationError

from github3 import (login, GitHub)
from github3.repos.release import Release

from gitenberg.metadata.pandata import Pandata

# regluit imports

import regluit
import regluit.core.isbn
from regluit.marc.models import inverse_marc_rels
from regluit.utils.localdatetime import now

from . import cc
from . import models
from .parameters import WORK_IDENTIFIERS
from .validation import identifier_cleaner
from .loaders.scrape import BaseScraper, scrape_sitemap

logger = logging.getLogger(__name__)
request_log = logging.getLogger("requests")
request_log.setLevel(logging.WARNING)

def add_by_oclc(isbn, work=None):
    # this is indirection in case we have a data source other than google
    return add_by_oclc_from_google(isbn)


def add_by_oclc_from_google(oclc):
    if oclc:
        logger.info("adding book by oclc %s" , oclc)
    else:
        return None
    try:
        return models.Identifier.objects.get(type='oclc', value=oclc).edition
    except:
        url = "https://www.googleapis.com/books/v1/volumes"
        try:
            results = _get_json(url, {"q": '"OCLC%s"' % oclc})
        except LookupFailure, e:
            logger.exception("lookup failure for %s", oclc)
            return None
        if not results.has_key('items') or len(results['items']) == 0:
            logger.warn("no google hits for %s" , oclc)
            return None

        try:
            e = add_by_googlebooks_id(results['items'][0]['id'], results=results['items'][0])
            models.Identifier(type='oclc', value=oclc, edition=e, work=e.work).save()
            return e
        except LookupFailure, e:
            logger.exception("failed to add edition for %s", oclc)
        except IntegrityError, e:
            logger.exception("google books data for %s didn't fit our db", oclc)
        return None

def valid_isbn(isbn):
    try:
        return identifier_cleaner('isbn')(isbn)
    except:
        logger.exception("invalid isbn: %s", isbn)
        return None

def add_by_isbn(isbn, work=None, language='xx', title=''):
    if not isbn:
        return None
    try:
        e = add_by_isbn_from_google(isbn, work=work)
    except LookupFailure:
        logger.exception("failed google lookup for %s", isbn)
        # try again some other time
        return None
    if e:
        return e

    logger.info("null came back from add_by_isbn_from_google: %s", isbn)

    # if there's a a title, we want to create stub editions and
    # works, even if google doesn't know about it # but if it's not valid,
    # forget it!

    if work:
        title = work.title if work.title else title
        if not title:
            return None
    if not title:
        return None

    isbn = valid_isbn(isbn)
    if not isbn:
        return None

    if not language or language == 'xx': # don't add unknown language
        # we don't know the language  ->'xx'
        work = models.Work(title=title, language='xx')
        work.save()
    elif not work:
        work = models.Work(title=title, language=language)
        work.save()
    e = models.Edition(title=title, work=work)
    e.save()
    e.new = True
    models.Identifier(type='isbn', value=isbn, work=work, edition=e).save()
    return e

def get_google_isbn_results(isbn):
    url = "https://www.googleapis.com/books/v1/volumes"
    try:
        results = _get_json(url, {"q": "isbn:%s" % isbn})
    except LookupFailure:
        logger.exception("lookup failure for %s", isbn)
        return None
    if not results.has_key('items') or len(results['items']) == 0:
        logger.warn("no google hits for %s" , isbn)
        return None
    else:
        return results

def add_ebooks(item, edition):
    access_info = item.get('accessInfo')
    if access_info:
        epub = access_info.get('epub')
        if epub and epub.get('downloadLink'):
            ebook = models.Ebook(edition=edition, format='epub',
                                 url=epub.get('downloadLink'),
                                 provider='Google Books')
            try:
                ebook.save()
            except IntegrityError:
                pass


        pdf = access_info.get('pdf')
        if pdf and pdf.get('downloadLink'):
            ebook = models.Ebook(edition=edition, format='pdf',
                                 url=pdf.get('downloadLink', None),
                                 provider='Google Books')
            try:
                ebook.save()
            except IntegrityError:
                pass


def update_edition(edition):
    """
    attempt to update data associated with input edition and return that updated edition
    """

    # if there is no ISBN associated with edition, just return the input edition
    try:
        isbn = edition.identifiers.filter(type='isbn')[0].value
    except (models.Identifier.DoesNotExist, IndexError):
        return edition

    # do a Google Books lookup on the isbn associated with the edition (there should be either 0 or 1 isbns associated
    # with an edition because of integrity constraint in Identifier)

    # if we get some data about this isbn back from Google, update the edition data accordingly
    results = get_google_isbn_results(isbn)
    if not results:
        return edition
    item = results['items'][0]
    googlebooks_id = item['id']
    d = item['volumeInfo']
    if d.has_key('title'):
        title = d['title']
    else:
        title = ''
    if len(title) == 0:
        # need a title to make an edition record; some crap records in GB. use title from parent if available
        title = edition.work.title

    # check for language change
    language = d['language']
    # allow variants in main language (e.g., 'zh-tw')
    if len(language) > 5:
        language = language[0:5]

    # if the language of the edition no longer matches that of the parent work, attach edition to the
    if edition.work.language != language:
        logger.info("reconnecting %s since it is %s instead of %s" %(googlebooks_id, language, edition.work.language))
        old_work = edition.work

        new_work = models.Work(title=title, language=language)
        new_work.save()
        edition.work = new_work
        edition.save()
        for identifier in edition.identifiers.all():
            logger.info("moving identifier %s" % identifier.value)
            identifier.work = new_work
            identifier.save()
        if old_work and old_work.editions.count()==0:
            #a dangling work; make sure nothing else is attached!
            merge_works(new_work, old_work)

    # update the edition
    edition.title = title
    edition.publication_date = d.get('publishedDate', '')
    edition.set_publisher(d.get('publisher'))
    edition.save()

    # create identifier if needed
    models.Identifier.get_or_add(type='goog', value=googlebooks_id, edition=edition, work=edition.work)

    for a in d.get('authors', []):
        edition.add_author(a)

    add_ebooks(item, edition)

    return edition


def add_by_isbn_from_google(isbn, work=None):
    """add a book to the UnglueIt database from google based on ISBN. The work parameter
    is optional, and if not supplied the edition will be associated with
    a stub work.
    """
    if not isbn:
        return None
    if len(isbn)==10:
        isbn = regluit.core.isbn.convert_10_to_13(isbn)


    # check if we already have this isbn
    edition = get_edition_by_id(type='isbn', value=isbn)
    if edition:
        edition.new = False
        return edition

    logger.info("adding new book by isbn %s", isbn)
    results = get_google_isbn_results(isbn)
    if results:
        try:
            return add_by_googlebooks_id(results['items'][0]['id'], work=work, results=results['items'][0], isbn=isbn)
        except LookupFailure, e:
            logger.exception("failed to add edition for %s", isbn)
        except IntegrityError, e:
            logger.exception("google books data for %s didn't fit our db", isbn)
        return None
    else:
        return None

def get_work_by_id(type, value):
    if value:
        try:
            return models.Identifier.objects.get(type=type, value=value).work
        except models.Identifier.DoesNotExist:
            return None

def get_edition_by_id(type, value):
    if value:
        try:
            return models.Identifier.objects.get(type=type, value=value).edition
        except models.Identifier.DoesNotExist:
            return None


def add_by_googlebooks_id(googlebooks_id, work=None, results=None, isbn=None):
    """add a book to the UnglueIt database based on the GoogleBooks ID. The
    work parameter is optional, and if not supplied the edition will be
    associated with a stub work. isbn can be passed because sometimes passed data won't include it

    """
    isbn = valid_isbn(isbn)

    # don't ping google again if we already know about the edition
    try:
        edition = models.Identifier.objects.get(type='goog', value=googlebooks_id).edition
        edition.new = False
        if isbn:
            # check that the isbn is in db; if not, then there are two isbns for the edition
            try:
                models.Identifier.objects.get(type='isbn', value=isbn).edition
                # not going to worry about isbn_edition != edition
            except models.Identifier.DoesNotExist:
                models.Identifier.objects.create(type='isbn', value=isbn, edition=edition, work=edition.work)
        return edition
    except models.Identifier.DoesNotExist:
        pass

    # if google has been queried by caller, don't call again
    if results:
        item = results
    else:
        logger.info("loading metadata from google for %s", googlebooks_id)
        url = "https://www.googleapis.com/books/v1/volumes/%s" % googlebooks_id
        item = _get_json(url)
    d = item['volumeInfo']

    if d.has_key('title'):
        title = d['title']
    else:
        title = ''
    if len(title)==0:
        # need a title to make an edition record; some crap records in GB. use title from parent if available
        if work:
            title = work.title
        else:
            return None

    # don't add the edition to a work with a different language
    # https://www.pivotaltracker.com/story/show/17234433
    language = d['language']
    if len(language) > 5:
        language = language[0:5]
    if work and work.language != language:
        logger.info("not connecting %s since it is %s instead of %s" %
                (googlebooks_id, language, work.language))
        work = None
    # isbn = None
    if not isbn:
        for i in d.get('industryIdentifiers', []):
            if i['type'] == 'ISBN_10' and not isbn:
                isbn = regluit.core.isbn.convert_10_to_13(i['identifier'])
            elif i['type'] == 'ISBN_13':
                isbn = i['identifier']

    # now check to see if there's an existing Work
    if work:
        work.new = False
    if isbn and not work:
        work = get_work_by_id(type='isbn', value=isbn)
        if work:
            work.new = False
    if not work:
        work = models.Work.objects.create(title=title, language=language)
        work.new = True
        work.save()

    # going off to google can take some time, so we want to make sure this edition has not
    # been created in another thread while we were waiting
    try:
        e = models.Identifier.objects.get(type='goog', value=googlebooks_id).edition
        e.new = False
        logger.warning( " whoa nellie, somebody else created an edition while we were working.")
        if work.new:
            work.delete()
        return e
    except models.Identifier.DoesNotExist:
        pass

    # because this is a new google id, we have to create a new edition
    e = models.Edition(work=work)
    e.title = title
    e.publication_date = d.get('publishedDate', '')
    e.set_publisher(d.get('publisher'))
    e.save()
    e.new = True

    # create identifier where needed
    models.Identifier(type='goog', value=googlebooks_id, edition=e, work=work).save()
    if isbn:
        models.Identifier.get_or_add(type='isbn', value=isbn, edition=e, work=work)

    for a in d.get('authors', []):
        a, created = models.Author.objects.get_or_create(name=a)
        e.add_author(a)

    add_ebooks(item, e)

    return e


def relate_isbn(isbn, cluster_size=1):
    """add a book by isbn and then see if there's an existing work to add it to so as to make a cluster
    bigger than cluster_size.
    """
    logger.info("finding a related work for %s", isbn)

    edition = add_by_isbn(isbn)
    if edition is None:
        return None
    if edition.work is None:
        logger.info("didn't add related to null work")
        return None
    if edition.work.editions.count()>cluster_size:
        return edition.work
    for other_isbn in thingisbn(isbn):
        # 979's come back as 13
        logger.debug("other_isbn: %s", other_isbn)
        if len(other_isbn)==10:
            other_isbn = regluit.core.isbn.convert_10_to_13(other_isbn)
        related_edition = add_by_isbn(other_isbn, work=edition.work)
        if related_edition:
            related_language = related_edition.work.language
            if edition.work.language == related_language:
                if related_edition.work is None:
                    related_edition.work = edition.work
                    related_edition.save()
                elif related_edition.work.id != edition.work.id:
                    logger.debug("merge_works path 1 %s %s", edition.work.id, related_edition.work.id )
                    merge_works(related_edition.work, edition.work)

                if related_edition.work.editions.count()>cluster_size:
                    return related_edition.work
    return edition.work

def add_related(isbn):
    """add all books related to a particular ISBN to the UnglueIt database.
    The initial seed ISBN will be added if it's not already there.
    """
    # make sure the seed edition is there
    logger.info("adding related editions for %s", isbn)

    new_editions = []

    edition = add_by_isbn(isbn)
    if edition is None:
        return new_editions
    if edition.work is None:
        logger.warning("didn't add related to null work")
        return new_editions
    # this is the work everything will hang off
    work = edition.work
    other_editions = {}
    for other_isbn in thingisbn(isbn):
        # 979's come back as 13
        logger.debug("other_isbn: %s", other_isbn)
        if len(other_isbn)==10:
            other_isbn = regluit.core.isbn.convert_10_to_13(other_isbn)
        related_edition = add_by_isbn(other_isbn, work=work)

        if related_edition:
            related_language = related_edition.work.language
            if edition.work.language == related_language:
                new_editions.append(related_edition)
                if related_edition.work is None:
                    related_edition.work = work
                    related_edition.save()
                elif related_edition.work.id != work.id:
                    logger.debug("merge_works path 1 %s %s", work.id, related_edition.work.id )
                    merge_works(work, related_edition.work)
            else:
                if other_editions.has_key(related_language):
                    other_editions[related_language].append(related_edition)
                else:
                    other_editions[related_language] = [related_edition]

    # group the other language editions together
    for lang_group in other_editions.itervalues():
        logger.debug("lang_group (ed, work): %s", [(ed.id, ed.work.id) for ed in lang_group])
        if len(lang_group)>1:
            lang_edition = lang_group[0]
            logger.debug("lang_edition.id: %s", lang_edition.id)
            # compute the distinct set of works to merge into lang_edition.work
            works_to_merge = set([ed.work for ed in lang_group[1:]]) - set([lang_edition.work])
            for w in works_to_merge:
                logger.debug("merge_works path 2 %s %s", lang_edition.work.id, w.id )
                merge_works(lang_edition.work, w)
            models.WorkRelation.objects.get_or_create(to_work=lang_edition.work, from_work=work, relation='translation')

    return new_editions


def thingisbn(isbn):
    """given an ISBN return a list of related edition ISBNs, according to
    Library Thing. (takes isbn_10 or isbn_13, returns isbn_10, except for 979 isbns, which come back as isbn_13')
    """
    logger.info("looking up %s at ThingISBN" , isbn)
    url = "https://www.librarything.com/api/thingISBN/%s" % isbn
    xml = requests.get(url, headers={"User-Agent": settings.USER_AGENT}).content
    doc = ElementTree.fromstring(xml)
    return [e.text for e in doc.findall('isbn')]


def merge_works(w1, w2, user=None):
    """will merge the second work (w2) into the first (w1)
    """
    logger.info("merging work %s into %s", w2.id, w1.id)
    # don't merge if the works are the same or at least one of the works has no id (for example, when w2 has already been deleted)
    if w1 is None or w2 is None or w1.id == w2.id or w1.id is None or w2.id is None:
        return
    if w2.selected_edition != None and w1.selected_edition == None:
        #the merge should be reversed
        temp = w1
        w1 = w2
        w2 = temp
    models.WasWork(was=w2.pk, work=w1, user=user).save()
    for ww in models.WasWork.objects.filter(work = w2):
        ww.work = w1
        ww.save()
    if w2.description and not w1.description:
        w1.description = w2.description
    if w2.featured and not w1.featured:
        w1.featured = w2.featured
    if w2.is_free and not w1.is_free:
        w1.is_free = True
    if w2.age_level and not w1.age_level:
        w1.age_level = w2.age_level
    w1.save()
    for wishlist in models.Wishlist.objects.filter(works__in=[w2]):
        w2source = wishlist.work_source(w2)
        wishlist.remove_work(w2)
        wishlist.add_work(w1, w2source)
    for identifier in w2.identifiers.all():
        identifier.work = w1
        identifier.save()
    for comment in Comment.objects.for_model(w2):
        comment.object_pk = w1.pk
        comment.save()
    for edition in w2.editions.all():
        edition.work = w1
        edition.save()
    for campaign in w2.campaigns.all():
        campaign.work = w1
        campaign.save()
    for claim in w2.claim.all():
        claim.work = w1
        claim.dont_notify = True
        claim.save()
    for offer in w2.offers.all():
        offer.work = w1
        offer.save()
    for acq in w2.acqs.all():
        acq.work = w1
        acq.save()
    for hold in w2.holds.all():
        hold.work = w1
        hold.save()
    for landing in w2.landings.all():
        landing.object_id = w1.id
        landing.save()
    for subject in w2.subjects.all():
        if subject not in w1.subjects.all():
            w1.subjects.add(subject)


    w2.delete()

def detach_edition(e):
    """will detach edition from its work, creating a new stub work. if remerge=true, will see if there's another work to attach to
    """
    logger.info("splitting edition %s from %s", e, e.work)
    w = models.Work(title=e.title, language = e.work.language)
    w.save()

    for identifier in e.identifiers.all():
        identifier.work = w
        identifier.save()

    e.work = w
    e.save()

def despam_description(description):
    """ a lot of descriptions from openlibrary have free-book promotion text; this removes some of it."""
    if description.find("GeneralBooksClub.com")>-1 or description.find("AkashaPublishing.Com")>-1:
        return ""
    pieces = description.split("1stWorldLibrary.ORG -")
    if len(pieces) > 1:
        return pieces[1]
    pieces = description.split("a million books for free.")
    if len(pieces) > 1:
        return pieces[1]
    return description

def add_openlibrary(work, hard_refresh = False):
    if (not hard_refresh) and work.openlibrary_lookup is not None:
        # don't hit OL if we've visited in the past month or so
        if now()- work.openlibrary_lookup < timedelta(days=30):
            return
    work.openlibrary_lookup = now()
    work.save()

    # find the first ISBN match in OpenLibrary
    logger.info("looking up openlibrary data for work %s", work.id)

    e = None # openlibrary edition json
    w = None # openlibrary work json

    # get the 1st openlibrary match by isbn that has an associated work
    url = "https://openlibrary.org/api/books"
    params = {"format": "json", "jscmd": "details"}
    subjects = []
    for edition in work.editions.all():
        isbn_key = "ISBN:%s" % edition.isbn_13
        params['bibkeys'] = isbn_key
        try:
            e = _get_json(url, params, type='ol')
        except LookupFailure:
            logger.exception("OL lookup failed for  %s", isbn_key)
            e = {}
        if e.has_key(isbn_key):
            if e[isbn_key].has_key('details'):
                if e[isbn_key]['details'].has_key('oclc_numbers'):
                    for oclcnum in e[isbn_key]['details']['oclc_numbers']:
                        models.Identifier.get_or_add(type='oclc', value=oclcnum, work=work, edition=edition)
                if e[isbn_key]['details'].has_key('identifiers'):
                    ids = e[isbn_key]['details']['identifiers']
                    if ids.has_key('goodreads'):
                        models.Identifier.get_or_add(type='gdrd', value=ids['goodreads'][0], work=work, edition=edition)
                    if ids.has_key('librarything'):
                        models.Identifier.get_or_add(type='ltwk', value=ids['librarything'][0], work=work)
                    if ids.has_key('google'):
                        models.Identifier.get_or_add(type='goog', value=ids['google'][0], work=work)
                    if ids.has_key('project_gutenberg'):
                        models.Identifier.get_or_add(type='gute', value=ids['project_gutenberg'][0], work=work)
                if e[isbn_key]['details'].has_key('works'):
                    work_key = e[isbn_key]['details']['works'].pop(0)['key']
                    logger.info("got openlibrary work %s for isbn %s", work_key, isbn_key)
                    models.Identifier.get_or_add(type='olwk', value=work_key, work=work)
                    try:
                        w = _get_json("https://openlibrary.org" + work_key, type='ol')
                        if w.has_key('description'):
                            description = w['description']
                            if isinstance(description, dict):
                                if description.has_key('value'):
                                    description = description['value']
                            description = despam_description(description)
                            if not work.description or work.description.startswith('{') or len(description) > len(work.description):
                                work.description = description
                                work.save()
                        if w.has_key('subjects') and len(w['subjects']) > len(subjects):
                            subjects = w['subjects']
                    except LookupFailure:
                        logger.exception("OL lookup failed for  %s", work_key)
    if not subjects:
        logger.warn("unable to find work %s at openlibrary", work.id)
        return

    # add the subjects to the Work
    for s in subjects:
        if valid_subject(s):
            logger.info("adding subject %s to work %s", s, work.id)
            subject, created = models.Subject.objects.get_or_create(name=s)
            work.subjects.add(subject)

    work.save()

def valid_xml_char_ordinal(c):
    codepoint = ord(c)
    # conditions ordered by presumed frequency
    return (
        0x20 <= codepoint <= 0xD7FF or
        codepoint in (0x9, 0xA, 0xD) or
        0xE000 <= codepoint <= 0xFFFD or
        0x10000 <= codepoint <= 0x10FFFF
        )

def valid_subject( subject_name ):
    num_commas = 0
    for c in subject_name:
        if not valid_xml_char_ordinal(c):
            return False
        if c == ',':
            num_commas += 1
            if num_commas > 2:
                return False
    return True



def _get_json(url, params={}, type='gb'):
    # TODO: should X-Forwarded-For change based on the request from client?
    headers = {'User-Agent': settings.USER_AGENT,
               'Accept': 'application/json',
               'X-Forwarded-For': '69.174.114.214'}
    if type == 'gb':
        params['key'] = settings.GOOGLE_BOOKS_API_KEY
        params['country'] = 'us'
    response = requests.get(url, params=params, headers=headers)
    if response.status_code == 200:
        return json.loads(response.content)
    else:
        logger.error("unexpected HTTP response: %s" % response)
        if response.content:
            logger.error("response content: %s" % response.content)
        raise LookupFailure("GET failed: url=%s and params=%s" % (url, params))


def load_gutenberg_edition(title, gutenberg_etext_id, ol_work_id, seed_isbn, url, format, license, lang, publication_date):

    # let's start with instantiating the relevant Work and Edition if they don't already exist

    try:
        work = models.Identifier.objects.get(type='olwk', value=ol_work_id).work
    except models.Identifier.DoesNotExist: # try to find an Edition with the seed_isbn and use that work to hang off of
        sister_edition = add_by_isbn(seed_isbn)
        if sister_edition.new:
            # add related editions asynchronously
            regluit.core.tasks.populate_edition.delay(sister_edition.isbn_13)
        work = sister_edition.work
        # attach the olwk identifier to this work if it's not none.
        if ol_work_id is not None:
            models.Identifier.get_or_add(type='olwk', value=ol_work_id, work=work)

    # Now pull out any existing Gutenberg editions tied to the work with the proper Gutenberg ID
    try:
        edition = models.Identifier.objects.get(type='gtbg', value=gutenberg_etext_id ).edition
    except models.Identifier.DoesNotExist:
        edition = models.Edition()
        edition.title = title
        edition.work = work

        edition.save()
        models.Identifier.get_or_add(type='gtbg', value=gutenberg_etext_id, edition=edition, work=work)

    # check to see whether the Edition hasn't already been loaded first
    # search by url
    ebooks = models.Ebook.objects.filter(url=url)

    # format: what's the controlled vocab?  -- from Google -- alternative would be mimetype

    if len(ebooks):
        ebook = ebooks[0]
    elif len(ebooks) == 0: # need to create new ebook
        ebook = models.Ebook()

    if len(ebooks) > 1:
        logger.warning("There is more than one Ebook matching url {0}".format(url))


    ebook.format = format
    ebook.provider = 'Project Gutenberg'
    ebook.url =  url
    ebook.rights = license

    # is an Ebook instantiable without a corresponding Edition? (No, I think)

    ebook.edition = edition
    ebook.save()

    return ebook

class LookupFailure(Exception):
    pass

IDTABLE = [('librarything', 'ltwk'), ('goodreads', 'gdrd'), ('openlibrary', 'olwk'),
    ('gutenberg', 'gtbg'), ('isbn', 'isbn'), ('oclc', 'oclc'),
    ('edition_id', 'edid'), ('googlebooks', 'goog'), ('doi', 'doi'),
]

def unreverse(name):
    if not ',' in name:
        return name
    (last, rest) = name.split(',', 1)
    if not ',' in rest:
        return '%s %s' % (rest.strip(), last.strip())
    (first, rest) = rest.split(',', 1)
    return '%s %s, %s' % (first.strip(), last.strip(), rest.strip())


def load_from_yaml(yaml_url, test_mode=False):
    """
    This really should be called 'load_from_github_yaml'

    if mock_ebook is True, don't construct list of ebooks from a release -- rather use an epub
    """
    all_metadata = Pandata(yaml_url)
    loader = GithubLoader(yaml_url)
    for metadata in all_metadata.get_edition_list():
        edition = loader.load_from_pandata(metadata)
        loader.load_ebooks(metadata, edition, test_mode)
    return edition.work.id if edition else None

def edition_for_ident(id_type, id_value):
    #print 'returning edition for {}: {}'.format(id_type, id_value)
    for ident in models.Identifier.objects.filter(type=id_type, value=id_value):
        return ident.edition if ident.edition else ident.work.editions[0]
    
def edition_for_etype(etype, metadata, default=None):
    '''
    assumes the metadata contains the isbn_etype attributes, and that the editions have been created.
    etype is 'epub', 'pdf', etc.
    '''
    isbn = metadata.identifiers.get('isbn_{}'.format(etype), None)
    if not isbn:
        isbn = metadata.identifiers.get('isbn_electronic', None)
    if isbn:
        return edition_for_ident('isbn', isbn)
    else:
        if default:
            return default
        # just return some edition
        for key in metadata.identifiers.keys():
            return edition_for_ident(key, metadata.identifiers[key])
        for key in metadata.edition_identifiers.keys():
            return edition_for_ident(key, metadata.identifiers[key])
    
MATCH_LICENSE = re.compile(r'creativecommons.org/licenses/([^/]+)/')

def load_ebookfile(url, etype):
    '''
    return a ContentFile if a new ebook has been loaded
    '''
    ebfs = models.EbookFile.objects.filter(source=url)
    if ebfs:
        return None
    try:
        r = requests.get(url)
        contentfile = ContentFile(r.content)
        test_file(contentfile, etype)
        return contentfile
    except IOError, e:
        logger.error(u'could not open {}'.format(url))
    except ValidationError, e:
        logger.error(u'downloaded {} was not a valid {}'.format(url, etype))
     
class BasePandataLoader(object):
    def __init__(self, url):
        self.base_url = url

    def load_from_pandata(self, metadata, work=None):
        ''' metadata is a Pandata object'''
        
        #find an work to associate
        edition = None
        has_ed_id = False
        if metadata.url:
            new_ids = [('http', 'http', metadata.url)]
        else:
            new_ids = []
        for (identifier, id_code) in IDTABLE:
            # note that the work chosen is the last associated
            value = metadata.edition_identifiers.get(identifier, None)
            value = identifier_cleaner(id_code)(value)
            if not value:
                value = metadata.identifiers.get(identifier, None)
            if value:
                if id_code not in WORK_IDENTIFIERS:
                    has_ed_id = True
                value =  value[0] if isinstance(value, list) else value
                try:
                    id = models.Identifier.objects.get(type=id_code, value=value)
                    work = id.work
                    if id.edition and not edition:
                        edition = id.edition
                except models.Identifier.DoesNotExist:
                    if id_code != 'edid' or not has_ed_id:  #last in loop
                        # only need to create edid if there is no edition id for the edition
                        new_ids.append((identifier, id_code, value))


        if not work:
            work = models.Work.objects.create(title=metadata.title, language=metadata.language)
        if not edition:
            if metadata.edition_note:
                (note, created) = models.EditionNote.objects.get_or_create(note=metadata.edition_note)
            else:
                note = None
            edition =  models.Edition.objects.create(
                title=metadata.title,
                work=work,
                note=note,
            )
        for (identifier, id_code, value) in new_ids:
            models.Identifier.set(
                type=id_code,
                value=value,
                edition=edition if id_code not in WORK_IDENTIFIERS else None,
                work=work,
            )
        if metadata.publisher: #always believe yaml
            edition.set_publisher(metadata.publisher)
        if metadata.publication_date: #always believe yaml
            edition.publication_date = metadata.publication_date
        if metadata.description and len(metadata.description) > len(work.description):
            #be careful about overwriting the work description
            work.description = metadata.description
        if metadata.creator and not edition.authors.count(): 
            edition.authors.clear()
            for key in metadata.creator.keys():
                creators = metadata.creator[key]
                rel_code = inverse_marc_rels.get(key, 'aut')
                creators = creators if isinstance(creators, list) else [creators]
                for creator in creators:
                    edition.add_author(unreverse(creator.get('agent_name', '')), relation=rel_code)
        for yaml_subject in metadata.subjects: #always add yaml subjects (don't clear)
            if isinstance(yaml_subject, tuple):
                (authority, heading)  = yaml_subject
            elif isinstance(yaml_subject, str):
                (authority, heading)  = ( '', yaml_subject)
            else:
                continue
            (subject, created) = models.Subject.objects.get_or_create(name=heading)
            if not subject.authority and authority:
                subject.authority = authority
                subject.save()
            subject.works.add(work)
        # the default edition uses the first cover in covers.
        for cover in metadata.covers:
            if cover.get('image_path', False):
                edition.cover_image = urljoin(self.base_url, cover['image_path'])
                break
            elif cover.get('image_url', False):
                edition.cover_image = cover['image_url']
                break
        work.save()
        edition.save()
        return edition

    def load_ebooks(self, metadata, edition, test_mode=False, user=None):
        default_edition = edition
        for key in ['epub', 'pdf', 'mobi']:
            url = metadata.metadata.get('download_url_{}'.format(key), None)
            if url:
                edition = edition_for_etype(key, metadata, default=default_edition)
                if edition:
                    contentfile = load_ebookfile(url, key)
                    if contentfile:
                        contentfile_name = '/loaded/ebook_{}.{}'.format(edition.id, key)
                        path = default_storage.save(contentfile_name, contentfile) 
                        lic = MATCH_LICENSE.search(metadata.rights_url)
                        license = 'CC {}'.format(lic.group(1).upper()) if lic else ''
                        ebf = models.EbookFile.objects.create(
                            format=key,
                            edition=edition,
                            source=url,
                        )
                        ebf.file.save(contentfile_name, contentfile)
                        ebf.file.close()
                        ebook = models.Ebook.objects.create(
                            url=ebf.file.url,
                            provider='Unglue.it',
                            rights=license,
                            format=key,
                            edition=edition,
                            filesize=contentfile.size,
                            active=False,
                            user=user,
                        )
                        ebf.ebook =  ebook
                        ebf.save()
                    
            
class GithubLoader(BasePandataLoader):
    def load_ebooks(self, metadata, edition, test_mode=False):
        # create Ebook for any ebook in the corresponding GitHub release
        # assuming yaml_url of form (from GitHub, though not necessarily GITenberg)
        # https://github.com/GITenberg/Adventures-of-Huckleberry-Finn_76/raw/master/metadata.yaml

        url_path = urlparse(self.base_url).path.split("/")
        (repo_owner, repo_name) = (url_path[1], url_path[2])
        repo_tag = metadata._version
        # allow for there not to be a token in the settings
        try:
            token = settings.GITHUB_PUBLIC_TOKEN
        except:
            token = None

        if metadata._version and not metadata._version.startswith('0.0.'):
            # use GitHub API to compute the ebooks in release until we're in test mode
            if test_mode:
                # not using ebook_name in this code
                ebooks_in_release = [('epub', 'book.epub')]
            else:
                ebooks_in_release =  ebooks_in_github_release(repo_owner, repo_name, repo_tag, token=token)

            for (ebook_format, ebook_name) in ebooks_in_release:
                (book_name_prefix, _ ) = re.search(r'(.*)\.([^\.]*)$', ebook_name).groups()
                (ebook, created) = models.Ebook.objects.get_or_create(
                    url=git_download_from_yaml_url(
                        self.base_url,
                        metadata._version,
                        edition_name=book_name_prefix,
                        format_= ebook_format
                    ),
                    provider='Github',
                    rights=cc.match_license(metadata.rights),
                    format=ebook_format,
                    edition=edition,
                    )
                ebook.set_version(metadata._version)


def git_download_from_yaml_url(yaml_url, version, edition_name='book', format_='epub'):
    # go from https://github.com/GITenberg/Adventures-of-Huckleberry-Finn_76/raw/master/metadata.yaml
    # to https://github.com/GITenberg/Adventures-of-Huckleberry-Finn_76/releases/download/v0.0.3/Adventures-of-Huckleberry-Finn.epub
    if yaml_url.endswith('raw/master/metadata.yaml'):
        repo_url = yaml_url[0:-24]
        #print (repo_url,version,edition_name)
        ebook_url = repo_url + 'releases/download/' + version + '/' + edition_name + '.' + format_
        return ebook_url


def release_from_tag(repo, tag_name):
    """Get a release by tag name.
    release_from_tag() returns a release with specified tag
    while release() returns a release with specified release id
    :param str tag_name: (required) name of tag
    :returns: :class:`Release <github3.repos.release.Release>`
    """
    # release_from_tag adapted from
    # https://github.com/sigmavirus24/github3.py/blob/38de787e465bffc63da73d23dc51f50d86dc903d/github3/repos/repo.py#L1781-L1793

    url = repo._build_url('releases', 'tags', tag_name,
                          base_url=repo._api)
    json_obj = repo._json(repo._get(url), 200)
    return Release(json_obj, repo) if json_obj else None

def ebooks_in_github_release(repo_owner, repo_name, tag, token=None):
    """
    returns a list of (book_type, book_name) for a given GitHub release (specified by
    owner, name, tag).  token is a GitHub authorization token -- useful for accessing
    higher rate limit in the GitHub API
    """

    # map mimetype to file extension
    EBOOK_FORMATS = dict([(v, k) for (k, v) in settings.CONTENT_TYPES.items()])

    if token is not None:
        gh = login(token=token)
    else:
        # anonymous access
        gh = GitHub()

    repo = gh.repository(repo_owner, repo_name)
    release = release_from_tag(repo, tag)

    return [(EBOOK_FORMATS.get(asset.content_type), asset.name)
            for asset in release.iter_assets()
            if EBOOK_FORMATS.get(asset.content_type) is not None]

def add_by_webpage(url, work=None, user=None):
    edition = None
    scraper = BaseScraper(url)
    loader = BasePandataLoader(url)
    pandata = Pandata()
    pandata.metadata = scraper.metadata
    for metadata in pandata.get_edition_list():
        edition = loader.load_from_pandata(metadata, work)
        work = edition.work
    loader.load_ebooks(pandata, edition, user=user)
    return edition if edition else None

def add_by_sitemap(url, maxnum=None):
    editions = []
    scraper = BaseScraper(url)
    for bookdata in scrape_sitemap(url, maxnum=maxnum):
        edition = None
        loader = BasePandataLoader(bookdata.base)
        pandata = Pandata()
        pandata.metadata = bookdata.metadata
        for metadata in pandata.get_edition_list():
            edition = loader.load_from_pandata(metadata, None)
            work = edition.work
        loader.load_ebooks(pandata, edition)
        if edition:
            editions.append(edition)
    return editions