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from django.core.cache import cache

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from django.http import HttpResponse, HttpResponseRedirect, Http404

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from django.shortcuts import render

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from django.utils import timezone, http

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from qrurls.models import URL, URLItem

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import calendar # timegm

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"""

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    Public frontend UI.

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"""

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class URLNotFound (Http404):

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    pass

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class URLItemNotFound (Http404):

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    pass

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def http_datetime (dt) :

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    return http.http_date(calendar.timegm(dt.utctimetuple()))

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def _get_url_item (shorturl=None, shorturl_id=None, item_id=None, related=()) :

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    # JOIN against shorturl, urlimage

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    url_item = URLItem.objects.select_related(*related)

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    if shorturl:

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        url_item = url_item.filter(shorturl__shorturl=shorturl)

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    elif shorturl_id:

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        shorturl_id = int(shorturl_id)

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        url_item = url_item.filter(shorturl__id=shorturl_id)

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    else:

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        raise URLNotFound()

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    # match for published items

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    now = timezone.now()

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    url_item = url_item.filter(published__lt=now).order_by('-published')

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    if item_id :

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    else :

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        # most recent

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        try:

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            return url_item[0]

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        except IndexError:

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            raise URLItemNotFound()

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def index (request) :

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    urls = URL.objects.all()

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    return render(request, 'qrurls/index.html', dict(

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        urls    = urls,

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    ))

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def shorturl (request, shorturl=None, shorturl_id=None) :

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    """

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        Primary frontend for redirecting based on current time.

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    """

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    key = 'qrurls/urlfeed/{shorturl}'.format(shorturl=(shorturl or shorturl_id)) # format as dict

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    data = cache.get(key)

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    if data :

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        url, modified = data

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    else:

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        url_item = _get_url_item(shorturl=shorturl, shorturl_id=shorturl_id)

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        modified = url_item.last_modified()

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        url = url_item.get_absolute_url()

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        cache.set(key, (url, modified)) # XXX: expiry

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    # redirect, either directly, or to image()

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    response = HttpResponseRedirect(url)

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    response['Vary'] = ''

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    response['Last-Modified'] = http_datetime(modified)

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    return response

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def item (request, shorturl, item_id) :

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    """

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        Frontend for a specific item.

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    """

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    url_item = _get_url_item(

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            shorturl=shorturl, item_id=item_id,

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            related=('shorturl', 'image')

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    )

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    if url_item.url :

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        response = HttpResponseRedirect(url_item.url)

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    elif url_item.image :

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        response = render(request, 'qrurls/image.html', dict(

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            title   = url_item.title(),

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            image   = url_item.image,

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        ))

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    else :

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        raise Http404()

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    # set cache

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    response['Vary'] = ''

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    response['Last-Modified'] = http_datetime(url_item.last_modified())

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    return response

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