from django.core.cache import cache
from django.http import HttpResponse, HttpResponseRedirect, Http404
from django.shortcuts import render
from django.utils import timezone, http

from qrurls.models import URL, URLItem

import calendar # timegm

"""
    Public frontend UI.
"""

class URLNotFound (Http404):
    pass

class URLItemNotFound (Http404):
    pass

def http_datetime (dt) :
    return http.http_date(calendar.timegm(dt.utctimetuple()))

def _get_url_item (shorturl=None, shorturl_id=None, item_id=None, related=()) :
    # JOIN against shorturl, urlimage
    url_item = URLItem.objects.select_related(*related)

    if shorturl:
        url_item = url_item.filter(shorturl__shorturl=shorturl)
    elif shorturl_id:
        shorturl_id = int(shorturl_id)
        url_item = url_item.filter(shorturl__id=shorturl_id)
    else:
        raise URLNotFound()
    
    # match for published items
    now = timezone.now()
    url_item = url_item.filter(published__lt=now).order_by('-published')
   
    if item_id :
        return url_item.get(id=int(item_id))
    else :
        # most recent
        try:
            return url_item[0]
        except IndexError:
            raise URLItemNotFound()

def index (request) :
    urls = URL.objects.all()
    return render(request, 'qrurls/index.html', dict(
        urls    = urls,
    ))

def shorturl (request, **opts) :
    """
        Primary frontend for redirecting based on current time.
    """
    
    key = 'qrurls/urlfeed/{shorturl}/url'.format(shorturl=opts) # format as dict
    data = cache.get(key)
    
    if data :
        url, modified = data
    else:
        url_item = _get_url_item(**opts)
        modified = url_item.last_modified()
        url = url_item.get_absolute_url()

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

    # redirect, either directly, or to image()
    response = HttpResponseRedirect(url)

    # set cache
    response['Vary'] = ''
    response['Last-Modified'] = http_datetime(modified)
    return response
    
def item (request, **opts) :
    """
        Frontend for a specific item.
    """

    url_item = _get_url_item(related=('shorturl', 'image',), **opts)

    if url_item.url :
        response = HttpResponseRedirect(url_item.url)
    elif url_item.image :
        title = url_item.image.title or url_item.shorturl.title

        response = render(request, 'qrurls/image.html', dict(
            title   = title,
            image   = url_item.image,
        ))
    else :
        raise Http404()

    # set cache
    response['Vary'] = ''
    response['Last-Modified'] = http_datetime(url_item.last_modified())
    return response