closes #2043: covers in ebooks
[wolnelektury.git] / apps / waiter / models.py
1 from os.path import join, isfile
2 from django.core.urlresolvers import reverse
3 from django.db import models
4 from waiter.settings import WAITER_URL, WAITER_MAX_QUEUE
5 from waiter.utils import check_abspath
6 from picklefield import PickledObjectField
7
8
9 class WaitedFile(models.Model):
10     path = models.CharField(max_length=255, unique=True, db_index=True)
11     task_id = models.CharField(max_length=128, db_index=True, null=True, blank=True)
12     task = PickledObjectField(null=True, editable=False)
13     description = models.CharField(max_length=255, null=True, blank=True)
14
15     @classmethod
16     def exists(cls, path):
17         """Returns opened file or None.
18         
19         `path` is relative to WAITER_ROOT.
20         Won't open a path leading outside of WAITER_ROOT.
21         """
22         abs_path = check_abspath(path)
23         # Pre-fetch objects for deletion to avoid minor race condition
24         relevant = [o.id for o in cls.objects.filter(path=path)]
25         if isfile(abs_path):
26             cls.objects.filter(id__in=relevant).delete()
27             return True
28         else:
29             return False
30
31     @classmethod
32     def can_order(cls, path):
33         return (cls.objects.filter(path=path).exists() or
34                 cls.exists(path) or
35                 cls.objects.count() < WAITER_MAX_QUEUE
36                 )
37
38     def is_stale(self):
39         if self.task is None:
40             # Race; just let the other task roll. 
41             return False
42         if self.task.status not in (u'PENDING', u'STARTED', u'SUCCESS', u'RETRY'):
43             return True
44         return False
45
46     @classmethod
47     def order(cls, path, task_creator, description=None):
48         """
49         Returns an URL for the user to follow.
50         If the file is ready, returns download URL.
51         If not, starts preparing it and returns waiting URL.
52
53         task_creator: function taking a path and generating the file;
54         description: a string or string proxy with a description for user;
55         """
56         already = cls.exists(path)
57         if not already:
58             waited, created = cls.objects.get_or_create(path=path)
59             if created or waited.is_stale():
60                 waited.task = task_creator(check_abspath(path))
61                 waited.task_id = waited.task.task_id
62                 waited.description = description
63                 waited.save()
64             return reverse("waiter", args=[path])
65         return join(WAITER_URL, path)