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e85a2047daecc92fbbe715ceb187b26b952d3816
[etc/taskwarrior.git] / tasklib / lazy.py
1 """
2 Provides lazy implementations for Task and TaskQuerySet.
3 """
4
5
6 class LazyUUIDTask(object):
7     """
8     A lazy wrapper around Task object, referenced by UUID.
9
10     - Supports comparison with LazyUUIDTask or Task objects (equality by UUIDs)
11     - If any attribute other than 'uuid' requested, a lookup in the
12       backend will be performed and this object will be replaced by a proper
13       Task object.
14     """
15
16     def __init__(self, tw, uuid):
17         self._tw = tw
18         self._uuid = uuid
19
20     def __getitem__(self, key):
21         # LazyUUIDTask does not provide anything else other than 'uuid'
22         if key is 'uuid':
23             return self._uuid
24         else:
25             self.replace()
26             return self[key]
27
28     def __getattr__(self, name):
29         # Getattr is called only if the attribute could not be found using
30         # normal means
31         self.replace()
32         return self.name
33
34     def __eq__(self, other):
35         if other['uuid']:
36             # For saved Tasks, just define equality by equality of uuids
37             return self['uuid'] == other['uuid']
38
39     def __hash__(self):
40         return self['uuid'].__hash__()
41
42     @property
43     def saved(self):
44         """
45         Implementation of the 'saved' property. Always returns True.
46         """
47         return True
48
49     def replace(self):
50         """
51         Performs conversion to the regular Task object, referenced by the
52         stored UUID.
53         """
54
55         replacement = self._tw.tasks.get(uuid=self._uuid)
56         self.__class__ = replacement.__class__
57         self.__dict__ = replacement.__dict__
58
59
60 class LazyUUIDTaskSet(object):
61     """
62     A lazy wrapper around TaskQuerySet object, for tasks referenced by UUID.
63
64     - Supports 'in' operator with LazyUUIDTask or Task objects
65     - If iteration over the objects in the LazyUUIDTaskSet is requested, the
66       LazyUUIDTaskSet will be converted to QuerySet and evaluated
67     """
68
69     def __init__(self, tw, uuids):
70         self._tw = tw
71         self._uuids = set(uuids)
72
73     def __getattr__(self, name):
74         # Getattr is called only if the attribute could not be found using
75         # normal means
76
77         if name.startswith('__'):
78             # If some internal method was being search, do not convert
79             # to TaskQuerySet just because of that
80             raise AttributeError
81         else:
82             self.replace()
83             return self.name
84
85     def __eq__(self, other):
86         return set(t['uuid'] for t in other) == self._uuids
87
88     def __contains__(self, task):
89         return task['uuid'] in self._uuids
90
91     def __len__(self):
92         return len(self._uuids)
93
94     def __iter__(self):
95         for uuid in self._uuids:
96             yield LazyUUIDTask(self._tw, uuid)
97
98     def replace(self):
99         """
100         Performs conversion to the regular TaskQuerySet object, referenced by
101         the stored UUIDs.
102         """
103
104         replacement = self._tw.tasks.filter(' '.join(self._uuids))
105         self.__class__ = replacement.__class__
106         self.__dict__ = replacement.__dict__