backends: Introduce a Backend base class

[etc/taskwarrior.git] / tasklib / task.py

diff --git a/tasklib/task.py b/tasklib/task.py
index f74e0d25510028853f52c4511b09d37956f32371..8374eb79998980b2af4a997db17cc026ac4bb229 100644 (file)
--- a/tasklib/task.py
+++ b/tasklib/task.py
@@ -1,103 +1,1075 @@
+from __future__ import print_function
+import copy
+import datetime

 import json
 import json

+import logging

 import os
 import os

+import pytz
+import re
+import six
+import sys

 import subprocess
 import subprocess

-import tempfile
-import uuid
-
+import tzlocal

 
 

+DATE_FORMAT = '%Y%m%dT%H%M%SZ'
+DATE_FORMAT_CALC = '%Y-%m-%dT%H:%M:%S'
+REPR_OUTPUT_SIZE = 10

 PENDING = 'pending'
 PENDING = 'pending'

+COMPLETED = 'completed'
+
+VERSION_2_1_0 = six.u('2.1.0')
+VERSION_2_2_0 = six.u('2.2.0')
+VERSION_2_3_0 = six.u('2.3.0')
+VERSION_2_4_0 = six.u('2.4.0')
+VERSION_2_4_1 = six.u('2.4.1')
+VERSION_2_4_2 = six.u('2.4.2')
+VERSION_2_4_3 = six.u('2.4.3')
+VERSION_2_4_4 = six.u('2.4.4')
+VERSION_2_4_5 = six.u('2.4.5')
+
+logger = logging.getLogger(__name__)
+local_zone = tzlocal.get_localzone()

 
 
 class TaskWarriorException(Exception):
     pass
 
 
 
 
 class TaskWarriorException(Exception):
     pass
 
 

-class Task(object):
+class ReadOnlyDictView(object):
+    """
+    Provides simplified read-only view upon dict object.
+    """
+
+    def __init__(self, viewed_dict):
+        self.viewed_dict = viewed_dict
+
+    def __getitem__(self, key):
+        return copy.deepcopy(self.viewed_dict.__getitem__(key))
+
+    def __contains__(self, k):
+        return self.viewed_dict.__contains__(k)
+
+    def __iter__(self):
+        for value in self.viewed_dict:
+            yield copy.deepcopy(value)
+
+    def __len__(self):
+        return len(self.viewed_dict)
+
+    def get(self, key, default=None):
+        return copy.deepcopy(self.viewed_dict.get(key, default))
+
+    def items(self):
+        return [copy.deepcopy(v) for v in self.viewed_dict.items()]
+
+    def values(self):
+        return [copy.deepcopy(v) for v in self.viewed_dict.values()]
+
+
+class SerializingObject(object):
+    """
+    Common ancestor for TaskResource & TaskFilter, since they both
+    need to serialize arguments.
+
+    Serializing method should hold the following contract:
+      - any empty value (meaning removal of the attribute)
+        is deserialized into a empty string
+      - None denotes a empty value for any attribute

 
 

-    def __init__(self, warrior, data={}):
+    Deserializing method should hold the following contract:
+      - None denotes a empty value for any attribute (however,
+        this is here as a safeguard, TaskWarrior currently does
+        not export empty-valued attributes) if the attribute
+        is not iterable (e.g. list or set), in which case
+        a empty iterable should be used.
+
+    Normalizing methods should hold the following contract:
+      - They are used to validate and normalize the user input.
+        Any attribute value that comes from the user (during Task
+        initialization, assignign values to Task attributes, or
+        filtering by user-provided values of attributes) is first
+        validated and normalized using the normalize_{key} method.
+      - If validation or normalization fails, normalizer is expected
+        to raise ValueError.
+    """
+
+    def __init__(self, warrior):

         self.warrior = warrior
         self.warrior = warrior

-        self._data = data
+
+    def _deserialize(self, key, value):
+        hydrate_func = getattr(self, 'deserialize_{0}'.format(key),
+                               lambda x: x if x != '' else None)
+        return hydrate_func(value)
+
+    def _serialize(self, key, value):
+        dehydrate_func = getattr(self, 'serialize_{0}'.format(key),
+                                 lambda x: x if x is not None else '')
+        return dehydrate_func(value)
+
+    def _normalize(self, key, value):
+        """
+        Use normalize_<key> methods to normalize user input. Any user
+        input will be normalized at the moment it is used as filter,
+        or entered as a value of Task attribute.
+        """
+
+        # None value should not be converted by normalizer
+        if value is None:
+            return None
+
+        normalize_func = getattr(self, 'normalize_{0}'.format(key),
+                                 lambda x: x)
+
+        return normalize_func(value)
+
+    def timestamp_serializer(self, date):
+        if not date:
+            return ''
+
+        # Any serialized timestamp should be localized, we need to
+        # convert to UTC before converting to string (DATE_FORMAT uses UTC)
+        date = date.astimezone(pytz.utc)
+
+        return date.strftime(DATE_FORMAT)
+
+    def timestamp_deserializer(self, date_str):
+        if not date_str:
+            return None
+
+        # Return timestamp localized in the local zone
+        naive_timestamp = datetime.datetime.strptime(date_str, DATE_FORMAT)
+        localized_timestamp = pytz.utc.localize(naive_timestamp)
+        return localized_timestamp.astimezone(local_zone)
+
+    def serialize_entry(self, value):
+        return self.timestamp_serializer(value)
+
+    def deserialize_entry(self, value):
+        return self.timestamp_deserializer(value)
+
+    def normalize_entry(self, value):
+        return self.datetime_normalizer(value)
+
+    def serialize_modified(self, value):
+        return self.timestamp_serializer(value)
+
+    def deserialize_modified(self, value):
+        return self.timestamp_deserializer(value)
+
+    def normalize_modified(self, value):
+        return self.datetime_normalizer(value)
+
+    def serialize_start(self, value):
+        return self.timestamp_serializer(value)
+
+    def deserialize_start(self, value):
+        return self.timestamp_deserializer(value)
+
+    def normalize_start(self, value):
+        return self.datetime_normalizer(value)
+
+    def serialize_end(self, value):
+        return self.timestamp_serializer(value)
+
+    def deserialize_end(self, value):
+        return self.timestamp_deserializer(value)
+
+    def normalize_end(self, value):
+        return self.datetime_normalizer(value)
+
+    def serialize_due(self, value):
+        return self.timestamp_serializer(value)
+
+    def deserialize_due(self, value):
+        return self.timestamp_deserializer(value)
+
+    def normalize_due(self, value):
+        return self.datetime_normalizer(value)
+
+    def serialize_scheduled(self, value):
+        return self.timestamp_serializer(value)
+
+    def deserialize_scheduled(self, value):
+        return self.timestamp_deserializer(value)
+
+    def normalize_scheduled(self, value):
+        return self.datetime_normalizer(value)
+
+    def serialize_until(self, value):
+        return self.timestamp_serializer(value)
+
+    def deserialize_until(self, value):
+        return self.timestamp_deserializer(value)
+
+    def normalize_until(self, value):
+        return self.datetime_normalizer(value)
+
+    def serialize_wait(self, value):
+        return self.timestamp_serializer(value)
+
+    def deserialize_wait(self, value):
+        return self.timestamp_deserializer(value)
+
+    def normalize_wait(self, value):
+        return self.datetime_normalizer(value)
+
+    def serialize_annotations(self, value):
+        value = value if value is not None else []
+
+        # This may seem weird, but it's correct, we want to export
+        # a list of dicts as serialized value
+        serialized_annotations = [json.loads(annotation.export_data())
+                                  for annotation in value]
+        return serialized_annotations if serialized_annotations else ''
+
+    def deserialize_annotations(self, data):
+        return [TaskAnnotation(self, d) for d in data] if data else []
+
+    def serialize_tags(self, tags):
+        return ','.join(tags) if tags else ''
+
+    def deserialize_tags(self, tags):
+        if isinstance(tags, six.string_types):
+            return tags.split(',') if tags else []
+        return tags or []
+
+    def serialize_depends(self, value):
+        # Return the list of uuids
+        value = value if value is not None else set()
+        return ','.join(task['uuid'] for task in value)
+
+    def deserialize_depends(self, raw_uuids):
+        raw_uuids = raw_uuids or []  # Convert None to empty list
+
+        # TW 2.4.4 encodes list of dependencies as a single string
+        if type(raw_uuids) is not list:
+            uuids = raw_uuids.split(',')
+        # TW 2.4.5 and later exports them as a list, no conversion needed
+        else:
+            uuids = raw_uuids
+
+        return set(self.warrior.tasks.get(uuid=uuid) for uuid in uuids if uuid)
+
+    def datetime_normalizer(self, value):
+        """
+        Normalizes date/datetime value (considered to come from user input)
+        to localized datetime value. Following conversions happen:
+
+        naive date -> localized datetime with the same date, and time=midnight
+        naive datetime -> localized datetime with the same value
+        localized datetime -> localized datetime (no conversion)
+        """
+
+        if (isinstance(value, datetime.date)
+            and not isinstance(value, datetime.datetime)):
+            # Convert to local midnight
+            value_full = datetime.datetime.combine(value, datetime.time.min)
+            localized = local_zone.localize(value_full)
+        elif isinstance(value, datetime.datetime):
+            if value.tzinfo is None:
+                # Convert to localized datetime object
+                localized = local_zone.localize(value)
+            else:
+                # If the value is already localized, there is no need to change
+                # time zone at this point. Also None is a valid value too.
+                localized = value
+        elif (isinstance(value, six.string_types)
+                and self.warrior.version >= VERSION_2_4_0):
+            # For strings, use 'task calc' to evaluate the string to datetime
+            # available since TW 2.4.0
+            args = value.split()
+            result = self.warrior.execute_command(['calc'] + args)
+            naive = datetime.datetime.strptime(result[0], DATE_FORMAT_CALC)
+            localized = local_zone.localize(naive)
+        else:
+            raise ValueError("Provided value could not be converted to "
+                             "datetime, its type is not supported: {}"
+                             .format(type(value)))
+
+        return localized
+
+    def normalize_uuid(self, value):
+        # Enforce sane UUID
+        if not isinstance(value, six.string_types) or value == '':
+            raise ValueError("UUID must be a valid non-empty string, "
+                             "not: {}".format(value))
+
+        return value
+
+
+class TaskResource(SerializingObject):
+    read_only_fields = []
+
+    def _load_data(self, data):
+        self._data = dict((key, self._deserialize(key, value))
+                          for key, value in data.items())
+        # We need to use a copy for original data, so that changes
+        # are not propagated.
+        self._original_data = copy.deepcopy(self._data)
+
+    def _update_data(self, data, update_original=False, remove_missing=False):
+        """
+        Low level update of the internal _data dict. Data which are coming as
+        updates should already be serialized. If update_original is True, the
+        original_data dict is updated as well.
+        """
+        self._data.update(dict((key, self._deserialize(key, value))
+                               for key, value in data.items()))
+
+        # In certain situations, we want to treat missing keys as removals
+        if remove_missing:
+            for key in set(self._data.keys()) - set(data.keys()):
+                self._data[key] = None
+
+        if update_original:
+            self._original_data = copy.deepcopy(self._data)
+

 
     def __getitem__(self, key):
 
     def __getitem__(self, key):

+        # This is a workaround to make TaskResource non-iterable
+        # over simple index-based iteration
+        try:
+            int(key)
+            raise StopIteration
+        except ValueError:
+            pass
+
+        if key not in self._data:
+            self._data[key] = self._deserialize(key, None)
+

         return self._data.get(key)
 
         return self._data.get(key)
 

-    def __setitem__(self, key, val):
-        self._data[key] = val
+    def __setitem__(self, key, value):
+        if key in self.read_only_fields:
+            raise RuntimeError('Field \'%s\' is read-only' % key)
+
+        # Normalize the user input before saving it
+        value = self._normalize(key, value)
+        self._data[key] = value
+
+    def __str__(self):
+        s = six.text_type(self.__unicode__())
+        if not six.PY3:
+            s = s.encode('utf-8')
+        return s
+
+    def __repr__(self):
+        return str(self)
+
+    def export_data(self):
+        """
+        Exports current data contained in the Task as JSON
+        """
+
+        # We need to remove spaces for TW-1504, use custom separators
+        data_tuples = ((key, self._serialize(key, value))
+                       for key, value in six.iteritems(self._data))
+
+        # Empty string denotes empty serialized value, we do not want
+        # to pass that to TaskWarrior.
+        data_tuples = filter(lambda t: t[1] is not '', data_tuples)
+        data = dict(data_tuples)
+        return json.dumps(data, separators=(',',':'))
+
+    @property
+    def _modified_fields(self):
+        writable_fields = set(self._data.keys()) - set(self.read_only_fields)
+        for key in writable_fields:
+            new_value = self._data.get(key)
+            old_value = self._original_data.get(key)
+
+            # Make sure not to mark data removal as modified field if the
+            # field originally had some empty value
+            if key in self._data and not new_value and not old_value:
+                continue
+
+            if new_value != old_value:
+                yield key
+
+    @property
+    def modified(self):
+        return bool(list(self._modified_fields))
+
+
+class TaskAnnotation(TaskResource):
+    read_only_fields = ['entry', 'description']
+
+    def __init__(self, task, data=None):
+        self.task = task
+        self._load_data(data or dict())
+        super(TaskAnnotation, self).__init__(task.warrior)
+
+    def remove(self):
+        self.task.remove_annotation(self)
+
+    def __unicode__(self):
+        return self['description']
+
+    def __eq__(self, other):
+        # consider 2 annotations equal if they belong to the same task, and
+        # their data dics are the same
+        return self.task == other.task and self._data == other._data
+
+    __repr__ = __unicode__
+
+
+class Task(TaskResource):
+    read_only_fields = ['id', 'entry', 'urgency', 'uuid', 'modified']
+
+    class DoesNotExist(Exception):
+        pass
+
+    class CompletedTask(Exception):
+        """
+        Raised when the operation cannot be performed on the completed task.
+        """
+        pass
+
+    class DeletedTask(Exception):
+        """
+        Raised when the operation cannot be performed on the deleted task.
+        """
+        pass
+
+    class ActiveTask(Exception):
+        """
+        Raised when the operation cannot be performed on the active task.
+        """
+        pass
+
+    class InactiveTask(Exception):
+        """
+        Raised when the operation cannot be performed on an inactive task.
+        """
+        pass
+
+    class NotSaved(Exception):
+        """
+        Raised when the operation cannot be performed on the task, because
+        it has not been saved to TaskWarrior yet.
+        """
+        pass
+
+    @classmethod
+    def from_input(cls, input_file=sys.stdin, modify=None, warrior=None):
+        """
+        Creates a Task object, directly from the stdin, by reading one line.
+        If modify=True, two lines are used, first line interpreted as the
+        original state of the Task object, and second line as its new,
+        modified value. This is consistent with the TaskWarrior's hook
+        system.
+
+        Object created by this method should not be saved, deleted
+        or refreshed, as t could create a infinite loop. For this
+        reason, TaskWarrior instance is set to None.
+
+        Input_file argument can be used to specify the input file,
+        but defaults to sys.stdin.
+        """
+
+        # Detect the hook type if not given directly
+        name = os.path.basename(sys.argv[0])
+        modify = name.startswith('on-modify') if modify is None else modify
+
+        # Create the TaskWarrior instance if none passed
+        if warrior is None:
+            hook_parent_dir = os.path.dirname(os.path.dirname(sys.argv[0]))
+            warrior = TaskWarrior(data_location=hook_parent_dir)
+
+        # TaskWarrior instance is set to None
+        task = cls(warrior)
+
+        # Load the data from the input
+        task._load_data(json.loads(input_file.readline().strip()))
+
+        # If this is a on-modify event, we are provided with additional
+        # line of input, which provides updated data
+        if modify:
+            task._update_data(json.loads(input_file.readline().strip()),
+                              remove_missing=True)
+
+        return task
+
+    def __init__(self, warrior, **kwargs):
+        super(Task, self).__init__(warrior)
+
+        # Check that user is not able to set read-only value in __init__
+        for key in kwargs.keys():
+            if key in self.read_only_fields:
+                raise RuntimeError('Field \'%s\' is read-only' % key)
+
+        # We serialize the data in kwargs so that users of the library
+        # do not have to pass different data formats via __setitem__ and
+        # __init__ methods, that would be confusing
+
+        # Rather unfortunate syntax due to python2.6 comaptiblity
+        self._data = dict((key, self._normalize(key, value))
+                          for (key, value) in six.iteritems(kwargs))
+        self._original_data = copy.deepcopy(self._data)
+
+        # Provide read only access to the original data
+        self.original = ReadOnlyDictView(self._original_data)

 
     def __unicode__(self):
 
     def __unicode__(self):

-        return self._data.get('description')
+        return self['description']
+
+    def __eq__(self, other):
+        if self['uuid'] and other['uuid']:
+            # For saved Tasks, just define equality by equality of uuids
+            return self['uuid'] == other['uuid']
+        else:
+            # If the tasks are not saved, compare the actual instances
+            return id(self) == id(other)
+
+
+    def __hash__(self):
+        if self['uuid']:
+            # For saved Tasks, just define equality by equality of uuids
+            return self['uuid'].__hash__()
+        else:
+            # If the tasks are not saved, return hash of instance id
+            return id(self).__hash__()
+
+    @property
+    def completed(self):
+        return self['status'] == six.text_type('completed')
+
+    @property
+    def deleted(self):
+        return self['status'] == six.text_type('deleted')
+
+    @property
+    def waiting(self):
+        return self['status'] == six.text_type('waiting')
+
+    @property
+    def pending(self):
+        return self['status'] == six.text_type('pending')
+
+    @property
+    def active(self):
+        return self['start'] is not None
+
+    @property
+    def saved(self):
+        return self['uuid'] is not None or self['id'] is not None
+
+    def serialize_depends(self, cur_dependencies):
+        # Check that all the tasks are saved
+        for task in (cur_dependencies or set()):
+            if not task.saved:
+                raise Task.NotSaved('Task \'%s\' needs to be saved before '
+                                    'it can be set as dependency.' % task)
+
+        return super(Task, self).serialize_depends(cur_dependencies)

 
 

-    def regenerate_uuid(self):
-        self['uuid'] = str(uuid.uuid4())
+    def format_depends(self):
+        # We need to generate added and removed dependencies list,
+        # since Taskwarrior does not accept redefining dependencies.
+
+        # This cannot be part of serialize_depends, since we need
+        # to keep a list of all depedencies in the _data dictionary,
+        # not just currently added/removed ones
+
+        old_dependencies = self._original_data.get('depends', set())
+
+        added = self['depends'] - old_dependencies
+        removed = old_dependencies - self['depends']
+
+        # Removed dependencies need to be prefixed with '-'
+        return 'depends:' + ','.join(
+                [t['uuid'] for t in added] +
+                ['-' + t['uuid'] for t in removed]
+            )
+
+    def format_description(self):
+        # Task version older than 2.4.0 ignores first word of the
+        # task description if description: prefix is used
+        if self.warrior.version < VERSION_2_4_0:
+            return self._data['description']
+        else:
+            return six.u("description:'{0}'").format(self._data['description'] or '')

 
     def delete(self):
 
     def delete(self):

-        self.warrior.delete_task(self['uuid'])
+        if not self.saved:
+            raise Task.NotSaved("Task needs to be saved before it can be deleted")
+
+        # Refresh the status, and raise exception if the task is deleted
+        self.refresh(only_fields=['status'])
+
+        if self.deleted:
+            raise Task.DeletedTask("Task was already deleted")
+
+        self.warrior.execute_command([self['uuid'], 'delete'])
+
+        # Refresh the status again, so that we have updated info stored
+        self.refresh(only_fields=['status', 'start', 'end'])
+
+    def start(self):
+        if not self.saved:
+            raise Task.NotSaved("Task needs to be saved before it can be started")
+
+        # Refresh, and raise exception if task is already completed/deleted
+        self.refresh(only_fields=['status'])
+
+        if self.completed:
+            raise Task.CompletedTask("Cannot start a completed task")
+        elif self.deleted:
+            raise Task.DeletedTask("Deleted task cannot be started")
+        elif self.active:
+            raise Task.ActiveTask("Task is already active")
+
+        self.warrior.execute_command([self['uuid'], 'start'])
+
+        # Refresh the status again, so that we have updated info stored
+        self.refresh(only_fields=['status', 'start'])
+
+    def stop(self):
+        if not self.saved:
+            raise Task.NotSaved("Task needs to be saved before it can be stopped")
+
+        # Refresh, and raise exception if task is already completed/deleted
+        self.refresh(only_fields=['status'])
+
+        if not self.active:
+            raise Task.InactiveTask("Cannot stop an inactive task")
+
+        self.warrior.execute_command([self['uuid'], 'stop'])
+
+        # Refresh the status again, so that we have updated info stored
+        self.refresh(only_fields=['status', 'start'])

 
     def done(self):
 
     def done(self):

-        self.warrior.complete_task(self['uuid'])
+        if not self.saved:
+            raise Task.NotSaved("Task needs to be saved before it can be completed")

 
 

-    def save(self, delete_first=True):
-        if self['uuid'] and delete_first:
-            self.delete()
-        if not self['uuid'] or delete_first:
-            self.regenerate_uuid()
-        self.warrior.import_tasks([self._data])
+        # Refresh, and raise exception if task is already completed/deleted
+        self.refresh(only_fields=['status'])

 
 

-    __repr__ = __unicode__
+        if self.completed:
+            raise Task.CompletedTask("Cannot complete a completed task")
+        elif self.deleted:
+            raise Task.DeletedTask("Deleted task cannot be completed")
+
+        # Older versions of TW do not stop active task at completion
+        if self.warrior.version < VERSION_2_4_0 and self.active:
+            self.stop()
+
+        self.warrior.execute_command([self['uuid'], 'done'])
+
+        # Refresh the status again, so that we have updated info stored
+        self.refresh(only_fields=['status', 'start', 'end'])
+
+    def save(self):
+        if self.saved and not self.modified:
+            return
+
+        args = [self['uuid'], 'modify'] if self.saved else ['add']
+        args.extend(self._get_modified_fields_as_args())
+        output = self.warrior.execute_command(args)
+
+        # Parse out the new ID, if the task is being added for the first time
+        if not self.saved:
+            id_lines = [l for l in output if l.startswith('Created task ')]
+
+            # Complain loudly if it seems that more tasks were created
+            # Should not happen
+            if len(id_lines) != 1 or len(id_lines[0].split(' ')) != 3:
+                raise TaskWarriorException("Unexpected output when creating "
+                                           "task: %s" % '\n'.join(id_lines))
+
+            # Circumvent the ID storage, since ID is considered read-only
+            identifier = id_lines[0].split(' ')[2].rstrip('.')
+
+            # Identifier can be either ID or UUID for completed tasks
+            try:
+                self._data['id'] = int(identifier)
+            except ValueError:
+                self._data['uuid'] = identifier
+
+        # Refreshing is very important here, as not only modification time
+        # is updated, but arbitrary attribute may have changed due hooks
+        # altering the data before saving
+        self.refresh(after_save=True)
+
+    def add_annotation(self, annotation):
+        if not self.saved:
+            raise Task.NotSaved("Task needs to be saved to add annotation")
+
+        args = [self['uuid'], 'annotate', annotation]
+        self.warrior.execute_command(args)
+        self.refresh(only_fields=['annotations'])
+
+    def remove_annotation(self, annotation):
+        if not self.saved:
+            raise Task.NotSaved("Task needs to be saved to remove annotation")
+
+        if isinstance(annotation, TaskAnnotation):
+            annotation = annotation['description']
+        args = [self['uuid'], 'denotate', annotation]
+        self.warrior.execute_command(args)
+        self.refresh(only_fields=['annotations'])
+
+    def _get_modified_fields_as_args(self):
+        args = []
+
+        def add_field(field):
+            # Add the output of format_field method to args list (defaults to
+            # field:value)
+            serialized_value = self._serialize(field, self._data[field])
+
+            # Empty values should not be enclosed in quotation marks, see
+            # TW-1510
+            if serialized_value is '':
+                escaped_serialized_value = ''
+            else:
+                escaped_serialized_value = six.u("'{0}'").format(serialized_value)
+
+            format_default = lambda: six.u("{0}:{1}").format(field,
+                                                      escaped_serialized_value)
+
+            format_func = getattr(self, 'format_{0}'.format(field),
+                                  format_default)
+
+            args.append(format_func())
+
+        # If we're modifying saved task, simply pass on all modified fields
+        if self.saved:
+            for field in self._modified_fields:
+                add_field(field)
+        # For new tasks, pass all fields that make sense
+        else:
+            for field in self._data.keys():
+                if field in self.read_only_fields:
+                    continue
+                add_field(field)
+
+        return args
+
+    def refresh(self, only_fields=None, after_save=False):
+        # Raise error when trying to refresh a task that has not been saved
+        if not self.saved:
+            raise Task.NotSaved("Task needs to be saved to be refreshed")
+
+        # We need to use ID as backup for uuid here for the refreshes
+        # of newly saved tasks. Any other place in the code is fine
+        # with using UUID only.
+        args = [self['uuid'] or self['id'], 'export']
+        output = self.warrior.execute_command(args)
+
+        def valid(output):
+            return len(output) == 1 and output[0].startswith('{')
+
+        # For older TW versions attempt to uniquely locate the task
+        # using the data we have if it has been just saved.
+        # This can happen when adding a completed task on older TW versions.
+        if (not valid(output) and self.warrior.version < VERSION_2_4_5
+                and after_save):
+
+            # Make a copy, removing ID and UUID. It's most likely invalid
+            # (ID 0) if it failed to match a unique task.
+            data = copy.deepcopy(self._data)
+            data.pop('id', None)
+            data.pop('uuid', None)
+
+            taskfilter = TaskFilter(self.warrior)
+            for key, value in data.items():
+                taskfilter.add_filter_param(key, value)
+
+            output = self.warrior.execute_command(['export', '--'] +
+                taskfilter.get_filter_params())
+
+        # If more than 1 task has been matched still, raise an exception
+        if not valid(output):
+            raise TaskWarriorException(
+                "Unique identifiers {0} with description: {1} matches "
+                "multiple tasks: {2}".format(
+                self['uuid'] or self['id'], self['description'], output)
+            )
+
+        new_data = json.loads(output[0])
+        if only_fields:
+            to_update = dict(
+                [(k, new_data.get(k)) for k in only_fields])
+            self._update_data(to_update, update_original=True)
+        else:
+            self._load_data(new_data)
+
+class TaskFilter(SerializingObject):
+    """
+    A set of parameters to filter the task list with.
+    """
+
+    def __init__(self, warrior, filter_params=None):
+        self.filter_params = filter_params or []
+        super(TaskFilter, self).__init__(warrior)
+
+    def add_filter(self, filter_str):
+        self.filter_params.append(filter_str)
+
+    def add_filter_param(self, key, value):
+        key = key.replace('__', '.')
+
+        # Replace the value with empty string, since that is the
+        # convention in TW for empty values
+        attribute_key = key.split('.')[0]
+
+        # Since this is user input, we need to normalize before we serialize
+        value = self._normalize(attribute_key, value)
+        value = self._serialize(attribute_key, value)
+
+        # If we are filtering by uuid:, do not use uuid keyword
+        # due to TW-1452 bug
+        if key == 'uuid':
+            self.filter_params.insert(0, value)
+        else:
+            # Surround value with aphostrophes unless it's a empty string
+            value = "'%s'" % value if value else ''
+
+            # We enforce equality match by using 'is' (or 'none') modifier
+            # Without using this syntax, filter fails due to TW-1479
+            # which is, however, fixed in 2.4.5
+            if self.warrior.version < VERSION_2_4_5:
+                modifier = '.is' if value else '.none'
+                key = key + modifier if '.' not in key else key
+
+            self.filter_params.append(six.u("{0}:{1}").format(key, value))
+
+    def get_filter_params(self):
+        return [f for f in self.filter_params if f]
+
+    def clone(self):
+        c = self.__class__(self.warrior)
+        c.filter_params = list(self.filter_params)
+        return c
+
+
+class TaskQuerySet(object):
+    """
+    Represents a lazy lookup for a task objects.
+    """
+
+    def __init__(self, warrior=None, filter_obj=None):
+        self.warrior = warrior
+        self._result_cache = None
+        self.filter_obj = filter_obj or TaskFilter(warrior)
+
+    def __deepcopy__(self, memo):
+        """
+        Deep copy of a QuerySet doesn't populate the cache
+        """
+        obj = self.__class__()
+        for k, v in self.__dict__.items():
+            if k in ('_iter', '_result_cache'):
+                obj.__dict__[k] = None
+            else:
+                obj.__dict__[k] = copy.deepcopy(v, memo)
+        return obj
+
+    def __repr__(self):
+        data = list(self[:REPR_OUTPUT_SIZE + 1])
+        if len(data) > REPR_OUTPUT_SIZE:
+            data[-1] = "...(remaining elements truncated)..."
+        return repr(data)
+
+    def __len__(self):
+        if self._result_cache is None:
+            self._result_cache = list(self)
+        return len(self._result_cache)
+
+    def __iter__(self):
+        if self._result_cache is None:
+            self._result_cache = self._execute()
+        return iter(self._result_cache)
+
+    def __getitem__(self, k):
+        if self._result_cache is None:
+            self._result_cache = list(self)
+        return self._result_cache.__getitem__(k)
+
+    def __bool__(self):
+        if self._result_cache is not None:
+            return bool(self._result_cache)
+        try:
+            next(iter(self))
+        except StopIteration:
+            return False
+        return True
+
+    def __nonzero__(self):
+        return type(self).__bool__(self)
+
+    def _clone(self, klass=None, **kwargs):
+        if klass is None:
+            klass = self.__class__
+        filter_obj = self.filter_obj.clone()
+        c = klass(warrior=self.warrior, filter_obj=filter_obj)
+        c.__dict__.update(kwargs)
+        return c
+
+    def _execute(self):
+        """
+        Fetch the tasks which match the current filters.
+        """
+        return self.warrior.filter_tasks(self.filter_obj)
+
+    def all(self):
+        """
+        Returns a new TaskQuerySet that is a copy of the current one.
+        """
+        return self._clone()
+
+    def pending(self):
+        return self.filter(status=PENDING)
+
+    def completed(self):
+        return self.filter(status=COMPLETED)
+
+    def filter(self, *args, **kwargs):
+        """
+        Returns a new TaskQuerySet with the given filters added.
+        """
+        clone = self._clone()
+        for f in args:
+            clone.filter_obj.add_filter(f)
+        for key, value in kwargs.items():
+            clone.filter_obj.add_filter_param(key, value)
+        return clone
+
+    def get(self, **kwargs):
+        """
+        Performs the query and returns a single object matching the given
+        keyword arguments.
+        """
+        clone = self.filter(**kwargs)
+        num = len(clone)
+        if num == 1:
+            return clone._result_cache[0]
+        if not num:
+            raise Task.DoesNotExist(
+                'Task matching query does not exist. '
+                'Lookup parameters were {0}'.format(kwargs))
+        raise ValueError(
+            'get() returned more than one Task -- it returned {0}! '
+            'Lookup parameters were {1}'.format(num, kwargs))

 
 
 class TaskWarrior(object):
 
 
 class TaskWarrior(object):

+    def __init__(self, data_location=None, create=True, taskrc_location='~/.taskrc'):
+        self.taskrc_location = os.path.expanduser(taskrc_location)
+
+        # If taskrc does not exist, pass / to use defaults and avoid creating
+        # dummy .taskrc file by TaskWarrior
+        if not os.path.exists(self.taskrc_location):
+            self.taskrc_location = '/'

 
 

-    def __init__(self, data_location='~/.task', create=True):
-        if not os.path.exists(data_location):
-            os.makedirs(data_location)
+        self.version = self._get_version()

         self.config = {
         self.config = {

-            'data.location': os.path.expanduser(data_location),
+            'confirmation': 'no',
+            'dependency.confirmation': 'no',  # See TW-1483 or taskrc man page
+            'recurrence.confirmation': 'no',  # Necessary for modifying R tasks
+
+            # Defaults to on since 2.4.5, we expect off during parsing
+            'json.array': 'off',
+
+            # 2.4.3 onwards supports 0 as infite bulk, otherwise set just
+            # arbitrary big number which is likely to be large enough
+            'bulk': 0 if self.version >= VERSION_2_4_3 else 100000,

         }
 
         }
 

-    def _generate_command(self, command):
-        args = ['task', 'rc:/']
-        for item in self.config.items():
-            args.append('rc.{0}={1}'.format(*item))
-        args.append(command)
-        return ' '.join(args)
-
-    def _execute(self, command):
-        p = subprocess.Popen(self._generate_command(command), shell=True,
-                             stdout=subprocess.PIPE, stderr=subprocess.PIPE)
-        stdout, stderr = p.communicate()
-        if p.returncode:
-            raise TaskWarriorException(stderr.strip())
-        return stdout.strip().split('\n')
-
-    def get_tasks(self, project=None, status=PENDING):
-        command = 'export status:{0}'.format(status)
-        if project is not None:
-            command += ' project:{0}'.format(project)
-        tasks = []
-        for line in self._execute(command):
-            if line:
-                tasks.append(Task(self, json.loads(line.strip(','))))
-        return tasks
+        # Set data.location override if passed via kwarg
+        if data_location is not None:
+            data_location = os.path.expanduser(data_location)
+            if create and not os.path.exists(data_location):
+                os.makedirs(data_location)
+            self.config['data.location'] = data_location
+
+        self.tasks = TaskQuerySet(self)
+
+    def _get_command_args(self, args, config_override=None):
+        command_args = ['task', 'rc:{0}'.format(self.taskrc_location)]
+        config = self.config.copy()
+        config.update(config_override or dict())
+        for item in config.items():
+            command_args.append('rc.{0}={1}'.format(*item))
+        command_args.extend(map(six.text_type, args))
+        return command_args
+
+    def _get_version(self):
+        p = subprocess.Popen(
+                ['task', '--version'],
+                stdout=subprocess.PIPE,
+                stderr=subprocess.PIPE)
+        stdout, stderr = [x.decode('utf-8') for x in p.communicate()]
+        return stdout.strip('\n')
+
+    def get_config(self):
+        raw_output = self.execute_command(
+                ['show'],
+                config_override={'verbose': 'nothing'}
+            )
+
+        config = dict()
+        config_regex = re.compile(r'^(?P<key>[^\s]+)\s+(?P<value>[^\s].+$)')

 
 

-    def get_task(self, task_id):
-        command = '{0} export'.format(task_id)
-        return Task(self, json.loads(self._execute(command)[0]))
+        for line in raw_output:
+            match = config_regex.match(line)
+            if match:
+                config[match.group('key')] = match.group('value').strip()

 
 

-    def add_task(self, description, project=None):
-        args = ['add', description]
-        if project is not None:
-            args.append('project:{0}'.format(project))
-        self._execute(' '.join(args))
+        return config

 
 

-    def delete_task(self, task_id):
-        self._execute('{0} rc.confirmation:no delete'.format(task_id))
+    def execute_command(self, args, config_override=None, allow_failure=True,
+                        return_all=False):
+        command_args = self._get_command_args(
+            args, config_override=config_override)
+        logger.debug(' '.join(command_args))
+        p = subprocess.Popen(command_args, stdout=subprocess.PIPE,
+                             stderr=subprocess.PIPE)
+        stdout, stderr = [x.decode('utf-8') for x in p.communicate()]
+        if p.returncode and allow_failure:
+            if stderr.strip():
+                error_msg = stderr.strip()
+            else:
+                error_msg = stdout.strip()
+            raise TaskWarriorException(error_msg)
+
+        # Return all whole triplet only if explicitly asked for
+        if not return_all:
+            return stdout.rstrip().split('\n')
+        else:
+            return (stdout.rstrip().split('\n'),
+                    stderr.rstrip().split('\n'),
+                    p.returncode)
+
+    def enforce_recurrence(self):
+        # Run arbitrary report command which will trigger generation
+        # of recurrent tasks.
+
+        # Only necessary for TW up to 2.4.1, fixed in 2.4.2.
+        if self.version < VERSION_2_4_2:
+            self.execute_command(['next'], allow_failure=False)
+
+    def filter_tasks(self, filter_obj):
+        self.enforce_recurrence()
+        args = ['export', '--'] + filter_obj.get_filter_params()
+        tasks = []
+        for line in self.execute_command(args):
+            if line:
+                data = line.strip(',')
+                try:
+                    filtered_task = Task(self)
+                    filtered_task._load_data(json.loads(data))
+                    tasks.append(filtered_task)
+                except ValueError:
+                    raise TaskWarriorException('Invalid JSON: %s' % data)
+        return tasks

 
 

-    def complete_task(self, task_id):
-        self._execute('{0} done'.format(task_id))
+    def merge_with(self, path, push=False):
+        path = path.rstrip('/') + '/'
+        self.execute_command(['merge', path], config_override={
+            'merge.autopush': 'yes' if push else 'no',
+        })

 
 

-    def import_tasks(self, tasks):
-        fd, path = tempfile.mkstemp()
-        with open(path, 'w') as f:
-            f.write(json.dumps(tasks))
-        self._execute('import {0}'.format(path))
+    def undo(self):
+        self.execute_command(['undo'])