Task: Move TW-specific refresh behaviour to TW backend

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

diff --git a/tasklib/task.py b/tasklib/task.py
index 1fa3faa675a5022057f70261ddba8f5c1e87fc4b..5a865293302ff15eb84b1ddf52b48fc8ff56b95a 100644 (file)
--- a/tasklib/task.py
+++ b/tasklib/task.py
@@ -4,34 +4,312 @@ import datetime
 import json
 import logging
 import os
 import json
 import logging
 import os

+import pytz

 import six
 import six

-import subprocess
+import sys
+import tzlocal
+
+from backends import TaskWarrior, TaskWarriorException

 
 DATE_FORMAT = '%Y%m%dT%H%M%SZ'
 
 DATE_FORMAT = '%Y%m%dT%H%M%SZ'

+DATE_FORMAT_CALC = '%Y-%m-%dT%H:%M:%S'

 REPR_OUTPUT_SIZE = 10
 PENDING = 'pending'
 COMPLETED = 'completed'
 
 REPR_OUTPUT_SIZE = 10
 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')
-

 logger = logging.getLogger(__name__)
 logger = logging.getLogger(__name__)

+local_zone = tzlocal.get_localzone()
+
+
+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
+
+    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
+
+    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)

 
 

-class TaskWarriorException(Exception):
-    pass
+    def serialize_end(self, value):
+        return self.timestamp_serializer(value)

 
 

+    def deserialize_end(self, value):
+        return self.timestamp_deserializer(value)

 
 

-class TaskResource(object):
+    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):
     read_only_fields = []
 
     def _load_data(self, data):

-        self._data = 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
         # We need to use a copy for original data, so that changes

-        # are not propagated
-        self._original_data = data.copy()
+        # 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):
         # This is a workaround to make TaskResource non-iterable
 
     def __getitem__(self, key):
         # This is a workaround to make TaskResource non-iterable


@@ -42,16 +320,18 @@ class TaskResource(object):
         except ValueError:
             pass
 
         except ValueError:
             pass
 

-        hydrate_func = getattr(self, 'deserialize_{0}'.format(key),
-                               lambda x: x)
-        return hydrate_func(self._data.get(key))
+        if key not in self._data:
+            self._data[key] = self._deserialize(key, None)
+
+        return self._data.get(key)

 
     def __setitem__(self, key, value):
         if key in self.read_only_fields:
             raise RuntimeError('Field \'%s\' is read-only' % key)
 
     def __setitem__(self, key, value):
         if key in self.read_only_fields:
             raise RuntimeError('Field \'%s\' is read-only' % key)

-        dehydrate_func = getattr(self, 'serialize_{0}'.format(key),
-                                 lambda x: x)
-        self._data[key] = dehydrate_func(value)
+
+        # 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__())
 
     def __str__(self):
         s = six.text_type(self.__unicode__())


@@ -62,19 +342,48 @@ class TaskResource(object):
     def __repr__(self):
         return str(self)
 
     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']
 
 
 class TaskAnnotation(TaskResource):
     read_only_fields = ['entry', 'description']
 

-    def __init__(self, task, data={}):
+    def __init__(self, task, data=None):

         self.task = task
         self.task = task

-        self._load_data(data)
-
-    def deserialize_entry(self, data):
-        return datetime.datetime.strptime(data, DATE_FORMAT) if data else None
-
-    def serialize_entry(self, date):
-        return date.strftime(DATE_FORMAT) if date else ''
+        self._load_data(data or dict())
+        super(TaskAnnotation, self).__init__(task.warrior)

 
     def remove(self):
         self.task.remove_annotation(self)
 
     def remove(self):
         self.task.remove_annotation(self)


@@ -82,11 +391,16 @@ class TaskAnnotation(TaskResource):
     def __unicode__(self):
         return self['description']
 
     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):
     __repr__ = __unicode__
 
 
 class Task(TaskResource):

-    read_only_fields = ['id', 'entry', 'urgency', 'uuid']
+    read_only_fields = ['id', 'entry', 'urgency', 'uuid', 'modified']

 
     class DoesNotExist(Exception):
         pass
 
     class DoesNotExist(Exception):
         pass


@@ -103,6 +417,18 @@ class Task(TaskResource):
         """
         pass
 
         """
         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
     class NotSaved(Exception):
         """
         Raised when the operation cannot be performed on the task, because


@@ -110,13 +436,65 @@ class Task(TaskResource):
         """
         pass
 
         """
         pass
 

-    def __init__(self, warrior, data={}, **kwargs):
-        self.warrior = warrior
+    @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

 
 

-        # We keep data for backwards compatibility
-        kwargs.update(data)
+    def __init__(self, warrior, **kwargs):
+        super(Task, self).__init__(warrior)

 
 

-        self._load_data(kwargs)
+        # 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):
         return self['description']
 
     def __unicode__(self):
         return self['description']


@@ -138,12 +516,6 @@ class Task(TaskResource):
             # If the tasks are not saved, return hash of instance id
             return id(self).__hash__()
 
             # If the tasks are not saved, return hash of instance id
             return id(self).__hash__()
 

-    @property
-    def _modified_fields(self):
-        for key in self._data.keys():
-            if self._data.get(key) != self._original_data.get(key):
-                yield key
-

     @property
     def completed(self):
         return self['status'] == six.text_type('completed')
     @property
     def completed(self):
         return self['status'] == six.text_type('completed')


@@ -160,32 +532,22 @@ class Task(TaskResource):
     def pending(self):
         return self['status'] == six.text_type('pending')
 
     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
 
     @property
     def saved(self):
         return self['uuid'] is not None or self['id'] is not None
 

-    def serialize_due(self, date):
-        return date.strftime(DATE_FORMAT)
-
-    def deserialize_due(self, date_str):
-        if not date_str:
-            return None
-        return datetime.datetime.strptime(date_str, DATE_FORMAT)
-

     def serialize_depends(self, cur_dependencies):
         # Check that all the tasks are saved
     def serialize_depends(self, cur_dependencies):
         # Check that all the tasks are saved

-        for task in cur_dependencies:
+        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)
 
             if not task.saved:
                 raise Task.NotSaved('Task \'%s\' needs to be saved before '
                                     'it can be set as dependency.' % task)
 

-        # Return the list of uuids
-        return ','.join(task['uuid'] for task in cur_dependencies)
-
-    def deserialize_depends(self, raw_uuids):
-        raw_uuids = raw_uuids or ''  # Convert None to empty string
-        uuids = raw_uuids.split(',')
-        return set(self.warrior.tasks.get(uuid=uuid) for uuid in uuids if uuid)
+        return super(Task, self).serialize_depends(cur_dependencies)

 
     def format_depends(self):
         # We need to generate added and removed dependencies list,
 
     def format_depends(self):
         # We need to generate added and removed dependencies list,


@@ -195,28 +557,24 @@ class Task(TaskResource):
         # to keep a list of all depedencies in the _data dictionary,
         # not just currently added/removed ones
 
         # to keep a list of all depedencies in the _data dictionary,
         # not just currently added/removed ones
 

-        old_dependencies_raw = self._original_data.get('depends','')
-        old_dependencies = self.deserialize_depends(old_dependencies_raw)
+        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 '-'
 
         added = self['depends'] - old_dependencies
         removed = old_dependencies - self['depends']
 
         # Removed dependencies need to be prefixed with '-'

-        return ','.join(
+        return 'depends:' + ','.join(

                 [t['uuid'] for t in added] +
                 ['-' + t['uuid'] for t in removed]
             )
 
                 [t['uuid'] for t in added] +
                 ['-' + t['uuid'] for t in removed]
             )
 

-    def deserialize_annotations(self, data):
-        return [TaskAnnotation(self, d) for d in data] if data else []
-
-    def deserialize_tags(self, tags):
-        if isinstance(tags, basestring):
-            return tags.split(',') if tags else []
-        return tags
-
-    def serialize_tags(self, tags):
-        return ','.join(tags) if tags else ''
+    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):
         if not self.saved:
 
     def delete(self):
         if not self.saved:


@@ -228,13 +586,44 @@ class Task(TaskResource):
         if self.deleted:
             raise Task.DeletedTask("Task was already deleted")
 
         if self.deleted:
             raise Task.DeletedTask("Task was already deleted")
 

-        self.warrior.execute_command([self['uuid'], 'delete'], config_override={
-            'confirmation': 'no',
-        })
+        self.backend.delete_task(self)
+
+        # 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.backend.start_task(self)

 
         # Refresh the status again, so that we have updated info stored
 
         # 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'])
 
         self.refresh(only_fields=['status'])
 

+        if not self.active:
+            raise Task.InactiveTask("Cannot stop an inactive task")
+
+        self.backend.stop_task(self)
+
+        # Refresh the status again, so that we have updated info stored
+        self.refresh(only_fields=['status', 'start'])

 
     def done(self):
         if not self.saved:
 
     def done(self):
         if not self.saved:


@@ -248,30 +637,17 @@ class Task(TaskResource):
         elif self.deleted:
             raise Task.DeletedTask("Deleted task cannot be completed")
 
         elif self.deleted:
             raise Task.DeletedTask("Deleted task cannot be completed")
 

-        self.warrior.execute_command([self['uuid'], 'done'])
+        self.backend.complete_task(self)

 
         # Refresh the status again, so that we have updated info stored
 
         # Refresh the status again, so that we have updated info stored

-        self.refresh(only_fields=['status'])
+        self.refresh(only_fields=['status', 'start', 'end'])

 
     def save(self):
 
     def save(self):

-        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
-            self._data['id'] = int(id_lines[0].split(' ')[2].rstrip('.'))
+        if self.saved and not self.modified:
+            return

 
 

-        self.refresh()
+        # All the actual work is done by the backend
+        self.backend.save_task(self)

 
     def add_annotation(self, annotation):
         if not self.saved:
 
     def add_annotation(self, annotation):
         if not self.saved:


@@ -283,7 +659,7 @@ class Task(TaskResource):
 
     def remove_annotation(self, annotation):
         if not self.saved:
 
     def remove_annotation(self, annotation):
         if not self.saved:

-            raise Task.NotSaved("Task needs to be saved to add annotation")
+            raise Task.NotSaved("Task needs to be saved to remove annotation")

 
         if isinstance(annotation, TaskAnnotation):
             annotation = annotation['description']
 
         if isinstance(annotation, TaskAnnotation):
             annotation = annotation['description']


@@ -295,14 +671,24 @@ class Task(TaskResource):
         args = []
 
         def add_field(field):
         args = []
 
         def add_field(field):

-            # 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 and field == 'description':
-                args.append(self._data[field])
-            elif field == 'depends':
-                args.append('{0}:{1}'.format(field, self.format_depends()))
+            # 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:
             else:

-                args.append('{0}:{1}'.format(field, self._data[field]))
+                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:
 
         # If we're modifying saved task, simply pass on all modified fields
         if self.saved:


@@ -317,36 +703,28 @@ class Task(TaskResource):
 
         return args
 
 
         return args
 

-    def refresh(self, only_fields=[]):
+    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")
 
         # 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']
-        new_data = json.loads(self.warrior.execute_command(args)[0])
+        new_data = self.backend.refresh_task(self, after_save=after_save)
+

         if only_fields:
             to_update = dict(
                 [(k, new_data.get(k)) for k in only_fields])
         if only_fields:
             to_update = dict(
                 [(k, new_data.get(k)) for k in only_fields])

-            self._data.update(to_update)
-            self._original_data.update(to_update)
+            self._update_data(to_update, update_original=True)

         else:
         else:

-            self._data = new_data
-            # We need to create a clone for original_data though
-            # Shallow copy is alright, since data dict uses only
-            # primitive data types
-            self._original_data = new_data.copy()
-
+            self._load_data(new_data)

 
 

-class TaskFilter(object):
+class TaskFilter(SerializingObject):

     """
     A set of parameters to filter the task list with.
     """
 
     """
     A set of parameters to filter the task list with.
     """
 

-    def __init__(self, filter_params=[]):
-        self.filter_params = filter_params
+    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(self, filter_str):
         self.filter_params.append(filter_str)


@@ -356,20 +734,34 @@ class TaskFilter(object):
 
         # Replace the value with empty string, since that is the
         # convention in TW for empty values
 
         # Replace the value with empty string, since that is the
         # convention in TW for empty values

-        value = value if value is not None else ''
+        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:
 
         # 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:

-            self.filter_params.append('{0}:{1}'.format(key, value))
+            # 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):
 
     def get_filter_params(self):
         return [f for f in self.filter_params if f]
 
     def clone(self):

-        c = self.__class__()
+        c = self.__class__(self.warrior)

         c.filter_params = list(self.filter_params)
         return c
 
         c.filter_params = list(self.filter_params)
         return c
 


@@ -382,7 +774,7 @@ class TaskQuerySet(object):
     def __init__(self, warrior=None, filter_obj=None):
         self.warrior = warrior
         self._result_cache = None
     def __init__(self, warrior=None, filter_obj=None):
         self.warrior = warrior
         self._result_cache = None

-        self.filter_obj = filter_obj or TaskFilter()
+        self.filter_obj = filter_obj or TaskFilter(warrior)

 
     def __deepcopy__(self, memo):
         """
 
     def __deepcopy__(self, memo):
         """


@@ -482,70 +874,3 @@ class TaskQuerySet(object):
         raise ValueError(
             'get() returned more than one Task -- it returned {0}! '
             'Lookup parameters were {1}'.format(num, kwargs))
         raise ValueError(
             'get() returned more than one Task -- it returned {0}! '
             'Lookup parameters were {1}'.format(num, kwargs))

-
-
-class TaskWarrior(object):
-    def __init__(self, data_location='~/.task', create=True):
-        data_location = os.path.expanduser(data_location)
-        if create and not os.path.exists(data_location):
-            os.makedirs(data_location)
-        self.config = {
-            'data.location': os.path.expanduser(data_location),
-        }
-        self.tasks = TaskQuerySet(self)
-        self.version = self._get_version()
-
-    def _get_command_args(self, args, config_override={}):
-        command_args = ['task', 'rc:/']
-        config = self.config.copy()
-        config.update(config_override)
-        for item in config.items():
-            command_args.append('rc.{0}={1}'.format(*item))
-        command_args.extend(map(str, 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 execute_command(self, args, config_override={}):
-        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:
-            if stderr.strip():
-                error_msg = stderr.strip().splitlines()[-1]
-            else:
-                error_msg = stdout.strip()
-            raise TaskWarriorException(error_msg)
-        return stdout.strip().split('\n')
-
-    def filter_tasks(self, filter_obj):
-        args = ['export', '--'] + filter_obj.get_filter_params()
-        tasks = []
-        for line in self.execute_command(args):
-            if line:
-                data = line.strip(',')
-                try:
-                    tasks.append(Task(self, json.loads(data)))
-                except ValueError:
-                    raise TaskWarriorException('Invalid JSON: %s' % data)
-        return tasks
-
-    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 undo(self):
-        self.execute_command(['undo'], config_override={
-            'confirmation': 'no',
-        })