import abc
import copy
import datetime
import json
import logging
import os
import re
import subprocess
from functools import lru_cache

from .task import Task, TaskQuerySet, ReadOnlyDictView
from .filters import TaskWarriorFilter

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

logger = logging.getLogger(__name__)


class Backend(object):

    @abc.abstractproperty
    def filter_class(self):
        """Returns the TaskFilter class used by this backend"""
        pass

    @abc.abstractmethod
    def filter_tasks(self, filter_obj):
        """Returns a list of Task objects matching the given filter"""
        pass

    @abc.abstractmethod
    def save_task(self, task):
        pass

    @abc.abstractmethod
    def delete_task(self, task):
        pass

    @abc.abstractmethod
    def start_task(self, task):
        pass

    @abc.abstractmethod
    def stop_task(self, task):
        pass

    @abc.abstractmethod
    def complete_task(self, task):
        pass

    @abc.abstractmethod
    def refresh_task(self, task, after_save=False):
        """
        Refreshes the given task. Returns new data dict with serialized
        attributes.
        """
        pass

    @abc.abstractmethod
    def annotate_task(self, task, annotation):
        pass

    @abc.abstractmethod
    def denotate_task(self, task, annotation):
        pass

    @abc.abstractmethod
    def sync(self):
        """Syncs the backend database with the taskd server"""
        pass

    def convert_datetime_string(self, value):
        """
        Converts TW syntax datetime string to a localized datetime
        object. This method is not mandatory.
        """
        raise NotImplementedError


class TaskWarriorException(Exception):
    pass


class TaskWarrior(Backend):

    VERSION_2_4_0 = '2.4.0'
    VERSION_2_4_1 = '2.4.1'
    VERSION_2_4_2 = '2.4.2'
    VERSION_2_4_3 = '2.4.3'
    VERSION_2_4_4 = '2.4.4'
    VERSION_2_4_5 = '2.4.5'

    def __init__(self, data_location=None, create=True,
                 taskrc_location=None, task_command='task',
                 version_override=None):
        self.taskrc_location = None
        if taskrc_location:
            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 = '/'

        self.task_command = task_command

        self._config = None
        self.version = version_override or self._get_version()
        self.overrides = {
            '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 >= self.VERSION_2_4_3 else 100000,
        }

        # 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.overrides['data.location'] = data_location

        self.tasks = TaskQuerySet(self)

    def _get_task_command(self):
        return self.task_command.split()

    def _get_command_args(self, args, config_override=None):
        command_args = self._get_task_command()
        overrides = self.overrides.copy()
        overrides.update(config_override or dict())
        for item in overrides.items():
            command_args.append('rc.{0}={1}'.format(*item))
        command_args.extend([
            x.decode('utf-8') if isinstance(x, bytes)
            else str(x) for x in args
        ])
        return command_args

    def _get_version(self):
        p = subprocess.Popen(
            self._get_task_command() + ['--version'],
            stdout=subprocess.PIPE,
            stderr=subprocess.PIPE)
        stdout, stderr = [x.decode('utf-8') for x in p.communicate()]
        return stdout.strip('\n')

    def _get_modified_task_fields_as_args(self, task):
        args = []

        def add_field(field):
            # Add the output of format_field method to args list (defaults to
            # field:value)
            serialized_value = task._serialize(field, task._data[field])

            # Empty values should not be enclosed in quotation marks, see
            # TW-1510
            if serialized_value == '':
                escaped_serialized_value = ''
            else:
                escaped_serialized_value = "'{0}'".format(
                    serialized_value)

            format_default = lambda task: "{0}:{1}".format(
                field, escaped_serialized_value)

            format_func = getattr(self, 'format_{0}'.format(field),
                                  format_default)

            args.append(format_func(task))

        # If we're modifying saved task, simply pass on all modified fields
        if task.saved:
            for field in task._modified_fields:
                add_field(field)

        # For new tasks, pass all fields that make sense
        else:
            for field in task._data.keys():
                # We cannot set stuff that's read only (ID, UUID, ..)
                if field in task.read_only_fields:
                    continue
                # We do not want to do field deletion for new tasks
                if task._data[field] is None:
                    continue
                # Otherwise we're fine
                add_field(field)

        return args

    def format_depends(self, task):
        # 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 = task._original_data.get('depends', set())

        added = task['depends'] - old_dependencies
        removed = old_dependencies - task['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):
        return "description:'{0}'".format(
            task._data['description'] or '',
        )

    def convert_datetime_string(self, value):
        # For strings, use 'calc' to evaluate the string to datetime
        # available since TW 2.4.0
        args = value.split()
        result = self.execute_command(['calc'] + args)
        naive = datetime.datetime.strptime(result[0], DATE_FORMAT_CALC)
        localized = naive.astimezone()
        return localized

    @property
    def filter_class(self):
        return TaskWarriorFilter

    # Public interface

    @property
    def config(self):
        # First, check if memoized information is available
        if self._config:
            return self._config

        # If not, fetch the config using the 'show' command
        raw_output = self.execute_command(
            ['show'],
            config_override={'verbose': 'nothing'}
        )

        config = dict()
        config_regex = re.compile(r'^(?P<key>[^\s]+)\s+(?P<value>[^\s].*$)')

        for line in raw_output:
            match = config_regex.match(line)
            if match:
                config[match.group('key')] = match.group('value').strip()

        # Memoize the config dict
        self._config = ReadOnlyDictView(config)

        return self._config

    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(u' '.join(command_args))

        env = os.environ.copy()
        if self.taskrc_location:
            env['TASKRC'] = self.taskrc_location
        p = subprocess.Popen(command_args, stdout=subprocess.PIPE,
                             stderr=subprocess.PIPE, env=env)
        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()
            error_msg += u'\nCommand used: ' + u' '.join(command_args)
            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 < self.VERSION_2_4_2:
            self.execute_command(['next'], allow_failure=False)

    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'])

    @lru_cache(maxsize=128)
    def get_task(self, uuid):
        return self.tasks.get(uuid=uuid)

    # Backend interface implementation

    def filter_tasks(self, filter_obj):
        self.enforce_recurrence()
        args = filter_obj.get_filter_params() + ["export"]
        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 save_task(self, task):
        """Save a task into TaskWarrior database using add/modify call"""

        args = [task['uuid'], 'modify'] if task.saved else ['add']
        args.extend(self._get_modified_task_fields_as_args(task))
        output = self.execute_command(
            args,
            config_override={'verbose': 'new-uuid'}
        )

        # Parse out the new ID, if the task is being added for the first time
        if not task.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.
            # Expected output: Created task bd23f69a-a078-48a4-ac11-afba0643eca9.
            #                  Created task bd23f69a-a078-48a4-ac11-afba0643eca9 (recurrence template).
            if len(id_lines) != 1 or len(id_lines[0].split(' ')) not in (3, 5):
                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 is UUID, because we used new-uuid verbosity override
            task._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
        task.refresh(after_save=True)

    def delete_task(self, task):
        self.execute_command([task['uuid'], 'delete'])

    def start_task(self, task):
        self.execute_command([task['uuid'], 'start'])

    def stop_task(self, task):
        self.execute_command([task['uuid'], 'stop'])

    def complete_task(self, task):
        self.execute_command([task['uuid'], 'done'])

    def annotate_task(self, task, annotation):
        args = [task['uuid'], 'annotate', annotation]
        self.execute_command(args)

    def denotate_task(self, task, annotation):
        args = [task['uuid'], 'denotate', annotation]
        self.execute_command(args)

    def refresh_task(self, task, after_save=False):
        # 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 = [task['uuid'] or task['id'], 'export']
        output = self.execute_command(
            args,
            # Supress GC, which can change ID numbers (undesirable for refresh)
            config_override={'gc': '0'}
        )

        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.version < self.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(task._data)
            data.pop('id', None)
            data.pop('uuid', None)

            taskfilter = self.filter_class(self)
            for key, value in data.items():
                taskfilter.add_filter_param(key, value)

            output = self.execute_command(taskfilter.get_filter_params() + ['export'])

        # 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(
                    task['uuid'] or task['id'], task['description'], output)
            )

        return json.loads(output[0])

    def sync(self):
        self.execute_command(['sync'])