import logging
import os
import socket
import sqlite3
from datetime import date, datetime, timedelta
from os.path import normpath, split
from uuid import uuid4

import icalendar
import pytz
from atomicwrites import AtomicWriter
from dateutil.rrule import rrulestr
from dateutil.tz import tzlocal

from todoman import exceptions

logger = logging.getLogger(name=__name__)

# Initialize this only once
# We were doing this all over the place (even if unused!), so at least only do
# it once.
LOCAL_TIMEZONE = tzlocal()


class cached_property:  # noqa
    '''A read-only @property that is only evaluated once. Only usable on class
    instances' methods.
    '''

    def __init__(self, fget, doc=None):
        self.__name__ = fget.__name__
        self.__module__ = fget.__module__
        self.__doc__ = doc or fget.__doc__
        self.fget = fget

    def __get__(self, obj, cls):
        if obj is None:
            return self
        obj.__dict__[self.__name__] = result = self.fget(obj)
        return result


class Todo:
    """
    Represents a task/todo, and wrapps around icalendar.Todo.

    All text attributes are always treated as text, and "" will be returned if
    they are not defined.
    Date attributes are treated as datetime objects, and None will be returned
    if they are not defined.
    All datetime objects have tzinfo, either the one defined in the file, or
    the local system's one.
    """

    def __init__(self, filename=None, mtime=None, new=False, list=None):
        """
        Creates a new todo using `todo` as a source.

        :param str filename: The name of the file for this todo. Defaults to
        the <uid>.ics
        :param mtime int: The last modified time for the file backing this
        Todo.
        :param bool new: Indicate that a new Todo is being created and should
        be populated with default values.
        :param List list: The list to which this Todo belongs.
        """
        self.list = list
        now = datetime.now(LOCAL_TIMEZONE)
        self.uid = '{}@{}'.format(uuid4().hex, socket.gethostname())
        self.list = list

        if new:
            self.created_at = now
        else:
            self.created_at = None

        # Default values for supported fields
        self.categories = []
        self.completed_at = None
        self.description = ''
        self.dtstamp = now
        self.due = None
        self.id = None
        self.last_modified = None
        self.location = ''
        self.percent_complete = 0
        self.priority = 0
        self.rrule = ''
        self.sequence = 0
        self.start = None
        self.status = 'NEEDS-ACTION'
        self.summary = ''

        self.filename = filename or "{}.ics".format(self.uid)
        self.related = []

        if os.path.basename(self.filename) != self.filename:
            raise ValueError(
                'Must not be an absolute path: {}'.format(self.filename)
            )
        self.mtime = mtime or datetime.now()

    def clone(self):
        """
        Returns a clone of this todo

        Returns a copy of this todo, which is almost identical, except that is
        has a different UUID and filename.
        """
        todo = Todo(new=True, list=self.list)

        fields = (
            Todo.STRING_FIELDS + Todo.INT_FIELDS + Todo.LIST_FIELDS +
            Todo.DATETIME_FIELDS
        )
        fields.remove('uid')

        for field in fields:
            setattr(todo, field, getattr(self, field))

        return todo

    STRING_FIELDS = [
        'description',
        'location',
        'status',
        'summary',
        'uid',
        'rrule',
    ]
    INT_FIELDS = [
        'percent_complete',
        'priority',
        'sequence',
    ]
    LIST_FIELDS = [
        'categories',
    ]
    DATETIME_FIELDS = [
        'completed_at',
        'created_at',
        'dtstamp',
        'start',
        'due',
        'last_modified',
    ]
    RRULE_FIELDS = [
        'rrule',
    ]
    ALL_SUPPORTED_FIELDS = (
        DATETIME_FIELDS + INT_FIELDS + LIST_FIELDS + RRULE_FIELDS +
        STRING_FIELDS
    )

    VALID_STATUSES = (
        "CANCELLED",
        "COMPLETED",
        "IN-PROCESS",
        "NEEDS-ACTION",
    )

    def __setattr__(self, name, value):
        """Check type and avoid setting fields to None"""
        """when that is not a valid attribue."""

        v = value

        if name in Todo.RRULE_FIELDS:
            if value is None:
                v = ''
            else:
                assert isinstance(value, str), (
                       "Got {0} for {1} where str was expected"
                       .format(type(value), name))

        if name in Todo.STRING_FIELDS:
            if value is None:
                v = ''
            else:
                assert isinstance(value, str), (
                       "Got {0} for {1} where str was expected"
                       .format(type(value), name))

        if name in Todo.INT_FIELDS:
            if value is None:
                v = 0
            else:
                assert isinstance(value, int), (
                       "Got {0} for {1} where int was expected"
                       .format(type(value), name))

        if name in Todo.LIST_FIELDS:
            if value is None:
                v = []
            else:
                assert isinstance(value, list), (
                       "Got {0} for {1} where list was expected"
                       .format(type(value), name))

        return object.__setattr__(self, name, v)

    @property
    def is_completed(self):
        return (
            bool(self.completed_at)
            or self.status in ('CANCELLED', 'COMPLETED')
        )

    @property
    def is_recurring(self):
        return bool(self.rrule)

    def _apply_recurrence_to_dt(self, dt):
        if not dt:
            return None

        recurrence = rrulestr(self.rrule, dtstart=dt)

        return recurrence.after(dt)

    def _create_next_instance(self):
        copy = self.clone()
        copy.due = self._apply_recurrence_to_dt(self.due)
        copy.start = self._apply_recurrence_to_dt(self.start)

        assert copy.uid != self.uid

        # TODO: Push copy's alarms.
        return copy

    def complete(self):
        """
        Immediately completes this todo

        Immediately marks this todo as completed, sets the percentage to 100%
        and the completed_at datetime to now.

        If this todo belongs to a series, newly created todo are added to the
        ``related`` list.
        """
        if self.is_recurring:
            related = self._create_next_instance()
            if related:
                self.rrule = None
                self.related.append(related)

        self.completed_at = datetime.now(tz=LOCAL_TIMEZONE)
        self.percent_complete = 100
        self.status = 'COMPLETED'

    @cached_property
    def path(self):
        return os.path.join(self.list.path, self.filename)

    def cancel(self):
        self.status = 'CANCELLED'


class VtodoWritter:
    """Writes a Todo as a VTODO file."""
    """Maps Todo field names to VTODO field names"""
    FIELD_MAP = {
        'summary': 'summary',
        'priority': 'priority',
        'sequence': 'sequence',
        'uid': 'uid',
        'categories': 'categories',
        'completed_at': 'completed',
        'description': 'description',
        'dtstamp': 'dtstamp',
        'start': 'dtstart',
        'due': 'due',
        'location': 'location',
        'percent_complete': 'percent-complete',
        'priority': 'priority',
        'status': 'status',
        'created_at': 'created',
        'last_modified': 'last-modified',
        'rrule': 'rrule',
    }

    def __init__(self, todo):
        self.todo = todo

    def normalize_datetime(self, dt):
        '''
        Eliminate several differences between dates, times and datetimes which
        are hindering comparison:

        - Convert everything to datetime
        - Add missing timezones
        - Cast to UTC

        Datetimes are cast to UTC because icalendar doesn't include the
        VTIMEZONE information upon serialization, and some clients have issues
        dealing with that.
        '''
        if isinstance(dt, date) and not isinstance(dt, datetime):
            dt = datetime(dt.year, dt.month, dt.day)

        if not dt.tzinfo:
            dt = dt.replace(tzinfo=LOCAL_TIMEZONE)

        return dt.astimezone(pytz.UTC)

    def serialize_field(self, name, value):
        if name in Todo.RRULE_FIELDS:
            return icalendar.vRecur.from_ical(value)
        if name in Todo.DATETIME_FIELDS:
            return self.normalize_datetime(value)
        if name in Todo.LIST_FIELDS:
            return value
        if name in Todo.INT_FIELDS:
            return int(value)
        if name in Todo.STRING_FIELDS:
            return value

        raise Exception('Unknown field {} serialized.'.format(name))

    def set_field(self, name, value):
        # If serialized value is None:
        self.vtodo.pop(name)
        if value:
            logger.debug("Setting field %s to %s.", name, value)
            self.vtodo.add(name, value)

    def serialize(self, original=None):
        """Serialize a Todo into a VTODO."""
        if not original:
            original = icalendar.Todo()
        self.vtodo = original

        for source, target in self.FIELD_MAP.items():
            self.vtodo.pop(target)
            if getattr(self.todo, source):
                self.set_field(
                    target,
                    self.serialize_field(source, getattr(self.todo, source)),
                )

        return self.vtodo

    def _read(self, path):
        with open(path, 'rb') as f:
            cal = f.read()
            cal = icalendar.Calendar.from_ical(cal)
            for component in cal.walk('VTODO'):
                return component

    def write(self):
        if os.path.exists(self.todo.path):
            self._write_existing(self.todo.path)
        else:
            self._write_new(self.todo.path)

        return self.vtodo

    def _write_existing(self, path):
        original = self._read(path)
        vtodo = self.serialize(original)

        with open(path, 'rb') as f:
            cal = icalendar.Calendar.from_ical(f.read())
            for index, component in enumerate(cal.subcomponents):
                if component.get('uid', None) == self.todo.uid:
                    cal.subcomponents[index] = vtodo

        with AtomicWriter(path, overwrite=True).open() as f:
            f.write(cal.to_ical().decode("UTF-8"))

    def _write_new(self, path):
        vtodo = self.serialize()

        c = icalendar.Calendar()
        c.add_component(vtodo)

        with AtomicWriter(path).open() as f:
            c.add('prodid', 'io.barrera.todoman')
            c.add('version', '2.0')
            f.write(c.to_ical().decode("UTF-8"))

        return vtodo


class Cache:
    """
    Caches Todos for faster read and simpler querying interface

    The Cache class persists relevant[1] fields into an SQL database, which is
    only updated if the actual file has been modified. This greatly increases
    load times, but, more importantly, provides a simpler interface for
    filtering/querying/sorting.

    [1]: Relevant fields are those we show when listing todos, or those which
    may be used for filtering/sorting.
    """

    SCHEMA_VERSION = 5

    def __init__(self, path):
        self.cache_path = str(path)
        os.makedirs(os.path.dirname(self.cache_path), exist_ok=True)

        self._conn = sqlite3.connect(self.cache_path)
        self._conn.row_factory = sqlite3.Row
        self._conn.execute("PRAGMA foreign_keys = ON")

        self.create_tables()

    def save_to_disk(self):
        self._conn.commit()

    def is_latest_version(self):
        """Checks if the cache DB schema is the latest version."""
        try:
            return self._conn.execute(
                'SELECT version FROM meta WHERE version = ?',
                (Cache.SCHEMA_VERSION,),
            ).fetchone()
        except sqlite3.OperationalError:
            return False

    def create_tables(self):
        if self.is_latest_version():
            return

        self._conn.executescript(
            '''
            DROP TABLE IF EXISTS lists;
            DROP TABLE IF EXISTS files;
            DROP TABLE IF EXISTS todos;
        '''
        )

        self._conn.execute('CREATE TABLE IF NOT EXISTS meta ("version" INT)')

        self._conn.execute(
            'INSERT INTO meta (version) VALUES (?)',
            (Cache.SCHEMA_VERSION,),
        )

        self._conn.execute(
            '''
            CREATE TABLE IF NOT EXISTS lists (
                "name" TEXT PRIMARY KEY,
                "path" TEXT,
                "colour" TEXT,
                CONSTRAINT path_unique UNIQUE (path)
            );
        '''
        )

        self._conn.execute(
            '''
            CREATE TABLE IF NOT EXISTS files (
                "path" TEXT PRIMARY KEY,
                "list_name" TEXT,
                "mtime" INTEGER,

                CONSTRAINT path_unique UNIQUE (path),
                FOREIGN KEY(list_name) REFERENCES lists(name) ON DELETE CASCADE
            );
        '''
        )

        self._conn.execute(
            '''
            CREATE TABLE IF NOT EXISTS todos (
                "file_path" TEXT,

                "id" INTEGER PRIMARY KEY,
                "uid" TEXT,
                "summary" TEXT,
                "due" INTEGER,
                "start" INTEGER,
                "priority" INTEGER,
                "created_at" INTEGER,
                "completed_at" INTEGER,
                "percent_complete" INTEGER,
                "dtstamp" INTEGER,
                "status" TEXT,
                "description" TEXT,
                "location" TEXT,
                "categories" TEXT,
                "sequence" INTEGER,
                "last_modified" INTEGER,
                "rrule" TEXT,

                FOREIGN KEY(file_path) REFERENCES files(path) ON DELETE CASCADE
            );
        '''
        )

    def clear(self):
        self._conn.close()
        os.remove(self.cache_path)
        self._conn = None

    def add_list(self, name, path, colour):
        """
        Inserts a new list into the cache.

        Returns the id of the newly inserted list.
        """

        result = self._conn.execute(
            'SELECT name FROM lists WHERE path = ?',
            (path,),
        ).fetchone()

        if result:
            return result['name']

        try:
            self._conn.execute(
                "INSERT INTO lists (name, path, colour) VALUES (?, ?, ?)",
                (
                    name,
                    path,
                    colour,
                ),
            )
        except sqlite3.IntegrityError as e:
            raise exceptions.AlreadyExists('list', name) from e

        return self.add_list(name, path, colour)

    def add_file(self, list_name, path, mtime):
        try:
            self._conn.execute(
                '''
                INSERT INTO files (
                    list_name,
                    path,
                    mtime
                ) VALUES (?, ?, ?);
                ''', (
                    list_name,
                    path,
                    mtime,
                )
            )
        except sqlite3.IntegrityError as e:
            raise exceptions.AlreadyExists('file', list_name) from e

    def _serialize_datetime(self, todo, field):
        dt = todo.decoded(field, None)
        if not dt:
            return None

        if isinstance(dt, date) and not isinstance(dt, datetime):
            dt = datetime(dt.year, dt.month, dt.day)

        if not dt.tzinfo:
            dt = dt.replace(tzinfo=LOCAL_TIMEZONE)
        return dt.timestamp()

    def _serialize_rrule(self, todo, field):
        rrule = todo.get(field)
        if not rrule:
            return None

        return rrule.to_ical().decode()

    def _serialize_categories(self, todo, field):
        categories = todo.get(field, [])
        if not categories:
            return ''

        return ','.join([str(category) for category in categories.cats])

    def add_vtodo(self, todo, file_path, id=None):
        """
        Adds a todo into the cache.

        :param icalendar.Todo todo: The icalendar component object on which
        """

        sql = '''
            INSERT INTO todos (
                {}
                file_path,
                uid,
                summary,
                due,
                start,
                priority,
                created_at,
                completed_at,
                percent_complete,
                dtstamp,
                status,
                description,
                location,
                categories,
                sequence,
                last_modified,
                rrule
            ) VALUES ({}?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)
            '''

        due = self._serialize_datetime(todo, 'due')
        start = self._serialize_datetime(todo, 'dtstart')

        if start and due:
            start = None if start >= due else start

        params = (
            file_path,
            todo.get('uid'),
            todo.get('summary'),
            due,
            start,
            todo.get('priority', 0) or None,
            self._serialize_datetime(todo, 'created'),
            self._serialize_datetime(todo, 'completed'),
            todo.get('percent-complete', None),
            self._serialize_datetime(todo, 'dtstamp'),
            todo.get('status', 'NEEDS-ACTION'),
            todo.get('description', None),
            todo.get('location', None),
            self._serialize_categories(todo, 'categories'),
            todo.get('sequence', 1),
            self._serialize_datetime(todo, 'last-modified'),
            self._serialize_rrule(todo, 'rrule'),
        )

        if id:
            params = (id,) + params
            sql = sql.format('id,\n', '?, ')
        else:
            sql = sql.format('', '')

        cursor = self._conn.cursor()
        try:
            cursor.execute(sql, params)
            rv = cursor.lastrowid
        finally:
            cursor.close()

        return rv

    def todos(
        self,
        lists=(),
        priority=None,
        location='',
        category='',
        grep='',
        sort=(),
        reverse=True,
        due=None,
        start=None,
        startable=False,
        status=(
            'NEEDS-ACTION',
            'IN-PROCESS',
        )
    ):
        """
        Returns filtered cached todos, in a specified order.

        If no order is specified, todos are sorted by the following fields::

            completed_at
            -priority
            due
            -created_at

        :param list lists: Only return todos for these lists.
        :param str location: Only return todos with a location containing this
            string.
        :param str category: Only return todos with a category containing this
            string.
        :param str grep: Filter common fields with this substring.
        :param list sort: Order returned todos by these fields. Field names
            with a ``-`` prepended will be used to sort in reverse order.
        :param bool reverse: Reverse the order of the todos after sorting.
        :param int due: Return only todos due within ``due`` hours.
        :param str priority: Only return todos with priority at least as
            high as specified.
        :param tuple(bool, datetime) start: Return only todos before/after
            ``start`` date
        :param list(str) status: Return only todos with any of the given
            statuses.
        :return: A sorted, filtered list of todos.
        :rtype: generator
        """
        extra_where = []
        params = []

        if 'ANY' not in status:
            extra_where.append(
                'AND status IN ({})'.format(', '.join(['?'] * len(status)))
            )
            params.extend(s.upper() for s in status)

        if lists:
            lists = [l.name if isinstance(l, List) else l for l in lists]
            q = ', '.join(['?'] * len(lists))
            extra_where.append('AND files.list_name IN ({})'.format(q))
            params.extend(lists)
        if priority:
            extra_where.append('AND PRIORITY > 0 AND PRIORITY <= ?')
            params.append('{}'.format(priority))
        if location:
            extra_where.append('AND location LIKE ?')
            params.append('%{}%'.format(location))
        if category:
            extra_where.append('AND categories LIKE ?')
            params.append('%{}%'.format(category))
        if grep:
            # # requires sqlite with pcre, which won't be available everywhere:
            # extra_where.append('AND summary REGEXP ?')
            # params.append(grep)
            extra_where.append('AND summary LIKE ?')
            params.append('%{}%'.format(grep))
        if due:
            max_due = (datetime.now() + timedelta(hours=due)).timestamp()
            extra_where.append('AND due IS NOT NULL AND due < ?')
            params.append(max_due)
        if start:
            is_before, dt = start
            dt = dt.timestamp()
            if is_before:
                extra_where.append('AND start <= ?')
                params.append(dt)
            else:
                extra_where.append('AND start >= ?')
                params.append(dt)
        if startable:
            extra_where.append('AND (start IS NULL OR start <= ?)')
            params.append(datetime.now().timestamp())
        if sort:
            order = []
            for s in sort:
                if s.startswith('-'):
                    order.append(' {} ASC'.format(s[1:]))
                else:
                    order.append(' {} DESC'.format(s))
            order = ','.join(order)
        else:
            order = '''
                completed_at DESC,
                priority IS NOT NULL, priority DESC,
                due IS NOT NULL, due DESC,
                created_at ASC
            '''

        if not reverse:
            # Note the change in case to avoid swapping all of them. sqlite
            # doesn't care about casing anyway.
            order = order.replace(' DESC', ' asc').replace(' ASC', ' desc')

        query = '''
              SELECT todos.*, files.list_name, files.path
                FROM todos, files
               WHERE todos.file_path = files.path {}
            ORDER BY {}
        '''.format(
            ' '.join(extra_where),
            order,
        )

        logger.debug(query)
        logger.debug(params)

        result = self._conn.execute(query, params)

        seen_paths = set()
        warned_paths = set()

        for row in result:
            todo = self._todo_from_db(row)
            path = row['path']

            if path in seen_paths and path not in warned_paths:
                logger.warning(
                    'Todo is in read-only mode because there are '
                    'multiple todos in %s', path
                )
                warned_paths.add(path)
            seen_paths.add(path)
            yield todo

    def _dt_from_db(self, dt):
        if dt:
            return datetime.fromtimestamp(dt, LOCAL_TIMEZONE)
        return None

    def _todo_from_db(self, row):
        todo = Todo()
        todo.id = row['id']
        todo.uid = row['uid']
        todo.summary = row['summary']
        todo.due = self._dt_from_db(row['due'])
        todo.start = self._dt_from_db(row['start'])
        todo.priority = row['priority']
        todo.created_at = self._dt_from_db(row['created_at'])
        todo.completed_at = self._dt_from_db(row['completed_at'])
        todo.dtstamp = self._dt_from_db(row['dtstamp'])
        todo.percent_complete = row['percent_complete']
        todo.status = row['status']
        todo.description = row['description']
        todo.location = row['location']
        todo.sequence = row['sequence']
        todo.last_modified = row['last_modified']
        todo.list = self.lists_map[row['list_name']]
        todo.filename = os.path.basename(row['path'])
        todo.rrule = row['rrule']
        return todo

    def lists(self):
        result = self._conn.execute("SELECT * FROM lists")
        for row in result:
            yield List(
                name=row['name'],
                path=row['path'],
                colour=row['colour'],
            )

    @cached_property
    def lists_map(self):
        return {l.name: l for l in self.lists()}

    def expire_lists(self, paths):
        results = self._conn.execute("SELECT path, name from lists")
        for result in results:
            if result['path'] not in paths:
                self.delete_list(result['name'])

    def delete_list(self, name):
        self._conn.execute("DELETE FROM lists WHERE lists.name = ?", (name,))

    def todo(self, id, read_only=False):
        # XXX: DON'T USE READ_ONLY
        result = self._conn.execute(
            '''
            SELECT todos.*, files.list_name, files.path
              FROM todos, files
            WHERE files.path = todos.file_path
              AND todos.id = ?
        ''', (id,)
        ).fetchone()

        if not result:
            raise exceptions.NoSuchTodo(id)

        if not read_only:
            count = self._conn.execute(
                '''
                SELECT count(id) AS c
                  FROM files, todos
                 WHERE todos.file_path = files.path
                   AND path=?
            ''', (result['path'],)
            ).fetchone()
            if count['c'] > 1:
                raise exceptions.ReadOnlyTodo(result['path'])

        return self._todo_from_db(result)

    def expire_files(self, paths_to_mtime):
        """Remove stale cache entries based on the given fresh data."""
        result = self._conn.execute("SELECT path, mtime FROM files")
        for row in result:
            path, mtime = row['path'], row['mtime']
            if paths_to_mtime.get(path, None) != mtime:
                self.expire_file(path)

    def expire_file(self, path):
        self._conn.execute("DELETE FROM files WHERE path = ?", (path,))


class List:
    def __init__(self, name, path, colour=None):
        self.path = path
        self.name = name
        self.colour = colour

    @staticmethod
    def colour_for_path(path):
        try:
            with open(os.path.join(path, 'color')) as f:
                return f.read().strip()
        except (OSError, IOError):
            logger.debug('No colour for list %s', path)

    @staticmethod
    def name_for_path(path):
        try:
            with open(os.path.join(path, 'displayname')) as f:
                return f.read().strip()
        except (OSError, IOError):
            return split(normpath(path))[1]

    def __eq__(self, other):
        if isinstance(other, List):
            return self.name == other.name
        return object.__eq__(self, other)

    def __str__(self):
        return self.name


class Database:
    """
    This class is essentially a wrapper around all the lists (which in turn,
    contain all the todos).

    Caching in abstracted inside this class, and is transparent to outside
    classes.
    """

    def __init__(self, paths, cache_path):
        self.cache = Cache(cache_path)
        self.paths = [str(path) for path in paths]
        self.update_cache()

    def update_cache(self):
        self.cache.expire_lists(self.paths)

        paths_to_mtime = {}
        paths_to_list_name = {}

        for path in self.paths:
            list_name = self.cache.add_list(
                List.name_for_path(path),
                path,
                List.colour_for_path(path),
            )
            for entry in os.listdir(path):
                if not entry.endswith('.ics'):
                    continue
                entry_path = os.path.join(path, entry)
                mtime = _getmtime(entry_path)
                paths_to_mtime[entry_path] = mtime
                paths_to_list_name[entry_path] = list_name

        self.cache.expire_files(paths_to_mtime)

        for entry_path, mtime in paths_to_mtime.items():
            list_name = paths_to_list_name[entry_path]

            try:
                self.cache.add_file(list_name, entry_path, mtime)
            except exceptions.AlreadyExists:
                logger.debug('File already in cache: %s', entry_path)
                continue

            try:
                with open(entry_path, 'rb') as f:
                    cal = f.read()
                    cal = icalendar.Calendar.from_ical(cal)
                    for component in cal.walk('VTODO'):
                        self.cache.add_vtodo(component, entry_path)
            except Exception:
                logger.exception("Failed to read entry %s.", entry_path)

        self.cache.save_to_disk()

    def todos(self, **kwargs):
        return self.cache.todos(**kwargs)

    def todo(self, id, **kwargs):
        return self.cache.todo(id, **kwargs)

    def lists(self):
        return self.cache.lists()

    def move(self, todo, new_list, from_list=None):
        from_list = from_list or todo.list
        orig_path = os.path.join(from_list.path, todo.filename)
        dest_path = os.path.join(new_list.path, todo.filename)

        os.rename(orig_path, dest_path)

    def delete(self, todo):
        path = os.path.join(todo.list.path, todo.filename)
        os.remove(path)

    def flush(self):
        for todo in self.todos(status=['ANY']):
            if todo.is_completed:
                yield todo
                self.delete(todo)

        self.cache.clear()
        self.cache = None

    def save(self, todo):
        for related in todo.related:
            self.save(related)

        todo.sequence += 1
        todo.last_modified = datetime.now(LOCAL_TIMEZONE)

        vtodo = VtodoWritter(todo).write()

        self.cache.expire_file(todo.path)
        mtime = _getmtime(todo.path)

        self.cache.add_file(todo.list.name, todo.path, mtime)
        todo.id = self.cache.add_vtodo(vtodo, todo.path, todo.id)
        self.cache.save_to_disk()


def _getmtime(path):
    stat = os.stat(path)
    return getattr(stat, 'st_mtime_ns', stat.st_mtime)
