kodi_plugin/framework/storage.py

import os
import csv
import json
import time
try:
    import cPickle as pickle
except ImportError:
    import pickle
import shutil
import collections
from datetime import datetime


class _PersistentDictMixin(object):

    def __init__(self, filename, flag='c', mode=None, file_format='pickle'):
        self.flag = flag                    # r=readonly, c=create, or n=new
        self.mode = mode                    # None or an octal triple like 0644
        self.file_format = file_format      # 'csv', 'json', or 'pickle'
        self.filename = filename
        if flag != 'n' and os.access(filename, os.R_OK):
            fileobj = open(filename, 'rb' if file_format == 'pickle' else 'r')
            with fileobj:
                self.load(fileobj)

    def sync(self):
        '''Write the dict to disk'''
        if self.flag == 'r':
            return
        filename = self.filename
        tempname = filename + '.tmp'
        fileobj = open(tempname, 'wb' if self.file_format == 'pickle' else 'w')
        try:
            self.dump(fileobj)
        except Exception:
            os.remove(tempname)
            raise
        finally:
            fileobj.close()
        shutil.move(tempname, self.filename)    # atomic commit
        if self.mode is not None:
            os.chmod(self.filename, self.mode)

    def close(self):
        '''Calls sync'''
        self.sync()

    def __enter__(self):
        return self

    def __exit__(self, *exc_info):
        self.close()

    def dump(self, fileobj):
        '''Handles the writing of the dict to the file object'''
        if self.file_format == 'csv':
            csv.writer(fileobj).writerows(self.raw_dict().items())
        elif self.file_format == 'json':
            json.dump(self.raw_dict(), fileobj, separators=(',', ':'))
        elif self.file_format == 'pickle':
            pickle.dump(dict(self.raw_dict()), fileobj, 2)
        else:
            raise NotImplementedError('Unknown format: ' +
                                      repr(self.file_format))

    def load(self, fileobj):
        '''Load the dict from the file object'''
        # try formats from most restrictive to least restrictive
        for loader in (pickle.load, json.load, csv.reader):
            fileobj.seek(0)
            try:
                return self.initial_update(loader(fileobj))
            except Exception as e:
                pass
        raise ValueError('File not in a supported format')

    def raw_dict(self):
        '''Returns the underlying dict'''
        raise NotImplementedError


class _Storage(collections.MutableMapping, _PersistentDictMixin):

    '''Storage that acts like a dict but also can persist to disk.

    :param filename: An absolute filepath to reprsent the storage on disk. The
                     storage will loaded from this file if it already exists,
                     otherwise the file will be created.
    :param file_format: 'pickle', 'json' or 'csv'. pickle is the default. Be
                        aware that json and csv have limited support for python
                        objets.

    .. warning:: Currently there are no limitations on the size of the storage.
                 Please be sure to call :meth:`~xbmcswift2._Storage.clear`
                 periodically.
    '''

    def __init__(self, filename, file_format='pickle'):
        '''Acceptable formats are 'csv', 'json' and 'pickle'.'''
        self._items = {}
        _PersistentDictMixin.__init__(self, filename, file_format=file_format)

    def __setitem__(self, key, val):
        self._items.__setitem__(key, val)

    def __getitem__(self, key):
        return self._items.__getitem__(key)

    def __delitem__(self, key):
        self._items.__delitem__(key)

    def __iter__(self):
        return iter(self._items)

    def __len__(self):
        return self._items.__len__

    def raw_dict(self):
        '''Returns the wrapped dict'''
        return self._items

    initial_update = collections.MutableMapping.update

    def clear(self):
        super(_Storage, self).clear()
        self.sync()


class TimedStorage(_Storage):

    '''A dict with the ability to persist to disk and TTL for items.'''

    def __init__(self, filename, file_format='pickle', TTL=None):
        '''TTL if provided should be a datetime.timedelta. Any entries
        older than the provided TTL will be removed upon load and upon item
        access.
        '''
        self.TTL = TTL
        _Storage.__init__(self, filename, file_format=file_format)

    def __setitem__(self, key, val, raw=False):
        if raw:
            self._items[key] = val
        else:
            self._items[key] = (val, time.time())

    def __getitem__(self, key):
        val, timestamp = self._items[key]
        if self.TTL and (datetime.utcnow() -
                         datetime.utcfromtimestamp(timestamp) > self.TTL):
            del self._items[key]
            return self._items[key][0]  # Will raise KeyError
        return val

    def initial_update(self, mapping):
        '''Initially fills the underlying dictionary with keys, values and
        timestamps.
        '''
        for key, val in mapping.items():
            _, timestamp = val
            if not self.TTL or (datetime.utcnow() -
                                datetime.utcfromtimestamp(timestamp) < self.TTL):
                self.__setitem__(key, val, raw=True)