!/usr/bin/env python

-- coding: utf-8 --

"""智能缓存基类 适用于更新不频繁并且数据需要实时同步的情景"""

import abc
from django.conf import settings
from django.core.cache import cache

try:
import simplejson as json
except:
import json

class BaseSmartCache(object):
metaclass = abc.ABCMeta

def __init__(self, force_cache=False, force_source=False, smart=False,
             *args, **kwargs):
    """智能缓存类

    :param force_cache: 强制使用缓存的数据
    :param force_source:  强制使用源数据
    :param smart: 智能检查开关
    """
    assert not all([force_cache, force_source]), \
        ('force_cache and force_source can not assign to True '
         'at the same time')
    self._force_cache = force_cache
    self._force_source = force_source
    self._smart = smart
    self._data = None
    self._cache_id = None
    self._cache_key = None
    self._client = self.client()
    self._latest_update = None

def client(self):
    return cache

def prepare(self):
    pass

def fetch(self):
    self.prepare()
    if self._force_source or not settings.ENABLE_CACHE:
        self._data = self.source()
    else:
        _cache = self.get()
        self._data = _cache and _cache['value']
        if not self._force_cache and (_cache is None or (
                    self._smart and _cache['id'] != self.cache_id)):
                self.refresh()
    return self.handle()

def handle(self):
    return self.data

def pre_set(self):
    pass

def set(self):
    data = {'id': self.cache_id, 'value': self.data}
    return self._client.set(self.cache_key, data, self.expires)

def get(self):
    return self._client.get(self.cache_key)

def delete(self):
    return self._client.delete(self.cache_key)

def refresh(self):
    self._data = self.source()
    self.pre_set()
    self.set()

@property
def data(self):
    return self._data

@property
def cache_key(self):
    if not self._cache_key:
        self._cache_key = self.get_cache_key()
    return self._cache_key

@property
def cache_id(self):
    if not self._cache_id:
        self._cache_id = self.get_cache_id()
    return self._cache_id

@abc.abstractproperty
def expires(self):
    pass

@abc.abstractmethod
def get_cache_key(self):
    pass

@abc.abstractmethod
def get_cache_id(self):
    pass

@abc.abstractmethod
def source(self):
    pass