"File-based cache backend"

import md5

import os, time

try:

    import cPickle as pickle

except ImportError:

    import pickle

from django.core.cache.backends.base import BaseCache

class CacheClass(BaseCache):

    def __init__(self, dir, params):

        BaseCache.__init__(self, params)

        max_entries = params.get('max_entries', 300)

        try:

            self._max_entries = int(max_entries)

        except (ValueError, TypeError):

            self._max_entries = 300

        cull_frequency = params.get('cull_frequency', 3)

        try:

            self._cull_frequency = int(cull_frequency)

        except (ValueError, TypeError):

            self._cull_frequency = 3

        self._dir = dir

        if not os.path.exists(self._dir):

            self._createdir()

    def add(self, key, value, timeout=None):

        if self.has_key(key):

            return None

        self.set(key, value, timeout)

    def get(self, key, default=None):

        fname = self._key_to_file(key)

        try:

            f = open(fname, 'rb')

            exp = pickle.load(f)

            now = time.time()

            if exp < now:

                f.close()

                self._delete(fname)

            else:

                return pickle.load(f)

        except (IOError, OSError, EOFError, pickle.PickleError):

            pass

        return default

    def set(self, key, value, timeout=None):

        fname = self._key_to_file(key)

        dirname = os.path.dirname(fname)

        if timeout is None:

            timeout = self.default_timeout

        self._cull()

        try:

            if not os.path.exists(dirname):

                os.makedirs(dirname)

            f = open(fname, 'wb')

            now = time.time()

            pickle.dump(now + timeout, f, pickle.HIGHEST_PROTOCOL)

            pickle.dump(value, f, pickle.HIGHEST_PROTOCOL)

        except (IOError, OSError):

            pass

    def delete(self, key):

        try:

            self._delete(self._key_to_file(key))

        except (IOError, OSError):

            pass

    def _delete(self, fname):

        os.remove(fname)

        try:

            # Remove the 2 subdirs if they're empty

            dirname = os.path.dirname(fname)

            os.rmdir(dirname)

            os.rmdir(os.path.dirname(dirname))

        except (IOError, OSError):

            pass

    def has_key(self, key):

        fname = self._key_to_file(key)

        try:

            f = open(fname, 'rb')

            exp = pickle.load(f)

            now = time.time()

            if exp < now:

                f.close()

                self._delete(fname)

                return False

            else:

                return True

        except (IOError, OSError, EOFError, pickle.PickleError):

            return False

    def _cull(self):

        if int(self._num_entries) < self._max_entries:

            return

        try:

            filelist = os.listdir(self._dir)

        except (IOError, OSError):

            return

        if self._cull_frequency == 0:

            doomed = filelist

        else:

            doomed = [os.path.join(self._dir, k) for (i, k) in enumerate(filelist) if i % self._cull_frequency == 0]

        for topdir in doomed:

            try:

                for root, _, files in os.walk(topdir):

                    for f in files:

                        self._delete(os.path.join(root, f))

            except (IOError, OSError):

                pass

    def _createdir(self):

        try:

            os.makedirs(self._dir)

        except OSError:

            raise EnvironmentError, "Cache directory '%s' does not exist and could not be created'" % self._dir

    def _key_to_file(self, key):

        """

        Convert the filename into an md5 string. We'll turn the first couple

        bits of the path into directory prefixes to be nice to filesystems

        that have problems with large numbers of files in a directory.

        Thus, a cache key of "foo" gets turnned into a file named

        ``{cache-dir}ac/bd/18db4cc2f85cedef654fccc4a4d8``.

        """

        path = md5.new(key.encode('utf-8')).hexdigest()

        path = os.path.join(path[:2], path[2:4], path[4:])

        return os.path.join(self._dir, path)

    def _get_num_entries(self):

        count = 0

        for _,_,files in os.walk(self._dir):

            count += len(files)

        return count

    _num_entries = property(_get_num_entries)