# Copyright (C) 2014 SUSE Linux Products GmbH
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License along
# with this program; if not, write to the Free Software Foundation, Inc.,
# 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.

import fcntl
import glob
import hashlib
import os.path
try:
    import cPickle as pickle
except:
    import pickle
import shelve
import shutil
from UserDict import DictMixin


class PkgCache(DictMixin):
    def __init__(self, basecachedir, force_clean=False):
        self.cachedir = os.path.join(basecachedir, 'pkgcache')
        self.index_fn = os.path.join(self.cachedir, 'index.db')

        if force_clean:
            try:
                shutil.rmtree(self.cachedir)
            except OSError:
                pass

        if not os.path.exists(self.cachedir):
            os.makedirs(self.cachedir)

    def _lock(self, filename):
        """Get a lock for the index file."""
        lckfile = open(filename + '.lck', 'w')
        fcntl.flock(lckfile.fileno(), fcntl.LOCK_EX)
        return lckfile

    def _unlock(self, lckfile):
        """Release the lock for the index file."""
        fcntl.flock(lckfile.fileno(), fcntl.LOCK_UN)
        lckfile.close()

    def _open_index(self):
        """Open the index file for the cache / container."""
        lckfile = self._lock(self.index_fn)
        index = shelve.open(self.index_fn, protocol=-1)
        # Store a reference to the lckfile to avoid to be closed by gc
        index.lckfile = lckfile
        return index

    def _close_index(self, index):
        """Close the index file for the cache / container."""
        index.close()
        self._unlock(index.lckfile)

    # def _clean_cache(self, index=None):
    #     """Remove elements in the cache that thare the same prefix of the key
    #     (all except the mtime), and keep the latest one.

    #     """
    #     _i = self._open_index() if not index else index
    #     keys = sorted(_i)

    #     last = []
    #     for key in keys:
    #         if last[:-1] == key[:-1]:
    #             self.__delitem__(key, _i)
    #         last = key

    #     if not index:
    #         self._close_index(_i)

    def __getitem__(self, key, index=None):
        """Get a element in the cache.

        For the container perspective, the key is a tuple like this:
        (project, repository, arch, package, filename, mtime)

        """
        _i = self._open_index() if not index else index
        key = pickle.dumps(key, protocol=-1)
        value = pickle.loads(_i[key])
        if not index:
            self._close_index(_i)
        return value

    def __setitem__(self, key, value, index=None):
        """Add a new file in the cache. 'value' is expected to contains the
        path of file.

        """
        _i = self._open_index() if not index else index
        key = pickle.dumps(key, protocol=-1)

        original_value = value

        md5 = hashlib.md5(open(value, 'rb').read()).hexdigest()
        filename = os.path.basename(value)
        value = (md5, filename)
        value = pickle.dumps(value, protocol=-1)
        _i[key] = value

        # Move the file into the container using a hard link
        cache_fn = os.path.join(self.cachedir, md5[:2], md5[2:])
        if os.path.exists(cache_fn):
            # Manage collisions using hard links and refcount
            collisions = sorted(glob.glob(cache_fn + '-*'))
            next_refcount = 1
            if collisions:
                next_refcount = int(collisions[-1][-3:]) + 1
            next_cache_fn = cache_fn + '-%03d' % next_refcount
            os.link(cache_fn, next_cache_fn)
        else:
            dirname = os.path.dirname(cache_fn)
            if not os.path.exists(dirname):
                os.makedirs(dirname)
            os.link(original_value, cache_fn)

        if not index:
            self._close_index(_i)

    def __delitem__(self, key, index=None):
        """Remove a file from the cache."""
        _i = self._open_index() if not index else index
        key = pickle.dumps(key, protocol=-1)
        value = pickle.loads(_i[key])

        md5, _ = value

        # Remove the file (taking care of collision) and the directory
        # if it is empty
        cache_fn = os.path.join(self.cachedir, md5[:2], md5[2:])
        collisions = sorted(glob.glob(cache_fn + '-*'))
        if collisions:
            os.unlink(collisions[-1])
        else:
            os.unlink(cache_fn)

        dirname = os.path.dirname(cache_fn)
        if not os.listdir(dirname):
            os.rmdir(dirname)

        del _i[key]

        if not index:
            self._close_index(_i)

    def keys(self, index=None):
        _i = self._open_index() if not index else index
        keys = [pickle.loads(key) for key in _i]
        if not index:
            self._close_index(_i)
        return keys

    def linkto(self, key, target, index=None):
        """Create a link between the cached object and the target"""
        _i = self._open_index() if not index else index

        md5, filename = self.__getitem__(key, index=_i)
        if filename != target:
            pass
            # print 'Warning. The target name (%s) is different from the original name (%s)' % (target, filename)
        cache_fn = os.path.join(self.cachedir, md5[:2], md5[2:])
        os.link(cache_fn, target)

        if not index:
            self._close_index(_i)