# contact http://www.logilab.fr/ -- mailto:contact@logilab.fr

#

# This file is part of CubicWeb.

#

# CubicWeb is free software: you can redistribute it and/or modify it under the

# terms of the GNU Lesser General Public License as published by the Free

# Software Foundation, either version 2.1 of the License, or (at your option)

# any later version.

#

# CubicWeb 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 Lesser General Public License for more

# details.

#

# You should have received a copy of the GNU Lesser General Public License along

# with CubicWeb.  If not, see <http://www.gnu.org/licenses/>.

"""custom storages for the system source"""

import os

import sys

from os import unlink, path as osp

from contextlib import contextmanager

from yams.schema import role_name

from cubicweb import Binary, ValidationError

from cubicweb.server import hook

from cubicweb.server.edition import EditedEntity

def set_attribute_storage(repo, etype, attr, storage):

    repo.system_source.set_storage(etype, attr, storage)

def unset_attribute_storage(repo, etype, attr):

    repo.system_source.unset_storage(etype, attr)

class Storage(object):

    """abstract storage

    * If `source_callback` is true (by default), the callback will be run during

      query result process of fetched attribute's value and should have the

      following prototype::

        callback(self, source, session, value)

      where `value` is the value actually stored in the backend. None values

      will be skipped (eg callback won't be called).

    * if `source_callback` is false, the callback will be run during sql

      generation when some attribute with a custom storage is accessed and

      should have the following prototype::

        callback(self, generator, relation, linkedvar)

      where `generator` is the sql generator, `relation` the current rql syntax

      tree relation and linkedvar the principal syntax tree variable holding the

      attribute.

    """

    is_source_callback = True

    def callback(self, *args):

        """see docstring for prototype, which vary according to is_source_callback

        """

        raise NotImplementedError()

    def entity_added(self, entity, attr):

        """an entity using this storage for attr has been added"""

        raise NotImplementedError()

    def entity_updated(self, entity, attr):

        """an entity using this storage for attr has been updatded"""

        raise NotImplementedError()

    def entity_deleted(self, entity, attr):

        """an entity using this storage for attr has been deleted"""

        raise NotImplementedError()

    def migrate_entity(self, entity, attribute):

        """migrate an entity attribute to the storage"""

        raise NotImplementedError()

# TODO

# * make it configurable without code

# * better file path attribution

# * handle backup/restore

def uniquify_path(dirpath, basename):

    """return a unique file name for `basename` in `dirpath`, or None

    if all attemps failed.

    XXX subject to race condition.

    """

    path = osp.join(dirpath, basename.replace(osp.sep, '-'))

    if not osp.isfile(path):

        return path

    base, ext = osp.splitext(path)

    for i in xrange(1, 256):

        path = '%s%s%s' % (base, i, ext)

        if not osp.isfile(path):

            return path

    return None

@contextmanager

def fsimport(session):

    present = 'fs_importing' in session.transaction_data

    old_value = session.transaction_data.get('fs_importing')

    session.transaction_data['fs_importing'] = True

    yield

    if present:

        session.transaction_data['fs_importing'] = old_value

    else:

        del session.transaction_data['fs_importing']

class BytesFileSystemStorage(Storage):

    """store Bytes attribute value on the file system"""

    def __init__(self, defaultdir, fsencoding='utf-8', wmode=0444):

        if type(defaultdir) is unicode:

            defaultdir = defaultdir.encode(fsencoding)

        self.default_directory = defaultdir

        self.fsencoding = fsencoding

        # extra umask to use when creating file

        # 0444 as in "only allow read bit in permission"

        self._wmode = wmode

    def _writecontent(self, path, binary):

        """write the content of a binary in readonly file

        As the bfss never alter a create file it does not prevent it to work as

        intended. This is a beter safe than sorry approach.

        """

        write_flag = os.O_WRONLY | os.O_CREAT | os.O_EXCL

        if sys.platform == 'win32':

            write_flag |= os.O_BINARY

        fd = os.open(path, write_flag, self._wmode)

        fileobj = os.fdopen(fd, 'wb')

        binary.to_file(fileobj)

        fileobj.close()

    def callback(self, source, session, value):

        """sql generator callback when some attribute with a custom storage is

        accessed

        """

        fpath = source.binary_to_str(value)

        try:

            return Binary.from_file(fpath)

        except EnvironmentError as ex:

            source.critical("can't open %s: %s", value, ex)

            return None

    def entity_added(self, entity, attr):

        """an entity using this storage for attr has been added"""

        if entity._cw.transaction_data.get('fs_importing'):

            binary = Binary.from_file(entity.cw_edited[attr].getvalue())

            entity._cw_dont_cache_attribute(attr, repo_side=True)

        else:

            binary = entity.cw_edited.pop(attr)

            fpath = self.new_fs_path(entity, attr)

            # bytes storage used to store file's path

            entity.cw_edited.edited_attribute(attr, Binary(fpath))

            self._writecontent(fpath, binary)

            AddFileOp.get_instance(entity._cw).add_data(fpath)

        return binary

    def entity_updated(self, entity, attr):

        """an entity using this storage for attr has been updated"""

        # get the name of the previous file containing the value

        oldpath = self.current_fs_path(entity, attr)

        if entity._cw.transaction_data.get('fs_importing'):

            # If we are importing from the filesystem, the file already exists.

            # We do not need to create it but we need to fetch the content of

            # the file as the actual content of the attribute

            fpath = entity.cw_edited[attr].getvalue()

            entity._cw_dont_cache_attribute(attr, repo_side=True)

            assert fpath is not None

            binary = Binary.from_file(fpath)

        else:

            # We must store the content of the attributes

            # into a file to stay consistent with the behaviour of entity_add.

            # Moreover, the BytesFileSystemStorage expects to be able to

            # retrieve the current value of the attribute at anytime by reading

            # the file on disk. To be able to rollback things, use a new file

            # and keep the old one that will be removed on commit if everything

            # went ok.

            #

            # fetch the current attribute value in memory

            binary = entity.cw_edited.pop(attr)

            if binary is None:

                fpath = None

            else:

                # Get filename for it

                fpath = self.new_fs_path(entity, attr)

                assert not osp.exists(fpath)

                # write attribute value on disk

                self._writecontent(fpath, binary)

                # Mark the new file as added during the transaction.

                # The file will be removed on rollback

                AddFileOp.get_instance(entity._cw).add_data(fpath)

            # reinstall poped value

            if fpath is None:

                entity.cw_edited.edited_attribute(attr, None)

            else:

                # register the new location for the file.

                entity.cw_edited.edited_attribute(attr, Binary(fpath))

        if oldpath is not None and oldpath != fpath:

            # Mark the old file as useless so the file will be removed at

            # commit.

            DeleteFileOp.get_instance(entity._cw).add_data(oldpath)

        return binary

    def entity_deleted(self, entity, attr):

        """an entity using this storage for attr has been deleted"""

        fpath = self.current_fs_path(entity, attr)

        if fpath is not None:

            DeleteFileOp.get_instance(entity._cw).add_data(fpath)

    def new_fs_path(self, entity, attr):

        # We try to get some hint about how to name the file using attribute's

        # name metadata, so we use the real file name and extension when

        # available. Keeping the extension is useful for example in the case of

        # PIL processing that use filename extension to detect content-type, as

        # well as providing more understandable file names on the fs.

        basename = [str(entity.eid), attr]

        name = entity.cw_attr_metadata(attr, 'name')

        if name is not None:

            basename.append(name.encode(self.fsencoding))

        fspath = uniquify_path(self.default_directory,

                               '_'.join(basename))

        if fspath is None:

            msg = entity._cw._('failed to uniquify path (%s, %s)') % (

                self.default_directory, '_'.join(basename))

            raise ValidationError(entity.eid, {role_name(attr, 'subject'): msg})

        return fspath

    def current_fs_path(self, entity, attr):

        """return the current fs_path of the attribute, or None is the attr is

        not stored yet.

        """

        sysource = entity._cw.repo.system_source

        cu = sysource.doexec(entity._cw,

                             'SELECT cw_%s FROM cw_%s WHERE cw_eid=%s' % (

                             attr, entity.cw_etype, entity.eid))

        rawvalue = cu.fetchone()[0]

        if rawvalue is None: # no previous value

            return None

        return sysource._process_value(rawvalue, cu.description[0],

                                       binarywrap=str)

    def migrate_entity(self, entity, attribute):

        """migrate an entity attribute to the storage"""

        entity.cw_edited = EditedEntity(entity, **entity.cw_attr_cache)

        self.entity_added(entity, attribute)

        session = entity._cw

        source = session.repo.system_source

        attrs = source.preprocess_entity(entity)

        sql = source.sqlgen.update('cw_' + entity.cw_etype, attrs,

                                   ['cw_eid'])

        source.doexec(session, sql, attrs)

        entity.cw_edited = None

class AddFileOp(hook.DataOperationMixIn, hook.Operation):

    def rollback_event(self):

        for filepath in self.get_data():

            try:

                unlink(filepath)

            except Exception as ex:

                self.error('cant remove %s: %s' % (filepath, ex))

class DeleteFileOp(hook.DataOperationMixIn, hook.Operation):

    def postcommit_event(self):

        for filepath in self.get_data():

            try:

                unlink(filepath)

            except Exception as ex:

                self.error('cant remove %s: %s' % (filepath, ex))