# copyright 2003-2013 LOGILAB S.A. (Paris, FRANCE), all rights reserved.

# 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

import tempfile

from logilab.common import nullobject

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, cnx, 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 file descriptor and unique file name for `basename` in `dirpath`

    """

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

    base, ext = osp.splitext(path)

    return tempfile.mkstemp(prefix=base, suffix=ext, dir=dirpath)

@contextmanager

def fsimport(cnx):

    present = 'fs_importing' in cnx.transaction_data

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

    cnx.transaction_data['fs_importing'] = True

    yield

    if present:

        cnx.transaction_data['fs_importing'] = old_value

    else:

        del cnx.transaction_data['fs_importing']

_marker = nullobject()

class BytesFileSystemStorage(Storage):

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

    def __init__(self, defaultdir, fsencoding=_marker, wmode=0o444):

        self.default_directory = defaultdir

        # extra umask to use when creating file

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

        self._wmode = wmode

    def _writecontent(self, fd, binary):

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

        As the bfss never alters an existing file it does not prevent it from

        working as intended. This is a better safe than sorry approach.

        """

        os.fchmod(fd, self._wmode)

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

        binary.to_file(fileobj)

        fileobj.close()

    def callback(self, source, cnx, 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)

            if binary is not None:

                fd, fpath = self.new_fs_path(entity, attr)

                # bytes storage used to store file's path

                entity.cw_edited.edited_attribute(attr, binary_obj)

                self._writecontent(fd, 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

                fd, fpath = self.new_fs_path(entity, attr)

                # write attribute value on disk

                self._writecontent(fd, 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_obj)

        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:

        fd, 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 fd, 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

        fspath = sysource._process_value(rawvalue, cu.description[0],

    def migrate_entity(self, entity, attribute):

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

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

        binary = self.entity_added(entity, attribute)

        if binary is not None:

            cnx = entity._cw

            source = cnx.repo.system_source

            attrs = source.preprocess_entity(entity)

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

                                       ['cw_eid'])

            source.doexec(cnx, 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("can't 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("can't remove %s: %s" % (filepath, ex))