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

from os import unlink, path as osp

from cubicweb import Binary

from cubicweb.server.hook import Operation

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 valu and should have the

      following prototype::

        callback(self, source, 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()

# TODO

# * make it configurable without code

# * better file path attribution

# * handle backup/restore

class BytesFileSystemStorage(Storage):

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

    def __init__(self, defaultdir):

        self.default_directory = defaultdir

    def callback(self, source, value):

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

        accessed

        """

        fpath = source.binary_to_str(value)

        try:

            return Binary(file(fpath).read())

        except OSError, 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"""

    def entity_updated(self, entity, attr):

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

    def entity_deleted(self, entity, attr):

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

        DeleteFileOp(entity._cw, filepath=self.current_fs_path(entity, attr))

    def new_fs_path(self, entity, attr):

        fspath = osp.join(self.default_directory, '%s_%s' % (entity.eid, attr))

        while osp.exists(fspath):

            fspath = '_' + fspath

        return fspath

    def current_fs_path(self, entity, attr):

        sysource = entity._cw.pool.source('system')

        cu = sysource.doexec(entity._cw,

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

                                 attr, entity.__regid__, entity.eid))

                                       binarywrap=str)

class AddFileOp(Operation):

    def rollback_event(self):

        try:

            unlink(self.filepath)

        except:

            pass

class DeleteFileOp(Operation):

    def commit_event(self):

        try:

            unlink(self.filepath)

        except:

            pass

class UpdateFileOp(Operation):

    def precommit_event(self):

        try:

            file(self.filepath, 'w').write(self.filedata)

        except Exception, ex:

            self.exception(str(ex))