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

from os import unlink, path as osp

from cubicweb.server.hook import Operation

ETYPE_ATTR_STORAGE = {}

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

    ETYPE_ATTR_STORAGE.setdefault(etype, {})[attr] = storage

    repo.system_source.map_attribute(etype, attr, storage.sqlgen_callback)

class Storage(object):

    """abstract storage"""

    def sqlgen_callback(self, generator, relation, linkedvar):

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

        accessed

        """

        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 sqlgen_callback(self, generator, linkedvar, relation):

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

        accessed

        """

        linkedvar.accept(generator)

        return '_fsopen(%s.cw_%s)' % (

            linkedvar._q_sql.split('.', 1)[0], # table name

            relation.r_type) # attribute name

    def entity_added(self, entity, attr):

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

        if not entity._cw.transaction_data.get('fs_importing'):

            try:

                value = entity.pop(attr)

            except KeyError:

                pass

            else:

                fpath = self.new_fs_path(entity, attr)

                # bytes storage used to store file's path

                entity[attr]= Binary(fpath)

                file(fpath, 'w').write(value.getvalue())

                AddFileOp(entity._cw, filepath=fpath)

        # else entity[attr] is expected to be an already existant file path

    def entity_updated(self, entity, attr):

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

        try:

            value = entity.pop(attr)

        except KeyError:

            pass

        else:

            fpath = self.current_fs_path(entity, attr)

            UpdateFileOp(entity._cw, filepath=fpath, filedata=value.getvalue())

    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):

        while osp.exists(fspath):

            fspath = '_' + fspath

        return fspath

    def current_fs_path(self, entity, attr):

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)