--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/server/sources/storages.py	Fri Jan 22 08:49:16 2010 +0100
@@ -0,0 +1,110 @@
+"""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
+
+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):
+        fpath = osp.join(self.default_directory, '%s_%s_%s' % (
+            self.default_directory, entity.eid, attr))
+        while osp.exists(fspath):
+            fspath = '_' + fspath
+        return fspath
+
+    def current_fs_path(self, entity, attr):
+        cu = entity._cw.system_sql('SELECT cw_%s.%s WHERE cw_eid=%s' %
+                                   (entity.__regid__, attr, entity.eid))
+        return cu.fetchone()[0]
+
+
+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:
+            pass