Split out the local backend (#2052)

This splits the backend into two parts: the local backend for desktop cellxgene and the AWS backend for hosted cellxgene. The local backend is in local_server while the hosted remains in server. The general idea is to copy everything from server to local_server, pull unneeded stuff out of local_server, and keep server as-is for this PR. Not touching server means all the infra and deployment code will continue working just as it did before so we can make those changes incrementally.

local_server/common/annotations/annotations.py

@@ -0,0 +1,70 @@
+from abc import ABCMeta, abstractmethod
+
+import fastobo
+import fsspec
+
+from local_server.common.errors import OntologyLoadFailure
+from local_server.common.utils.type_conversion_utils import get_schema_type_hint_of_array
+
+
+class Annotations(metaclass=ABCMeta):
+    """ baseclass for annotations, including ontologies"""
+
+    """ our default ontology is the PURL for the Cell Ontology.
+    See http://www.obofoundry.org/ontology/cl.html """
+    DefaultOnotology = "http://purl.obolibrary.org/obo/cl.obo"
+
+    def __init__(self):
+        self.ontology_data = None
+
+    def load_ontology(self, path):
+        """Load and parse ontologies - currently support OBO files only."""
+        if path is None:
+            path = self.DefaultOnotology
+
+        try:
+            with fsspec.open(path) as f:
+                obo = fastobo.iter(f)
+                terms = filter(lambda stanza: type(stanza) is fastobo.term.TermFrame, obo)
+                names = [tag.name for term in terms for tag in term if type(tag) is fastobo.term.NameClause]
+                self.ontology_data = names
+
+        except FileNotFoundError as e:
+            raise OntologyLoadFailure("Unable to find OBO ontology path") from e
+
+        except SyntaxError as e:
+            raise OntologyLoadFailure("Syntax error loading OBO ontology") from e
+
+        except Exception as e:
+            raise OntologyLoadFailure("Error loading OBO file") from e
+
+    def get_schema(self, data_adaptor):
+        schema = []
+        labels = self.read_labels(data_adaptor)
+        if labels is not None and not labels.empty:
+            for col in labels.columns:
+                col_schema = dict(name=col, writable=True)
+                col_schema.update(get_schema_type_hint_of_array(labels[col]))
+                schema.append(col_schema)
+
+        return schema
+
+    @abstractmethod
+    def set_collection(self, name):
+        """set or create a new annotation collection"""
+        pass
+
+    @abstractmethod
+    def read_labels(self, data_adaptor):
+        """Return the labels as a pandas.DataFrame"""
+        pass
+
+    @abstractmethod
+    def write_labels(self, df, data_adaptor):
+        """Write the labels (df) to a persistent storage such that it can later be read"""
+        pass
+
+    @abstractmethod
+    def update_parameters(self, parameters, data_adaptor):
+        """Update configuration parameters that describe information about the annotations feature"""
+        pass