Add OSM charms

Change-Id: Iec1c915c77ac24080bfc8813eecc1970ee8c0213
Signed-off-by: David Garcia <david.garcia@canonical.com>
diff --git a/installers/charm/interfaces/osm-nbi/requires.py b/installers/charm/interfaces/osm-nbi/requires.py
new file mode 100644
index 0000000..a5e8e29
--- /dev/null
+++ b/installers/charm/interfaces/osm-nbi/requires.py
@@ -0,0 +1,56 @@
+# Copyright 2020 Canonical Ltd.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+#     Unless required by applicable law or agreed to in writing, software
+#     distributed under the License is distributed on an "AS IS" BASIS,
+#     WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+#     See the License for the specific language governing permissions and
+#     limitations under the License.
+
+from charms.reactive import RelationBase
+from charms.reactive import hook
+from charms.reactive import scopes
+
+
+class OsmNBIRequires(RelationBase):
+    scope = scopes.GLOBAL
+
+    @hook("{requires:osm-nbi}-relation-joined")
+    def joined(self):
+        conv = self.conversation()
+        conv.set_state("{relation_name}.joined")
+
+    @hook("{requires:osm-nbi}-relation-changed")
+    def changed(self):
+        conv = self.conversation()
+        if self.nbis():
+            conv.set_state("{relation_name}.ready")
+        else:
+            conv.remove_state("{relation_name}.ready")
+
+    @hook("{requires:osm-nbi}-relation-departed")
+    def departed(self):
+        conv = self.conversation()
+        conv.remove_state("{relation_name}.ready")
+        conv.remove_state("{relation_name}.joined")
+
+    def nbis(self):
+        """Return the NBI's host and port.
+
+        [{
+            'host': <host>,
+            'port': <port>,
+        }]
+        """
+        nbis = []
+        for conv in self.conversations():
+            port = conv.get_remote("port")
+            host = conv.get_remote("host") or conv.get_remote("private-address")
+            if host and port:
+                nbis.append({"host": host, "port": port})
+        return nbis