Adding manual external DB URI config

Change-Id: I24782d5b9594aebae2ec97b1196acfa2bafb6dbd
Signed-off-by: sousaedu <eduardo.sousa@canonical.com>
diff --git a/installers/charm/pol/src/charm.py b/installers/charm/pol/src/charm.py
index d339e1c..b2e5883 100755
--- a/installers/charm/pol/src/charm.py
+++ b/installers/charm/pol/src/charm.py
@@ -24,7 +24,7 @@
 
 
 import logging
-from typing import NoReturn
+from typing import NoReturn, Optional
 
 from ops.main import main
 from opslib.osm.charm import CharmedOsmBase, RelationsMissing
@@ -44,6 +44,7 @@
 
 class ConfigModel(ModelValidator):
     log_level: str
+    mongodb_uri: Optional[str]
 
     @validator("log_level")
     def validate_log_level(cls, v):
@@ -51,6 +52,12 @@
             raise ValueError("value must be INFO or DEBUG")
         return v
 
+    @validator("mongoddb_uri")
+    def validate_mongodb_uri(cls, v):
+        if v and not v.startswith("mongodb://"):
+            raise ValueError("mongodb_uri is not properly formed")
+        return v
+
 
 class PolCharm(CharmedOsmBase):
     def __init__(self, *args) -> NoReturn:
@@ -69,7 +76,7 @@
 
         if self.kafka_client.is_missing_data_in_unit():
             missing_relations.append("kafka")
-        if self.mongodb_client.is_missing_data_in_unit():
+        if not config.mongodb_uri and self.mongodb_client.is_missing_data_in_unit():
             missing_relations.append("mongodb")
 
         if missing_relations:
@@ -78,10 +85,16 @@
     def build_pod_spec(self, image_info):
         # Validate config
         config = ConfigModel(**dict(self.config))
+
+        if config.mongodb_uri and not self.mongodb_client.is_missing_data_in_unit():
+            raise Exception("Mongodb data cannot be provided via config and relation")
+
         # Check relations
         self._check_missing_dependencies(config)
+
         # Create Builder for the PodSpec
         pod_spec_builder = PodSpecV3Builder()
+
         # Build Container
         container_builder = ContainerV3Builder(self.app.name, image_info)
         container_builder.add_port(name=self.app.name, port=PORT)
@@ -96,13 +109,15 @@
                 "OSMPOL_MESSAGE_PORT": self.kafka_client.port,
                 # Database configuration
                 "OSMPOL_DATABASE_DRIVER": "mongo",
-                "OSMPOL_DATABASE_URI": self.mongodb_client.connection_string,
+                "OSMPOL_DATABASE_URI": config.mongodb_uri
+                or self.mongodb_client.connection_string,
             }
         )
-
         container = container_builder.build()
+
         # Add container to pod spec
         pod_spec_builder.add_container(container)
+
         return pod_spec_builder.build()