Add incomplete `ApplicationDatabaseService`

src/ctp_slack_bot/services/application_database_service.py

@@ -0,0 +1,29 @@
+from datetime import datetime
+from loguru import logger
+from pydantic import BaseModel, PrivateAttr
+from typing import Iterable, Mapping, Self
+
+from ctp_slack_bot.core import Settings
+from ctp_slack_bot.db import MongoDB
+
+
+class ApplicationDatabaseService(BaseModel):
+    """Service for retrieving and persisting application state."""
+
+    settings: Settings
+    mongo_db: MongoDB # TODO: This should be replaced following the repository pattern―one repository class per collection.
+
+    class Config:
+        frozen=True
+
+    def __init__(self: Self, **data) -> None:
+        super().__init__(**data)
+        logger.debug("Created {}", self.__class__.__name__)
+
+    async def get_last_modification_times_by_file_paths(self: Self, file_paths: Iterable[str]) -> Mapping[str, datetime]:
+        """Retrieve the last modification time for each file path."""
+        raise NotImplementedError() # TODO
+
+    async def set_last_modification_time_by_file_path(self: Self, file_path: str, modification_time: datetime) -> None:
+        """Set the last modification time for a file path."""
+        raise NotImplementedError() # TODO