[rewrite] Updated models a bit, preparing to make first functional routes

backend/app/database/exceptions.py

@@ -0,0 +1,20 @@
+class DatabaseError(Exception):
+    # Inspired by OSError which also uses errno's
+    # It's a better approach than using a class for each error
+    UNKNOWN_ERROR = -1
+
+    CONNECTION_ERROR = 1
+    EMPTY_CONFIG = 2
+    DUPLICATE_ENTRY = 3
+
+    def __init__(self, message: str, errno: int, **kwargs):
+
+        super().__init__(message)
+        self.message = message
+        self.errno = errno
+
+        for key, value in kwargs.items():
+            setattr(self, key, value)
+
+
+__all__ = ["DatabaseError"]

backend/app/database/manager.py

@@ -0,0 +1,68 @@
+import logging
+from typing import Generator
+from contextlib import contextmanager
+
+from sqlalchemy.orm import sessionmaker, Session
+from sqlalchemy import create_engine, text
+from sqlalchemy.exc import DatabaseError as SqlAlchemyDatabaseError
+
+from app.database.exceptions import DatabaseError
+from app.models.base_model import Base
+
+
+class DatabaseManager():
+
+    _instance: 'DatabaseManager' = None
+
+    def __new__(cls, *args, **kwargs):
+        if cls._instance is None:
+            cls._instance = super().__new__(cls)
+        return cls._instance
+
+    def __init__(self) -> None:
+        if hasattr(self, "engine"):
+            return
+
+        self.logger = logging.getLogger(__name__)
+        self.logger.info("Initializing Database")
+
+        self.engine = create_engine('sqlite:///bank.db')
+
+        self.Session = sessionmaker(bind=self.engine)
+        self.create_tables()
+
+    def create_tables(self):
+        self.logger.debug("Creating tables")
+        Base.metadata.create_all(self.engine)
+
+    def cleanup(self) -> None:
+        self.engine.dispose()
+
+    def test_connection(self) -> bool:
+        self.logger.debug("Testing database connection")
+        try:
+            with self.engine.connect() as connection:
+                connection.execute(text("select 1"))
+            self.logger.debug("Database connection successful")
+            return True
+        except SqlAlchemyDatabaseError as e:
+            self.logger.critical("Database connection failed: %s", e)
+            raise DatabaseError("Database connection failed", DatabaseError.CONNECTION_ERROR) from e
+
+        return False
+
+    @classmethod
+    @contextmanager
+    def get_session(cls) -> Generator[Session, None, None]:
+        session = cls._instance.Session()
+        try:
+            yield session
+        except Exception as e:
+            session.rollback()
+            cls._instance.logger.error("Transaction failed: %s", e)
+            raise
+        finally:
+            session.close()
+
+
+__all__ = ["DatabaseManager"]