import logging
from typing import Generator
from contextlib import contextmanager

from sqlalchemy.orm import sessionmaker, Session
from sqlalchemy import create_engine, text

from app.database.exceptions import DatabaseError


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, mysql_user: str, mysql_password: str, mysql_host: str, mysql_port: str, mysql_db_name: str) -> None:
        self.logger = logging.getLogger(__name__)
        self.logger.info("Reading database config")
        self.engine = create_engine('mysql+mysqlconnector://%s:%s@%s:%s/%s' % (
            mysql_user,
            mysql_password,
            mysql_host,
            mysql_port,
            mysql_db_name),
            pool_pre_ping=True)
        self.test_connection()
        self.Session = sessionmaker(bind=self.engine) # NOSONAR

    def cleanup(self) -> None:
        self.logger.debug("Closing connection")
        self.engine.dispose()

    def test_connection(self):
        self.logger.debug("Testing database connection")
        try:
            with self.engine.connect() as connection:
                connection.execute(text("select 1"))
            self.logger.debug("Database connection successful")
        except DatabaseError as e:
            self.logger.critical("Database connection failed: %s", e)
            raise DatabaseError("Database connection failed", DatabaseError.CONNECTION_ERROR) from e


    @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"]