"""数据库引擎 / 会话 / 依赖注入 / 自动建库。"""

from __future__ import annotations

import logging
from collections.abc import Generator

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

from app.core.config import settings

logger = logging.getLogger(__name__)


def _build_engine() -> Engine:
    if settings.DB_DRIVER.startswith("sqlite"):
        return create_engine(
            settings.database_url,
            echo=settings.DB_ECHO,
            connect_args={"check_same_thread": False},
        )
    return create_engine(
        settings.database_url,
        echo=settings.DB_ECHO,
        pool_size=settings.DB_POOL_SIZE,
        pool_recycle=settings.DB_POOL_RECYCLE,
        pool_pre_ping=True,
        future=True,
    )


engine: Engine = _build_engine()
SessionLocal = sessionmaker(bind=engine, autocommit=False, autoflush=False, class_=Session)


def ensure_database_exists() -> None:
    """MySQL 下若目标库不存在则自动创建，省去手工建库。"""
    if settings.DB_DRIVER.startswith("sqlite"):
        return
    root_engine = create_engine(settings.server_url_without_db, future=True)
    try:
        with root_engine.connect() as conn:
            conn.execute(
                text(
                    f"CREATE DATABASE IF NOT EXISTS `{settings.DB_NAME}` "
                    f"DEFAULT CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci"
                )
            )
            conn.commit()
    finally:
        root_engine.dispose()


def get_db() -> Generator[Session, None, None]:
    """FastAPI 依赖：每个请求一个会话，结束即关闭。"""
    db = SessionLocal()
    try:
        yield db
    finally:
        db.close()


def dialect_name() -> str:
    return engine.dialect.name