"""数据库引擎与初始化。

init_db():
- 若目标库不存在则自动创建（连到默认 postgres 库执行 CREATE DATABASE）
- 建表
"""
from __future__ import annotations

import psycopg2
from sqlalchemy import create_engine
from sqlalchemy.orm import sessionmaker

import config
from models import Base

engine = create_engine(config.DB_URL, pool_pre_ping=True, future=True)
SessionLocal = sessionmaker(bind=engine, autoflush=False, expire_on_commit=False, future=True)


def _ensure_database():
    try:
        conn = psycopg2.connect(
            host=config.PG_HOST, port=config.PG_PORT, user=config.PG_USER,
            password=config.PG_PASSWORD, dbname="postgres", connect_timeout=5)
        conn.autocommit = True
        cur = conn.cursor()
        cur.execute("SELECT 1 FROM pg_database WHERE datname = %s", (config.PG_DB,))
        if not cur.fetchone():
            cur.execute(f'CREATE DATABASE "{config.PG_DB}"')
        cur.close()
        conn.close()
    except Exception as e:  # 数据库已存在或无权限时不阻断
        print("[db] ensure_database:", repr(e)[:120])


def init_db():
    _ensure_database()
    Base.metadata.create_all(engine)
    print("[db] tables ready")


def get_session():
    return SessionLocal()