"""数据库后端选择：配置了 MYSQL_DSN 时走 MySQL，否则回退本地 SQLite。"""

from __future__ import annotations

from typing import Literal
from urllib.parse import unquote, urlparse

from jiangchang_skill_core import config

DbBackend = Literal["sqlite", "mysql"]


def get_mysql_dsn() -> str:
    return (config.get("MYSQL_DSN") or "").strip()


def resolve_backend() -> DbBackend:
    return "mysql" if get_mysql_dsn() else "sqlite"


def parse_mysql_dsn(dsn: str) -> dict[str, object]:
    text = dsn.strip()
    if not text.startswith(("mysql://", "mysql2://")):
        raise ValueError("MYSQL_DSN must be a mysql:// URL.")
    parsed = urlparse(text)
    database = (parsed.path or "").lstrip("/")
    if not database:
        raise ValueError("MYSQL_DSN must include a database name.")
    return {
        "host": parsed.hostname or "127.0.0.1",
        "port": parsed.port or 3306,
        "user": unquote(parsed.username or ""),
        "password": unquote(parsed.password or ""),
        "database": database,
    }