"""
启动时执行 Alembic 迁移（与 CLI `uv run alembic upgrade head` 等价）。

- 对瞬时连接错误重试（数据库尚未就绪、网络抖动）。
- 可通过 settings 关闭迁移、或失败时中止进程（生产推荐）。
"""

from __future__ import annotations

import time
from pathlib import Path
from typing import Final

from sqlalchemy.exc import OperationalError

from app.core.config import settings
from app.core.logging import get_logger

logger = get_logger(__name__)

_API_DIR: Final[Path] = Path(__file__).resolve().parent.parent.parent


def _run_alembic_upgrade_once() -> None:
    from alembic.command import upgrade
    from alembic.config import Config

    cfg = Config(str(_API_DIR / "alembic.ini"))
    upgrade(cfg, "head")


def _is_retryable_migration_error(err: BaseException) -> bool:
    if isinstance(err, OperationalError):
        return True
    msg = str(err).lower()
    needles = (
        "connection refused",
        "could not connect",
        "connection reset",
        "timeout",
        "server closed the connection",
        "the database system is starting",
        "database system is shutting down",
        "too many connections",
    )
    return any(n in msg for n in needles)


def run_alembic_upgrade_at_startup() -> None:
    """
    同步执行迁移；失败时按 settings 记录日志或抛出。

    在 asyncio 中请使用 ``asyncio.to_thread(run_alembic_upgrade_at_startup)``，
    避免阻塞事件循环。
    """
    if not settings.alembic_run_on_startup:
        logger.info("跳过 Alembic 迁移（alembic_run_on_startup=False）")
        return

    max_tries = max(1, settings.alembic_startup_max_retries)
    base_delay = float(settings.alembic_startup_retry_base_seconds)
    last: BaseException | None = None

    for attempt in range(max_tries):
        try:
            _run_alembic_upgrade_once()
            if attempt > 0:
                logger.info(
                    "Alembic 迁移成功（第 {} 次尝试）",
                    attempt + 1,
                )
            else:
                logger.info("Alembic 迁移已就绪")
            return
        except Exception as e:
            last = e
            will_retry = attempt < max_tries - 1 and _is_retryable_migration_error(e)
            if will_retry:
                delay = base_delay * (2**attempt)
                logger.warning(
                    "Alembic 迁移失败（将重试）: {} — {:.1f}s 后重试 ({}/{})",
                    e,
                    delay,
                    attempt + 1,
                    max_tries,
                )
                time.sleep(delay)
            else:
                break

    assert last is not None
    logger.exception("Alembic 迁移失败: {}", last)
    if settings.alembic_startup_fail_fast:
        raise RuntimeError(
            "Alembic migration failed; set ALEMBIC_STARTUP_FAIL_FAST=false "
            "for dev-only tolerate mode"
        ) from last
    logger.error(
        "应用将继续启动，但数据库结构可能未更新；请检查 DATABASE_URL 与 PostgreSQL 是否可达"
    )