"""
数据库引擎、会话工厂、Base 声明基类。

- 异步（FastAPI）与同步（Celery、Alembic、脚本）均使用 psycopg（psycopg3）。
- database_url 由 settings 指定；若为 postgresql://... 则在此拼接为 postgresql+psycopg:// 以使用 psycopg3。

事务规则：
- get_async_db() 只负责创建和关闭 session，不自动 commit/rollback。
- service / Celery task 层优先使用 transactional() / transactional_sync() 管理多步写操作。
- repo 层禁止调用 commit() / rollback()。

transactional 语义：
- transactional() / transactional_sync() 是顶层事务边界；成功 exit 时 commit 整个 session，异常时 rollback 整个 session。
- 不支持嵌套自身：同一 session 上连续两次 transactional() = 两次独立 commit（WS pipeline 分段持久化属于此模式）。
- 需要嵌套回滚时：在已开启的事务内使用 transactional_nested() / transactional_nested_sync()（基于 SQLAlchemy begin_nested() savepoint）。
- 选择指南：单步/整段业务原子提交 → transactional；长生命周期 session 内局部试错、可独立回滚的子步骤 → transactional_nested（必须在外层事务 active 期间）。

transactional_nested 示例（外层提交、内层失败仅回滚 savepoint）::

    async with transactional(session):
        session.add(parent_row)
        try:
            async with transactional_nested(session):
                await attempt_optional_side_effect(session)
        except RecoverableError:
            pass  # savepoint rolled back; parent_row still commits
"""

from contextlib import asynccontextmanager, contextmanager
from typing import AsyncGenerator

from sqlalchemy import create_engine, text
from sqlalchemy.ext.asyncio import AsyncSession, async_sessionmaker, create_async_engine
from sqlalchemy.orm import DeclarativeBase, Session, sessionmaker

from app.core.config import settings


class Base(DeclarativeBase):
    pass


def utc_now():
    """返回当前 UTC 时间（带时区信息）"""
    from datetime import datetime, timezone

    return datetime.now(timezone.utc)


# ── Database URL（纯 postgresql:// 时拼接为 postgresql+psycopg://）────────────────


def ensure_psycopg_url(url: str) -> str:
    """若为 postgresql://... 则改为 postgresql+psycopg://...，否则原样返回。"""
    if url.startswith("postgresql://") and not url.startswith("postgresql+psycopg://"):
        return "postgresql+psycopg://" + url[len("postgresql://") :]
    return url


def _database_url() -> str:
    return ensure_psycopg_url(settings.database_url)


# ── Async engine & session (FastAPI) ───────────────────────────

async_engine = create_async_engine(
    _database_url(),
    echo=False,
    pool_size=5,
    max_overflow=10,
    pool_pre_ping=True,
)

AsyncSessionLocal = async_sessionmaker(
    async_engine, class_=AsyncSession, expire_on_commit=False
)


async def get_async_db() -> AsyncGenerator[AsyncSession, None]:
    """Yield a clean async session — callers are responsible for commit/rollback."""
    async with AsyncSessionLocal() as session:
        try:
            yield session
        finally:
            await session.close()


@asynccontextmanager
async def transactional(session: AsyncSession):
    """Top-level async transaction: commit on success, rollback on any exception.

    Do not nest transactional() on the same session; each call commits independently.
    For partial rollback within an active transaction, use transactional_nested().
    """
    try:
        yield session
        await session.commit()
    except Exception:
        await session.rollback()
        raise


@asynccontextmanager
async def transactional_nested(session: AsyncSession):
    """Savepoint boundary; roll back only this block on error.

    Must be used while the session already has an active transaction (e.g. inside
    transactional() before it commits, or after autobegin from a prior write).
    """
    async with session.begin_nested():
        yield session


# ── Sync engine & session (Celery, Alembic, scripts) ─────────

sync_engine = create_engine(
    _database_url(),
    echo=False,
    pool_size=5,
    max_overflow=10,
    pool_pre_ping=True,
)

SyncSessionLocal = sessionmaker(
    bind=sync_engine,
    autocommit=False,
    autoflush=False,
    expire_on_commit=False,
)

SessionLocal = SyncSessionLocal


def init_db_schema() -> None:
    """根据当前已注册的 Model 创建缺失的表（开发/空库时自动建表，与 api-bak 行为一致）。
    不执行 DROP/ALTER，仅 create_all；生产环境仍建议用 Alembic 做可控迁移。
    memory 模块依赖 pgvector，建表前先确保扩展已启用。
    """
    with sync_engine.connect() as conn:
        conn.execute(text("CREATE EXTENSION IF NOT EXISTS vector"))
        conn.commit()
    Base.metadata.create_all(bind=sync_engine)


@contextmanager
def transactional_sync(session: Session):
    """Top-level sync transaction: commit on success, rollback on any exception.

    Do not nest transactional_sync() on the same session; each call commits independently.
    For partial rollback within an active transaction, use transactional_nested_sync().
    """
    try:
        yield session
        session.commit()
    except Exception:
        session.rollback()
        raise


@contextmanager
def transactional_nested_sync(session: Session):
    """Savepoint boundary for sync Celery / scripts; roll back only this block on error."""
    with session.begin_nested():
        yield session


@contextmanager
def get_sync_db():
    """Context-managed synchronous session for Celery tasks."""
    db = SessionLocal()
    try:
        yield db
    except Exception:
        db.rollback()
        raise
    finally:
        db.close()