"""HTTP 幂等键服务。

``run_idempotent`` 自管 ``AsyncSessionLocal``：在同一 session 内查幂等记录、执行 handler、
写入结果（保证三者同事务）。``handler`` 接收该 session，供需要在同事务跑的业务（如发消息）
复用。调用方（路由）不持有 session。
"""

import hashlib
from collections.abc import Awaitable, Callable

from pydantic import BaseModel
from sqlalchemy.ext.asyncio import AsyncSession

from app.core.config import settings
from app.core.errors import AppError, current_trace_id
from app.db.session import AsyncSessionLocal
from app.models.idempotency import IdempotencyKey
from app.repositories import idempotency as idempotency_repo
from app.repositories.json_utils import dumps, loads_dict


def request_hash(payload: BaseModel) -> str:
    body = payload.model_dump_json(exclude_unset=True)
    return hashlib.sha256(body.encode("utf-8")).hexdigest()


async def run_idempotent[T: BaseModel](
    *,
    key: str | None,
    method: str,
    path: str,
    payload: BaseModel,
    response_type: type[T],
    resource_type: str,
    handler: Callable[[AsyncSession], Awaitable[T]],
    owner_scope: str = settings.default_owner_scope,
) -> T:
    """按 Idempotency-Key 保证请求只执行一次；handler 在本函数管理的 session 内执行。"""
    async with AsyncSessionLocal() as session:
        if not key:
            return await handler(session)

        scope = owner_scope
        digest = request_hash(payload)
        existing = await idempotency_repo.get_by_scope_key(session, scope=scope, key=key)
        if existing is not None:
            if existing.request_hash != digest:
                raise AppError("conflict", "Idempotency-Key 已用于不同请求。")
            return response_type.model_validate(loads_dict(existing.response_body_json))

        response = await handler(session)
        resource_id = getattr(response, "run_id", None) or getattr(response, "id", None)
        record = IdempotencyKey(
            key=key,
            scope=scope,
            method=method,
            path=path,
            request_hash=digest,
            status="completed",
            response_status_code=200,
            response_body_json=dumps(response.model_dump(mode="json")),
            resource_type=resource_type,
            resource_id=str(resource_id) if resource_id else None,
            trace_id=current_trace_id(),
        )
        session.add(record)
        await session.commit()
        return response