"""用量记账落库（ARCH §4.8）。

`LedgerSink` 为接口，便于测试注入内存替身；生产用 SQLAlchemy 实现写 usage_ledger。
"""

from __future__ import annotations

from typing import Protocol

from sqlalchemy.ext.asyncio import AsyncSession
from ww_db.models import UsageLedger

from .types import Scope, Usage


class LedgerSink(Protocol):
    async def record(self, scope: Scope, usage: Usage) -> None: ...


class SqlAlchemyLedgerSink:
    """把每次调用写入 usage_ledger（owner_id 取 scope.user_id，单用户 stub）。"""

    def __init__(self, session: AsyncSession) -> None:
        self._session = session

    async def record(self, scope: Scope, usage: Usage) -> None:
        row = UsageLedger(
            owner_id=scope.user_id,
            project_id=scope.project_id,
            provider=usage.provider,
            model=usage.model,
            input_tokens=usage.input_tokens,
            output_tokens=usage.output_tokens,
            cache_read=usage.cache_read_tokens,
            cost_minor=usage.cost_minor,
            currency=usage.currency,
        )
        self._session.add(row)
        await self._session.flush()