from __future__ import annotations

from sqlalchemy import select
from sqlalchemy.ext.asyncio import AsyncSession

from app.models.llm_billing.policy import LlmBillingPolicyModel
from app.services.llm_billing.context import LlmBillingPolicy


async def get_llm_billing_policy(
    db: AsyncSession,
    *,
    scene_code: str | None = None,
) -> LlmBillingPolicy:
    """按业务场景读取固定消费积分；不再读取旧 SystemConfig 冻结/预扣配置。"""
    resolved_scene = scene_code
    if not resolved_scene:
        return LlmBillingPolicy(
            charge_credits=0.0,
            valid=False,
            error="LLM业务场景不能为空",
        )
    result = await db.execute(
        select(LlmBillingPolicyModel)
        .where(LlmBillingPolicyModel.scene_code == resolved_scene)
        .limit(1)
    )
    model = result.scalar_one_or_none()
    if model is None:
        return LlmBillingPolicy(
            charge_credits=0.0,
            valid=False,
            error=f"未配置LLM场景消费积分：{resolved_scene}",
        )
    # 数据库物理字段 pre_deduct_credits 为历史命名，本轮不迁移字段；业务语义统一为 charge_credits。
    amount = float(model.pre_deduct_credits)
    if not model.is_active or amount <= 0:
        return LlmBillingPolicy(
            charge_credits=amount,
            valid=False,
            error=f"LLM场景积分配置未启用或金额无效：{resolved_scene}",
            policy_id=model.id,
            version=model.version,
            scene_name=model.scene_name,
        )
    return LlmBillingPolicy(
        charge_credits=round(amount, 2),
        valid=True,
        policy_id=model.id,
        version=model.version,
        scene_name=model.scene_name,
    )