"""Quota three-phase protocol: reserve → commit → refund (架构文档 §7.4).

为什么预扣而不是直接扣: 长耗时任务可能失败，直接扣会产生「扣了额度没拿到
结果」的客诉。V1 没有客服退款兜底手段，只能靠机制保证 (FR-BILL-05).

Nothing here decides *how much* a feature costs — that comes from
``bl_quota_rule`` so it can change without a release (FR-BILL-04).
"""

from __future__ import annotations

from dataclasses import dataclass
from datetime import UTC, datetime
from typing import Any, cast

from sqlalchemy.exc import IntegrityError
from sqlalchemy.ext.asyncio import AsyncSession

from packages.billing import repo
from packages.domain.billing import quota as quota_rules
from packages.domain.errors import QuotaExceededError
from packages.domain.ids import next_id
from packages.shared.errors import AppError, ErrorCode, QuotaExhaustedError
from packages.shared.logging import get_logger
from packages.shared.models import Ledger, QuotaRule
from packages.shared.observability import QUOTA_EVENTS

logger = get_logger(__name__)


@dataclass(frozen=True, slots=True)
class Reservation:
    tx_id: int
    user_id: int
    quota_key: str
    period_key: str
    amount: int
    remaining: int
    idempotency_key: str


@dataclass(frozen=True, slots=True)
class QuotaSnapshot:
    quota_key: str
    period_key: str
    used: int
    limit_value: int
    bonus_granted: int
    remaining: int
    reset_at: datetime | None


@dataclass(frozen=True, slots=True)
class TaskBonusClaim:
    """一次成功领取的结果（路由层据此组装 TaskBonusClaimResponse）."""

    task_key: str
    quota_key: str
    amount: int
    bonus_granted: int
    remaining: int


def _parse_task_rule(
    task_key: str, conf: dict[str, Any]
) -> tuple[str, int, quota_rules.PeriodType]:
    """解析 ``settings.task_bonus_rules`` 的一条配置.

    坏配置是运维错误（5xxxx），不是用户错误：提前在这里拦下，比让
    ``period_key`` 在请求路径上抛 ValueError 变成 500 清晰得多。
    """
    quota_key = conf.get("quota_key")
    amount = conf.get("amount")
    claim_period = conf.get("claim_period")
    if not isinstance(quota_key, str) or not quota_key:
        raise AppError(
            ErrorCode.CONFIG_ERROR, message="任务奖励配置不合法", data={"task_key": task_key}
        )
    if not isinstance(amount, int) or isinstance(amount, bool) or amount <= 0:
        raise AppError(
            ErrorCode.CONFIG_ERROR, message="任务奖励配置不合法", data={"task_key": task_key}
        )
    if not isinstance(claim_period, str) or claim_period not in quota_rules.PERIOD_TYPES:
        raise AppError(
            ErrorCode.CONFIG_ERROR, message="任务奖励配置不合法", data={"task_key": task_key}
        )
    return quota_key, amount, cast(quota_rules.PeriodType, claim_period)


class BillingService:
    def __init__(self, session: AsyncSession, *, tz_offset_hours: int = 8) -> None:
        self._session = session
        self._tz_offset = tz_offset_hours

    # -- read ---------------------------------------------------------------

    async def get_quota(self, *, user_id: int, quota_key: str) -> QuotaSnapshot:
        rule = await self._require_rule(quota_key)
        period_type = cast(quota_rules.PeriodType, rule.period_type)
        now = datetime.now(UTC)
        period_key = quota_rules.period_key(now, period_type, self._tz_offset)
        row = await repo.lock_or_create_quota(
            self._session,
            user_id=user_id,
            quota_key=quota_key,
            period_key=period_key,
            limit_value=rule.base_limit,
        )
        state = quota_rules.QuotaState(
            used=row.used,
            base_limit=row.limit_value,
            bonus=row.bonus_granted,
            hard_cap=rule.hard_cap,
        )
        return QuotaSnapshot(
            quota_key=quota_key,
            period_key=period_key,
            used=row.used,
            limit_value=row.limit_value,
            bonus_granted=row.bonus_granted,
            remaining=state.remaining,
            reset_at=quota_rules.period_reset_at(now, period_type, self._tz_offset),
        )

    async def list_ledger(self, *, user_id: int, limit: int = 50) -> list[Ledger]:
        return await repo.list_ledger(self._session, user_id, limit)

    # -- phase 1: reserve ---------------------------------------------------

    async def reserve(
        self,
        *,
        user_id: int,
        quota_key: str,
        request_key: str,
        amount: int = 1,
        reason: str | None = None,
        ref_type: str | None = None,
        ref_id: str | None = None,
    ) -> Reservation:
        """Freeze ``amount`` units. Idempotent on ``request_key``."""
        idem_key = quota_rules.reserve_idempotency_key(
            user_id=user_id, quota_key=quota_key, request_key=request_key
        )
        existing = await repo.get_ledger_by_idempotency_key(self._session, idem_key)
        if existing is not None:
            QUOTA_EVENTS.labels(quota_key, "reserve", "idempotent_hit").inc()
            return Reservation(
                tx_id=existing.tx_id,
                user_id=user_id,
                quota_key=quota_key,
                period_key=existing.period_key or "",
                amount=abs(existing.delta),
                remaining=existing.balance_after,
                idempotency_key=idem_key,
            )

        rule = await self._require_rule(quota_key)
        period_type = cast(quota_rules.PeriodType, rule.period_type)
        now = datetime.now(UTC)
        period_key = quota_rules.period_key(now, period_type, self._tz_offset)
        row = await repo.lock_or_create_quota(
            self._session,
            user_id=user_id,
            quota_key=quota_key,
            period_key=period_key,
            limit_value=rule.base_limit,
        )
        state = quota_rules.QuotaState(
            used=row.used,
            base_limit=row.limit_value,
            bonus=row.bonus_granted,
            hard_cap=rule.hard_cap,
        )

        try:
            new_state = quota_rules.reserve(state, amount)
        except QuotaExceededError as exc:
            QUOTA_EVENTS.labels(quota_key, "reserve", "exhausted").inc()
            reset_at = quota_rules.period_reset_at(now, period_type, self._tz_offset)
            raise QuotaExhaustedError(
                required=exc.required,
                remaining=exc.remaining,
                reset_at=reset_at.isoformat() if reset_at else None,
            ) from exc

        row.used = new_state.used
        tx_id = next_id()
        repo.add_ledger(
            self._session,
            Ledger(
                tx_id=tx_id,
                user_id=user_id,
                delta=-amount,
                tx_type="consume",
                status="reserved",
                reason=reason,
                ref_type=ref_type,
                ref_id=ref_id,
                quota_key=quota_key,
                period_key=period_key,
                balance_after=quota_rules.balance_after(new_state),
                idempotency_key=idem_key,
            ),
        )
        await self._session.flush()
        QUOTA_EVENTS.labels(quota_key, "reserve", "ok").inc()
        logger.info(
            "quota_reserved",
            tx_id=tx_id,
            quota_key=quota_key,
            amount=amount,
            remaining=new_state.remaining,
        )
        return Reservation(
            tx_id=tx_id,
            user_id=user_id,
            quota_key=quota_key,
            period_key=period_key,
            amount=amount,
            remaining=new_state.remaining,
            idempotency_key=idem_key,
        )

    # -- phase 2: commit ----------------------------------------------------

    async def commit(self, reservation: Reservation) -> None:
        """Confirm the deduction. Safe to call twice."""
        ledger = await repo.get_ledger(self._session, reservation.tx_id)
        if ledger is None:
            raise AppError(ErrorCode.STATE_CONFLICT, message="配额流水不存在")
        if ledger.status == "reserved":
            ledger.status = "committed"
            await self._session.flush()
            QUOTA_EVENTS.labels(reservation.quota_key, "commit", "ok").inc()
            logger.info("quota_committed", tx_id=ledger.tx_id)
        else:
            QUOTA_EVENTS.labels(reservation.quota_key, "commit", "noop").inc()

    # -- phase 3: refund ----------------------------------------------------

    async def refund(self, reservation: Reservation, *, reason: str = "task_failed") -> None:
        """Release a reservation and write the reverse ledger entry.

        FR-BILL-05 requires refunds to be idempotent; the refund ledger key is
        derived from the reserve key so a retry can never double-refund.
        """
        ledger = await repo.get_ledger(self._session, reservation.tx_id)
        if ledger is None:
            raise AppError(ErrorCode.STATE_CONFLICT, message="配额流水不存在")
        if ledger.status != "reserved":
            QUOTA_EVENTS.labels(reservation.quota_key, "refund", "noop").inc()
            return

        refund_key = quota_rules.refund_idempotency_key(reservation.idempotency_key)
        if await repo.get_ledger_by_idempotency_key(self._session, refund_key) is not None:
            QUOTA_EVENTS.labels(reservation.quota_key, "refund", "noop").inc()
            return

        rule = await self._require_rule(reservation.quota_key)
        row = await repo.lock_or_create_quota(
            self._session,
            user_id=reservation.user_id,
            quota_key=reservation.quota_key,
            period_key=reservation.period_key,
            limit_value=rule.base_limit,
        )
        state = quota_rules.QuotaState(
            used=row.used,
            base_limit=row.limit_value,
            bonus=row.bonus_granted,
            hard_cap=rule.hard_cap,
        )
        new_state = quota_rules.refund(state, reservation.amount)
        row.used = new_state.used
        ledger.status = "refunded"

        repo.add_ledger(
            self._session,
            Ledger(
                tx_id=next_id(),
                user_id=reservation.user_id,
                delta=reservation.amount,
                tx_type="refund",
                status="committed",
                reason=reason,
                ref_type=ledger.ref_type,
                ref_id=ledger.ref_id,
                quota_key=reservation.quota_key,
                period_key=reservation.period_key,
                balance_after=quota_rules.balance_after(new_state),
                idempotency_key=refund_key,
            ),
        )
        await self._session.flush()
        QUOTA_EVENTS.labels(reservation.quota_key, "refund", "ok").inc()
        logger.info(
            "quota_refunded",
            tx_id=ledger.tx_id,
            amount=reservation.amount,
            remaining=new_state.remaining,
        )

    # -- task bonus (FR-BILL-03) --------------------------------------------

    async def claim_task_bonus(
        self,
        *,
        user_id: int,
        task_key: str,
        rules: dict[str, dict[str, Any]],
    ) -> TaskBonusClaim:
        """领取任务奖励：发放即到账、幂等、封顶（FR-BILL-03）.

        ``rules`` 来自 ``settings.task_bonus_rules``（FR-BILL-04 配置化）：
        amount 目前是占位值，产品在产品方案 §3.2 定稿后改 env 即生效，
        不需要改代码。
        """
        conf = rules.get(task_key)
        if conf is None:
            raise AppError(ErrorCode.TASK_BONUS_UNKNOWN, data={"task_key": task_key})
        quota_key, amount, claim_period = _parse_task_rule(task_key, conf)

        rule = await self._require_rule(quota_key)
        quota_period_type = cast(quota_rules.PeriodType, rule.period_type)
        now = datetime.now(UTC)
        # 幂等粒度跟任务的 claim_period 走，额度行周期跟 bl_quota_rule 走：
        # 「每天可领」的任务可以给「按月计量」的额度加成，两套周期不能混。
        quota_pk = quota_rules.period_key(now, quota_period_type, self._tz_offset)
        claim_pk = quota_rules.period_key(now, claim_period, self._tz_offset)
        idem_key = quota_rules.grant_idempotency_key(
            user_id=user_id, task_key=task_key, claim_period_key=claim_pk
        )

        # 幂等快捷路径：本周期已发放过就直接拒绝，不进任何写路径。
        if await repo.get_ledger_by_idempotency_key(self._session, idem_key) is not None:
            QUOTA_EVENTS.labels(quota_key, "grant", "idempotent_hit").inc()
            raise AppError(ErrorCode.TASK_BONUS_ALREADY_CLAIMED, data={"task_key": task_key})

        row = await repo.lock_or_create_quota(
            self._session,
            user_id=user_id,
            quota_key=quota_key,
            period_key=quota_pk,
            limit_value=rule.base_limit,
        )
        state = quota_rules.QuotaState(
            used=row.used,
            base_limit=row.limit_value,
            bonus=row.bonus_granted,
            hard_cap=rule.hard_cap,
        )
        decision = quota_rules.grant_bonus(state, amount, rule.task_bonus_max)
        if not decision.allowed:
            # 封顶拒绝：不写任何流水，bonus_granted 保持原值（验收 3）。
            QUOTA_EVENTS.labels(quota_key, "grant", "capped").inc()
            raise AppError(
                ErrorCode.TASK_BONUS_CAP_REACHED,
                data={
                    "task_key": task_key,
                    "bonus_granted": state.bonus,
                    "task_bonus_max": rule.task_bonus_max,
                },
            )

        row.bonus_granted = decision.bonus
        tx_id = next_id()
        try:
            repo.add_ledger(
                self._session,
                Ledger(
                    tx_id=tx_id,
                    user_id=user_id,
                    # delta=0：system_grant 不改变 used，只提高有效额度；balance_after
                    # 仍按 remaining 语义记录 —— 流水可重算的是 used，不是余额本身，
                    # 与 reserve/commit 的记账口径一致。
                    delta=0,
                    tx_type="system_grant",
                    status="committed",
                    reason=task_key,
                    ref_type="task_bonus",
                    ref_id=task_key,
                    quota_key=quota_key,
                    period_key=quota_pk,
                    balance_after=decision.remaining,
                    idempotency_key=idem_key,
                ),
            )
            await self._session.flush()
        except IntegrityError as exc:
            # 并发兜底：两个请求同时通过上面的快捷检查，idempotency_key 唯一约束
            # 让后提交者失败。对用户来说结果与快捷路径等价 —— 已领取，而非 500。
            await self._session.rollback()
            QUOTA_EVENTS.labels(quota_key, "grant", "idempotent_hit").inc()
            raise AppError(
                ErrorCode.TASK_BONUS_ALREADY_CLAIMED, data={"task_key": task_key}
            ) from exc

        QUOTA_EVENTS.labels(quota_key, "grant", "ok").inc()
        logger.info(
            "task_bonus_granted",
            tx_id=tx_id,
            task_key=task_key,
            quota_key=quota_key,
            amount=amount,
            bonus=decision.bonus,
            remaining=decision.remaining,
        )
        return TaskBonusClaim(
            task_key=task_key,
            quota_key=quota_key,
            amount=amount,
            bonus_granted=decision.bonus,
            remaining=decision.remaining,
        )

    # -- helpers ------------------------------------------------------------

    async def _require_rule(self, quota_key: str) -> QuotaRule:
        rule = await repo.get_rule(self._session, quota_key)
        if rule is None:
            raise AppError(
                ErrorCode.CONFIG_ERROR,
                message="配额规则未配置",
                data={"quota_key": quota_key},
            )
        return rule