package gateway

import (
	"context"
	"errors"
	"log"
	"time"

	"github.com/wangjia/pay/internal/model"
	"github.com/wangjia/pay/internal/provider"
	"github.com/wangjia/pay/internal/store"
)

type SettleResult string

const (
	SettleIgnored        SettleResult = "ignored"         // 非成功状态(pending/failed)
	SettleNotFound       SettleResult = "not_found"       // provider_ref 无对应 attempt
	SettleAmountMismatch SettleResult = "amount_mismatch" // 币种不符 / 少付
	SettleDuplicate      SettleResult = "duplicate"       // 订单已非 pending(幂等 no-op)
	SettleProcessed      SettleResult = "processed"       // 本次真正翻转为 paid
	SettleFailed         SettleResult = "failed"          // 暂时性失败(outbox 入队失败等):未翻转,渠道应重投
)

var ErrAmountMismatch = errors.New("gateway: paid amount/currency mismatch")

// Settle normalizes a PaidEvent into activation: locate order via provider_ref →
// attempt → order (设计 §4「归一化 PaidEvent」), reconcile currency+amount, then
// enqueue-before-flip:先幂等入队 payment.succeeded(unique 键,重复 no-op),
// 再经 P1 MarkAttemptPaid 幂等翻转(order=pending 原子守卫)。
//
// 顺序不变量(资金命脉):**订单为 paid ⇒ outbox 行必已存在**。
//   - 先翻转后入队:两步间崩溃 → 已收钱但业务方永不知情,且无任何机制重试 → 客诉才发现。
//   - 先入队后翻转:两步间崩溃 → outbox 里躺着一条"单还没付"的行;Notifier 投递前有
//     "订单已付"门禁(Task 6),不会把未付单通知出去。渠道因拿不到 200 会重投回调
//     (查单兜底同样收敛),重投时入队/翻转都幂等,自愈。
//   - 入队本身失败:返回 SettleFailed 且不翻转,同样交给渠道重投恢复。
func (g *Gateway) Settle(ctx context.Context, ev *provider.PaidEvent) (SettleResult, error) {
	if ev.Status != provider.PaidSucceeded {
		return SettleIgnored, nil // 非成功状态:确认收到即可
	}
	att, err := g.orders.AttemptByProviderRef(ev.ProviderRef)
	if err != nil {
		if errors.Is(err, store.ErrAttemptNotFound) {
			return SettleNotFound, nil
		}
		// 读库瞬时失败是可重试态,不能与"查无此单"终态混淆。
		return SettleFailed, err
	}
	// 金额/币种核对:币种须一致,实付须 ≥ 应收(允许 crypto 多付,拒少付)。
	if ev.PaidCurrency != att.Currency || ev.PaidAmountMinor < att.AmountMinor {
		return SettleAmountMismatch, ErrAmountMismatch
	}
	// paid_at 优先用渠道报的支付时间(对账时与渠道流水对得上),渠道不报才落收到时间。
	paidAt := time.Now()
	if ev.PaidAt != nil {
		paidAt = *ev.PaidAt
	}

	if err := g.enqueuePaymentSucceeded(att, paidAt); err != nil {
		return SettleFailed, err // 未入队绝不翻转;渠道重投时幂等恢复
	}
	flipped, err := g.orders.MarkAttemptPaid(att.OutTradeNo, att.Channel, ev.ProviderRef, paidAt)
	if err != nil {
		return SettleFailed, err
	}
	if !flipped {
		return SettleDuplicate, nil // 已处理过 / 已取消 / 已过期 → 幂等 no-op
	}
	return SettleProcessed, nil
}

// enqueuePaymentSucceeded 组 webhook 领域 payload 并幂等入队。仅订单仍 pending 时入队:
// 订单已 paid 说明翻转已发生,而翻转严格发生在成功入队之后(顺序不变量),行必已存在;
// 订单已 canceled 则不该通知(晚到支付走 P4 退款/P6 对账,不自动开通)。
func (g *Gateway) enqueuePaymentSucceeded(att *model.Attempt, paidAt time.Time) error {
	o, err := g.orders.GetOrder(att.OutTradeNo)
	if err != nil {
		return err
	}
	if o.BizSystem == "" || o.Status != model.OrderPendingV2 {
		return nil // 独立收款无业务方回调;或已翻转/已取消
	}
	data := map[string]any{
		"event_type":       "payment.succeeded",
		"out_trade_no":     o.OutTradeNo,
		"biz_system":       o.BizSystem,
		"biz_ref":          o.BizRef,
		"product_biz_code": o.BizCode, // 设计 §5:业务方按套餐码映射权益(时长/档位),不硬编码 product_id
		"amount_minor":     o.AmountMinor,
		"currency":         o.Currency,
		"channel":          att.Channel,
		"paid_at":          paidAt.Format(time.RFC3339),
	}
	return g.webhook.Enqueue(o.OutTradeNo, o.BizSystem, "payment.succeeded", "", data)
}

// HandleCallback runs a channel's raw callback through its Provider.VerifyCallback
// (验签/解析封死在渠道内) then settles the normalized event.
func (g *Gateway) HandleCallback(ctx context.Context, method string, in provider.CallbackInput) (SettleResult, error) {
	prov, err := g.providers.Get(method)
	if err != nil {
		return SettleNotFound, err
	}
	ev, err := prov.VerifyCallback(ctx, in)
	if err != nil {
		return SettleNotFound, err
	}
	return g.Settle(ctx, ev)
}

// SyncPendingAttempts polls every pending attempt via its Provider.Query and
// settles hits — the query-based backstop for lost webhooks (设计 §8 对账优先).
// Returns how many attempts were newly settled to paid.
func (g *Gateway) SyncPendingAttempts(ctx context.Context, limit int) (int, error) {
	atts, err := g.orders.ListAttemptsByStatus(model.AttemptPending, limit)
	if err != nil {
		return 0, err
	}
	settled := 0
	for i := range atts {
		att := &atts[i]
		prov, err := g.providers.Get(att.Channel)
		if err != nil {
			continue
		}
		// 查单带尝试完整上下文(crypto 需要地址/金额/时间窗才能扫链核对)。
		ev, err := prov.Query(ctx, provider.QueryRequest{
			ProviderRef: att.ProviderRef, OutTradeNo: att.OutTradeNo, AccountID: att.AccountID,
			AmountMinor: att.AmountMinor, Currency: att.Currency,
			CreatedAt: att.CreatedAt, ExpiresAt: att.ExpiresAt,
		})
		if err != nil || ev == nil {
			continue
		}
		res, serr := g.Settle(ctx, ev)
		switch res {
		case SettleProcessed:
			settled++
		case SettleIgnored, SettleDuplicate:
			// 常态:未付/已处理,不刷日志
		default: // not_found / amount_mismatch / failed —— 对账兜底的盲区,必须可见
			log.Printf("[settle-sync] attempt=%s channel=%s result=%s err=%v", att.ProviderRef, att.Channel, res, serr)
		}
	}
	return settled, nil
}