package pay

import (
	"context"
	"database/sql"
	"encoding/json"
	"fmt"
	"io"
	"log/slog"
	"net/http"
	"strconv"
	"time"

	"github.com/redis/go-redis/v9"

	"github.com/wangjia/pangolin/server/internal/codes"
)

// Granter 抽象 codes.Service 的支付授予入口(测试可替身;生产传 *codes.Service)。
type Granter interface {
	GrantPaidSubscriptionTx(ctx context.Context, tx *sql.Tx, userID int64, plan codes.PlanCode, days int, ref string) (int64, time.Time, error)
}

// WebhookHandler 接收 pay 的 payment.succeeded 出站 webhook。
// 验签与 pay verifyBizSign 对称:同 secret,parts=[system, ts, nonce, rawBody],
// ±tolerance 时间窗。幂等三层:nonce SETNX(传输重放)→ out_trade_no 锁内
// CAS(业务幂等,重投唯一可靠键)→ biz_ref 兜底(台账缺行自修复)。
type WebhookHandler struct {
	store     *Store
	granter   Granter
	db        *sql.DB
	rdb       *redis.Client // 可为 nil:跳过 nonce 层,业务幂等仍成立
	system    string
	secret    string
	tolerance time.Duration
	nonceTTL  time.Duration
	now       func() time.Time // 测试注入
}

func NewWebhookHandler(store *Store, granter Granter, db *sql.DB, rdb *redis.Client,
	system, secret string, tolerance, nonceTTL time.Duration) *WebhookHandler {
	return &WebhookHandler{store: store, granter: granter, db: db, rdb: rdb,
		system: system, secret: secret, tolerance: tolerance, nonceTTL: nonceTTL, now: time.Now}
}

// webhookEvent 对应 pay settle.go::enqueuePaymentSucceeded 的 payload
// (注意:payment.succeeded 无 refund_id 字段)。
type webhookEvent struct {
	EventType      string `json:"event_type"`
	OutTradeNo     string `json:"out_trade_no"`
	BizSystem      string `json:"biz_system"`
	BizRef         string `json:"biz_ref"`
	ProductBizCode string `json:"product_biz_code"`
	AmountMinor    int64  `json:"amount_minor"`
	Currency       string `json:"currency"`
	Channel        string `json:"channel"`
	PaidAt         string `json:"paid_at"` // RFC3339
}

func (h *WebhookHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	body, err := io.ReadAll(io.LimitReader(r.Body, 64<<10))
	if err != nil {
		http.Error(w, "read body", http.StatusBadRequest)
		return
	}
	if !h.verify(r, body) {
		http.Error(w, "signature verification failed", http.StatusUnauthorized)
		return
	}
	// nonce 防重放(仅传输层;pay 每次重投换新 nonce,业务幂等靠 out_trade_no)。
	if h.rdb != nil {
		if nonce := r.Header.Get("X-Pay-Nonce"); nonce != "" {
			ok, err := h.rdb.SetNX(r.Context(), "pay:webhook:nonce:"+nonce, 1, h.nonceTTL).Result()
			if err == nil && !ok {
				writeSuccess(w) // 同 nonce 重放:已处理过,直接确认
				return
			}
		}
	}
	var ev webhookEvent
	if err := json.Unmarshal(body, &ev); err != nil {
		http.Error(w, "bad payload", http.StatusBadRequest)
		return
	}
	if ev.EventType != "payment.succeeded" {
		// 事件白名单外(pay 侧只应配 payment.succeeded):确认不处理,免重投。
		slog.Warn("pay webhook: 未知事件已 ack 未处理", "event_type", ev.EventType, "out_trade_no", ev.OutTradeNo)
		writeSuccess(w)
		return
	}
	if err := h.settle(r.Context(), &ev); err != nil {
		slog.Error("pay webhook 开通失败(pay 将退避重投)", "order_no", ev.OutTradeNo, "err", err)
		http.Error(w, "settle failed", http.StatusInternalServerError)
		return
	}
	writeSuccess(w)
}

// writeSuccess:pay 的 ACK 判据是 HTTP 200 且 body 含 "SUCCESS"(大写包含)。
func writeSuccess(w http.ResponseWriter) {
	w.WriteHeader(http.StatusOK)
	_, _ = w.Write([]byte("SUCCESS"))
}

func (h *WebhookHandler) verify(r *http.Request, body []byte) bool {
	if r.Header.Get("X-Pay-System") != h.system {
		return false
	}
	ts := r.Header.Get("X-Pay-Timestamp")
	nonce := r.Header.Get("X-Pay-Nonce")
	sign := r.Header.Get("X-Pay-Sign")
	if ts == "" || nonce == "" || sign == "" {
		return false
	}
	tsi, err := strconv.ParseInt(ts, 10, 64)
	if err != nil {
		return false
	}
	tol := int64(h.tolerance.Seconds())
	if d := h.now().Unix() - tsi; d > tol || d < -tol {
		return false
	}
	return hmacVerify(h.secret, sign, h.system, ts, nonce, string(body))
}

// settle 幂等开通:锁台账行 → created→paid 翻转 + 同事务 grant(叠加语义
// 复用 codes.applySubscription)。已 paid 直接返回 nil(重投/并发输家)。
// canceled 行也照常开通——钱已实收,本地 cancel 只是未支付单的整理。
func (h *WebhookHandler) settle(ctx context.Context, ev *webhookEvent) error {
	item, ok := CatalogBySKU(ev.ProductBizCode)
	if !ok {
		return fmt.Errorf("未知 product_biz_code %q(与 pay 种子漂移?)", ev.ProductBizCode)
	}
	tx, err := h.store.BeginTx(ctx)
	if err != nil {
		return err
	}
	defer func() { _ = tx.Rollback() }()

	var purchaseID, userID int64
	row, err := h.store.LockByOutTradeNoTx(ctx, tx, ev.OutTradeNo)
	switch {
	case err == sql.ErrNoRows:
		// 台账缺行(下单后本地写失败)→ 按 biz_ref=用户 uuid 兜底定位补建。
		// 与正常路径(row.UserID 直接开通,不看 user 状态)对齐:钱已实收,
		// 兜底定位不应因用户被停用(suspended)而拒绝开通——否则静默丢钱。
		if err := h.db.QueryRowContext(ctx,
			`SELECT id FROM users WHERE uuid = ?`, ev.BizRef).Scan(&userID); err != nil {
			return fmt.Errorf("biz_ref %q 定位用户失败: %w", ev.BizRef, err)
		}
		purchaseID, err = h.store.InsertFromWebhookTx(ctx, tx, userID, ev.BizRef, ev.ProductBizCode, ev.OutTradeNo, ev.Channel)
		if err != nil {
			return err
		}
	case err != nil:
		return err
	case row.Status == "paid":
		return nil // 幂等:已消费,直接 SUCCESS
	default:
		purchaseID, userID = row.ID, row.UserID
	}

	subID, _, err := h.granter.GrantPaidSubscriptionTx(ctx, tx, userID,
		codes.PlanCode(item.Plan), item.Days, "pay:"+ev.OutTradeNo)
	if err != nil {
		return err
	}
	paidAt, perr := time.Parse(time.RFC3339, ev.PaidAt)
	if perr != nil {
		paidAt = h.now().UTC()
	}
	if err := h.store.MarkPaidTx(ctx, tx, purchaseID, ev.AmountMinor, ev.Currency, ev.Channel, subID, paidAt); err != nil {
		return err
	}
	return tx.Commit()
}