package handler

import (
	"crypto/subtle"
	"encoding/json"
	"errors"
	"io"
	"log"
	"net/http"
	"os"

	"github.com/gin-gonic/gin"

	"github.com/wangjia/pay/internal/gateway"
	"github.com/wangjia/pay/internal/store"
	"github.com/wangjia/pay/internal/util"
)

type refundRequest struct {
	OutTradeNo  string `json:"out_trade_no"`
	AmountMinor int64  `json:"amount_minor"`
	Reason      string `json:"reason,omitempty"`
	BizSystem   string `json:"biz_system"`
}

// CreateRefund POST /api/v2/refunds —— 业务发起退款(HMAC 验签)。
func (h *GatewayHandler) CreateRefund(c *gin.Context) {
	raw, err := io.ReadAll(http.MaxBytesReader(c.Writer, c.Request.Body, maxOrderBodyBytes))
	if err != nil {
		util.RespondError(c, http.StatusBadRequest, "bad_request", "请求体过大或读取失败")
		return
	}
	var req refundRequest
	if err := json.Unmarshal(raw, &req); err != nil {
		util.RespondError(c, http.StatusBadRequest, "bad_request", "参数格式错误")
		return
	}
	if req.OutTradeNo == "" || req.AmountMinor <= 0 || req.BizSystem == "" {
		util.RespondError(c, http.StatusBadRequest, "bad_request", "缺少 out_trade_no / amount_minor / biz_system")
		return
	}
	if err := verifyBizSign(c, req.BizSystem, raw); err != nil {
		util.RespondError(c, http.StatusUnauthorized, "unauthorized", err.Error())
		return
	}
	res, err := h.g.Refund(c.Request.Context(), gateway.RefundInput{
		OutTradeNo: req.OutTradeNo, AmountMinor: req.AmountMinor, Reason: req.Reason,
		BizSystem: req.BizSystem, InitiatedBy: "business",
	})
	if err != nil {
		h.writeRefundErr(c, err)
		return
	}
	util.RespondSuccess(c, res)
}

// GetRefund GET /api/v2/refunds/:refund_id
func (h *GatewayHandler) GetRefund(c *gin.Context) {
	v, err := h.g.GetRefund(c.Param("refund_id"))
	if err != nil {
		if errors.Is(err, store.ErrRefundNotFound) {
			util.RespondError(c, http.StatusNotFound, "refund_not_found", "退款单不存在")
			return
		}
		log.Printf("[v2 refund] 查询退款单失败 %s: %v", c.Param("refund_id"), err)
		util.RespondError(c, http.StatusInternalServerError, "get_refund_failed", "查询失败,请稍后重试")
		return
	}
	util.RespondSuccess(c, v)
}

func (h *GatewayHandler) adminAuthorized(c *gin.Context) bool {
	tok := os.Getenv("PAY_ADMIN_TOKEN")
	if tok == "" {
		return false // 未配置管理密钥 → 端点禁用
	}
	return subtle.ConstantTimeCompare([]byte(c.GetHeader("X-Pay-Admin")), []byte(tok)) == 1
}

// ListManualRefunds GET /api/v2/admin/manual-refunds —— 捞 crypto 人工待办。
func (h *GatewayHandler) ListManualRefunds(c *gin.Context) {
	if !h.adminAuthorized(c) {
		util.RespondError(c, http.StatusForbidden, "forbidden", "无管理权限")
		return
	}
	rs, err := h.g.ListManualPendingRefunds(50)
	if err != nil {
		util.RespondError(c, http.StatusInternalServerError, "list_failed", "查询失败")
		return
	}
	util.RespondSuccess(c, gin.H{"refunds": rs})
}

type completeRefundRequest struct {
	ProviderRefundRef string `json:"provider_refund_ref"`
}

// CompleteRefund POST /api/v2/admin/refunds/:refund_id/complete —— 运营回填人工退款完成。
func (h *GatewayHandler) CompleteRefund(c *gin.Context) {
	if !h.adminAuthorized(c) {
		util.RespondError(c, http.StatusForbidden, "forbidden", "无管理权限")
		return
	}
	c.Request.Body = http.MaxBytesReader(c.Writer, c.Request.Body, maxOrderBodyBytes)
	var req completeRefundRequest
	if err := c.ShouldBindJSON(&req); err != nil {
		util.RespondError(c, http.StatusBadRequest, "bad_request", "参数格式错误")
		return
	}
	res, err := h.g.CompleteManualRefund(c.Request.Context(), c.Param("refund_id"), req.ProviderRefundRef)
	if err != nil {
		switch {
		case errors.Is(err, store.ErrRefundNotFound):
			util.RespondError(c, http.StatusNotFound, "refund_not_found", "退款单不存在")
		case errors.Is(err, gateway.ErrRefundNotManual):
			util.RespondError(c, http.StatusConflict, "not_manual", "该退款单非人工待办态")
		default:
			log.Printf("[v2 refund] 人工完成失败 %s: %v", c.Param("refund_id"), err)
			util.RespondError(c, http.StatusInternalServerError, "complete_failed", "完成失败")
		}
		return
	}
	util.RespondSuccess(c, res)
}

func (h *GatewayHandler) writeRefundErr(c *gin.Context, err error) {
	switch {
	case errors.Is(err, store.ErrOrderNotFound):
		util.RespondError(c, http.StatusNotFound, "order_not_found", "订单不存在")
	case errors.Is(err, gateway.ErrOrderNotRefundable):
		util.RespondError(c, http.StatusConflict, "order_not_refundable", "订单不可退款(未支付/已全额退款/非本业务)")
	case errors.Is(err, gateway.ErrRefundAmountInvalid):
		util.RespondError(c, http.StatusUnprocessableEntity, "refund_amount_invalid", "退款金额无效或超过可退余额")
	case errors.Is(err, store.ErrAttemptNotFound):
		util.RespondError(c, http.StatusConflict, "no_paid_attempt", "订单无已支付记录")
	default:
		log.Printf("[v2 refund] 退款失败: %v", err)
		util.RespondError(c, http.StatusInternalServerError, "refund_failed", "退款失败,请稍后重试")
	}
}