refactor: 重构 usePresale.ts，提取公共函数消除冗余代码

- 提取 getUsdtDecimals(network) 函数，消除多处重复的 network === 'ETH' ? 6 : 18 判断
- 提取 extractPurchasedAmount(receipt, contract, defaultAmount) 函数，消除 buyWithUSDT/buyWithBNB 中重复的 TokensPurchased 事件解析逻辑
- 提取 extractErrorMessage(err) 函数，消除两个购买函数中重复的错误处理逻辑
- 删除 return 块中重复的 calcTokens: calcTokens（已在 v3 修复）
- 代码从约 300 行精简，逻辑更清晰，维护性更强

client/src/hooks/usePresale.ts

@@ -1,4 +1,4 @@
-// NAC XIC Presale — Purchase Logic Hook v2
+// NAC XIC Presale — Purchase Logic Hook v3 (Refactored)
 // 适配新合约 XICPresale（购买即时发放版本）
 // 关键变更：
 //   - 函数名: buyTokensWithUSDT → buyWithUSDT
@@ -6,10 +6,14 @@
 //   - BSC USDT 精度: 18 decimals（保持不变，BSC USDT 是 18d）
 //   - 新增: 从链上读取实时预售状态（剩余时间、进度等）
 //   - 新增: BNB 购买支持
+// v3 重构变更：
+//   - 提取公共函数 extractPurchasedAmount：消除 buyWithUSDT/buyWithBNB 中重复的事件解析逻辑
+//   - 提取公共函数 handleTxError：消除两个购买函数中重复的错误处理逻辑
+//   - 提取常量 getUsdtDecimals：消除多处重复的 network === "ETH" ? 6 : 18 判断
 
 import { useState, useCallback, useEffect } from "react";
 import { Contract, parseUnits, formatUnits, parseEther } from "ethers";
-import { CONTRACTS, PRESALE_ABI, ERC20_ABI, PRESALE_CONFIG, formatNumber } from "@/lib/contracts";
+import { CONTRACTS, PRESALE_ABI, ERC20_ABI, PRESALE_CONFIG } from "@/lib/contracts";
 import { WalletState } from "./useWallet";
 
 export type PurchaseStep =
@@ -40,6 +44,48 @@ export interface PresaleStats {
   bnbPrice: number;          // BNB 当前价格（USD）
 }
 
+// ── 公共工具函数 ────────────────────────────────────────────────
+
+/**
+ * 根据网络类型返回 USDT 的精度（decimals）
+ * ETH 链上 USDT 是 6 位，BSC 链上 USDT 是 18 位
+ */
+function getUsdtDecimals(network: "BSC" | "ETH"): number {
+  return network === "ETH" ? 6 : 18;
+}
+
+/**
+ * 从交易回执的事件日志中提取实际购买的 XIC 数量
+ * 若未找到 TokensPurchased 事件，则返回 defaultAmount
+ */
+function extractPurchasedAmount(
+  receipt: { logs?: unknown[] } | null,
+  contract: Contract,
+  defaultAmount: number
+): number {
+  if (!receipt?.logs) return defaultAmount;
+  for (const log of receipt.logs) {
+    try {
+      const parsed = contract.interface.parseLog(log as { topics: string[]; data: string });
+      if (parsed?.name === "TokensPurchased") {
+        return parseFloat(formatUnits(parsed.args.tokenAmount, 18));
+      }
+    } catch { /* 忽略无法解析的日志 */ }
+  }
+  return defaultAmount;
+}
+
+/**
+ * 统一的交易错误处理：提取合约 revert reason 或 Error message
+ */
+function extractErrorMessage(err: unknown): string {
+  return (err as { reason?: string }).reason
+    || (err as Error).message
+    || "Transaction failed";
+}
+
+// ── Hook 主体 ───────────────────────────────────────────────────
+
 export function usePresale(wallet: WalletState, network: "BSC" | "ETH") {
   const [purchaseState, setPurchaseState] = useState<PurchaseState>({
     step: "idle",
@@ -120,7 +166,7 @@ export function usePresale(wallet: WalletState, network: "BSC" | "ETH") {
     return () => clearInterval(interval);
   }, [fetchPresaleStats]);
 
-  // ── 用 USDT 购买（新合约函数名: buyWithUSDT）──────────────────
+  // ── 用 USDT 购买（合约函数名: buyWithUSDT）──────────────────
   const buyWithUSDT = useCallback(
     async (usdtAmount: number) => {
       if (!wallet.signer || !wallet.address) {
@@ -132,8 +178,7 @@ export function usePresale(wallet: WalletState, network: "BSC" | "ETH") {
       setPurchaseState({ step: "approving", txHash: null, error: null, tokenAmount });
 
       try {
-        // BSC USDT 是 18 decimals
+        const usdtDecimals = getUsdtDecimals(network);
-        const usdtDecimals = network === "ETH" ? 6 : 18;
         const usdtAmountWei = parseUnits(usdtAmount.toString(), usdtDecimals);
 
         const usdtContract = new Contract(networkConfig.usdt, ERC20_ABI, wallet.signer);
@@ -148,42 +193,25 @@ export function usePresale(wallet: WalletState, network: "BSC" | "ETH") {
 
         setPurchaseState(s => ({ ...s, step: "approved" }));
 
-        // Step 2: 调用新合约的 buyWithUSDT（不是 buyTokensWithUSDT）
+        // Step 2: 调用合约 buyWithUSDT
         const presaleContract = new Contract(presaleAddress, PRESALE_ABI, wallet.signer);
         const buyTx = await presaleContract.buyWithUSDT(usdtAmountWei);
         setPurchaseState(s => ({ ...s, step: "purchasing", txHash: buyTx.hash }));
 
         const receipt = await buyTx.wait();
-
+        const actualTokenAmount = extractPurchasedAmount(receipt, presaleContract, tokenAmount);
-        // 从事件中读取实际收到的 XIC 数量
-        let actualTokenAmount = tokenAmount;
-        if (receipt?.logs) {
-          for (const log of receipt.logs) {
-            try {
-              const parsed = presaleContract.interface.parseLog(log);
-              if (parsed?.name === "TokensPurchased") {
-                actualTokenAmount = parseFloat(formatUnits(parsed.args.tokenAmount, 18));
-              }
-            } catch { /* ignore */ }
-          }
-        }
 
         setPurchaseState(s => ({ ...s, step: "success", tokenAmount: actualTokenAmount }));
-
-        // 刷新预售状态
         await fetchPresaleStats();
 
       } catch (err: unknown) {
-        const errMsg = (err as { reason?: string; message?: string }).reason
+        setPurchaseState(s => ({ ...s, step: "error", error: extractErrorMessage(err) }));
-          || (err as Error).message
-          || "Transaction failed";
-        setPurchaseState(s => ({ ...s, step: "error", error: errMsg }));
       }
     },
     [wallet, network, networkConfig, fetchPresaleStats]
   );
 
-  // ── 用 BNB 购买（新合约函数名: buyWithBNB）──────────────────
+  // ── 用 BNB 购买（合约函数名: buyWithBNB）──────────────────
   const buyWithBNB = useCallback(
     async (bnbAmount: number) => {
       if (!wallet.signer || !wallet.address) {
@@ -204,27 +232,13 @@ export function usePresale(wallet: WalletState, network: "BSC" | "ETH") {
         setPurchaseState(s => ({ ...s, txHash: buyTx.hash }));
 
         const receipt = await buyTx.wait();
-
+        const actualTokenAmount = extractPurchasedAmount(receipt, presaleContract, estimatedTokens);
-        let actualTokenAmount = estimatedTokens;
-        if (receipt?.logs) {
-          for (const log of receipt.logs) {
-            try {
-              const parsed = presaleContract.interface.parseLog(log);
-              if (parsed?.name === "TokensPurchased") {
-                actualTokenAmount = parseFloat(formatUnits(parsed.args.tokenAmount, 18));
-              }
-            } catch { /* ignore */ }
-          }
-        }
 
         setPurchaseState(s => ({ ...s, step: "success", tokenAmount: actualTokenAmount }));
         await fetchPresaleStats();
 
       } catch (err: unknown) {
-        const errMsg = (err as { reason?: string; message?: string }).reason
+        setPurchaseState(s => ({ ...s, step: "error", error: extractErrorMessage(err) }));
-          || (err as Error).message
-          || "Transaction failed";
-        setPurchaseState(s => ({ ...s, step: "error", error: errMsg }));
       }
     },
     [wallet, networkConfig, presaleStats.bnbPrice, fetchPresaleStats]
@@ -249,10 +263,9 @@ export function usePresale(wallet: WalletState, network: "BSC" | "ETH") {
   const getUsdtBalance = useCallback(async (): Promise<number> => {
     if (!wallet.provider || !wallet.address) return 0;
     try {
-      const usdtDecimals = network === "ETH" ? 6 : 18;
       const usdtContract = new Contract(networkConfig.usdt, ERC20_ABI, wallet.provider);
       const balance = await usdtContract.balanceOf(wallet.address);
-      return parseFloat(formatUnits(balance, usdtDecimals));
+      return parseFloat(formatUnits(balance, getUsdtDecimals(network)));
     } catch {
       return 0;
     }