feat: 汇率换算功能完整实现

- 首页双向换算：30种主流货币，实时计算，一键互换
- 汇率总览页：一对多查看所有货币换算结果
- 数据源 open.er-api.com，4小时本地缓存 + 失败兜底
- UI 美化：渐变背景、分色货币块、紫色互换按钮

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

miniprogram/app.js

@@ -1,7 +1,3 @@
 App({
   globalData: {},
-
-  onLaunch() {
-    console.log('App launched');
-  },
 });

miniprogram/app.wxss

@@ -1,6 +1,6 @@
 page {
-  background-color: #F5F5F5;
-  color: #333333;
+  background: linear-gradient(180deg, #EEF2FF 0%, #F5F5F5 320rpx);
+  color: #1E293B;
   font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
   font-size: 28rpx;
   line-height: 1.6;
@@ -8,24 +8,12 @@ page {
 
 .container {
   padding: 32rpx;
+  padding-top: 24rpx;
 }
 
 .card {
   background-color: #FFFFFF;
-  border-radius: 16rpx;
-  padding: 32rpx;
+  border-radius: 24rpx;
   margin-bottom: 24rpx;
-  box-shadow: 0 2rpx 8rpx rgba(0, 0, 0, 0.04);
-}
-
-.page-title {
-  font-size: 40rpx;
-  font-weight: 700;
-  margin-bottom: 16rpx;
-}
-
-.page-subtitle {
-  font-size: 26rpx;
-  color: #999999;
-  margin-bottom: 32rpx;
+  box-shadow: 0 4rpx 24rpx rgba(0, 0, 0, 0.06);
 }

miniprogram/pages/index/index.js

@@ -1,7 +1,106 @@
+const { CURRENCIES, getPickerData } = require('../../utils/currencies');
+const { getRates, convert, formatAmount, formatRate } = require('../../utils/rate');
+
+const pickerData = getPickerData();
+const DEFAULT_FROM = 0;  // CNY
+const DEFAULT_TO = 1;    // USD
+
 Page({
-  data: {},
+  data: {
+    pickerData,
+    fromIndex: DEFAULT_FROM,
+    toIndex: DEFAULT_TO,
+    amount: '100',
+    result: '',
+    unitRate: '',
+    reverseRate: '',
+    updatedAt: '',
+    loading: true,
+    error: '',
+    rates: null,
+    baseCurrency: 'CNY',
+  },
 
   onLoad() {
-    console.log('Index page loaded');
+    this.loadRates();
+  },
+
+  onPullDownRefresh() {
+    this.loadRates().then(() => {
+      wx.stopPullDownRefresh();
+    });
+  },
+
+  async loadRates() {
+    this.setData({ loading: true, error: '' });
+    try {
+      const { rates, updatedAt } = await getRates('CNY');
+      this.setData({
+        rates,
+        baseCurrency: 'CNY',
+        updatedAt,
+        loading: false,
+      });
+      this.calculate();
+    } catch (e) {
+      this.setData({
+        loading: false,
+        error: '汇率获取失败，请检查网络后下拉刷新',
+      });
+    }
+  },
+
+  calculate() {
+    const { rates, fromIndex, toIndex, amount, baseCurrency } = this.data;
+    if (!rates) return;
+
+    const num = parseFloat(amount);
+    if (isNaN(num) || num <= 0) {
+      this.setData({ result: '', unitRate: '', reverseRate: '' });
+      return;
+    }
+
+    const fromCode = CURRENCIES[fromIndex].code;
+    const toCode = CURRENCIES[toIndex].code;
+    const converted = convert(num, fromCode, toCode, rates);
+    const unitForward = convert(1, fromCode, toCode, rates);
+    const unitReverse = convert(1, toCode, fromCode, rates);
+
+    this.setData({
+      result: formatAmount(converted, toCode),
+      unitRate: `1 ${fromCode} = ${formatRate(unitForward)} ${toCode}`,
+      reverseRate: `1 ${toCode} = ${formatRate(unitReverse)} ${fromCode}`,
+    });
+  },
+
+  handleAmountInput(e) {
+    const value = e.detail.value;
+    this.setData({ amount: value });
+    this.calculate();
+  },
+
+  handleFromChange(e) {
+    this.setData({ fromIndex: Number(e.detail.value) });
+    this.calculate();
+  },
+
+  handleToChange(e) {
+    this.setData({ toIndex: Number(e.detail.value) });
+    this.calculate();
+  },
+
+  handleSwap() {
+    const { fromIndex, toIndex } = this.data;
+    this.setData({
+      fromIndex: toIndex,
+      toIndex: fromIndex,
+    });
+    this.calculate();
+  },
+
+  goOverview() {
+    wx.navigateTo({
+      url: '/pages/overview/overview',
+    });
   },
 });

miniprogram/pages/index/index.json

@@ -1,3 +1,5 @@
 {
+  "navigationBarTitleText": "汇率换算",
+  "enablePullDownRefresh": true,
   "usingComponents": {}
 }

miniprogram/pages/index/index.wxml

@@ -1,8 +1,76 @@
 <view class="container">
-  <view class="page-title">汇率换算</view>
-  <view class="page-subtitle">实时汇率，主流货币换算</view>
+  <!-- 顶部标题区 -->
+  <view class="hero">
+    <view class="hero-title">💱 汇率换算</view>
+    <view class="hero-desc" wx:if="{{updatedAt}}">{{updatedAt}} 更新</view>
+    <view class="hero-desc" wx:if="{{loading}}">正在获取最新汇率...</view>
+  </view>
 
-  <view class="card">
-    <view class="placeholder-text">功能开发中</view>
+  <!-- 换算主卡片 -->
+  <view class="card converter-card">
+    <!-- 源币种 -->
+    <view class="currency-block from-block">
+      <picker range="{{pickerData}}" value="{{fromIndex}}" bindchange="handleFromChange">
+        <view class="currency-tag">
+          <text class="currency-tag-text">{{pickerData[fromIndex]}}</text>
+          <text class="tag-arrow">▼</text>
+        </view>
+      </picker>
+      <input
+        class="amount-input"
+        type="digit"
+        value="{{amount}}"
+        bindinput="handleAmountInput"
+        placeholder="输入金额"
+        placeholder-class="amount-placeholder"
+      />
+    </view>
+
+    <!-- 互换按钮 -->
+    <view class="swap-wrapper">
+      <view class="swap-line"></view>
+      <view class="swap-btn" bindtap="handleSwap">
+        <text class="swap-icon">⇅</text>
+      </view>
+      <view class="swap-line"></view>
+    </view>
+
+    <!-- 目标币种 -->
+    <view class="currency-block to-block">
+      <picker range="{{pickerData}}" value="{{toIndex}}" bindchange="handleToChange">
+        <view class="currency-tag">
+          <text class="currency-tag-text">{{pickerData[toIndex]}}</text>
+          <text class="tag-arrow">▼</text>
+        </view>
+      </picker>
+      <view class="result-display">{{result || '—'}}</view>
+    </view>
+  </view>
+
+  <!-- 单位汇率卡片 -->
+  <view class="card rate-card" wx:if="{{unitRate}}">
+    <view class="rate-row">
+      <text class="rate-dot from-dot"></text>
+      <text class="rate-text">{{unitRate}}</text>
+    </view>
+    <view class="rate-row">
+      <text class="rate-dot to-dot"></text>
+      <text class="rate-text">{{reverseRate}}</text>
+    </view>
+  </view>
+
+  <!-- 错误提示 -->
+  <view class="card error-card" wx:if="{{error}}">
+    <text class="error-icon">⚠</text>
+    <text class="error-text">{{error}}</text>
+  </view>
+
+  <!-- 汇率总览入口 -->
+  <view class="card overview-entry" bindtap="goOverview">
+    <view class="overview-left">
+      <text class="overview-icon">📊</text>
+      <text class="overview-label">查看汇率总览</text>
+    </view>
+    <text class="overview-arrow">›</text>
   </view>
 </view>

miniprogram/pages/index/index.wxss

@@ -1,6 +1,192 @@
-.placeholder-text {
-  color: #999999;
-  font-size: 28rpx;
-  text-align: center;
-  padding: 48rpx 0;
+/* ===== 顶部标题 ===== */
+.hero {
+  padding: 16rpx 8rpx 24rpx;
+}
+
+.hero-title {
+  font-size: 48rpx;
+  font-weight: 800;
+  color: #1E293B;
+  letter-spacing: 2rpx;
+}
+
+.hero-desc {
+  font-size: 24rpx;
+  color: #94A3B8;
+  margin-top: 8rpx;
+}
+
+/* ===== 换算主卡片 ===== */
+.converter-card {
+  padding: 40rpx 36rpx;
+}
+
+.currency-block {
+  border-radius: 20rpx;
+  padding: 28rpx;
+}
+
+.from-block {
+  background: #F8FAFC;
+  border: 2rpx solid #E2E8F0;
+}
+
+.to-block {
+  background: linear-gradient(135deg, #EEF2FF 0%, #E0E7FF 100%);
+  border: 2rpx solid #C7D2FE;
+}
+
+.currency-tag {
+  display: inline-flex;
+  align-items: center;
+  background: #FFFFFF;
+  border-radius: 12rpx;
+  padding: 10rpx 20rpx;
+  box-shadow: 0 2rpx 8rpx rgba(0, 0, 0, 0.05);
+}
+
+.currency-tag-text {
+  font-size: 26rpx;
+  font-weight: 500;
+  color: #334155;
+}
+
+.tag-arrow {
+  font-size: 18rpx;
+  color: #94A3B8;
+  margin-left: 10rpx;
+}
+
+.amount-input {
+  width: 100%;
+  margin-top: 20rpx;
+  font-size: 56rpx;
+  font-weight: 800;
+  color: #1E293B;
+  text-align: right;
+}
+
+.amount-placeholder {
+  color: #CBD5E1;
+  font-weight: 400;
+}
+
+.result-display {
+  margin-top: 20rpx;
+  font-size: 56rpx;
+  font-weight: 800;
+  color: #4F46E5;
+  text-align: right;
+}
+
+/* ===== 互换按钮 ===== */
+.swap-wrapper {
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  padding: 12rpx 0;
+}
+
+.swap-line {
+  flex: 1;
+  height: 2rpx;
+  background: #E2E8F0;
+}
+
+.swap-btn {
+  width: 80rpx;
+  height: 80rpx;
+  border-radius: 50%;
+  background: #4F46E5;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  margin: 0 24rpx;
+  box-shadow: 0 6rpx 20rpx rgba(79, 70, 229, 0.3);
+}
+
+.swap-icon {
+  font-size: 36rpx;
+  color: #FFFFFF;
+}
+
+/* ===== 单位汇率 ===== */
+.rate-card {
+  padding: 28rpx 36rpx;
+}
+
+.rate-row {
+  display: flex;
+  align-items: center;
+  padding: 8rpx 0;
+}
+
+.rate-dot {
+  width: 14rpx;
+  height: 14rpx;
+  border-radius: 50%;
+  margin-right: 16rpx;
+  flex-shrink: 0;
+}
+
+.from-dot {
+  background: #64748B;
+}
+
+.to-dot {
+  background: #4F46E5;
+}
+
+.rate-text {
+  font-size: 26rpx;
+  color: #64748B;
+  font-weight: 500;
+}
+
+/* ===== 错误提示 ===== */
+.error-card {
+  display: flex;
+  align-items: center;
+  padding: 28rpx 36rpx;
+  background: #FEF2F2;
+}
+
+.error-icon {
+  font-size: 32rpx;
+  margin-right: 16rpx;
+}
+
+.error-text {
+  font-size: 26rpx;
+  color: #DC2626;
+}
+
+/* ===== 汇率总览入口 ===== */
+.overview-entry {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  padding: 36rpx;
+}
+
+.overview-left {
+  display: flex;
+  align-items: center;
+}
+
+.overview-icon {
+  font-size: 36rpx;
+  margin-right: 16rpx;
+}
+
+.overview-label {
+  font-size: 30rpx;
+  font-weight: 500;
+  color: #334155;
+}
+
+.overview-arrow {
+  font-size: 40rpx;
+  color: #CBD5E1;
+  font-weight: 300;
 }

miniprogram/pages/overview/overview.js

@@ -1,7 +1,84 @@
+const { CURRENCIES, getPickerData } = require('../../utils/currencies');
+const { getRates, convert, formatAmount, formatRate } = require('../../utils/rate');
+
+const pickerData = getPickerData();
+
 Page({
-  data: {},
+  data: {
+    pickerData,
+    baseIndex: 0, // CNY
+    amount: '100',
+    list: [],
+    updatedAt: '',
+    loading: true,
+    error: '',
+    rates: null,
+  },
 
   onLoad() {
-    console.log('Overview page loaded');
+    this.loadRates();
+  },
+
+  onPullDownRefresh() {
+    this.loadRates().then(() => {
+      wx.stopPullDownRefresh();
+    });
+  },
+
+  async loadRates() {
+    this.setData({ loading: true, error: '' });
+    try {
+      const baseCode = CURRENCIES[this.data.baseIndex].code;
+      const { rates, updatedAt } = await getRates(baseCode);
+      this.setData({
+        rates,
+        updatedAt,
+        loading: false,
+      });
+      this.buildList();
+    } catch (e) {
+      this.setData({
+        loading: false,
+        error: '汇率获取失败，请检查网络后下拉刷新',
+      });
+    }
+  },
+
+  buildList() {
+    const { rates, baseIndex, amount } = this.data;
+    if (!rates) return;
+
+    const num = parseFloat(amount);
+    if (isNaN(num) || num <= 0) {
+      this.setData({ list: [] });
+      return;
+    }
+
+    const baseCode = CURRENCIES[baseIndex].code;
+    const list = CURRENCIES
+      .filter((c) => c.code !== baseCode)
+      .map((c) => {
+        const converted = convert(num, baseCode, c.code, rates);
+        const unitRate = convert(1, baseCode, c.code, rates);
+        return {
+          flag: c.flag,
+          code: c.code,
+          name: c.name,
+          converted: formatAmount(converted, c.code),
+          unitRate: formatRate(unitRate),
+        };
+      });
+
+    this.setData({ list });
+  },
+
+  handleBaseChange(e) {
+    this.setData({ baseIndex: Number(e.detail.value) });
+    this.loadRates();
+  },
+
+  handleAmountInput(e) {
+    this.setData({ amount: e.detail.value });
+    this.buildList();
   },
 });

miniprogram/pages/overview/overview.json

@@ -1,4 +1,5 @@
 {
   "navigationBarTitleText": "汇率总览",
+  "enablePullDownRefresh": true,
   "usingComponents": {}
 }

miniprogram/pages/overview/overview.wxml

@@ -1,8 +1,64 @@
 <view class="container">
-  <view class="page-title">汇率总览</view>
-  <view class="page-subtitle">一个基准货币对所有主流货币</view>
+  <!-- 顶部控制区 -->
+  <view class="card header-card">
+    <view class="header-top">
+      <text class="header-title">📊 汇率总览</text>
+    </view>
 
-  <view class="card">
-    <view class="placeholder-text">功能开发中</view>
+    <view class="control-row">
+      <text class="control-label">基准</text>
+      <picker range="{{pickerData}}" value="{{baseIndex}}" bindchange="handleBaseChange">
+        <view class="base-tag">
+          <text class="base-tag-text">{{pickerData[baseIndex]}}</text>
+          <text class="tag-arrow">▼</text>
+        </view>
+      </picker>
+    </view>
+
+    <view class="control-row">
+      <text class="control-label">金额</text>
+      <input
+        class="amount-input"
+        type="digit"
+        value="{{amount}}"
+        bindinput="handleAmountInput"
+        placeholder="输入金额"
+        placeholder-class="amount-placeholder"
+      />
+    </view>
+
+    <view class="updated-at" wx:if="{{updatedAt}}">{{updatedAt}} 更新</view>
+  </view>
+
+  <!-- 错误提示 -->
+  <view class="card error-card" wx:if="{{error}}">
+    <text class="error-icon">⚠</text>
+    <text class="error-text">{{error}}</text>
+  </view>
+
+  <!-- 加载中 -->
+  <view class="loading-card" wx:if="{{loading}}">
+    <text>正在获取汇率数据...</text>
+  </view>
+
+  <!-- 汇率列表 -->
+  <view class="card list-card" wx:if="{{list.length}}">
+    <view
+      class="rate-item"
+      wx:for="{{list}}"
+      wx:key="code"
+    >
+      <view class="rate-left">
+        <text class="rate-flag">{{item.flag}}</text>
+        <view class="rate-info">
+          <text class="rate-code">{{item.code}}</text>
+          <text class="rate-name">{{item.name}}</text>
+        </view>
+      </view>
+      <view class="rate-right">
+        <text class="rate-value">{{item.converted}}</text>
+        <text class="rate-unit">1 = {{item.unitRate}}</text>
+      </view>
+    </view>
   </view>
 </view>

miniprogram/pages/overview/overview.wxss

@@ -1,6 +1,157 @@
-.placeholder-text {
-  color: #999999;
-  font-size: 28rpx;
-  text-align: center;
-  padding: 48rpx 0;
+/* ===== 顶部控制区 ===== */
+.header-card {
+  padding: 36rpx;
+}
+
+.header-top {
+  margin-bottom: 28rpx;
+}
+
+.header-title {
+  font-size: 40rpx;
+  font-weight: 800;
+  color: #1E293B;
+}
+
+.control-row {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  padding: 20rpx 0;
+  border-top: 2rpx solid #F1F5F9;
+}
+
+.control-label {
+  font-size: 28rpx;
+  color: #64748B;
+  font-weight: 500;
+}
+
+.base-tag {
+  display: inline-flex;
+  align-items: center;
+  background: #F8FAFC;
+  border: 2rpx solid #E2E8F0;
+  border-radius: 12rpx;
+  padding: 10rpx 20rpx;
+}
+
+.base-tag-text {
+  font-size: 26rpx;
+  font-weight: 500;
+  color: #334155;
+}
+
+.tag-arrow {
+  font-size: 18rpx;
+  color: #94A3B8;
+  margin-left: 10rpx;
+}
+
+.amount-input {
+  flex: 1;
+  text-align: right;
+  font-size: 40rpx;
+  font-weight: 800;
+  color: #1E293B;
+  margin-left: 24rpx;
+}
+
+.amount-placeholder {
+  color: #CBD5E1;
+  font-weight: 400;
+}
+
+.updated-at {
+  font-size: 22rpx;
+  color: #94A3B8;
+  margin-top: 16rpx;
+}
+
+/* ===== 错误 & 加载 ===== */
+.error-card {
+  display: flex;
+  align-items: center;
+  padding: 28rpx 36rpx;
+  background: #FEF2F2;
+}
+
+.error-icon {
+  font-size: 32rpx;
+  margin-right: 16rpx;
+}
+
+.error-text {
+  font-size: 26rpx;
+  color: #DC2626;
+}
+
+.loading-card {
+  padding: 40rpx;
+  text-align: center;
+  color: #94A3B8;
+  font-size: 26rpx;
+}
+
+/* ===== 汇率列表 ===== */
+.list-card {
+  padding: 8rpx 0;
+}
+
+.rate-item {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  padding: 28rpx 36rpx;
+  border-bottom: 2rpx solid #F8FAFC;
+  transition: background 0.15s;
+}
+
+.rate-item:last-child {
+  border-bottom: none;
+}
+
+.rate-left {
+  display: flex;
+  align-items: center;
+}
+
+.rate-flag {
+  font-size: 44rpx;
+  margin-right: 20rpx;
+}
+
+.rate-info {
+  display: flex;
+  flex-direction: column;
+}
+
+.rate-code {
+  font-size: 30rpx;
+  font-weight: 700;
+  color: #1E293B;
+}
+
+.rate-name {
+  font-size: 22rpx;
+  color: #94A3B8;
+  margin-top: 4rpx;
+}
+
+.rate-right {
+  display: flex;
+  flex-direction: column;
+  align-items: flex-end;
+}
+
+.rate-value {
+  font-size: 32rpx;
+  font-weight: 800;
+  color: #1E293B;
+}
+
+.rate-unit {
+  font-size: 22rpx;
+  color: #94A3B8;
+  margin-top: 4rpx;
 }

miniprogram/utils/currencies.js

@@ -0,0 +1,65 @@
+/**
+ * 主流货币配置（约 30 种）
+ * flag: emoji 国旗
+ * code: ISO 4217 货币代码
+ * name: 中文名
+ */
+const CURRENCIES = [
+  { flag: '🇨🇳', code: 'CNY', name: '人民币' },
+  { flag: '🇺🇸', code: 'USD', name: '美元' },
+  { flag: '🇪🇺', code: 'EUR', name: '欧元' },
+  { flag: '🇬🇧', code: 'GBP', name: '英镑' },
+  { flag: '🇯🇵', code: 'JPY', name: '日元' },
+  { flag: '🇰🇷', code: 'KRW', name: '韩元' },
+  { flag: '🇭🇰', code: 'HKD', name: '港币' },
+  { flag: '🇹🇼', code: 'TWD', name: '新台币' },
+  { flag: '🇲🇴', code: 'MOP', name: '澳门元' },
+  { flag: '🇸🇬', code: 'SGD', name: '新加坡元' },
+  { flag: '🇦🇺', code: 'AUD', name: '澳元' },
+  { flag: '🇨🇦', code: 'CAD', name: '加元' },
+  { flag: '🇳🇿', code: 'NZD', name: '新西兰元' },
+  { flag: '🇹🇭', code: 'THB', name: '泰铢' },
+  { flag: '🇲🇾', code: 'MYR', name: '马来西亚林吉特' },
+  { flag: '🇵🇭', code: 'PHP', name: '菲律宾比索' },
+  { flag: '🇮🇩', code: 'IDR', name: '印尼盾' },
+  { flag: '🇻🇳', code: 'VND', name: '越南盾' },
+  { flag: '🇮🇳', code: 'INR', name: '印度卢比' },
+  { flag: '🇷🇺', code: 'RUB', name: '俄罗斯卢布' },
+  { flag: '🇧🇷', code: 'BRL', name: '巴西雷亚尔' },
+  { flag: '🇲🇽', code: 'MXN', name: '墨西哥比索' },
+  { flag: '🇿🇦', code: 'ZAR', name: '南非兰特' },
+  { flag: '🇹🇷', code: 'TRY', name: '土耳其里拉' },
+  { flag: '🇸🇦', code: 'SAR', name: '沙特里亚尔' },
+  { flag: '🇦🇪', code: 'AED', name: '阿联酋迪拉姆' },
+  { flag: '🇨🇭', code: 'CHF', name: '瑞士法郎' },
+  { flag: '🇸🇪', code: 'SEK', name: '瑞典克朗' },
+  { flag: '🇩🇰', code: 'DKK', name: '丹麦克朗' },
+  { flag: '🇳🇴', code: 'NOK', name: '挪威克朗' },
+];
+
+const CURRENCY_MAP = {};
+CURRENCIES.forEach((c) => {
+  CURRENCY_MAP[c.code] = c;
+});
+
+function getCurrency(code) {
+  return CURRENCY_MAP[code] || null;
+}
+
+function getCurrencyLabel(code) {
+  const c = CURRENCY_MAP[code];
+  if (!c) return code;
+  return `${c.flag} ${c.code} ${c.name}`;
+}
+
+function getPickerData() {
+  return CURRENCIES.map((c) => `${c.flag} ${c.code} ${c.name}`);
+}
+
+module.exports = {
+  CURRENCIES,
+  CURRENCY_MAP,
+  getCurrency,
+  getCurrencyLabel,
+  getPickerData,
+};

miniprogram/utils/rate.js

@@ -0,0 +1,130 @@
+/**
+ * 汇率 API 调用 + 本地缓存
+ * 数据源：https://open.er-api.com/v6/latest/{base}
+ * 免费，无需 key，每日更新，1500 次/月
+ */
+
+const CACHE_KEY = 'exchange_rates';
+const CACHE_TTL = 4 * 60 * 60 * 1000; // 4 小时
+
+function getCache() {
+  try {
+    const data = wx.getStorageSync(CACHE_KEY);
+    if (!data) return null;
+    return data;
+  } catch (e) {
+    return null;
+  }
+}
+
+function setCache(data) {
+  try {
+    wx.setStorageSync(CACHE_KEY, data);
+  } catch (e) {
+    console.warn('cache write failed', e);
+  }
+}
+
+function isCacheValid(cache, base) {
+  if (!cache || !cache.rates || !cache.timestamp) return false;
+  if (cache.base !== base) return false;
+  return Date.now() - cache.timestamp < CACHE_TTL;
+}
+
+function fetchRates(base) {
+  return new Promise((resolve, reject) => {
+    wx.request({
+      url: `https://open.er-api.com/v6/latest/${base}`,
+      method: 'GET',
+      success(res) {
+        if (res.statusCode === 200 && res.data && res.data.result === 'success') {
+          resolve(res.data.rates);
+        } else {
+          reject(new Error('API 返回异常'));
+        }
+      },
+      fail(err) {
+        reject(err);
+      },
+    });
+  });
+}
+
+async function getRates(base) {
+  const cache = getCache();
+
+  if (isCacheValid(cache, base)) {
+    return {
+      rates: cache.rates,
+      updatedAt: cache.updatedAt,
+      fromCache: true,
+    };
+  }
+
+  try {
+    const rates = await fetchRates(base);
+    const now = new Date();
+    const cacheData = {
+      base,
+      rates,
+      timestamp: now.getTime(),
+      updatedAt: formatTime(now),
+    };
+    setCache(cacheData);
+    return {
+      rates,
+      updatedAt: cacheData.updatedAt,
+      fromCache: false,
+    };
+  } catch (e) {
+    // API 失败时用过期缓存兜底
+    if (cache && cache.rates) {
+      return {
+        rates: cache.rates,
+        updatedAt: cache.updatedAt + '（缓存）',
+        fromCache: true,
+      };
+    }
+    throw e;
+  }
+}
+
+function convert(amount, fromCode, toCode, rates) {
+  if (!rates || !rates[fromCode] || !rates[toCode]) return 0;
+  if (fromCode === toCode) return amount;
+  return (amount / rates[fromCode]) * rates[toCode];
+}
+
+function formatAmount(value, code) {
+  // 日元、韩元、越南盾、印尼盾等无小数货币
+  const noDecimal = ['JPY', 'KRW', 'VND', 'IDR'];
+  if (noDecimal.includes(code)) {
+    return Math.round(value).toLocaleString('en-US');
+  }
+  return Number(value.toFixed(2)).toLocaleString('en-US', {
+    minimumFractionDigits: 2,
+    maximumFractionDigits: 2,
+  });
+}
+
+function formatRate(value) {
+  if (value >= 100) return value.toFixed(2);
+  if (value >= 1) return value.toFixed(4);
+  return value.toFixed(6);
+}
+
+function formatTime(date) {
+  const y = date.getFullYear();
+  const m = String(date.getMonth() + 1).padStart(2, '0');
+  const d = String(date.getDate()).padStart(2, '0');
+  const h = String(date.getHours()).padStart(2, '0');
+  const min = String(date.getMinutes()).padStart(2, '0');
+  return `${y}-${m}-${d} ${h}:${min}`;
+}
+
+module.exports = {
+  getRates,
+  convert,
+  formatAmount,
+  formatRate,
+};