♻️ refactor: 重构余额系统 - 基于 usePricing 逻辑优化

主要改进：
- 🔄 完全重构 balance.ts，参考 usePricing.md 的最佳实践
- ✅ 集成余额检查、扣费、错误处理到单一 API
- 🎯 使用 authClient.subscription.meterEvent 替代自定义 API
- 💡 添加 checkTokenBalance 和 redirectToPricePage 辅助方法
- 🧹 简化 form.tsx 中的扣费流程，减少60%代码量

技术细节：
- 从 metered 订阅类型获取 creditBalance
- 使用 React Native Alert 替代 Web toast
- 余额不足时自动引导用户充值
- 扣费成功后自动刷新余额显示

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

lib/api/balance.ts

@@ -1,50 +1,214 @@
-import { apiClient } from './client';
+import { Alert } from 'react-native';
+import { router } from 'expo-router';
+import { authClient } from '../auth/client';
 
 export interface UserBalance {
-  userId: string;
-  balance: number;
-  currency: string;
+  remainingTokenBalance: number;
+  totalTokenBalance: number;
+  usedTokenBalance: number;
 }
 
 export interface BalanceResponse {
   success: boolean;
   data: UserBalance;
+  message?: string;
 }
 
-export interface ChargeRequest {
-  amount: number;
-  description?: string;
+export interface TokenUsageRequest {
+  price: number;
+  name: string;
   metadata?: Record<string, any>;
 }
 
-export interface ChargeTransaction {
-  id: string;
-  userId: string;
-  amount: number;
-  type: 'charge' | 'refund';
-  description?: string;
-  metadata?: Record<string, any>;
-  createdAt: string;
-}
-
-export interface ChargeResponse {
+export interface TokenUsageResponse {
   success: boolean;
-  data: ChargeTransaction;
+  data?: {
+    identifier: string;
+    remainingBalance: number;
+  };
+  message?: string;
+}
+
+export interface BalanceCheckResult {
+  hasEnough: boolean;
+  currentBalance: number;
+  isLoading: boolean;
+  message?: string;
 }
 
 /**
  * 获取用户余额
+ * 从 metered 类型的订阅中获取 creditBalance
  */
 export async function getUserBalance(): Promise<BalanceResponse> {
-  return apiClient<BalanceResponse>('/api/users/balance');
+  try {
+    const { data, error } = await authClient.subscription.list({});
+
+    if (error) {
+      return {
+        success: false,
+        data: {
+          remainingTokenBalance: 0,
+          totalTokenBalance: 0,
+          usedTokenBalance: 0,
+        },
+        message: error.message || '获取余额失败',
+      };
+    }
+
+    // 找到 metered 类型的订阅
+    const meteredSubscriptions = data?.filter((sub: any) => sub.type === 'metered') || [];
+
+    if (meteredSubscriptions.length === 0) {
+      return {
+        success: false,
+        data: {
+          remainingTokenBalance: 0,
+          totalTokenBalance: 0,
+          usedTokenBalance: 0,
+        },
+        message: '未找到计费订阅',
+      };
+    }
+
+    const creditBalance = (meteredSubscriptions[0] as any)?.creditBalance || {};
+
+    return {
+      success: true,
+      data: {
+        remainingTokenBalance: creditBalance.remainingTokenBalance || 0,
+        totalTokenBalance: creditBalance.totalTokenBalance || 0,
+        usedTokenBalance: creditBalance.usedTokenBalance || 0,
+      },
+    };
+  } catch (error) {
+    console.error('Failed to get user balance:', error);
+    return {
+      success: false,
+      data: {
+        remainingTokenBalance: 0,
+        totalTokenBalance: 0,
+        usedTokenBalance: 0,
+      },
+      message: '网络错误，请稍后重试',
+    };
+  }
 }
 
 /**
- * 扣费
+ * 检查用户余额是否足够
  */
-export async function chargeUser(data: ChargeRequest): Promise<ChargeResponse> {
-  return apiClient<ChargeResponse>('/api/users/charge', {
-    method: 'POST',
-    body: JSON.stringify(data),
-  });
+export async function checkTokenBalance(tokens: number): Promise<BalanceCheckResult> {
+  const balanceResponse = await getUserBalance();
+
+  if (!balanceResponse.success) {
+    return {
+      hasEnough: false,
+      currentBalance: 0,
+      isLoading: false,
+      message: balanceResponse.message || '无法获取余额',
+    };
+  }
+
+  const currentBalance = balanceResponse.data.remainingTokenBalance;
+  const hasEnough = currentBalance >= tokens;
+
+  return {
+    hasEnough,
+    currentBalance,
+    isLoading: false,
+    message: hasEnough
+      ? undefined
+      : `余额不足，当前: ${currentBalance.toLocaleString()}, 需要: ${tokens.toLocaleString()}`,
+  };
+}
+
+/**
+ * 扣除 Token 使用量
+ * 参考 usePricing 中的 recordTokenUsage 方法
+ */
+export async function recordTokenUsage(
+  request: TokenUsageRequest
+): Promise<TokenUsageResponse> {
+  const { price, name, metadata } = request;
+
+  // price 的单位就是 token
+  const tokens = Math.ceil(price);
+
+  try {
+    // 1. 检查余额是否足够
+    const balanceCheck = await checkTokenBalance(tokens);
+
+    if (balanceCheck.isLoading) {
+      return {
+        success: false,
+        message: '正在检查余额...',
+      };
+    }
+
+    if (!balanceCheck.hasEnough) {
+      // 余额不足，提示用户并引导充值
+      Alert.alert(
+        '余额不足',
+        `当前余额: ${balanceCheck.currentBalance}\n需要费用: ${tokens}\n请先充值`,
+        [
+          { text: '取消', style: 'cancel' },
+          {
+            text: '去充值',
+            onPress: () => {
+              router.push('/(tabs)' as any);
+            },
+          },
+        ]
+      );
+
+      return {
+        success: false,
+        message: balanceCheck.message || '余额不足',
+      };
+    }
+
+    // 2. 余额充足，执行消费操作
+    const { data, error } = await authClient.subscription.meterEvent({
+      event_name: 'token_usage',
+      payload: {
+        value: tokens.toString(),
+        ...(metadata && { metadata }),
+      } as any,
+    });
+
+    if (error) {
+      Alert.alert('扣费失败', error.message || '请稍后重试');
+      return {
+        success: false,
+        message: error.message || '扣费失败',
+      };
+    }
+
+    // 3. 扣费成功，返回结果
+    const balanceAfter = await getUserBalance();
+    return {
+      success: true,
+      data: {
+        identifier: data?.identifier || '',
+        remainingBalance: balanceAfter.data.remainingTokenBalance,
+      },
+      message: '扣费成功',
+    };
+  } catch (error) {
+    console.error('Failed to record token usage:', error);
+    const errorMessage = error instanceof Error ? error.message : '扣费失败，请稍后重试';
+    Alert.alert('错误', errorMessage);
+    return {
+      success: false,
+      message: errorMessage,
+    };
+  }
+}
+
+/**
+ * 跳转到充值页面
+ */
+export function redirectToPricePage() {
+  router.push('/(tabs)' as any);
 }