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frontend/src/api/client.ts

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+import axios from 'axios';
+import type { APIEnvelope } from '../lib/types';
+import { useAuthStore } from '../stores/authStore';
+
+/**
+ * Typed error class for API errors, providing structured error handling
+ * across the application.
+ */
+export class ApiError extends Error {
+  constructor(message: string) {
+    super(message);
+    this.name = 'ApiError';
+  }
+}
+
+/**
+ * Central Axios instance configured for the Stock Data Backend API.
+ * - Base URL: /api/v1/
+ * - Timeout: 30 seconds
+ * - JSON content type
+ */
+const apiClient = axios.create({
+  baseURL: '/api/v1/',
+  timeout: 30_000,
+  headers: { 'Content-Type': 'application/json' },
+});
+
+/**
+ * Request interceptor: attaches JWT Bearer token from the auth store
+ * to every outgoing request when a token is available.
+ */
+apiClient.interceptors.request.use((config) => {
+  const token = useAuthStore.getState().token;
+  if (token) {
+    config.headers.Authorization = `Bearer ${token}`;
+  }
+  return config;
+});
+
+/**
+ * Response interceptor:
+ * - Success path: unwraps the { status, data, error } envelope, returning
+ *   only the `data` field. Throws ApiError if envelope status is 'error'.
+ * - Error path: handles 401 by clearing auth and redirecting to login.
+ *   All other errors are wrapped in ApiError with a descriptive message.
+ */
+apiClient.interceptors.response.use(
+  (response) => {
+    const envelope = response.data as APIEnvelope;
+    if (envelope.status === 'error') {
+      throw new ApiError(envelope.error ?? 'Unknown API error');
+    }
+    // Return unwrapped data — callers receive the inner payload directly.
+    // We override the response shape here; downstream API functions cast as needed.
+    response.data = envelope.data;
+    return response;
+  },
+  (error) => {
+    if (axios.isAxiosError(error) && error.response?.status === 401) {
+      useAuthStore.getState().logout();
+      window.location.href = '/login';
+    }
+    const msg =
+      error.response?.data?.error ?? error.message ?? 'Network error';
+    throw new ApiError(msg);
+  },
+);
+
+export default apiClient;