frontend/src/utils/axios.ts

import axios from 'axios';
import qs from 'qs';

const instance = axios.create({
  baseURL: process.env.REACT_APP_API_URL || 'http://localhost:8000',
  headers: {
    'Content-Type': 'application/json',
  },
});

// Token refresh mechanism
let isRefreshing = false;
let failedQueue: any[] = [];

const processQueue = (error: any, token: string | null = null) => {
  failedQueue.forEach(prom => {
    if (error) {
      prom.reject(error);
    } else {
      prom.resolve(token);
    }
  });
  failedQueue = [];
};

// Add a request interceptor
instance.interceptors.request.use(
  (config) => {
    const token = localStorage.getItem('token');
    if (token) {
      config.headers.Authorization = `Bearer ${token}`;
    }

    // Handle form data
    if (config.data instanceof FormData) {
      config.headers['Content-Type'] = 'application/x-www-form-urlencoded';
      config.data = qs.stringify(Object.fromEntries(config.data));
    }

    return config;
  },
  (error) => {
    return Promise.reject(error);
  }
);

// Add a response interceptor
instance.interceptors.response.use(
  (response) => response,
  async (error) => {
    const originalRequest = error.config;

    if (error.response?.status === 401 && !originalRequest._retry) {
      if (isRefreshing) {
        return new Promise((resolve, reject) => {
          failedQueue.push({ resolve, reject });
        })
          .then(token => {
            originalRequest.headers.Authorization = `Bearer ${token}`;
            return instance(originalRequest);
          })
          .catch(err => Promise.reject(err));
      }

      originalRequest._retry = true;
      isRefreshing = true;

      try {
        const refreshToken = localStorage.getItem('refreshToken');
        if (!refreshToken) {
          throw new Error('No refresh token available');
        }

        const response = await axios.post('/api/auth/refresh', {
          refresh_token: refreshToken,
        });

        const { access_token, refresh_token } = response.data;
        localStorage.setItem('token', access_token);
        localStorage.setItem('refreshToken', refresh_token);

        instance.defaults.headers.common.Authorization = `Bearer ${access_token}`;
        processQueue(null, access_token);
        return instance(originalRequest);
      } catch (refreshError) {
        processQueue(refreshError, null);
        localStorage.removeItem('token');
        localStorage.removeItem('refreshToken');
        window.location.href = '/login';
        return Promise.reject(refreshError);
      } finally {
        isRefreshing = false;
      }
    }

    return Promise.reject(error);
  }
);

// Error handling utility
export const handleApiError = (error: any): string => {
  if (error.response) {
    // The request was made and the server responded with a status code
    // that falls out of the range of 2xx
    return error.response.data.message || 'An error occurred while processing your request';
  } else if (error.request) {
    // The request was made but no response was received
    return 'No response received from server. Please check your internet connection';
  } else {
    // Something happened in setting up the request that triggered an Error
    return error.message || 'An unexpected error occurred';
  }
};

export default instance;