import axios, { AxiosInstance, AxiosRequestConfig } from 'axios';

const API_URL = process.env.NEXT_PUBLIC_API_URL || 'http://localhost:4000';

const GENERIC_ERROR_MESSAGE = 'Something went wrong. Please try again.';
const NETWORK_ERROR_MESSAGE = 'Could not reach the server. Please check your connection and try again.';
const FORBIDDEN_MESSAGE =
  'You do not have permission to do that. Ask an administrator if you need access.';

/**
 * Extracts a user-facing message from a failed request. Prefers a real backend-provided message
 * (joining a NestJS validation array into one line); otherwise falls back to a friendly generic
 * message — never raw client/network text like "Request failed with status code 500" or
 * "Network Error", which is what axios puts in `error.message` when there's nothing better.
 * Every page in this app should use this (or rely on the response interceptor below, which
 * normalizes the same error in place) instead of reading `err.message` directly.
 */
export function getErrorMessage(error: unknown, fallback: string = GENERIC_ERROR_MESSAGE): string {
  const err = error as any;
  const raw = err?.response?.data?.message;
  if (Array.isArray(raw) && raw.length > 0) {
    const joined = raw.filter((m: unknown) => typeof m === 'string' && m.trim()).join('; ');
    if (joined) return joined;
  } else if (typeof raw === 'string' && raw.trim()) {
    return raw;
  }
  if (err?.isAxiosError && !err.response) return NETWORK_ERROR_MESSAGE;
  return fallback;
}

class ApiClient {
  private client: AxiosInstance;

  constructor() {
    this.client = axios.create({
      baseURL: API_URL,
      headers: {
        'Content-Type': 'application/json',
      },
    });

    this.client.interceptors.request.use((config) => {
      const token = typeof window !== 'undefined' ? localStorage.getItem('auth_token') : null;
      if (token) {
        config.headers.Authorization = `Bearer ${token}`;
      }
      return config;
    });

    this.client.interceptors.response.use(
      (response) => response,
      (error) => {
        if (error.response?.status === 401) {
          if (typeof window !== 'undefined') {
            localStorage.removeItem('auth_token');
            window.location.href = '/login';
          }
        }

        // A 403 from this API is always a permission check, and the server's own text
        // names raw permission keys ("Missing permission. Required one of: …") which
        // means nothing to a user. Replace it with something actionable, but only when
        // the server did not send a more specific message of its own.
        if (error.response?.status === 403) {
          const body = error.response.data;
          const serverMessage = typeof body?.message === 'string' ? body.message : '';
          if (!serverMessage || serverMessage.startsWith('Missing permission')) {
            const friendly = FORBIDDEN_MESSAGE;
            if (body && typeof body === 'object') body.message = friendly;
            error.message = friendly;
            return Promise.reject(error);
          }
        }

        // Normalize in place so every existing `err?.response?.data?.message || err?.message ||
        // '<fallback>'` call site across the app picks up a friendly message automatically,
        // instead of raw axios/network text or an unjoined NestJS validation array.
        try {
          const friendly = getErrorMessage(error);
          if (error.response?.data && typeof error.response.data === 'object') {
            error.response.data.message = friendly;
          }
          error.message = friendly;
        } catch {
          // Best-effort — never let normalization itself break the original rejection.
        }

        return Promise.reject(error);
      },
    );
  }

  async get<T>(url: string, config?: AxiosRequestConfig): Promise<T> {
    const response = await this.client.get<{ success: boolean; data: T }>(url, config);
    return response.data.data;
  }

  /**
   * GET without the `{ success, data }` unwrap. Binary endpoints (file streams)
   * have no envelope to unwrap, so `get` would hand back `undefined`.
   */
  async getRaw<T>(url: string, config?: AxiosRequestConfig): Promise<T> {
    const response = await this.client.get<T>(url, config);
    return response.data;
  }

  async post<T>(url: string, data?: any, config?: AxiosRequestConfig): Promise<T> {
    const response = await this.client.post<{ success: boolean; data: T }>(url, data, config);
    return response.data.data;
  }

  async put<T>(url: string, data?: any, config?: AxiosRequestConfig): Promise<T> {
    const response = await this.client.put<{ success: boolean; data: T }>(url, data, config);
    return response.data.data;
  }

  async patch<T>(url: string, data?: any, config?: AxiosRequestConfig): Promise<T> {
    const response = await this.client.patch<{ success: boolean; data: T }>(url, data, config);
    return response.data.data;
  }

  async delete<T>(url: string, config?: AxiosRequestConfig): Promise<T> {
    const response = await this.client.delete<{ success: boolean; data: T }>(url, config);
    return response.data.data;
  }
}

export const apiClient = new ApiClient();