// Thin fetch wrapper. Always sends cookies (credentials: 'include'). Throws on
// non-2xx with the server's error.message.
//
// In dev, requests go to /api/* (rewritten by next.config.js to the API).
// In prod, Nginx routes /api/* to the backend.

export class ApiError extends Error {
  constructor(
    message: string,
    public status: number,
    public details?: unknown,
  ) {
    super(message);
    this.name = 'ApiError';
  }
}

interface RequestOptions extends Omit<RequestInit, 'body'> {
  body?: unknown;
  query?: Record<string, string | number | boolean | undefined | null>;
}

const BASE = ''; // Empty: /api/* via Next rewrites in dev, Nginx in prod.

function buildUrl(path: string, query?: RequestOptions['query']): string {
  const url = `${BASE}${path.startsWith('/') ? path : `/${path}`}`;
  if (!query) return url;
  const params = new URLSearchParams();
  for (const [k, v] of Object.entries(query)) {
    if (v === undefined || v === null) continue;
    params.set(k, String(v));
  }
  const qs = params.toString();
  return qs ? `${url}?${qs}` : url;
}

export async function apiRequest<T>(path: string, opts: RequestOptions = {}): Promise<T> {
  const { body, query, headers, ...rest } = opts;
  const init: RequestInit = {
    credentials: 'include',
    headers: {
      'Content-Type': 'application/json',
      ...(headers as Record<string, string> | undefined),
    },
    ...rest,
  };
  if (body !== undefined) init.body = JSON.stringify(body);

  const res = await fetch(buildUrl(path, query), init);

  // 204 No Content
  if (res.status === 204) return undefined as T;

  let payload: unknown;
  const contentType = res.headers.get('content-type') ?? '';
  if (contentType.includes('application/json')) {
    payload = await res.json();
  } else {
    payload = await res.text();
  }

  if (!res.ok) {
    const err = (payload as { message?: string; error?: string })?.message ?? `Request failed (${res.status})`;
    throw new ApiError(err, res.status, payload);
  }
  return payload as T;
}

export const api = {
  get: <T>(path: string, opts?: Omit<RequestOptions, 'body'>) =>
    apiRequest<T>(path, { ...opts, method: 'GET' }),
  post: <T>(path: string, body?: unknown, opts?: Omit<RequestOptions, 'body' | 'method'>) =>
    apiRequest<T>(path, { ...opts, method: 'POST', body }),
  patch: <T>(path: string, body?: unknown, opts?: Omit<RequestOptions, 'body' | 'method'>) =>
    apiRequest<T>(path, { ...opts, method: 'PATCH', body }),
  delete: <T>(path: string, opts?: Omit<RequestOptions, 'body'>) =>
    apiRequest<T>(path, { ...opts, method: 'DELETE' }),
};