/**
 * Configurable API client factory.
 * Creates a fetch wrapper with base URL, auth token injection, and error handling.
 */

import type { ApiClient, ApiClientConfig, ApiResult } from './types.js';

/**
 * Create an API client with a base URL and optional auth token.
 *
 * @example
 * ```ts
 * const api = createApiClient({
 *   baseUrl: "/api",
 *   getToken: () => localStorage.getItem("access_token"),
 * });
 *
 * // Throws on error
 * const users = await api.fetch<User[]>("/users");
 *
 * // Never throws
 * const { data, error } = await api.safeFetch<User[]>("/users");
 * ```
 */
export function createApiClient(config: ApiClientConfig): ApiClient {
  const { baseUrl, getToken, defaultHeaders } = config;

  function buildHeaders(options?: RequestInit): HeadersInit {
    const headers: Record<string, string> = {
      'Content-Type': 'application/json',
      ...defaultHeaders,
    };

    if (getToken) {
      const token = getToken();
      if (token) {
        headers['Authorization'] = `Bearer ${token}`;
      }
    }

    if (options?.headers) {
      const extra =
        options.headers instanceof Headers
          ? Object.fromEntries(options.headers as any)
          : Array.isArray(options.headers)
            ? Object.fromEntries(options.headers)
            : (options.headers as Record<string, string>);
      Object.assign(headers, extra);
    }

    return headers;
  }

  return {
    async fetch<T>(path: string, options?: RequestInit): Promise<T> {
      const res = await globalThis.fetch(`${baseUrl}${path}`, {
        ...options,
        headers: buildHeaders(options),
      });

      if (!res.ok) {
        const body = await res.json().catch(() => ({ error: res.statusText }));
        throw new Error(body.error || `HTTP ${res.status}`);
      }

      return res.json() as Promise<T>;
    },

    async safeFetch<T>(path: string, options?: RequestInit): Promise<ApiResult<T>> {
      try {
        const res = await globalThis.fetch(`${baseUrl}${path}`, {
          ...options,
          headers: buildHeaders(options),
        });

        if (!res.ok) {
          const body = await res.json().catch(() => ({ error: res.statusText }));
          return { data: null, error: body.error || `HTTP ${res.status}` };
        }

        const data = (await res.json()) as T;
        return { data, error: null };
      } catch {
        return { data: null, error: 'API unavailable' };
      }
    },
  };
}