import { loadConfig } from "./configLoader";
import type { ConfigResult } from "./types";

/**
 * Fetch and validate config.json at runtime. The URL is resolved against the
 * app's configured base (import.meta.env.BASE_URL), so it works whether the app
 * is served from a domain root or a subpath.
 */
export async function fetchConfig(): Promise<ConfigResult> {
  const url = configUrl();

  let response: Response;
  try {
    response = await fetch(url.toString(), { cache: "no-cache" });
  } catch (err) {
    return {
      ok: false,
      errors: [`Could not fetch config.json (${describe(err)}).`],
    };
  }

  if (!response.ok) {
    return {
      ok: false,
      errors: [
        `Could not load config.json (HTTP ${response.status} ${response.statusText}).`,
      ],
    };
  }

  let raw: unknown;
  try {
    raw = await response.json();
  } catch {
    return {
      ok: false,
      errors: ["config.json is not valid JSON."],
    };
  }

  return loadConfig(raw);
}

/**
 * Resolve the config.json URL for the deployed location. Uses Vite's configured
 * base when it is an absolute path (e.g. "/meal-estimator/"); otherwise falls
 * back to the directory of the current document so a relative "./" base works
 * whether or not the URL has a trailing slash.
 */
function configUrl(): string {
  const base = import.meta.env.BASE_URL;

  if (base.startsWith("/")) {
    // Absolute base path: config sits directly under it.
    return new URL(`${base}config.json`, window.location.origin).toString();
  }

  // Relative base: resolve against the current document's directory.
  const path = window.location.pathname;
  const dir = path.endsWith("/") ? path : path.slice(0, path.lastIndexOf("/") + 1);
  return new URL(`${dir}config.json`, window.location.origin).toString();
}

function describe(err: unknown): string {
  return err instanceof Error ? err.message : "network error";
}