import { sep } from "node:path";

/**
 * A `.env` inside the installed package directory does not survive an update:
 * `npm i -g` replaces that directory wholesale, and postinstall recreates the
 * file from `.env.example`. The CLI announces every env file it loads without
 * distinguishing the ones that last from the one that doesn't.
 *
 * Returns the warning to print, or null when there is nothing worth saying.
 *
 * Two conditions, both required, so a development checkout never sees this:
 *  - the file sits inside the package root, and that root is inside a
 *    `node_modules` directory — i.e. an installed package, not a checkout,
 *    where the same path is stable and documented in SETUP_GUIDE.md;
 *  - the file actually supplied at least one value. First writer wins, so a
 *    file entirely shadowed by a durable one supplied nothing, and losing it
 *    costs nothing.
 *
 * @param {{ envPath: string, packageRoot: string, durableEnvPath: string, suppliedKeys: boolean }} args
 * @returns {string | null}
 */
export function describeVolatileEnvWarning({ envPath, packageRoot, durableEnvPath, suppliedKeys }) {
  if (!suppliedKeys) return null;
  if (envPath === durableEnvPath) return null;
  if (!isInsideInstalledPackage(packageRoot)) return null;
  if (!envPath.startsWith(packageRoot + sep)) return null;

  return (
    `${envPath} lives inside the installed package: updating OmniRoute replaces it. ` +
    `Move the values you set to ${durableEnvPath}, which updates leave alone.`
  );
}

/** True when the path sits under a `node_modules` directory. */
function isInsideInstalledPackage(dir) {
  return typeof dir === "string" && dir.split(sep).includes("node_modules");
}