import fs from "node:fs";
import path from "node:path";
import { RunsError } from "./errors.mjs";

export const RUNS_DIRNAME = "runs";
export const STATE_DIRNAME = "state";

export function isMissing(error) {
  return error?.code === "ENOENT" || error?.code === "ENOTDIR";
}

function isInside(root, target) {
  const relative = path.relative(root, target);
  return relative === "" || (relative !== ".." && !relative.startsWith(`..${path.sep}`) && !path.isAbsolute(relative));
}

// Resolves <dataRoot>/<parts...> through any symbolic links and returns the
// real path, or null when it doesn't exist. The data root is trusted as
// configured; a path below it that resolves outside it refuses, so no reader
// here follows a link out of the data root.
export function resolveInside(dataRoot, ...parts) {
  const target = path.join(dataRoot, ...parts);
  let root;
  let real;
  try {
    root = fs.realpathSync(dataRoot);
    real = fs.realpathSync(target);
  } catch (error) {
    if (isMissing(error)) return null;
    throw new RunsError(`cannot resolve ${target}: ${error.code ?? error.message}`);
  }
  if (!isInside(root, real)) {
    throw new RunsError(`${target} resolves outside the data root (${root})`);
  }
  return real;
}

// A JSON object read from <dataRoot>/<parts...>, or null when the file is
// missing, unreadable, not JSON, not an object or outside the data root.
export function readJsonObject(dataRoot, ...parts) {
  try {
    const file = resolveInside(dataRoot, ...parts);
    if (file === null) return null;
    const value = JSON.parse(fs.readFileSync(file, "utf8"));
    return typeof value === "object" && value !== null && !Array.isArray(value) ? value : null;
  } catch {
    return null;
  }
}