import { existsSync, readdirSync, readFileSync, statSync } from "node:fs";
import { dirname, join, resolve } from "node:path";
import { fileURLToPath } from "node:url";

const here = dirname(fileURLToPath(import.meta.url));

/** Course directory; override with COURSE_ROOT (used by tests). */
export function courseRoot() {
  return process.env.COURSE_ROOT
    ? resolve(process.env.COURSE_ROOT)
    : join(here, "..", "course");
}

/** Module directories `course/NN-slug/`, sorted by number. */
export function moduleDirs() {
  const root = courseRoot();
  if (!existsSync(root)) return [];
  return readdirSync(root)
    .map((name) => ({ name, m: /^(\d\d)-(.+)$/.exec(name) }))
    .filter(({ name, m }) => m && statSync(join(root, name)).isDirectory())
    .map(({ name, m }) => ({ num: m[1], slug: m[2], path: join(root, name) }))
    .sort((a, b) => a.num.localeCompare(b.num));
}

export function testFiles(path, lang) {
  const dir = join(path, "tests", lang === "rust" ? "rust" : "ts");
  if (!existsSync(dir)) return [];
  const ext = lang === "rust" ? /\.rs$/ : /\.test\.ts$/;
  return readdirSync(dir).filter((f) => ext.test(f)).sort().map((f) => join(dir, f));
}

/** Test names declared by a module's tests for `lang` ("rust" | "ts"). */
export function testNames(path, lang) {
  const re = lang === "rust" ? /fn\s+(test_\w+)/g : /test\(\s*["'](test_\w+)/g;
  const names = new Set();
  for (const f of testFiles(path, lang)) {
    for (const m of readFileSync(f, "utf8").matchAll(re)) names.add(m[1]);
  }
  return [...names].sort();
}

/** `### test_…` headings in a module's scenarios.md (or another file in `path`). */
export function scenarioNames(path, file = "scenarios.md") {
  const f = join(path, file);
  if (!existsSync(f)) return [];
  const names = new Set();
  for (const m of readFileSync(f, "utf8").matchAll(/^### (test_\w+)/gm)) names.add(m[1]);
  return [...names].sort();
}

/** First module whose workspace gets course/cards (Module 5 introduces the card data format). */
export const COURSE_CARDS_FROM = 5;

/**
 * The card data a workspace at module `upTo` has: course/cards (every module's) from
 * Module 5 only, since Modules 1-4 keep their cards in the learner's own code (spec
 * §6.2a), then the cards/ of each module up to `upTo` that has its own (Module 10's
 * SpellGrid cards), so earlier modules never see later modules' cards.
 */
export function cardDirs(upTo) {
  const shared = Number(upTo) >= COURSE_CARDS_FROM ? [join(courseRoot(), "cards")] : [];
  const local = moduleDirs()
    .filter((m) => Number(m.num) <= Number(upTo))
    .map((m) => join(m.path, "cards"));
  return [...shared, ...local].filter((d) => existsSync(d));
}

/** Read <ws>/.course.json, failing with a clear message if it is missing or invalid. */
export function readCourseConfig(ws) {
  const f = join(ws, ".course.json");
  if (!existsSync(f)) {
    fail(`No .course.json in ${resolve(ws)}.\n` +
      "Create your workspace first: copy workspace-template/rust or workspace-template/ts " +
      "to a new directory and run `git init` there (see README.md, Quick start).");
  }
  try {
    return JSON.parse(readFileSync(f, "utf8"));
  } catch (e) {
    fail(`Cannot parse ${f}: ${e.message}`);
  }
}

/** True when this module is the script node was asked to run (works on every Node version). */
export function isMain(metaUrl) {
  return Boolean(process.argv[1]) && fileURLToPath(metaUrl) === resolve(process.argv[1]);
}

export function loadCatalog() {
  const f = join(courseRoot(), "catalog.json");
  if (!existsSync(f)) throw new Error(`catalog not found: ${f}`);
  return JSON.parse(readFileSync(f, "utf8"));
}

export function fail(msg) {
  console.error(msg);
  process.exit(1);
}