import { readdirSync, readFileSync } from 'fs';
import { join } from 'path';

// Express 4 does not forward a rejected promise from an async handler, so an
// unwrapped async route never responds at all — the request hangs until the
// client gives up, nothing reaches the error middleware, and nothing is logged
// as a failure. That is the shape of the 2026-08-17 incident that put an empty
// storefront in front of customers.
//
// `asyncRoute` fixes it, but a convention only holds while everyone remembers
// it, and this one was already half-forgotten once: 30 handlers were added
// unwrapped after the wrapper existed. This test is the part that remembers.
//
// Express 5 forwards rejections natively. When the project upgrades, delete
// `asyncRoute` and delete this test with it.

const SRC = join(__dirname, '..', '..', 'src');

// `router.get(`, `app.use(`, and friends — where a handler gets registered.
// Any `*Router` name counts, not just `router`: cartCheckout.ts registers the
// PayPal webhook on a second router, and matching only the common name is how
// that one stayed unwrapped while everything around it was audited.
const REGISTRATION = /\b(?:app|\w*[Rr]outer)\.(?:get|post|put|patch|delete|all|use)\s*\(/g;

/**
 * Returns the full text of the registration call starting at `open` (the index
 * of its `(`), by counting parens to the matching close. Quotes and comments
 * are skipped so a path like `'/items/:id'` or a `)` inside a string cannot
 * throw the count off.
 */
function registrationAt(source: string, open: number): string {
  let depth = 0;
  for (let i = open; i < source.length; i++) {
    const c = source[i];

    if (c === "'" || c === '"' || c === '`') {
      i = skipString(source, i);
      continue;
    }
    if (c === '/' && source[i + 1] === '/') {
      i = source.indexOf('\n', i);
      if (i === -1) break;
      continue;
    }
    if (c === '/' && source[i + 1] === '*') {
      i = source.indexOf('*/', i) + 1;
      continue;
    }

    if (c === '(') depth++;
    if (c === ')') {
      depth--;
      if (depth === 0) return source.slice(open, i + 1);
    }
  }
  return source.slice(open);
}

/** Returns the index of the closing quote of the string opening at `start`. */
function skipString(source: string, start: number): number {
  const quote = source[start];
  for (let i = start + 1; i < source.length; i++) {
    if (source[i] === '\\') {
      i++;
      continue;
    }
    if (source[i] === quote) return i;
  }
  return source.length;
}

/**
 * Every `async` inside a registration must sit directly behind `asyncRoute(`.
 * Checking the token rather than the line catches a handler whose `async`
 * lands on its own line, which a line-oriented grep would wave through.
 */
function unwrappedHandlers(source: string): string[] {
  const offenders: string[] = [];

  for (const match of source.matchAll(REGISTRATION)) {
    const open = match.index! + match[0].length - 1;
    const call = registrationAt(source, open);

    for (const found of call.matchAll(/\basync\b/g)) {
      const before = call.slice(0, found.index!).trimEnd();
      if (!before.endsWith('asyncRoute(')) {
        offenders.push(`line ${lineOf(source, match.index!)}: ${match[0].trim()}`);
      }
    }
  }

  return offenders;
}

function lineOf(source: string, index: number): number {
  return source.slice(0, index).split('\n').length;
}

const routeFiles = readdirSync(join(SRC, 'routes'))
  .filter((f) => f.endsWith('.ts'))
  .map((f) => join('routes', f));

describe.each([...routeFiles, 'app.ts'])('%s', (relative) => {
  it('wraps every async handler in asyncRoute', () => {
    const source = readFileSync(join(SRC, relative), 'utf8');

    expect(unwrappedHandlers(source)).toEqual([]);
  });
});

describe('async middleware', () => {
  // `attachCustomer` is mounted globally, so a rejection there hangs every
  // request in the application — including the routes that are wrapped
  // correctly. It is the one handler whose failure is not contained.
  it('wraps attachCustomer where app.ts mounts it', () => {
    const source = readFileSync(join(SRC, 'app.ts'), 'utf8');

    expect(source).toContain('app.use(asyncRoute(attachCustomer))');
  });
});

// Keeps the helper honest: if the paren-walking ever silently stops finding
// registrations, the tests above would pass by finding nothing at all.
describe('the guard itself', () => {
  it('finds a bare async handler', () => {
    const bad = `router.get('/', requireCustomer, async (req, res) => { res.json({}); });`;

    expect(unwrappedHandlers(bad)).toHaveLength(1);
  });

  it('accepts a wrapped one', () => {
    const good = `router.get('/', requireCustomer, asyncRoute(async (req, res) => { res.json({}); }));`;

    expect(unwrappedHandlers(good)).toEqual([]);
  });

  it('sees an async handler that starts on a later line', () => {
    const bad = `router.post(\n  '/items/:id',\n  uploadImages,\n  async (req, res) => { res.json({}); }\n);`;

    expect(unwrappedHandlers(bad)).toHaveLength(1);
  });

  it('is not fooled by a paren inside a route path', () => {
    const bad = `router.get('/odd(path', async (req, res) => { res.json({}); });`;

    expect(unwrappedHandlers(bad)).toHaveLength(1);
  });

  it('leaves a synchronous handler alone', () => {
    const sync = `router.get('/', (req, res) => { res.json({}); });`;

    expect(unwrappedHandlers(sync)).toEqual([]);
  });
});