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 text from `start` to the delimiter matching the one it opens
 * with, counting depth. Quotes and comments are skipped so a route path like
 * `'/items/:id'`, or a brace inside a string, cannot throw the count off.
 *
 * Parameterised over the delimiter pair because two callers need the same walk:
 * a registration is bounded by parens and a function body by braces, and #307
 * added the second one as a near-copy of the first before this was factored.
 */
function matchedSpan(source: string, start: number, open: string, close: string): string {
  let depth = 0;

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

  return source.slice(start);
}

/**
 * The full text of the registration call starting at `open`, the index of its
 * `(`.
 */
function registrationAt(source: string, open: number): string {
  return matchedSpan(source, 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;
}

/** The body of the function declared at `declared`, braces included. */
function bodyOf(source: string, declared: number): string {
  const start = source.indexOf('{', declared);
  return start === -1 ? '' : matchedSpan(source, start, '{', '}');
}

/**
 * The bodies of any handler factories a registration calls.
 *
 * `router.post('/x', rotationRoute('left'))` carries no `async` token of its
 * own, so the token check below passes it by finding nothing at all. That is
 * exactly how the two rotation routes added in #301 sailed through a guard that
 * exists because this convention had already been half-forgotten once — it did
 * not find them wrapped, it found nothing and said yes. The handler lives in
 * the factory, so the factory is what has to be read.
 *
 * Only functions declared in the same file are followed. `express.json()` and
 * `cookieParser()` are imported and are not handler factories at all; there is
 * no honest way to resolve those textually, and guessing at them would trade
 * this hole for false positives on every library call in app.ts.
 */
function factoryBodies(source: string, call: string): string[] {
  const bodies: string[] = [];

  for (const [, name] of call.matchAll(/\b([a-zA-Z_]\w*)\s*\(/g)) {
    if (name === 'asyncRoute') continue;

    const declared = new RegExp(`function\\s+${name}\\s*\\(`).exec(source);
    if (!declared) continue;

    bodies.push(bodyOf(source, declared.index));
  }

  return bodies;
}

/** Whether `text` contains an `async` that is not directly behind `asyncRoute(`. */
function hasUnwrappedAsync(text: string): boolean {
  for (const found of text.matchAll(/\basync\b/g)) {
    if (!text.slice(0, found.index!).trimEnd().endsWith('asyncRoute(')) return true;
  }
  return false;
}

/**
 * Every `async` inside a registration must sit directly behind `asyncRoute(`,
 * and so must every `async` inside a factory that registration calls.
 * 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);

    const suspect = [call, ...factoryBodies(source, call)];
    if (suspect.some(hasUnwrappedAsync)) {
      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([]);
  });

  // The hole #307 closed. A registration built by a factory carries no `async`
  // of its own, so before this the guard looked at these two lines, found
  // nothing to object to, and passed — which is not the same as finding them
  // wrapped. The rotation routes in #301 were the first factory in src/routes
  // and went through exactly this way.
  it('follows a factory to the handler it returns', () => {
    const bad = `
      function rotationRoute(direction) {
        return async (req, res) => { res.json({ direction }); };
      }
      router.post('/rotate-left', rotationRoute('left'));`;

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

  it('accepts a factory that returns a wrapped handler', () => {
    const good = `
      function rotationRoute(direction) {
        return asyncRoute(async (req, res) => { res.json({ direction }); });
      }
      router.post('/rotate-left', rotationRoute('left'));`;

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

  // Imported calls are left alone deliberately. app.ts registers
  // `express.json()`, `cookieParser()` and `uploadsRouter()`, none of which is
  // a handler factory and none of which can be read from this file — treating
  // an unresolvable name as an offender would trade one hole for a permanently
  // red test.
  it('ignores a call it cannot resolve in the same file', () => {
    const imported = `router.use('/uploads', uploadsRouter());`;

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