import { describe, it, expect } from 'vitest';

// Mirrors safeNext() in apps/web/src/pages/LoginPage.tsx — the post-login redirect guard. `next`
// rides in the login URL and is therefore attacker-supplied, so an open redirect here lands a
// freshly authenticated user on a phishing page. Lives in the API suite because the web workspace
// has no test runner configured; keep the two copies in step.
function safeNext(raw: string | null): string {
  const FALLBACK = '/app';
  if (!raw) return FALLBACK;
  const cleaned = raw.replace(/[\t\n\r]/g, '');
  if (!cleaned.startsWith('/') || cleaned.startsWith('//')) return FALLBACK;
  try {
    const probe = 'https://redirect-guard.invalid';
    const url = new URL(cleaned, probe);
    if (url.origin !== probe) return FALLBACK;
    return `${url.pathname}${url.search}${url.hash}`;
  } catch {
    return FALLBACK;
  }
}

const PROBE = 'https://redirect-guard.invalid';
const staysInternal = (value: string) => new URL(value, PROBE).origin === PROBE;

describe('safeNext — post-login open-redirect guard', () => {
  it('passes through legitimate internal destinations', () => {
    expect(safeNext('/app/cases')).toBe('/app/cases');
    expect(safeNext('/app?tab=open#row')).toBe('/app?tab=open#row');
    expect(safeNext('/admin')).toBe('/admin');
  });

  it('falls back when nothing was requested', () => {
    expect(safeNext(null)).toBe('/app');
    expect(safeNext('')).toBe('/app');
  });

  it('rejects absolute URLs to another origin', () => {
    expect(safeNext('https://evil.com')).toBe('/app');
    expect(safeNext('http://evil.com/path')).toBe('/app');
  });

  it('rejects protocol-relative URLs', () => {
    expect(safeNext('//evil.com')).toBe('/app');
    expect(safeNext('////evil.com')).toBe('/app');
  });

  it('rejects backslash variants that browsers normalise into an authority', () => {
    // URL parsing rewrites \ as / for special schemes, so each of these would otherwise become
    // protocol-relative and point off-origin. The origin check is what catches them.
    for (const attack of ['/\\\\evil.com', '/\\/evil.com', '\\\\evil.com', '/\\\\\\evil.com']) {
      expect(safeNext(attack)).toBe('/app');
    }
  });

  it('rejects schemes smuggled past the leading-slash check with whitespace', () => {
    expect(safeNext('\tjavascript:alert(1)')).toBe('/app');
    expect(safeNext('\njavascript:alert(1)')).toBe('/app');
    expect(safeNext('javascript:alert(1)')).toBe('/app');
    expect(safeNext('data:text/html,<script>alert(1)</script>')).toBe('/app');
  });

  it('never returns a value that resolves off-origin', () => {
    const attacks = [
      '//evil.com',
      '/\\evil.com',
      '/\\\\evil.com',
      'https://evil.com',
      '\tjavascript:alert(1)',
      '////evil.com',
      '/%5cevil.com',
      '/%2f%2fevil.com',
      '/\t/evil.com',
      'data:text/html,<script>alert(1)</script>',
    ];
    for (const attack of attacks) {
      expect(staysInternal(safeNext(attack))).toBe(true);
    }
  });
});