import { describe, it, expect, beforeEach } from 'vitest';
import i18n from '../i18n';

// i18n.ts already initialized this shared instance as a module-scope side
// effect when it was first imported (simulating "the library loaded first").
// These tests simulate the opposite/merge scenario: an app that has already
// called i18n.init() with its own custom resources, followed by the library
// merging its defaults in via the same addResourceBundle(..., true, false)
// call used by the guarded branch in i18n.ts.
describe('i18next singleton merge behavior', () => {
  beforeEach(async () => {
    await i18n.changeLanguage('pt-BR');
  });

  it('is already initialized by the time i18n.ts has been imported', () => {
    expect(i18n.isInitialized).toBe(true);
  });

  it('preserves an app-customized key when the library merges its defaults with overwrite: false', () => {
    // Simulate the app registering a customized string before the library's
    // guarded init runs its `else` branch.
    i18n.addResourceBundle('pt-BR', 'translation', { home: { welcome: 'Custom Welcome' } }, true, true);
    expect(i18n.t('home.welcome')).toBe('Custom Welcome');

    // Simulate the library's merge branch: it must not clobber the app's key,
    // even though its own default bundle also defines `home.welcome`. It must
    // still add a genuinely new key the app never defined.
    i18n.addResourceBundle(
      'pt-BR',
      'translation',
      { home: { welcome: 'Bem-vindo ao Design System!', mergeOnlyKey: 'Default merge value' } },
      true,
      false
    );

    expect(i18n.t('home.welcome')).toBe('Custom Welcome');
    // Keys the app never defined should still be filled in by the merge.
    expect(i18n.t('home.mergeOnlyKey')).toBe('Default merge value');
  });

  it('would silently overwrite the app key if overwrite were true (regression guard)', () => {
    i18n.addResourceBundle('pt-BR', 'translation', { home: { welcome: 'Custom Welcome' } }, true, true);
    expect(i18n.t('home.welcome')).toBe('Custom Welcome');

    // This mirrors the *bug* the guard prevents — kept here only to document
    // why `overwrite: false` is required in the real merge branch.
    i18n.addResourceBundle(
      'pt-BR',
      'translation',
      { home: { welcome: 'Bem-vindo ao Design System!' } },
      true,
      true
    );

    expect(i18n.t('home.welcome')).toBe('Bem-vindo ao Design System!');
  });
});