import i18n from 'i18next';
import { globalStorageAdapter } from './setup';

/**
 * Changes the active language, saves the preference locally, and optionally syncs with the backend.
 *
 * @param newLng The new language code (e.g., 'en', 'id')
 * @param syncCallback An optional callback to sync the preference to the backend. It receives the new language and the previous language.
 */
export async function changeLanguage(
  newLng: string,
  syncCallback?: (newLng: string, prevLng: string) => Promise<void>,
): Promise<void> {
  const prevLng = i18n.language;

  if (prevLng === newLng) return;

  // 1. Update local storage & i18next optimistically
  if (globalStorageAdapter) {
    await globalStorageAdapter.setLanguage(newLng);
  }
  await i18n.changeLanguage(newLng);

  // 2. Trigger optional backend sync
  if (syncCallback) {
    try {
      await syncCallback(newLng, prevLng);
    } catch (error) {
      console.error('[i18n] Backend sync failed, rolling back language', error);
      // Rollback on failure
      if (globalStorageAdapter) {
        await globalStorageAdapter.setLanguage(prevLng);
      }
      await i18n.changeLanguage(prevLng);
      throw error; // Rethrow so the caller can show an error toast
    }
  }
}

/**
 * Injects tenant-specific vocabulary overrides dynamically at runtime.
 *
 * Uses a deep-merge strategy. Overrides are applied to the currently active language,
 * or across all loaded languages if needed.
 *
 * @param namespace The i18n namespace to override (e.g., 'common', 'booking')
 * @param overrides A deeply nested object containing the overridden string keys and values.
 * @param lng Specific language to override. Defaults to currently active language.
 */
export function applyTenantOverrides(namespace: string, overrides: Record<string, unknown>, lng?: string): void {
  const targetLng = lng || i18n.language;

  // deep: true -> merges with existing keys rather than replacing the whole namespace
  // overwrite: true -> allows replacing existing specific keys
  i18n.addResourceBundle(targetLng, namespace, overrides, true, true);
}