import 'package:dio/dio.dart';

/// A value from the API, or the last one [CacheInterceptor] had on file for the
/// same endpoint+params when the live request failed. `fetchedAt` is null for
/// a live answer — that is the one bit a screen needs to decide whether to
/// show a `StaleBanner`. See `docs/ai/offline-cache.md`.
class Cached<T> {
  const Cached(this.data, {this.fetchedAt});

  final T data;
  final DateTime? fetchedAt;
}

extension CachedResponseX<T> on Response<T> {
  /// Wraps this response's data with the staleness [CacheInterceptor] recorded
  /// in `extra['fetchedAt']`. A provider that wants offline support returns
  /// `r.cached` instead of `r.data!`.
  Cached<T> get cached =>
      Cached(data as T, fetchedAt: extra['fetchedAt'] as DateTime?);
}

/// The oldest of several fetch times, or null if none of them is stale.
/// Screens with several cached providers show one banner for the lot rather
/// than one per tile.
DateTime? oldestFetch(Iterable<DateTime?> fetchedAt) {
  DateTime? oldest;
  for (final at in fetchedAt) {
    if (at == null) continue;
    if (oldest == null || at.isBefore(oldest)) oldest = at;
  }
  return oldest;
}