import 'dart:async';

import 'package:flutter/material.dart';
import 'package:lucide_icons/lucide_icons.dart';
import 'package:flutter_riverpod/flutter_riverpod.dart';

import '../providers/api_client_provider.dart';
import '../providers/auth_provider.dart';

/// Sticky banner shown when the backend is unreachable. Surfaces a retry
/// action plus a "last sync X ago" hint when there is cached content to
/// fall back on (Tier 2 offline mode).
class OfflineBanner extends ConsumerStatefulWidget {
  const OfflineBanner({super.key});

  @override
  ConsumerState<OfflineBanner> createState() => _OfflineBannerState();
}

class _OfflineBannerState extends ConsumerState<OfflineBanner> {
  bool _retrying = false;
  DateTime? _lastSync;
  Timer? _refreshTimer;

  @override
  void initState() {
    super.initState();
    _loadLastSync();
    // Refresh the relative-time string every 30s so "5 min ago" rolls
    // forward without the user having to interact with the banner.
    _refreshTimer = Timer.periodic(
      const Duration(seconds: 30),
      (_) => _loadLastSync(),
    );
  }

  @override
  void dispose() {
    _refreshTimer?.cancel();
    super.dispose();
  }

  Future<void> _loadLastSync() async {
    if (!mounted) return;
    try {
      // Most-recent sync across all cached domains so the hint reads as
      // "your data was current as of X" regardless of which screen the
      // user is looking at.
      final ts = await ref.read(fabledDatabaseProvider).getLatestSync();
      if (!mounted) return;
      setState(() => _lastSync = ts);
    } catch (_) {
      // Non-critical — banner just won't show the sync hint.
    }
  }

  Future<void> _retry() async {
    if (_retrying) return;
    setState(() => _retrying = true);
    try {
      await ref.read(authProvider.notifier).verify();
    } finally {
      if (mounted) setState(() => _retrying = false);
    }
  }

  String? _relativeAgo(DateTime ts) {
    final diff = DateTime.now().difference(ts);
    if (diff.isNegative) return null;
    if (diff.inMinutes < 1) return 'just now';
    if (diff.inMinutes < 60) return '${diff.inMinutes} min ago';
    if (diff.inHours < 24) {
      final h = diff.inHours;
      return '$h ${h == 1 ? 'hour' : 'hours'} ago';
    }
    final d = diff.inDays;
    return '$d ${d == 1 ? 'day' : 'days'} ago';
  }

  @override
  Widget build(BuildContext context) {
    final status = ref.watch(authProvider);
    if (status != AuthStatus.offline) return const SizedBox.shrink();

    final scheme = Theme.of(context).colorScheme;
    final ago = _lastSync == null ? null : _relativeAgo(_lastSync!);
    // Pending queue depth — shown on the Retry button so the user knows
    // there's offline work waiting to land when they come back online.
    final pending = ref.watch(writeQueueDepthProvider).asData?.value ?? 0;

    final baseMessage = ago == null
        ? 'Offline — showing cached data.'
        : 'Offline — last sync $ago.';
    final message = pending > 0
        ? '$baseMessage $pending pending change${pending == 1 ? '' : 's'}.'
        : baseMessage;
    final retryLabel = pending > 0 ? 'Retry ($pending)' : 'Retry';

    return Material(
      color: scheme.errorContainer,
      child: SafeArea(
        bottom: false,
        child: Padding(
          padding: const EdgeInsets.symmetric(horizontal: 12, vertical: 8),
          child: Row(
            children: [
              Icon(LucideIcons.cloudOff,
                  size: 18, color: scheme.onErrorContainer),
              const SizedBox(width: 8),
              Expanded(
                child: Text(
                  message,
                  style: TextStyle(color: scheme.onErrorContainer),
                ),
              ),
              TextButton(
                onPressed: _retrying ? null : _retry,
                style: TextButton.styleFrom(
                  foregroundColor: scheme.onErrorContainer,
                  padding: const EdgeInsets.symmetric(horizontal: 12),
                ),
                child: _retrying
                    ? const SizedBox(
                        width: 14,
                        height: 14,
                        child: CircularProgressIndicator(strokeWidth: 2),
                      )
                    : Text(retryLabel),
              ),
            ],
          ),
        ),
      ),
    );
  }
}