import 'package:flutter/material.dart';
import 'package:flutter_riverpod/flutter_riverpod.dart';
import '../../core/providers/mood_provider.dart';
import 'day_detail_screen.dart';
import 'widgets/calendar_heatmap.dart';
import 'widgets/day_entry_card.dart';

const _months = [
  'January', 'February', 'March', 'April', 'May', 'June',
  'July', 'August', 'September', 'October', 'November', 'December',
];

class CalendarScreen extends ConsumerStatefulWidget {
  const CalendarScreen({super.key});

  @override
  ConsumerState<CalendarScreen> createState() => _CalendarScreenState();
}

class _CalendarScreenState extends ConsumerState<CalendarScreen> {
  late DateTime _month;

  @override
  void initState() {
    super.initState();
    final now = DateTime.now();
    _month = DateTime(now.year, now.month);
  }

  void _prevMonth() => setState(() => _month = DateTime(_month.year, _month.month - 1));

  void _nextMonth() {
    final now = DateTime.now();
    final next = DateTime(_month.year, _month.month + 1);
    if (!next.isAfter(DateTime(now.year, now.month))) {
      setState(() => _month = next);
    }
  }

  static String _dayLabel(DateTime day) {
    final now = DateTime.now();
    final today = DateTime(now.year, now.month, now.day);
    final yesterday = today.subtract(const Duration(days: 1));
    if (day == today) return 'Today';
    if (day == yesterday) return 'Yesterday';
    return '${_months[day.month - 1]} ${day.day}';
  }

  bool get _canGoForward {
    final now = DateTime.now();
    return _month.year < now.year ||
        (_month.year == now.year && _month.month < now.month);
  }

  @override
  Widget build(BuildContext context) {
    final selectedDay = ref.watch(selectedDayProvider);
    final entriesAsync = ref.watch(moodEntriesForDayProvider(selectedDay));

    return Scaffold(
      appBar: AppBar(
        title: const Text('History'),
        centerTitle: false,
      ),
      body: Column(
        children: [
          _MonthNav(
            label: '${_months[_month.month - 1]} ${_month.year}',
            onPrev: _prevMonth,
            onNext: _canGoForward ? _nextMonth : null,
          ),
          CalendarHeatmap(
            month: _month,
            selectedDay: selectedDay,
            onDayTap: (day) {
              ref.read(selectedDayProvider.notifier).select(day);
              // Follow the selected day's month
              final m = DateTime(day.year, day.month);
              if (m != _month) setState(() => _month = m);
            },
          ),
          const Divider(height: 1),
          InkWell(
            onTap: () => Navigator.of(context).push(
              MaterialPageRoute(
                builder: (_) => DayDetailScreen(day: selectedDay),
              ),
            ),
            child: Padding(
              padding: const EdgeInsets.symmetric(horizontal: 16, vertical: 10),
              child: Row(
                children: [
                  Text(
                    _dayLabel(selectedDay),
                    style: Theme.of(context).textTheme.titleSmall,
                  ),
                  const Spacer(),
                  Icon(Icons.chevron_right,
                      color: Theme.of(context).colorScheme.outline),
                ],
              ),
            ),
          ),
          const Divider(height: 1),
          Expanded(
            child: entriesAsync.when(
              data: (entries) => entries.isEmpty
                  ? _EmptyDay(day: selectedDay)
                  : ListView.builder(
                      padding: const EdgeInsets.symmetric(vertical: 8),
                      itemCount: entries.length,
                      itemBuilder: (context, i) =>
                          DayEntryCard(entry: entries[i]),
                    ),
              loading: () =>
                  const Center(child: CircularProgressIndicator()),
              error: (_, __) => const SizedBox.shrink(),
            ),
          ),
        ],
      ),
    );
  }
}

class _MonthNav extends StatelessWidget {
  const _MonthNav({
    required this.label,
    required this.onPrev,
    required this.onNext,
  });

  final String label;
  final VoidCallback onPrev;
  final VoidCallback? onNext;

  @override
  Widget build(BuildContext context) {
    return Padding(
      padding: const EdgeInsets.symmetric(horizontal: 4),
      child: Row(
        children: [
          IconButton(icon: const Icon(Icons.chevron_left), onPressed: onPrev),
          Expanded(
            child: Text(
              label,
              textAlign: TextAlign.center,
              style: Theme.of(context).textTheme.titleMedium,
            ),
          ),
          IconButton(
            icon: const Icon(Icons.chevron_right),
            onPressed: onNext,
          ),
        ],
      ),
    );
  }
}

class _EmptyDay extends StatelessWidget {
  const _EmptyDay({required this.day});

  final DateTime day;

  @override
  Widget build(BuildContext context) {
    final now = DateTime.now();
    final today = DateTime(now.year, now.month, now.day);
    final label = day == today ? 'today' : '${day.day}/${day.month}/${day.year}';

    return Center(
      child: Text(
        'No entries for $label',
        style: Theme.of(context)
            .textTheme
            .bodyMedium
            ?.copyWith(color: Theme.of(context).colorScheme.outline),
      ),
    );
  }
}