import 'package:flutter/material.dart';
import 'package:flutter_gen/gen_l10n/app_localizations.dart';
import 'package:go_router/go_router.dart';
import 'package:intl/intl.dart';

class CalendarPage extends StatefulWidget {
  const CalendarPage({super.key});

  @override
  State<CalendarPage> createState() => _CalendarPageState();
}

class _CalendarPageState extends State<CalendarPage> {
  late DateTime _focusedMonth;
  DateTime? _selectedDate;

  @override
  void initState() {
    super.initState();
    _focusedMonth = DateTime.now();
  }

  @override
  Widget build(BuildContext context) {
    final l10n = AppLocalizations.of(context)!;
    final locale = Localizations.localeOf(context).languageCode;

    return Scaffold(
      appBar: AppBar(
        title: Text(l10n.calendar),
        leading: IconButton(
          icon: const Icon(Icons.close),
          onPressed: () => context.pop(),
        ),
      ),
      body: Column(
        children: [
          _MonthNavigation(
            month: _focusedMonth,
            locale: locale,
            onPrevious: () {
              setState(() {
                _focusedMonth = DateTime(_focusedMonth.year, _focusedMonth.month - 1);
              });
            },
            onNext: () {
              setState(() {
                _focusedMonth = DateTime(_focusedMonth.year, _focusedMonth.month + 1);
              });
            },
          ),
          _WeekdayHeaders(locale: locale),
          Expanded(
            child: _CalendarGrid(
              focusedMonth: _focusedMonth,
              selectedDate: _selectedDate,
              onDateSelected: (date) {
                setState(() => _selectedDate = date);
              },
            ),
          ),
        ],
      ),
      bottomNavigationBar: _selectedDate != null
          ? SafeArea(
              child: Padding(
                padding: const EdgeInsets.all(16),
                child: ElevatedButton(
                  onPressed: () {
                    final dateStr = DateFormat('yyyy-MM-dd').format(_selectedDate!);
                    context.go('/?date=$dateStr');
                  },
                  child: Text(l10n.goToDay),
                ),
              ),
            )
          : null,
    );
  }
}

class _MonthNavigation extends StatelessWidget {
  final DateTime month;
  final String locale;
  final VoidCallback onPrevious;
  final VoidCallback onNext;

  const _MonthNavigation({
    required this.month,
    required this.locale,
    required this.onPrevious,
    required this.onNext,
  });

  @override
  Widget build(BuildContext context) {
    final monthFormat = DateFormat.yMMMM(locale);

    return Padding(
      padding: const EdgeInsets.symmetric(horizontal: 8, vertical: 16),
      child: Row(
        mainAxisAlignment: MainAxisAlignment.spaceBetween,
        children: [
          IconButton(
            icon: const Icon(Icons.chevron_left),
            onPressed: onPrevious,
          ),
          Text(
            monthFormat.format(month),
            style: Theme.of(context).textTheme.titleLarge,
          ),
          IconButton(
            icon: const Icon(Icons.chevron_right),
            onPressed: onNext,
          ),
        ],
      ),
    );
  }
}

class _WeekdayHeaders extends StatelessWidget {
  final String locale;

  const _WeekdayHeaders({required this.locale});

  @override
  Widget build(BuildContext context) {
    final weekdays = DateFormat.E(locale);
    final today = DateTime.now();
    final monday = today.subtract(Duration(days: today.weekday - 1));

    return Padding(
      padding: const EdgeInsets.symmetric(horizontal: 8),
      child: Row(
        children: List.generate(7, (index) {
          final day = monday.add(Duration(days: index));
          return Expanded(
            child: Center(
              child: Text(
                weekdays.format(day).substring(0, 2),
                style: Theme.of(context).textTheme.bodySmall?.copyWith(
                      fontWeight: FontWeight.bold,
                    ),
              ),
            ),
          );
        }),
      ),
    );
  }
}

class _CalendarGrid extends StatelessWidget {
  final DateTime focusedMonth;
  final DateTime? selectedDate;
  final ValueChanged<DateTime> onDateSelected;

  const _CalendarGrid({
    required this.focusedMonth,
    required this.selectedDate,
    required this.onDateSelected,
  });

  @override
  Widget build(BuildContext context) {
    final firstDayOfMonth = DateTime(focusedMonth.year, focusedMonth.month, 1);
    final lastDayOfMonth = DateTime(focusedMonth.year, focusedMonth.month + 1, 0);
    final startOffset = (firstDayOfMonth.weekday - 1) % 7;
    final totalDays = startOffset + lastDayOfMonth.day;
    final rowCount = (totalDays / 7).ceil();
    final today = DateTime.now();

    return GridView.builder(
      padding: const EdgeInsets.all(8),
      gridDelegate: const SliverGridDelegateWithFixedCrossAxisCount(
        crossAxisCount: 7,
        childAspectRatio: 1,
      ),
      itemCount: rowCount * 7,
      itemBuilder: (context, index) {
        final dayOffset = index - startOffset;
        if (dayOffset < 0 || dayOffset >= lastDayOfMonth.day) {
          return const SizedBox();
        }

        final date = DateTime(focusedMonth.year, focusedMonth.month, dayOffset + 1);
        final isToday = date.year == today.year &&
            date.month == today.month &&
            date.day == today.day;
        final isSelected = selectedDate != null &&
            date.year == selectedDate!.year &&
            date.month == selectedDate!.month &&
            date.day == selectedDate!.day;

        return GestureDetector(
          onTap: () => onDateSelected(date),
          child: Container(
            margin: const EdgeInsets.all(2),
            decoration: BoxDecoration(
              color: isSelected
                  ? Theme.of(context).colorScheme.primary
                  : isToday
                      ? Theme.of(context).colorScheme.primaryContainer
                      : null,
              borderRadius: BorderRadius.circular(8),
            ),
            child: Center(
              child: Text(
                '${dayOffset + 1}',
                style: TextStyle(
                  color: isSelected
                      ? Theme.of(context).colorScheme.onPrimary
                      : isToday
                          ? Theme.of(context).colorScheme.onPrimaryContainer
                          : null,
                  fontWeight: isToday || isSelected ? FontWeight.bold : null,
                ),
              ),
            ),
          ),
        );
      },
    );
  }
}