flutter-assertion

main.dart

import 'package:flutter/material.dart';

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({super.key});
  @override
  Widget build(BuildContext context) {
    return MaterialApp(title: "test", home: CalendarScreen());
  }
}

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

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

class _CalendarScreenState extends State<CalendarScreen> {
  int selectedChildIndex = 0;
  late DateTime visibleMonth;
  late DateTime selectedDate;
  int viewIndex = 0; // 0: Calendar, 1: List

  late final DraggableScrollableController _sheetController;

  @override
  void initState() {
    super.initState();
    final DateTime now = DateTime.now();
    visibleMonth = DateTime(now.year, now.month, 1);
    selectedDate = DateTime(now.year, now.month, now.day);
    _sheetController = DraggableScrollableController();
  }

  @override
  void dispose() {
    _sheetController.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text('Calendar')),
      body: _buildBody(context),
    );
  }

  Widget _buildBody(BuildContext context) {
    return Column(
      crossAxisAlignment: CrossAxisAlignment.stretch,
      children: [
        Expanded(
          child: LayoutBuilder(
            builder: (context, constraints) {
              return Stack(
                children: [
                  Column(
                    crossAxisAlignment: CrossAxisAlignment.stretch,
                    children: [
                      _buildCalendar(context),
                      const SizedBox(height: 12),
                    ],
                  ),
                  // Placeholder(),
                  Positioned(
                    left: 0,
                    right: 0,
                    bottom: 0,
                    top: 0,
                    child: _buildEventsBottomSheet(context),
                  ),
                ],
              );
            },
          ),
        ),
      ],
    );
  }

  Widget _buildCalendar(BuildContext context) {
    final DateTime firstOfMonth = DateTime(
      visibleMonth.year,
      visibleMonth.month,
      1,
    );
    final int daysInMonth = DateUtils.getDaysInMonth(
      visibleMonth.year,
      visibleMonth.month,
    );
    final int firstWeekday = firstOfMonth.weekday; // 1 Mon - 7 Sun
    final int leadingEmpty = (firstWeekday - 1); // make Sunday as 0 leading

    final List<Widget> dayCells = [];

    // Weekday labels
    const List<String> weekdays = ['M', 'T', 'W', 'T', 'F', 'S', 'S'];
    dayCells.addAll(
      weekdays
          .map(
            (d) => Center(
              child: Text(
                d,
                style: Theme.of(
                  context,
                ).textTheme.bodySmall?.copyWith(fontWeight: FontWeight.bold),
              ),
            ),
          )
          .toList(),
    );

    // Leading blanks
    for (int i = 0; i < leadingEmpty; i++) {
      dayCells.add(const SizedBox.shrink());
    }

    // Days
    for (int day = 1; day <= daysInMonth; day++) {
      final DateTime date = DateTime(
        visibleMonth.year,
        visibleMonth.month,
        day,
      );

      dayCells.add(
        GestureDetector(
          onTap: () {
            setState(() {
              selectedDate = date;
            });
            // _scheduleSheetCollapse();
          },
          child: Container(
            margin: const EdgeInsets.all(4),
            decoration: BoxDecoration(
              color: Colors.orange.shade100,
              borderRadius: BorderRadius.circular(8),
              //border: border,
            ),
            child: Stack(
              children: [
                Center(
                  child: Text(
                    '$day',
                    style: Theme.of(context).textTheme.bodyMedium?.copyWith(
                      //color: textColor,
                      fontWeight: FontWeight.w600,
                    ),
                  ),
                ),
              ],
            ),
          ),
        ),
      );
    }

    // Grid: 7 columns, auto rows
    return Padding(
      padding: const EdgeInsets.symmetric(horizontal: 12.0),
      child: Column(
        children: [
          GridView.count(
            physics: const NeverScrollableScrollPhysics(),
            shrinkWrap: true,
            crossAxisCount: 7,
            children: dayCells,
          ),
        ],
      ),
    );
  }

  Widget _buildEventsBottomSheet(BuildContext context) {
    final ThemeData theme = Theme.of(context);
    final double minChildSize = 0.15;
    final double initialChildSize = 0.3;

    return DraggableScrollableSheet(
      key: ValueKey<DateTime>(selectedDate),
      controller: _sheetController,
      minChildSize: minChildSize,
      initialChildSize: initialChildSize,
      maxChildSize: 0.8,
      expand: false,
      builder: (context, scrollController) {
        return Container(
          alignment: Alignment.bottomCenter,
          decoration: BoxDecoration(
            color: theme.colorScheme.surface,
            borderRadius: const BorderRadius.vertical(top: Radius.circular(24)),
            boxShadow: const [
              BoxShadow(
                color: Color(0x14000000),
                offset: Offset(0, -4),
                blurRadius: 16,
              ),
            ],
          ),
          child: Placeholder(),
        );
      },
    );
  }
}