custom_calendar_generator.dart

import 'package:collection/collection.dart';
import 'package:flutter/material.dart';
import 'package:intl/intl.dart';

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

class CalendarGeneratorApp extends StatelessWidget {
  const CalendarGeneratorApp({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      themeMode: ThemeMode.light,
      theme: ThemeData(
          brightness: Brightness.light,
          useMaterial3: true,
          scaffoldBackgroundColor: Colors.grey.shade200,
          colorSchemeSeed: Colors.blueAccent),
      home: const YearlyCalendarScreen(),
    );
  }
}

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

  @override
  State<YearlyCalendarScreen> createState() => _YearlyCalendarScreenState();
}

class _YearlyCalendarScreenState extends State<YearlyCalendarScreen> {
  final DateTime _today = DateTime.now();
  final Map<int, List<DateTime>> _monthCellsMap = {};

  final List<String> _holidays = [];
  final Map<String, String> _holidaysMap = {};

  @override
  void initState() {
    setHolidays();
    List.generate(12, (index) {
      generateMonthCells(DateTime(_today.year, index + 1, 1));
    });
    super.initState();
  }

  setHolidays() {
    // US United States / Public holidays (2024)
    _holidaysMap.addAll({
      "2024-01-01": "New Year's Day",
      "2024-01-15": "Martin Luther King Jr. Day",
      "2024-02-19": "Presidents' Day",
      "2024-05-27": "Memorial Day",
      "2024-06-19": "Juneteenth National Independence Day",
      "2024-07-04": "Independence Day",
      "2024-09-02": "Labor Day",
      "2024-10-14": "Columbus Day",
      "2024-11-11": "Veterans Day",
      "2024-11-28": "Thanksgiving Day",
      "2024-12-25": "Christmas Day",
    });
    _holidays.addAll(_holidaysMap.keys.toList());
  }

  generateMonthCells(DateTime month) async {
    List<DateTime> cells = [];
    var totalDaysInMonth = DateUtils.getDaysInMonth(month.year, month.month);

    var firstDayDt = DateTime(month.year, month.month, 1);
    var previousMonthDt = firstDayDt.subtract(const Duration(days: 1));
    var nextMonthDt = DateTime(month.year, month.month, totalDaysInMonth)
        .add(const Duration(days: 1));

    var firstDayOfWeek = firstDayDt.weekday;
    var previousMonthDays =
        DateUtils.getDaysInMonth(previousMonthDt.year, previousMonthDt.month);

    // previous month days
    var previousMonthCells = List.generate(
        firstDayOfWeek - 1,
        (index) => DateTime(previousMonthDt.year, previousMonthDt.month,
            previousMonthDays - index));
    cells.addAll(previousMonthCells.reversed);

    // current month days
    var currentMonthCells = List.generate(totalDaysInMonth,
        (index) => DateTime(month.year, month.month, index + 1));
    cells.addAll(currentMonthCells);

    // next month days
    var remainingCellCount = 35 - cells.length;
    if (cells.length > 35) {
      remainingCellCount = 42 - cells.length;
    }
    var nextMonthCells = List.generate(remainingCellCount,
        (index) => DateTime(nextMonthDt.year, nextMonthDt.month, index + 1));
    cells.addAll(nextMonthCells);
    _monthCellsMap[month.month] = cells;
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text("Custom Yearly Calendar"),
      ),
      body: SafeArea(
        child: SingleChildScrollView(
          padding: const EdgeInsets.all(20),
          child: Column(
            children: [
              ...List.generate(12, (index) {
                var calendarMonth = DateTime(_today.year, index + 1, 1);
                var cells = _monthCellsMap[index + 1] ?? [];
                return Card(
                  color: Colors.white,
                  margin: const EdgeInsets.only(bottom: 20),
                  shape: RoundedRectangleBorder(
                      borderRadius: BorderRadius.circular(10)),
                  child: CalendarBlock(
                    calendarMonth,
                    cells,
                    _holidaysMap,
                    today: _today,
                    isJapanese: true,
                    header: Padding(
                      padding: const EdgeInsets.all(8.0),
                      child: Text(
                        calendarMonth.calendarTitle,
                        style: Theme.of(context).textTheme.titleLarge,
                      ),
                    ),
                  ),
                );
              }),
            ],
          ),
        ),
      ),
    );
  }
}

class CalendarBlock extends StatelessWidget {
  const CalendarBlock(
    this.month,
    this.cells,
    this.holidaysMap, {
    required this.today,
    this.header,
    this.isJapanese = true,
    super.key,
  });

  final DateTime today;
  final DateTime month;
  final List<DateTime> cells;
  final Map<String, String> holidaysMap;
  final Widget? header;
  final bool isJapanese;

  @override
  Widget build(BuildContext context) {
    var holidays = holidaysMap.keys.toList();
    return Container(
      padding: const EdgeInsets.all(4),
      decoration: BoxDecoration(
          color: Colors.white, borderRadius: BorderRadius.circular(14)),
      child: Column(
        children: [
          Align(alignment: Alignment.center, child: header ?? const SizedBox()),
          const _WeekHeaders(),
          GridView.builder(
              shrinkWrap: true,
              physics: const NeverScrollableScrollPhysics(),
              gridDelegate: const SliverGridDelegateWithFixedCrossAxisCount(
                crossAxisCount: 7,
                childAspectRatio: 0.9,
                mainAxisSpacing: 2,
                crossAxisSpacing: 2,
              ),
              itemCount: cells.length,
              itemBuilder: (context, index) {
                var item = cells[index];
                var isToday = item.isToday;
                var isSameMonth = item.month == month.month;
                var isHoliday = holidays.contains(item.dateDash);

                Color? bgColor;
                Color? textColor;

                if (item.isSaturday) {
                  textColor = Colors.blueAccent;
                }

                if (item.isSunday) {
                  textColor = Colors.red;
                }

                if (item.isToday && isHoliday) {
                  bgColor = Colors.red;
                  textColor = Colors.white;
                } else if (isToday) {
                  bgColor = Colors.blueAccent;
                  textColor = Colors.white;
                } else if (isHoliday) {
                  bgColor = const Color(0xFFFFEFEF);
                  textColor = Colors.red;
                }

                return Card(
                  color: bgColor,
                  shape: RoundedRectangleBorder(
                    borderRadius: BorderRadius.circular(10),
                  ),
                  child: InkWell(
                    onTap: isHoliday
                        ? () {
                            var holidayText = holidaysMap[item.dateDash] ??
                                "This day is Holiday";
                            showModalBottomSheet(
                                context: context,
                                backgroundColor: Colors.white,
                                builder: (_) {
                                  return Padding(
                                      padding: const EdgeInsets.all(20),
                                      child: Column(
                                        crossAxisAlignment:
                                            CrossAxisAlignment.stretch,
                                        mainAxisSize: MainAxisSize.min,
                                        children: [
                                          Text(
                                            "${item.dateDashEEEE} (Holiday)",
                                            style: Theme.of(context)
                                                .textTheme
                                                .headlineSmall,
                                          ),
                                          vs10x2,
                                          Container(
                                            padding: const EdgeInsets.all(20),
                                            decoration: BoxDecoration(
                                                color: const Color(0xFFffcc17)
                                                    .withOpacity(0.1),
                                                borderRadius:
                                                    BorderRadius.circular(4)),
                                            child: Text(holidayText),
                                          ),
                                          vs10x2,
                                          FilledButton(
                                            onPressed: () {
                                              Navigator.pop(context);
                                            },
                                            child: const Text("Close"),
                                          ),
                                          vs10x2,
                                        ],
                                      ));
                                });
                          }
                        : null,
                    borderRadius: BorderRadius.circular(10),
                    child: Opacity(
                      opacity: isSameMonth ? 1 : 0.3,
                      child: Stack(
                        children: [
                          Center(
                              child: Text(
                            item.day.toString(),
                            style: TextStyle(
                                fontSize: 20,
                                fontWeight: FontWeight.w600,
                                color: textColor),
                          )),
                        ],
                      ),
                    ),
                  ),
                );
              })
        ],
      ),
    );
  }
}

class _WeekHeaders extends StatelessWidget {
  const _WeekHeaders({super.key});

  @override
  Widget build(BuildContext context) {
    return SizedBox(
      height: 28,
      child: Row(
          mainAxisAlignment: MainAxisAlignment.spaceEvenly,
          children: ["Mon", "Tue", "Wed", "Thu", "Fri", "Sat", "Sun"]
              .mapIndexed(
                (i, item) => Expanded(
                  child: Text(
                    item,
                    style: TextStyle(
                      fontSize: 14,
                      fontWeight: FontWeight.w700,
                      color: _getTitleColor(i),
                    ),
                    textAlign: TextAlign.center,
                  ),
                ),
              )
              .toList()),
    );
  }

  _getTitleColor(int index) {
    if (index == 5) {
      return Colors.blueAccent;
    }

    if (index == 6) {
      return const Color(0xFFFF8181);
    }

    return const Color(0xAD1A1642);
  }
}

extension DateTimeExt on DateTime {
  toFormat([String? newPattern, String? locale]) {
    return DateFormat(newPattern, locale).format(this);
  }

  String get dateDash => toFormat("yyyy-MM-dd");

  String get dateDashTime => toFormat("yyyy-MM-dd HH:mm");

  String get dateDashEEEE => toFormat("yyyy-MM-dd EEEE");

  String get monthName => toFormat("MMMM");

  String get calendarTitle => toFormat("MMMM yyyy");

  bool get isSaturday => weekday == 6;

  bool get isSunday => weekday == 7;

  bool get isToday {
    var today = DateTime.now();
    return year == today.year && month == today.month && day == today.day;
  }
}

const vs10x2 = SizedBox(height: 20);