Calendar Widget flutter

CalendarWidget.dart

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

class CalendarWidget extends StatefulWidget {
  final Function(DateTime dateTime) onDateSelect;

  CalendarWidget(this.onDateSelect, {Key? key}) : super(key: key);

  @override
  State<CalendarWidget> createState() => _CalendarWidgetState();
}

class _CalendarWidgetState extends State<CalendarWidget> {
  List<List<DateData>> listLists = List.empty(growable: true);

  var cellWidth = 47.0;
  var cellHeight = 38.0;

  var selectedEpochMilli = 0;
  var showingMonthEpochMilli = 0;

  @override
  void initState() {
    listLists.clear();
    var now = DateTime.now();
    selectedEpochMilli = now.millisecondsSinceEpoch;
    widget.onDateSelect(now);
    showingMonthEpochMilli = selectedEpochMilli;
    listLists.addAll(getDates(showingMonthEpochMilli).chunked(7));
    super.initState();
  }

  @override
  Widget build(BuildContext context) {
    return Column(
      children: [
        Container(height: 44),
        Row(mainAxisAlignment: MainAxisAlignment.spaceBetween, children: [
          InkWell(
            splashFactory: NoSplash.splashFactory,
            child: Padding(
              padding: const EdgeInsets.only(
                  left: 15.0, right: 8.0, top: 8.0, bottom: 8.0),
              child: Icon(
                Icons.keyboard_arrow_left_outlined,
                size: 30,
              ),
            ),
            onTap: () {
              clickNextPrevMonth(-1);
            },
          ),
          Text(
            DateFormat("MMMM - yyyy").format(
                DateTime.fromMillisecondsSinceEpoch(showingMonthEpochMilli)),
            style: TextStyle(
                color: Color(
                  0xffDA137C,
                ),

                fontSize: 18 ),
          ),
          InkWell(
            splashFactory: NoSplash.splashFactory,
            child: Padding(
              padding: const EdgeInsets.only(
                  left: 8.0, right: 25.0, top: 8.0, bottom: 8.0),
              child: Icon(
                Icons.keyboard_arrow_right_outlined,
                size: 30,
              ),
            ),
            onTap: () {
              clickNextPrevMonth(1);
            },
          ),
        ]),
        Container(height: 14),
        Padding(
          padding: const EdgeInsets.only(left: 5, right: 13),
          child: Container(
            padding: EdgeInsets.symmetric(horizontal: 0, vertical: 0),
            decoration: BoxDecoration(
              color: Color(0xFFF4F4F4),
              borderRadius: BorderRadius.all(Radius.circular(23 )),
            ),
            child: Row(
                children: ["S", "S", "M", "T", "W", "T", "F"]
                    .map((i) => Container(
                          height: cellHeight,
                          width: cellWidth,
                          child: Center(
                            child: Text(
                              i,
                              style: TextStyle(
                                  color: Color(
                                    0xff67646D,
                                  ),
                                  fontSize: 16),
                            ),
                          ),
                        ))
                    .toList()),
          ),
        ),
        Padding(
          padding:
              const EdgeInsets.only(left: 10, right: 0, bottom: 0, top: 10),
          child: Column(
            children: listLists
                .map((list) => Row(
                        children: list.map((data) {
                      var color = Color(
                        0xfff67646D,
                      );
                      var bgColor = Colors.transparent;
                      if (data.epochMilli == selectedEpochMilli) {
                        color = Colors.white;
                        bgColor = Color(
                          0xFFDA137C,
                        );
                      }
                      if (data.isCurrentMonth != 0) {
                        color = Color(
                          0xffB7B7B7,
                        );
                        bgColor = Colors.transparent;
                      }

                      return InkWell(
                        splashFactory: NoSplash.splashFactory,
                        onTap: () {
                          if (data.isCurrentMonth == 0)
                            setState(() {
                              selectedEpochMilli = data.epochMilli;
                              widget.onDateSelect(DateTime.fromMillisecondsSinceEpoch(selectedEpochMilli));
                            });
                        },
                        child: Container(
                          height: cellHeight,
                          width: cellWidth,
                          child: Padding(
                            padding: const EdgeInsets.all(4.0),
                            child: Container(
                              decoration: BoxDecoration(
                                color: bgColor,
                                shape: BoxShape.circle,
                              ),
                              child: Center(
                                child: Text(
                                  data.date.toString(),
                                  style: TextStyle(
                                      color: color,
                                      fontSize: 16),
                                  textAlign: TextAlign.center,
                                ),
                              ),
                            ),
                          ),
                        ),
                      );
                    }).toList()))
                .toList(),
          ),
        )
      ],
    );
    ;
  }

  void clickNextPrevMonth(int i) {
    var dt = DateTime.fromMillisecondsSinceEpoch(showingMonthEpochMilli);
    dt = DateTime(dt.year, dt.month + i, dt.day, dt.hour, dt.minute, dt.second,
        dt.millisecond, dt.microsecond);
    showingMonthEpochMilli = dt.millisecondsSinceEpoch;
    listLists.clear();
    listLists.addAll(getDates(showingMonthEpochMilli).chunked(7));
    setState(() {});
  }

  List<DateData> getDates(int showingMonthEpochMilli) {
    List<DateData> list = List.empty(growable: true);
    var iDate = DateTime.fromMillisecondsSinceEpoch(showingMonthEpochMilli);
    var showMonth = iDate.month;
    iDate = DateTime(iDate.year, iDate.month, 1, iDate.hour, iDate.minute,
        iDate.second, iDate.millisecond, iDate.microsecond);
    while (iDate.month == showMonth) {
      list.add(DateData(iDate.day, iDate.millisecondsSinceEpoch, 0));
      iDate = iDate.add(Duration(days: 1));
    }
    while (iDate.weekday != DateTime.saturday) {
      list.add(DateData(iDate.day, iDate.millisecondsSinceEpoch, 1));
      iDate = iDate.add(Duration(days: 1));
    }
    iDate = DateTime(iDate.year, iDate.month - 1, 1, iDate.hour, iDate.minute,
        iDate.second, iDate.millisecond, iDate.microsecond);
    iDate = iDate.subtract(Duration(days: 1));
    while (iDate.weekday != DateTime.friday) {
      list.insert(0, DateData(iDate.day, iDate.millisecondsSinceEpoch, -1));
      iDate = iDate.subtract(Duration(days: 1));
    }

    return list;
  }
}

class DateData {
  final int date;
  final int epochMilli;
  final int isCurrentMonth;

  DateData(this.date, this.epochMilli, this.isCurrentMonth);

  /// 0 for current month //1 for next // -1 for prev
}

extension IterableExtensions<E> on Iterable<E> {
  Iterable<List<E>> chunked(int chunkSize) sync* {
    if (length <= 0) {
      yield [];
      return;
    }
    int skip = 0;
    while (skip < length) {
      final chunk = this.skip(skip).take(chunkSize);
      yield chunk.toList(growable: false);
      skip += chunkSize;
      if (chunk.length < chunkSize) return;
    }
  }
}