android – How to calculate total days from my birthdate in FLUTTER . Keep in mind for leap year

I want to make an age calculator app where I want to show Ages as different format.
Example:
My code output vs Expected output

• Ages: 25 years 03 month 28 days //Gives correct output
• Total Months : 303 months 28 days // Gives correct output
• Total Weeks : 1322 weeks 3 days//Correct output is:1321 weeks 4 days
• Total Days : 9249 days //Correct is : 9251
• Todal Hours : 221976 Hours // Correct is : 222,024 hours

Just like that.

But the problem is my code doesnot gives exact output counting leap years.As I want to calculate exactly total days or weeks. How can I do that?

Here is my code…..

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

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

  @override
  State<AgeCalculator> createState() => _AgeCalculatorState();
}

class _AgeCalculatorState extends State<AgeCalculator> {
  final TextEditingController _dateController = TextEditingController();
  final currentDate = DateTime.now();
  String _ageResult="";

  @override
  void initState() {
    super.initState();
    _dateController.text = DateFormat('yyyy-MM-dd').format(currentDate);
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        centerTitle: true,
        backgroundColor: Colors.grey[200],
        title: Text(
          'Age Calculator',
          style: TextStyle(
            fontWeight: FontWeight.w600,
            fontFamily: GoogleFonts.audiowide().fontFamily,
          ),
        ),
      ),
      body: Column(
        mainAxisAlignment: MainAxisAlignment.start,
        children: <Widget>[
          const SizedBox(
            height: 20,
          ),
          Text(
            'Todays Date : ${DateFormat('dd-MM-yyyy').format(currentDate)}',
            style: TextStyle(
              fontSize: 20,
              fontWeight: FontWeight.w400,
              fontFamily: GoogleFonts.audiowide().fontFamily,
            ),
          ),
          const SizedBox(height: 20),
          Text(
            'Select Your Date of Birth : ',
            style: TextStyle(
              fontFamily: GoogleFonts.audiowide().fontFamily,
            ),
          ),
          Padding(
            padding: const EdgeInsets.all(20.0),
            child: TextField(
              controller: _dateController,
              readOnly: true,
              onTap: () async {
                final DateTime? date = await showDatePicker(
                  context: context,
                  initialDate: DateTime.now(),
                  firstDate: DateTime(1900),
                  lastDate: DateTime(2100),
                );
                if (date != null) {
                  _dateController.text = DateFormat('yyyy-MM-dd').format(date);
                }
              },
              decoration: const InputDecoration(
                border: OutlineInputBorder(),
                labelText: 'Select Date',
                hintText: 'Select Date',
                suffixIcon: Icon(Icons.calendar_today),
              ),
            ),
          ),
          const SizedBox(height: 20),
          ElevatedButton(
            onPressed: () {
              final birthDate =
                  DateFormat('yyyy-MM-dd').parse(_dateController.text);
              final age = calculateAge(birthDate, currentDate);
              setState(() {
                _ageResult="$age";
              });
            },
            child: Text(
              'Calculate',
              style: TextStyle(
                fontFamily: GoogleFonts.audiowide().fontFamily,
                fontWeight: FontWeight.w600,
              ),
            ),
          ),
          Text(
            'Your Age is : $_ageResult',
            style: TextStyle(
              fontSize: 20,
              fontWeight: FontWeight.w400,
              fontFamily: GoogleFonts.audiowide().fontFamily,
            ),
          ),
          if (_ageResult.isNotEmpty) ...[
            const SizedBox(height: 10),
            Text(
              'Total Months: ${calculateTotalMonths(_ageResult)} months ${calculateRemainingDays(_ageResult)} days',
              style: TextStyle(
                fontSize: 16,
                fontWeight: FontWeight.w400,
                fontFamily: GoogleFonts.audiowide().fontFamily,
              ),
            ),
            Text(
              'Total Weeks: ${calculateTotalWeeks(_ageResult)} weeks ${calculateTotalDaysAfterWeek(_ageResult)} days',
              style: TextStyle(
                fontSize: 16,
                fontWeight: FontWeight.w400,
                fontFamily: GoogleFonts.audiowide().fontFamily,
              ),
            ),
            Text(
              'Total Hours: ${calculateTotalHours(_ageResult)} hours',
              style: TextStyle(
                fontSize: 16,
                fontWeight: FontWeight.w400,
                fontFamily: GoogleFonts.audiowide().fontFamily,
              ),
            ),
            Text(
              'Total Days: ${calculateTotalDays(_ageResult)} days',
              style: TextStyle(
                fontSize: 16,
                fontWeight: FontWeight.w400,
                fontFamily: GoogleFonts.audiowide().fontFamily,
              ),
            ),
          ],
        ],
      ),
    );
  }

  String calculateAge(DateTime birthDate, DateTime currentDate) {
    int years = currentDate.year - birthDate.year;
    int months = currentDate.month - birthDate.month;
    int days = currentDate.day - birthDate.day;

    if (months < 0 || (months == 0 && days < 0)) {
      years--;
      months += 12;
    }

    return '$years years $months months $days days';
  }

  int calculateTotalMonths(String age) {
    List<String> parts = age.split(' ');
    int years = int.parse(parts[0]);
    int months = int.parse(parts[2]);
    return years * 12 + months;
  }

  int calculateRemainingDays(String age) {
    List<String> parts = age.split(' ');
    return int.parse(parts[4]);
  }

  int calculateTotalWeeks(String age) {
    List<String> parts = age.split(' ');
    int totalDays = int.parse(parts[0]) * 365 +
        countLeapYears(int.parse(parts[0])) +
        int.parse(parts[2]) * 30 +
        int.parse(parts[4]);
    return (totalDays / 7).ceil();
  }

  int calculateTotalDaysAfterWeek(String age) {
    List<String> parts = age.split(' ');
    int totalDays = int.parse(parts[0]) * 365 +
        int.parse(parts[2]) * 30 +
        int.parse(parts[4]);
    return (totalDays % 7).ceil();
  }

  int calculateTotalHours(String age) {
    List<String> parts = age.split(' ');
    int totalDays = int.parse(parts[0]) * 365 +
        countLeapYears(int.parse(parts[0])) +
        int.parse(parts[2]) * 30 +
        int.parse(parts[4]);
    return totalDays * 24;
  }

  int calculateTotalDays(String age) {
    List<String> parts = age.split(' ');
    return int.parse(parts[0]) * 365 +
        countLeapYears(int.parse(parts[0])) +
        int.parse(parts[2]) * 30 +
        int.parse(parts[4]);
  }

  int countLeapYears(int years) {
    // Logic to count leap years
    return (years / 4).floor() - (years / 100).floor() + (years / 400).floor();
  }
}