using System;

using System.Globalization; //For CultureInfo and used for the time zone around the world.

public class BirthdayProgram

{

    public static void Main()

    {

        Console.Write("Enter your date of birth (ddmmyyyy): "); //Prompts the user to enter their date of birth in the specified format.

        string dobInput = Console.ReadLine(); // Reads the user's input and stores it in the dobInput variable.

        bool isValid = isValidDob(dobInput,out DateTime dob); 

        if (!isValid)  // Checks if the date validation failed.

        {             

             Console.WriteLine("Invalid date format given"); //Displays an error message if the date is invalid.

            return;

        }

        // calling Method

        int daysUntilNextBirthday = DaysUntilNextBirthday(dob);   

        string ageGroup = GetAgeGroup(dob);

        int daysSinceBirth = DaysSinceBirth(dob);

        Console.WriteLine($"Days until your next birthday: {daysUntilNextBirthday}"); //Displays the number of days until the user's next birthday.

        Console.WriteLine($"You are {ageGroup}"); // Displays whether the user is "Over 18" or "Under 18".

        Console.WriteLine($"Days since your birth: {daysSinceBirth}"); // Displays the number of days since the user's birth.

    }

    // Date Validation Method

    static bool isValidDob(string input ,out DateTime date)

    {

        string format = "ddMMyyyy";

        //Tries to parse the input string into a DateTime object using the specified format and culture. Stores the result in dateFormatCheck

        bool dateFormatCheck = DateTime.TryParseExact(input, format, CultureInfo.InvariantCulture, DateTimeStyles.None, out date);

​

        if (!dateFormatCheck) // Checks if the date format is invalid

        {

            return false; //Returns false if the date format is invalid

        }

​

        //Checks if the date is in the future.

        if (date > DateTime.Now) // 

        {

            return false; // Returns false if the date is in the future.

        }

​

        return true; // Ensure that true is returned if the format is correct and the date is not in the future

    }

    // Calculate Days Until Next Birthday

    static int DaysUntilNextBirthday(DateTime  dob)

    {

        DateTime nextBirthday = new DateTime(DateTime.Now.Year, dob.Month, dob.Day); // Creates a DateTime object for the user's next birthday in the current year.

​

        // If birthday has already occurred this year, calculate for next year

        if (nextBirthday < DateTime.Now) //  Checks if the next birthday has already occurred this year.

        {

            nextBirthday = nextBirthday.AddYears(1); // If the next birthday has already occurred, adds one year to the next birthday.

        }

​

        return (nextBirthday - DateTime.Now).Days; // Returns the number of days until the next birthday.

    }

    // Determining the age group

    static string GetAgeGroup(DateTime dob)

        //Declares a static method GetAgeGroup that takes a DateTime object dob and returns a string indicating if the user is "Over 18" or "Under 18

    {

        int age = DateTime.Now.Year - dob.Year; //Calculates the initial age by subtracting the birth year from the current year.

        if (DateTime.Now < dob.AddYears(age)) // Checks if the birthday has not yet occurred this year.

        {

            age--; // If the birthday has not yet occurred, subtracts one year from the age.

        }

​

        return age >= 18 ? "Over 18" : "Under 18";  //  Returns "Over 18" if the age is 18 or more; otherwise, returns "Under 18".

    } 

    // Calculate Days Since Birth

     static int DaysSinceBirth(DateTime dob) //Declares a static method DaysSinceBirth that takes a DateTime object dob and returns the number of days since the user's birth.

    {

        return (DateTime.Now - dob).Days; //  Calculates and returns the number of days since the user's birth by subtracting the birth date from the current date.

    }

}