using System;

namespace Contacts
{
    /// <summary>
    /// Represents the birthday of a contact.
    /// </summary>
    /// <author>Josh A</author>
    public class Birthday : IEquatable<Birthday>
    {
        private readonly int day;
        private readonly int month;
        private readonly int year;
        public int Age { get; }

        /// <summary>
        /// Creates a new Birthday object.
        /// </summary>
        /// <param name="month"></param>
        /// <param name="day"></param>
        public Birthday(int month, int day)
        {
            this.month = month;
            this.day = day;
            year = -1;
            Age = -1;
        }

        /// <summary>
        /// Creates a new Birthday and determines the age.
        /// </summary>
        /// <param name="month"></param>
        /// <param name="day"></param>
        /// <param name="year"></param>
        public Birthday(int month, int day, int year)
        {
            this.month = month;
            this.day = day;
            this.year = year;
            Age = 2023 - year;
        }

        /// <summary>
        /// Determines if two birthdays are equal, to avoid potential duplication.
        /// </summary>
        /// <param name="birthdayToCompare">Birthday to compare to. If null, returns false.</param>
        /// <returns>Whether or not the two birthdays are the same.</returns>
        public bool Equals(Birthday? birthdayToCompare)
        {
            if (birthdayToCompare == null)
                return false;

            return this.ToString().Equals(birthdayToCompare.ToString());
        }

        /// <summary>
        /// Formats a birthday to "MM-DD" or "MM-DD-YYYY", if a birthyear was provided.
        /// </summary>
        /// <returns>Formatted birthdate.</returns>
        public override string ToString()
        {
            if (year == -1)
                return month + "-" + day;
            return month + "-" + day + "-" + year;
        }
    }
}