using System;
using System.Diagnostics.CodeAnalysis;

public class Clock : IEquatable<Clock>
{
    private int _hour;
    private int _minute;

    public Clock(int hours, int minutes)
    {
        _hour = (hours                                    // just take the given hours and
            + minutes / 60                                // add full hours of minutes if we have more than 60
                                                          // minutes
            - (minutes < 0 && minutes % 60 != 0 ? 1 : 0)  // but the part of negative minutes that is not an full
                                                          // hour subtracts one hour, e.g. 01:-10 means (00:50)
            ) % 24;                                       // at last, ensure hours roll over when longer as a day

        if (_hour < 0) _hour += 24;      // finally avoid negative hours: e.g. -3 means 21 (3 hours befor midnight)

        _minute = minutes % 60;          // just take the minutes, but to ensure they roll over when longer as an
                                         // hour, contribution to the hour was already added above
        if (_minute < 0) _minute += 60;  // e.g. -10 means 50 (10 minutes befor the next full hour)
    }

    public Clock Add(int minutesToAdd) => new Clock(_hour, _minute + minutesToAdd);

    public Clock Subtract(int minutesToSubtract) => new Clock(_hour, _minute - minutesToSubtract);

    public override string ToString() => $"{_hour:00}:{_minute:00}";

    public bool Equals([AllowNull] Clock other)
    {
        if (other == null)
            return false;
        if (this == other)
            return true;
        return _hour == other._hour && _minute == other._minute;
    }

    // these methods are not needed to make the tests running but it is recommended to override Equals(object) and
    // GetHashCode() when implementing IEquatable
    public override bool Equals(object obj) => Equals(obj as Clock);
    public override int GetHashCode() => _hour * 60 + _minute;
}