Money klasa

public class Money
{
    public decimal Amount { get; private set; } // privatni setter, vrednost se postavlja samo u konstruktoru
    public string Currency { get; private set; } // privatni setter

    public Money(decimal amount, string currency)
    {
        // Self-validating: Validacija pri konstrukciji
        if (amount < 0)
        {
            throw new ArgumentException("Amount must be positive.");
        }
        if (string.IsNullOrWhiteSpace(currency))
        {
            throw new ArgumentException("Currency cannot be null or empty.");
        }

        Amount = amount;
        Currency = currency;
    }

    // Behavior-rich i Immutable: Vraća novi objekat, ne menja postojeći
    public Money Add(Money other)
    {
        if (!IsSameCurrency(other))
        {
            throw new InvalidOperationException("Cannot add money of different currencies.");
        }
        return new Money(Amount + other.Amount, Currency);
    }

    // Behavior-rich i Immutable: Vraća novi objekat, ne menja postojeći
    public Money Subtract(Money other)
    {
        if (!IsSameCurrency(other))
        {
            throw new InvalidOperationException("Cannot subtract money of different currencies.");
        }
        // Možda dodatna validacija da rezultat ne ide u minus ako je to poslovno pravilo
        return new Money(Amount - other.Amount, Currency);
    }

    private bool IsSameCurrency(Money other)
    {
        return Currency.Equals(other.Currency, StringComparison.OrdinalIgnoreCase);
    }

    // Jednakost po vrednostima: Override Equals i GetHashCode metode
    public override bool Equals(object obj)
    {
        if (obj == null || GetType() != obj.GetType())
        {
            return false;
        }

        Money other = (Money)obj;
        return Amount == other.Amount && Currency.Equals(other.Currency, StringComparison.OrdinalIgnoreCase);
    }

    public override int GetHashCode()
    {
        return HashCode.Combine(Amount, Currency.ToUpperInvariant());
    }

    // Moguće i predefinisanje operatora za jednakost i nejednakost
    public static bool operator ==(Money a, Money b)
    {
        if (ReferenceEquals(a, null))
        {
            return ReferenceEquals(b, null);
        }
        return a.Equals(b);
    }

    public static bool operator !=(Money a, Money b)
    {
        return !(a == b);
    }
}