Money.cs

using Domain.Common;

namespace Domain.ValueObjects;

public class Money : ValueObject
{
    public decimal Amount { get; set; }
    public Currency Currency { get; set; }

    public Money(decimal amount, Currency currency)
    {
        this.Amount = amount;
        this.Currency = currency;
    }

    public static Money operator +(Money left, Money right)
    {
        if (left.Currency != right.Currency)
        {
            throw new InvalidOperationException("Currencies have to be equal.");
        }

        return new Money(left.Amount + right.Amount, left.Currency);
    }

    public static Money operator -(Money left, Money right)
    {
        if (left.Currency != right.Currency)
        {
            throw new InvalidOperationException("Currencies have to be equal.");
        }

        if (left < right)
        {
            throw new InvalidOperationException("Not enough funds.");
        }

        return new Money(left.Amount - right.Amount, left.Currency);
    }

    public static Money operator *(Money amount, decimal factor) =>
        new(amount.Amount * factor, amount.Currency);

    public static Money operator *(decimal factor, Money amount) =>
        new(amount.Amount * factor, amount.Currency);

    public static Money operator /(Money amount, decimal factor) =>
        new(amount.Amount / factor, amount.Currency);

    public static decimal operator /(Money a, Money b) =>
        a.Currency == b.Currency ? a.Amount / b.Amount
        : RaiseCurrencyError<decimal>("divide", a, b);

    public static bool operator >(Money left, Money right) =>
        left.Currency == right.Currency ? left.Amount > right.Amount
        : RaiseCurrencyComparisonError(left, right);

    public static bool operator <(Money left, Money right) =>
        left.Currency == right.Currency ? left.Amount < right.Amount
        : RaiseCurrencyComparisonError(left, right);

    public static bool operator >=(Money left, Money right) =>
        left.Currency == right.Currency ? left.Amount >= right.Amount
        : RaiseCurrencyComparisonError(left, right);

    public static bool operator <=(Money left, Money right) =>
        left.Currency == right.Currency ? left.Amount <= right.Amount
        : RaiseCurrencyComparisonError(left, right);

    public static implicit operator decimal(Money a) =>
        a.Amount;

    private static bool RaiseCurrencyComparisonError(Money a, Money b) =>
       RaiseCurrencyError<bool>("compare", a, b);

    private static T RaiseCurrencyError<T>(string operation, Money a, Money b) =>
        throw new ArgumentException($"Cannot {operation} {a.Currency} and {b.Currency}");

    public static Money Zero() => new(0, Currency.None);
    public static Money Zero(Currency currency) => new(0, currency);

    public bool IsZero() => this == Zero();

    protected override IEnumerable<object> GetEqualityComponents()
    {
        yield return Amount;
        yield return Currency;
    }
}