namespace Distribution.Features.Grn;

/// <summary>
/// GRN costing. Per line: gross = accepted qty x unit cost; discount = gross x disc%;
/// VAT = (gross - discount) x VAT%; total = gross - discount + VAT. Rejected units are never costed.
/// Each amount is rounded to 2 dp per line so the GRN totals equal the sum of what the lines show.
/// </summary>
public static class GrnPricing
{
    public static decimal Round(decimal value) => Math.Round(value, 2, MidpointRounding.AwayFromZero);

    public static (decimal Gross, decimal Discount, decimal Vat, decimal Total) Line(
        int acceptedQty, decimal unitCost, decimal discountPercent, decimal vatPercent)
    {
        var gross = Round(acceptedQty * unitCost);
        var discount = Round(gross * discountPercent / 100m);
        var vat = Round((gross - discount) * vatPercent / 100m);
        return (gross, discount, vat, gross - discount + vat);
    }

    public static void ValidatePercent(decimal value, string label)
    {
        if (value < 0 || value > 100)
            throw new InvalidOperationException($"{label} must be between 0 and 100.");
    }

    public static void ValidateCost(decimal value, string label)
    {
        if (value < 0)
            throw new InvalidOperationException($"{label} cannot be negative.");
    }
}