using Tau.Acuvim.Portal.DTOs;

namespace Tau.Acuvim.Portal.Services;

// Pure validator for UpsertTariffRequest. Returns null when valid, otherwise an error string.
public static class TariffValidator
{
    public static string? Validate(UpsertTariffRequest req)
    {
        if (req is null) return "Request body is required.";
        if (string.IsNullOrWhiteSpace(req.Name)) return "Tariff name is required.";
        if (req.EffectiveTo.HasValue && req.EffectiveTo.Value < req.EffectiveFrom)
            return "EffectiveTo must be on or after EffectiveFrom.";
        if (req.DefaultRatePerKwh < 0) return "DefaultRatePerKwh must be non-negative.";
        if (req.FixedMonthlyCharge < 0) return "FixedMonthlyCharge must be non-negative.";
        if (req.VatPercentage < 0 || req.VatPercentage > 100) return "VatPercentage must be 0–100.";

        foreach (var p in req.Periods)
        {
            if (string.IsNullOrWhiteSpace(p.Name)) return "Period name is required.";
            if (p.DaysOfWeek == 0) return $"Period '{p.Name}' must have at least one day.";
            if (!TimeOnly.TryParse(p.StartTime, out var start) || !TimeOnly.TryParse(p.EndTime, out var end))
                return $"Period '{p.Name}' has invalid times (HH:mm).";
            if (start >= end)
                return $"Period '{p.Name}' StartTime must be before EndTime (no midnight wrap; split the window).";
            if (p.RatePerKwh < 0)
                return $"Period '{p.Name}' RatePerKwh must be non-negative.";
        }
        return null;
    }
}