faturas_4docs/Compliance/Services/ValidationRules/ICMSValidationRule.cs

using System;
using System.Threading.Tasks;
using System.Text;
using Compliance.Domain.Models;
using Compliance.DTOs;
using Compliance.Infrastructure.Repositories;

namespace Compliance.Services.ValidationRules
{
    public class ICMSValidationRule(IDistributorRepository distributorRepository) : IValidationRule
    {
        private readonly IDistributorRepository _distributorRepository = distributorRepository;
        private const string RULE_NAME = "ICMS Validation";
        private const string AMOUNT_ERROR = "ICMS amount doesn't match the expected value";
        private const string EXEMPT_ERROR = "ICMS charged to exempt consumer";
        private const string BASE_ERROR = "ICMS base calculation is incorrect";
        private const decimal TOLERANCE = 0.01m;
        public int Priority => 6;  // Run after public lighting validation

        public async Task<ValidationResult> ValidateAsync(
            BillComplianceRequest request,
            DistributorInformation distributorInfo,
            Client clientInfo)
        {
            var icmsInfo = await _distributorRepository.GetICMSInformationAsync(
                request.DistributorName,
                request.ConsumerGroup,
                request.Month) ?? throw new InvalidOperationException("ICMS information not found");

            var isValid = true;
            var message = new StringBuilder();

            // Check if consumer is exempt from ICMS
            if (icmsInfo.ExemptGroups.Contains(request.ConsumerGroup.ToLower()))
            {
                if (request.ICMSAmount != 0)
                {
                    isValid = false;
                    message.AppendLine(EXEMPT_ERROR);
                }
                return new ValidationResult
                {
                    IsValid = isValid,
                    RuleName = RULE_NAME,
                    Message = message.ToString().TrimEnd()
                };
            }

            // Get applicable rate
            var rate = icmsInfo.GroupRates.TryGetValue(request.ConsumerGroup.ToLower(), out var groupRate)
                ? groupRate
                : icmsInfo.BaseRate;

            // Calculate base and expected ICMS
            var baseAmount = CalculateICMSBase(request, icmsInfo.IncludesTaxInBase);
            var expectedICMS = CalculateICMSAmount(baseAmount, rate, icmsInfo.IncludesTaxInBase);

            if (Math.Abs(request.ICMSBase - baseAmount) > TOLERANCE)
            {
                isValid = false;
                message.AppendLine($"{BASE_ERROR}. Expected: {baseAmount:F2}, Found: {request.ICMSBase:F2}");
            }

            if (Math.Abs(request.ICMSAmount - expectedICMS) > TOLERANCE)
            {
                isValid = false;
                message.AppendLine($"{AMOUNT_ERROR}. Expected: {expectedICMS:F2}, Found: {request.ICMSAmount:F2}");
            }

            return new ValidationResult
            {
                IsValid = isValid,
                RuleName = RULE_NAME,
                Message = message.ToString().TrimEnd()
            };
        }

        private static decimal CalculateICMSBase(BillComplianceRequest request, bool includesTaxInBase)
        {
            // Sum all components that are part of ICMS base
            return request.TUSDAmount +
                   request.TEAmount +
                   request.PowerFactorAdjustment +
                   request.FlagAmount;
        }

        private static decimal CalculateICMSAmount(decimal baseAmount, decimal rate, bool includesTaxInBase)
        {
            rate /= 100m; // Convert percentage to decimal

            if (!includesTaxInBase)
            {
                // Regular calculation ("por fora")
                return baseAmount * rate;
            }
            
            // "Por dentro" calculation where ICMS is included in its own base
            return baseAmount * rate / (1 - rate);
        }
    }
}