Distribution_GL/Services/TaxService.cs

using General_Ledger_Service.DTOs.Common;
using General_Ledger_Service.DTOs.Tax;
using General_Ledger_Service.Enums;
using General_Ledger_Service.Exceptions;
using General_Ledger_Service.Infra.UoW;
using General_Ledger_Service.Interfaces.Repositories;
using General_Ledger_Service.Interfaces.Services;
using General_Ledger_Service.Models;

namespace General_Ledger_Service.Services
{
    public class TaxService(
        ITaxRepository taxRepository,
        IAccountRepository accountRepository,
        IAuditLogRepository auditLogRepository,
        IUnitOfWork unitOfWork) : ITaxService
    {
        private readonly ITaxRepository _taxRepository = taxRepository;
        private readonly IAccountRepository _accountRepository = accountRepository;
        private readonly IAuditLogRepository _auditLogRepository = auditLogRepository;
        private readonly IUnitOfWork _unitOfWork = unitOfWork;

        public async Task<ApiResponse> CreateTaxCodeAsync(CreateTaxCodeRequest request)
        {
            if (request.EffectiveFrom == default)
            {
                throw new BadRequestException("effectiveFrom is required");
            }

            if (!Enum.TryParse<TaxCalculationBasis>(request.CalculationBasis, ignoreCase: true, out var calculationBasis))
            {
                throw new BadRequestException(
                    $"Invalid calculationBasis '{request.CalculationBasis}'. Must be one of: {string.Join(", ", Enum.GetNames<TaxCalculationBasis>())}.");
            }

            if (!Enum.TryParse<TaxAppliesTo>(request.AppliesTo, ignoreCase: true, out var appliesTo))
            {
                throw new BadRequestException(
                    $"Invalid appliesTo '{request.AppliesTo}'. Must be one of: {string.Join(", ", Enum.GetNames<TaxAppliesTo>())}.");
            }

            var taxType = await _taxRepository.GetTaxTypeByCodeAsync(request.TaxTypeCode)
                ?? throw new NotFoundException("Tax type not found");

            long? outputTaxAccountId = null;
            if (!string.IsNullOrWhiteSpace(request.OutputTaxAccountCode))
            {
                var outputAccount = await _accountRepository.GetByCodeAsync(request.OutputTaxAccountCode)
                    ?? throw new NotFoundException("Output tax account not found");
                outputTaxAccountId = outputAccount.AccountId;
            }

            long? inputTaxAccountId = null;
            if (!string.IsNullOrWhiteSpace(request.InputTaxAccountCode))
            {
                var inputAccount = await _accountRepository.GetByCodeAsync(request.InputTaxAccountCode)
                    ?? throw new NotFoundException("Input tax account not found");
                inputTaxAccountId = inputAccount.AccountId;
            }

            var code = await GenerateTaxCodeAsync(taxType);

            var taxCode = new TaxCode
            {
                TaxTypeId = taxType.TaxTypeId,
                Code = code,
                Name = request.Name,
                RatePercent = request.RatePercent,
                CalculationBasis = calculationBasis,
                AppliesTo = appliesTo,
                OutputTaxAccountId = outputTaxAccountId,
                InputTaxAccountId = inputTaxAccountId,
                EffectiveFrom = request.EffectiveFrom,
                EffectiveTo = request.EffectiveTo,
                IsActive = true
            };

            await _unitOfWork.BeginAsync();
            try
            {
                await _taxRepository.AddTaxCodeAsync(taxCode);
                await _unitOfWork.SaveChangesAsync();

                await _auditLogRepository.AddAsync(new AuditLog
                {
                    Category = AuditCategory.Ledger,
                    EntityName = "TaxCode",
                    EntityId = taxCode.TaxCodeId.ToString(),
                    Action = AuditAction.Create,
                    Description = $"Tax code {taxCode.Code} created",
                    PerformedBy = null
                });
                await _unitOfWork.SaveChangesAsync();

                await _unitOfWork.CommitAsync();
            }
            catch
            {
                await _unitOfWork.RollbackAsync();
                throw;
            }

            return ResponseHelpers.Created("Tax code created successfully", taxCode);
        }

        private async Task<string> GenerateTaxCodeAsync(TaxType taxType)
        {
            // Probes candidates directly rather than trusting a count (same fix as
            // AccountService.GenerateAccountCodeAsync) so a pre-existing, manually-coded tax code
            // can never collide with a generated one.
            for (var seq = 1; seq <= 999; seq++)
            {
                var code = $"{taxType.Code}-{seq:D3}";
                if (await _taxRepository.GetByCodeAsync(code) is null)
                {
                    return code;
                }
            }

            throw new BadRequestException("Maximum number of tax codes for this tax type has been reached.");
        }

        public async Task<ApiResponse> CalculateTaxAsync(CalculateTaxRequest request)
        {
            var taxCode = await _taxRepository.GetEffectiveTaxCodeByCodeAsync(request.TaxCode, request.TxnDate)
                ?? throw new NotFoundException("Tax code not found or not effective for the given date");

            var taxAmount = taxCode.CalculationBasis switch
            {
                TaxCalculationBasis.Exclusive => request.Amount * (taxCode.RatePercent / 100),
                TaxCalculationBasis.Inclusive => request.Amount - (request.Amount / (1 + (taxCode.RatePercent / 100))),
                _ => throw new BadRequestException($"Unsupported calculationBasis '{taxCode.CalculationBasis}'.")
            };

            return ResponseHelpers.Ok("Tax calculated successfully", new CalculateTaxResponse
            {
                TaxCodeId = taxCode.TaxCodeId,
                Code = taxCode.Code,
                RatePercent = taxCode.RatePercent,
                LineTotal = request.Amount,
                TaxAmount = taxAmount
            });
        }

        public async Task<ApiResponse> ListTaxTypesAsync()
        {
            var taxTypes = await _taxRepository.GetAllTaxTypesAsync();
            return ResponseHelpers.Ok("Tax types retrieved successfully", taxTypes);
        }

        public async Task<ApiResponse> ListTaxCodesAsync()
        {
            var taxCodes = await _taxRepository.GetAllTaxCodesAsync();
            return ResponseHelpers.Ok("Tax codes retrieved successfully", taxCodes);
        }
    }
}