books/backend/Books.Api/Commands/Invoices/InvoiceCommandHandlers.cs

using Books.Api.Domain;
using Books.Api.Domain.Invoices;
using Books.Api.EventFlow.Repositories;
using Books.Api.Invoicing.Services;
using EventFlow.Commands;

namespace Books.Api.Commands.Invoices;

/// <summary>
/// Command handler for creating invoices.
/// Always auto-assigns a sequential invoice number (Momsloven §52 - sequential numbering required).
/// Validates the company has a CVR number (required for invoicing).
/// </summary>
public class CreateInvoiceCommandHandler(
    IInvoiceNumberService invoiceNumberService,
    ICompanyRepository companyRepository)
    : CommandHandler<InvoiceAggregate, InvoiceId, CreateInvoiceCommand>
{
    public override async Task ExecuteAsync(
        InvoiceAggregate aggregate,
        CreateInvoiceCommand command,
        CancellationToken cancellationToken)
    {
        // Validate company has a CVR number (required for invoicing per Danish law)
        var company = await companyRepository.GetByIdAsync(command.CompanyId, cancellationToken);
        if (company == null)
        {
            throw new DomainException(
                "COMPANY_NOT_FOUND",
                $"Company '{command.CompanyId}' not found",
                $"Virksomheden '{command.CompanyId}' blev ikke fundet");
        }

        if (string.IsNullOrWhiteSpace(company.Cvr))
        {
            throw new DomainException(
                "CVR_REQUIRED_FOR_INVOICE",
                "Company must have a CVR number to create invoices. Please update company settings.",
                "Virksomheden skal have et CVR-nummer for at oprette fakturaer. Opdater venligst virksomhedsindstillinger.");
        }

        // Always auto-assign invoice number (Momsloven §52 requires unbroken sequential numbering)
        var invoiceNumber = await invoiceNumberService.GetNextInvoiceNumberAsync(
            command.CompanyId,
            command.InvoiceDate.Year,
            cancellationToken);

        // Build seller address from company info
        var sellerAddress = string.Join(", ",
            new[] { company.Address, company.PostalCode, company.City }
                .Where(s => !string.IsNullOrWhiteSpace(s)));

        aggregate.Create(
            command.CompanyId,
            command.FiscalYearId,
            command.CustomerId,
            command.CustomerName,
            command.CustomerNumber,
            invoiceNumber,
            command.InvoiceDate,
            command.DueDate,
            command.PaymentTermsDays,
            command.Currency,
            command.VatCode,
            command.Notes,
            command.Reference,
            command.CreatedBy,
            company.Cvr,
            company.Name,
            sellerAddress);
    }
}

public class AddInvoiceLineCommandHandler
    : CommandHandler<InvoiceAggregate, InvoiceId, AddInvoiceLineCommand>
{
    public override Task ExecuteAsync(
        InvoiceAggregate aggregate,
        AddInvoiceLineCommand command,
        CancellationToken cancellationToken)
    {
        aggregate.AddLine(
            command.Description,
            command.Quantity,
            command.UnitPrice,
            command.VatCode,
            command.AccountId,
            command.Unit,
            command.DiscountPercent);

        return Task.CompletedTask;
    }
}

public class UpdateInvoiceLineCommandHandler
    : CommandHandler<InvoiceAggregate, InvoiceId, UpdateInvoiceLineCommand>
{
    public override Task ExecuteAsync(
        InvoiceAggregate aggregate,
        UpdateInvoiceLineCommand command,
        CancellationToken cancellationToken)
    {
        aggregate.UpdateLine(
            command.LineNumber,
            command.Description,
            command.Quantity,
            command.UnitPrice,
            command.VatCode,
            command.AccountId,
            command.Unit,
            command.DiscountPercent);

        return Task.CompletedTask;
    }
}

public class RemoveInvoiceLineCommandHandler
    : CommandHandler<InvoiceAggregate, InvoiceId, RemoveInvoiceLineCommand>
{
    public override Task ExecuteAsync(
        InvoiceAggregate aggregate,
        RemoveInvoiceLineCommand command,
        CancellationToken cancellationToken)
    {
        aggregate.RemoveLine(command.LineNumber);

        return Task.CompletedTask;
    }
}

/// <summary>
/// Command handler for marking an invoice as sent.
/// Validates fiscal year status before allowing the invoice to be sent.
/// </summary>
public class MarkInvoiceSentCommandHandler(
    IInvoiceRepository invoiceRepository,
    IFiscalYearRepository fiscalYearRepository)
    : CommandHandler<InvoiceAggregate, InvoiceId, MarkInvoiceSentCommand>
{
    public override async Task ExecuteAsync(
        InvoiceAggregate aggregate,
        MarkInvoiceSentCommand command,
        CancellationToken cancellationToken)
    {
        // Load the invoice read model to get fiscal year ID
        var invoice = await invoiceRepository.GetByIdAsync(
            aggregate.Id.Value, cancellationToken);

        var fiscalYearId = invoice?.FiscalYearId;

        // Validate fiscal year is set
        if (string.IsNullOrWhiteSpace(fiscalYearId))
        {
            throw new DomainException(
                "FISCAL_YEAR_REQUIRED",
                "Fiscal year is required for sending an invoice",
                "Regnskabsår er påkrævet for afsendelse af en faktura");
        }

        // Fetch and validate fiscal year
        var fiscalYear = await fiscalYearRepository.GetByIdAsync(
            fiscalYearId, cancellationToken);

        if (fiscalYear == null)
        {
            throw new DomainException(
                "FISCAL_YEAR_NOT_FOUND",
                $"Fiscal year '{fiscalYearId}' not found",
                $"Regnskabsår '{fiscalYearId}' blev ikke fundet");
        }

        // Validate fiscal year is open (not Closed or Locked)
        if (fiscalYear.Status != "Open")
        {
            throw new DomainException(
                "FISCAL_YEAR_NOT_OPEN",
                $"Fiscal year is {fiscalYear.Status}. Only open fiscal years allow posting.",
                $"Regnskabsåret er {fiscalYear.Status}. Kun åbne regnskabsår tillader bogføring.");
        }

        aggregate.Send(
            command.LedgerTransactionId,
            command.SentBy);
    }
}

public class ReceiveInvoicePaymentCommandHandler
    : CommandHandler<InvoiceAggregate, InvoiceId, ReceiveInvoicePaymentCommand>
{
    public override Task ExecuteAsync(
        InvoiceAggregate aggregate,
        ReceiveInvoicePaymentCommand command,
        CancellationToken cancellationToken)
    {
        aggregate.ReceivePayment(
            command.Amount,
            command.BankTransactionId,
            command.LedgerTransactionId,
            command.PaymentReference,
            command.PaymentDate,
            command.RecordedBy);

        return Task.CompletedTask;
    }
}

public class VoidInvoiceCommandHandler
    : CommandHandler<InvoiceAggregate, InvoiceId, VoidInvoiceCommand>
{
    public override Task ExecuteAsync(
        InvoiceAggregate aggregate,
        VoidInvoiceCommand command,
        CancellationToken cancellationToken)
    {
        aggregate.Void(
            command.Reason,
            command.ReversalLedgerTransactionId,
            command.VoidedBy);

        return Task.CompletedTask;
    }
}

// =====================================================
// CREDIT NOTE COMMAND HANDLERS
// =====================================================

/// <summary>
/// Command handler for creating credit notes.
/// Auto-assigns sequential credit note numbers (Momsloven §52 - sequential numbering required).
/// </summary>
public class CreateCreditNoteCommandHandler(
    IInvoiceNumberService invoiceNumberService)
    : CommandHandler<InvoiceAggregate, InvoiceId, CreateCreditNoteCommand>
{
    public override async Task ExecuteAsync(
        InvoiceAggregate aggregate,
        CreateCreditNoteCommand command,
        CancellationToken cancellationToken)
    {
        // Auto-assign credit note number (Momsloven §52 requires unbroken sequential numbering)
        var creditNoteNumber = await invoiceNumberService.GetNextCreditNoteNumberAsync(
            command.CompanyId,
            command.CreditNoteDate.Year,
            cancellationToken);

        aggregate.CreateCreditNote(
            command.CompanyId,
            command.FiscalYearId,
            command.CustomerId,
            command.CustomerName,
            command.CustomerNumber,
            creditNoteNumber,
            command.CreditNoteDate,
            command.Currency,
            command.VatCode,
            command.Notes,
            command.Reference,
            command.CreatedBy,
            command.OriginalInvoiceId,
            command.OriginalInvoiceNumber,
            command.CreditReason);
    }
}

public class IssueCreditNoteCommandHandler
    : CommandHandler<InvoiceAggregate, InvoiceId, IssueCreditNoteCommand>
{
    public override Task ExecuteAsync(
        InvoiceAggregate aggregate,
        IssueCreditNoteCommand command,
        CancellationToken cancellationToken)
    {
        aggregate.Issue(
            command.LedgerTransactionId,
            command.IssuedBy);

        return Task.CompletedTask;
    }
}

public class ApplyCreditNoteCommandHandler
    : CommandHandler<InvoiceAggregate, InvoiceId, ApplyCreditNoteCommand>
{
    public override Task ExecuteAsync(
        InvoiceAggregate aggregate,
        ApplyCreditNoteCommand command,
        CancellationToken cancellationToken)
    {
        aggregate.ApplyCredit(
            command.TargetInvoiceId,
            command.TargetInvoiceNumber,
            command.Amount,
            command.AppliedDate,
            command.AppliedBy,
            command.LedgerTransactionId);

        return Task.CompletedTask;
    }
}