Document Flow System

public class DocumentNumberService
{
    public async Task<string> GenerateDocumentNumber(
        DocumentType docType, Dictionary<string, string> parameters = null)
    {
        // Use transaction to ensure unique numbers
        await using var transaction = await _sequenceRepo.BeginTransactionAsync();

        try
        {
            // Get or create sequence for this document type
            var sequence = await _sequenceRepo.GetSequenceAsync(
                docType, DateTime.UtcNow.Year);

            // Increment and save
            sequence.CurrentValue++;
            await _sequenceRepo.UpdateAsync(sequence);
            await transaction.CommitAsync();

            // Format the number
            return FormatDocumentNumber(sequence, parameters);
        }
        catch
        {
            await transaction.RollbackAsync();
            throw;
        }
    }
}

public class DocumentValidationService
{
    public async Task<ValidationResult> ValidateDocumentCreation(
        DocumentType docType, Guid? parentDocId)
    {
        var errors = new List<string>();

        switch (docType)
        {
            case DocumentType.RFQ:
                // RFQ requires approved PR
                var pr = await _prRepo.GetByIdAsync(parentDocId.Value);
                if (pr.Status != PrStatus.Approved)
                    errors.Add("PR must be approved before creating RFQ");
                break;

            case DocumentType.PurchaseOrder:
                // PO requires selected quotation within validity
                var quote = await _quoteRepo.GetByIdAsync(parentDocId.Value);
                if (!quote.IsSelected)
                    errors.Add("Quotation must be selected");
                if (quote.ValidityDate < DateTime.UtcNow)
                    errors.Add("Quotation has expired");
                break;

            case DocumentType.GRN:
                // GRN requires PO sent to vendor
                var po = await _poRepo.GetByIdAsync(parentDocId.Value);
                if (po.Status < PoStatus.SentToVendor)
                    errors.Add("PO must be sent to vendor");
                break;
        }

        return new ValidationResult { IsValid = errors.Count == 0, Errors = errors };
    }
}