Ship B2B Integrations
in Days, Not Months

// Domain layer — no framework imports
public class FileTemplate : AuditableEntity
{
    public string Name        { get; set; }
    public FileType FileType   { get; set; }
    public bool HasHeaderRow  { get; set; }
    public IList<ColumnDef> Columns { get; set; }
}

// Infrastructure implements the interface
// defined in Domain — dependency flows inward
public class FileTemplateRepository
    : GenericRepository<FileTemplate>
    , IFileTemplateRepository
{
    public FileTemplateRepository(AppDbContext db)
        : base(db) { }

    public async Task<IList<FileTemplate>>
        GetWithColumnsAsync() =>
            await _db.FileTemplates
                .Include(t => t.Columns)
                .ToListAsync();
}

// 1. Define the command
public record CreateTemplateCommand(
    string Name,
    FileType Type,
    List<ColumnDef> Columns
) : IRequest<Guid>;

// 2. Validation — runs automatically
public class CreateTemplateValidator
    : AbstractValidator<CreateTemplateCommand>
{
    public CreateTemplateValidator()
    {
        RuleFor(x => x.Name).NotEmpty().MaximumLength(200);
        RuleFor(x => x.Columns).NotEmpty();
    }
}

// 3. Handler — just your business logic
public class CreateTemplateHandler
    : IRequestHandler<CreateTemplateCommand, Guid>
{
    public async Task<Guid> Handle(
        CreateTemplateCommand cmd, CancellationToken ct)
    {
        var template = new FileTemplate { Name = cmd.Name };
        await _repo.AddAsync(template, ct);
        return template.Id;
    }
}

// POST /api/fileprocessing/parse
// multipart/form-data: file + optional templateId

// Input CSV:
CustomerID,Name,OrderDate,Amount
C001,Acme Corp,2026-01-15,1250.00
C002,Globex Inc,2026-01-16,875.50

// Response:
{
  "rowCount": 2,
  "columns": [
    { "name": "CustomerID", "type": "String"  },
    { "name": "OrderDate",  "type": "DateTime"},
    { "name": "Amount",     "type": "Decimal" }
  ],
  "rows": [
    { "CustomerID": "C001", "Name": "Acme Corp",
      "OrderDate": "2026-01-15", "Amount": 1250.00 },
    ...
  ]
}

// POST /api/fileprocessing/transform
{
  "mappings": [
    {
      "sourceColumn": "CustomerID",
      "targetColumn": "customer_id",
      "transform": { "type": "None" }
    },
    {
      "sourceColumn": "Name",
      "targetColumn": "customer_name",
      "transform": { "type": "Uppercase" }
    },
    {
      "sourceColumn": "OrderDate",
      "targetColumn": "order_date",
      "transform": {
        "type": "DateFormat",
        "parameters": {
          "inputFormat":  "MM/dd/yyyy",
          "outputFormat": "yyyy-MM-dd"
        }
      }
    },
    {
      "sourceColumn": null,
      "targetColumn": "source_system",
      "defaultValue": "CLIENT_A"
    }
  ]
}

// Middleware registered in Program.cs
app.UseMiddleware<ExceptionHandlingMiddleware>();
app.UseApiKeyAuthentication();  // ← here
app.MapControllers();

// Create a client key in SQL:
INSERT INTO ApiClients
  (Id, Name, ApiKey, IsActive, AllowedEndpoints)
VALUES
  (NEWID(), 'Acme Corp', 'acme-key-abc123',
   1, '["/api/fileprocessing"]');

// Client calls the API:
curl -X POST https://api.yourco.com/api/fileprocessing/parse \
  -H "X-Api-Key: acme-key-abc123" \
  -F "file=@orders.csv"

// Unauthorized response (no key):
{ "error": "API key is required" }  // 401

// Scoped endpoint violation:
{ "error": "Access to this endpoint is not allowed" } // 403

// Enqueue a file import job from a controller
await _queue.QueueAsync(async ct =>
{
    await _notifier.NotifyProgressAsync(
        jobId, 10, "Fetching from SFTP...", ct);

    using var stream = await _sftp
        .DownloadAsync("/inbox/orders.csv", ct);

    await _notifier.NotifyProgressAsync(
        jobId, 50, "Parsing rows...", ct);

    var result = await _parser
        .ParseAsync(stream, options, ct);

    await _notifier.NotifyProgressAsync(
        jobId, 90, "Sending to partner...", ct);

    foreach (var dest in _destinations
        .Where(d => d.Supports(config.Type)))
        await dest.SendAsync(payload, config, ct);

    await _notifier.NotifyCompletedAsync(
        jobId, "Import complete.", ct);
}, cancellationToken);