Complete Step 1.1: ValidatePDF Application Layer

Updated PHASENPLAN and ROADMAP to reflect progress on Feature 1 - ValidatePDF (75% complete). Marked Step 1.1 as completed, including MediatR setup, pipeline behaviors (`ValidationBehavior`, `LoggingBehavior`), ValidatePDF feature (Query, Handler, Validator), and DTOs.

Added `DependencyInjection.cs` for Application Layer DI configuration. Introduced `LoggingBehavior` and `ValidationBehavior` for MediatR pipelines. Implemented `ValidatePdfHandler`, `ValidatePdfQuery`, and `ValidatePdfValidator`.

Created DTOs (`ValidatePdfRequest`, `ValidatePdfResponse`) for the ValidatePDF feature. Added unit tests for `ValidatePdfHandler` to verify metadata handling and exception propagation.

Removed unused folder references in `DocumentOperator.Application.csproj`.

DocumentOperator.Application/Common/Behaviors/LoggingBehavior.cs

@@ -0,0 +1,66 @@
+using MediatR;
+using Microsoft.Extensions.Logging;
+using System.Diagnostics;
+
+namespace DocumentOperator.Application.Common.Behaviors;
+
+/// <summary>
+/// MediatR Pipeline Behavior that logs requests and tracks performance
+/// Executes AFTER ValidationBehavior, BEFORE Handler
+/// </summary>
+public class LoggingBehavior<TRequest, TResponse> : IPipelineBehavior<TRequest, TResponse>
+    where TRequest : IRequest<TResponse>
+{
+    private readonly ILogger<LoggingBehavior<TRequest, TResponse>> _logger;
+
+    public LoggingBehavior(ILogger<LoggingBehavior<TRequest, TResponse>> logger)
+    {
+        _logger = logger;
+    }
+
+    public async Task<TResponse> Handle(
+        TRequest request,
+        RequestHandlerDelegate<TResponse> next,
+        CancellationToken cancellationToken)
+    {
+        var requestName = typeof(TRequest).Name;
+
+        // Request Start
+        _logger.LogInformation("Handling {RequestName}: {@Request}", requestName, request);
+
+        // Performance Tracking
+        var stopwatch = Stopwatch.StartNew();
+
+        try
+        {
+            // Handler ausführen
+            var response = await next();
+
+            stopwatch.Stop();
+
+            // Request Success
+            _logger.LogInformation(
+                "Handled {RequestName} in {ElapsedMs}ms",
+                requestName,
+                stopwatch.ElapsedMilliseconds
+            );
+
+            return response;
+        }
+        catch (Exception ex)
+        {
+            stopwatch.Stop();
+
+            // Request Failed
+            _logger.LogError(
+                ex,
+                "Error handling {RequestName} after {ElapsedMs}ms: {ErrorMessage}",
+                requestName,
+                stopwatch.ElapsedMilliseconds,
+                ex.Message
+            );
+
+            throw; // Exception weiterwerfen (wird von Exception Middleware gefangen)
+        }
+    }
+}

DocumentOperator.Application/Common/Behaviors/ValidationBehavior.cs

@@ -0,0 +1,54 @@
+using FluentValidation;
+using MediatR;
+
+namespace DocumentOperator.Application.Common.Behaviors;
+
+/// <summary>
+/// MediatR Pipeline Behavior that validates requests using FluentValidation
+/// Executes BEFORE the Handler
+/// </summary>
+public class ValidationBehavior<TRequest, TResponse> : IPipelineBehavior<TRequest, TResponse>
+    where TRequest : IRequest<TResponse>
+{
+    private readonly IEnumerable<IValidator<TRequest>> _validators;
+
+    public ValidationBehavior(IEnumerable<IValidator<TRequest>> validators)
+    {
+        _validators = validators;
+    }
+
+    public async Task<TResponse> Handle(
+        TRequest request,
+        RequestHandlerDelegate<TResponse> next,
+        CancellationToken cancellationToken)
+    {
+        // Wenn keine Validators registriert sind, direkt weiter zum Handler
+        if (!_validators.Any())
+        {
+            return await next();
+        }
+
+        // Validation Context erstellen
+        var context = new ValidationContext<TRequest>(request);
+
+        // Alle Validators parallel ausführen
+        var validationResults = await Task.WhenAll(
+            _validators.Select(v => v.ValidateAsync(context, cancellationToken))
+        );
+
+        // Fehler sammeln
+        var failures = validationResults
+            .Where(r => !r.IsValid)
+            .SelectMany(r => r.Errors)
+            .ToList();
+
+        // Bei Fehlern: ValidationException werfen (wird von Exception Middleware gefangen)
+        if (failures.Any())
+        {
+            throw new ValidationException(failures);
+        }
+
+        // Validation erfolgreich ? weiter zum Handler
+        return await next();
+    }
+}

DocumentOperator.Application/Common/DTOs/ValidatePdfRequest.cs

@@ -0,0 +1,7 @@
+namespace DocumentOperator.Application.Common.DTOs;
+
+/// <summary>
+/// Request DTO for ValidatePdf endpoint
+/// </summary>
+/// <param name="Base64Pdf">PDF content as Base64 string</param>
+public record ValidatePdfRequest(string Base64Pdf);

DocumentOperator.Application/Common/DTOs/ValidatePdfResponse.cs

@@ -0,0 +1,14 @@
+namespace DocumentOperator.Application.Common.DTOs;
+
+/// <summary>
+/// Response DTO for ValidatePdf endpoint
+/// Contains PDF metadata
+/// </summary>
+public record ValidatePdfResponse(
+    int PageCount,
+    long FileSizeBytes,
+    double FileSizeMB,
+    string PdfVersion,
+    bool HasAttachments,
+    int AttachmentCount
+);

DocumentOperator.Application/DependencyInjection.cs

@@ -0,0 +1,33 @@
+using FluentValidation;
+using Microsoft.Extensions.DependencyInjection;
+
+namespace DocumentOperator.Application;
+
+/// <summary>
+/// Dependency Injection configuration for Application Layer
+/// </summary>
+public static class DependencyInjection
+{
+    /// <summary>
+    /// Registers Application Layer services (MediatR, FluentValidation, Behaviors)
+    /// </summary>
+    public static IServiceCollection AddApplication(this IServiceCollection services)
+    {
+        var assembly = typeof(DependencyInjection).Assembly;
+
+        // Register MediatR (scannt Assembly nach Handlers)
+        services.AddMediatR(config =>
+        {
+            config.RegisterServicesFromAssembly(assembly);
+
+            // Pipeline Behaviors (Reihenfolge wichtig!)
+            config.AddOpenBehavior(typeof(Common.Behaviors.ValidationBehavior<,>));
+            config.AddOpenBehavior(typeof(Common.Behaviors.LoggingBehavior<,>));
+        });
+
+        // Register FluentValidation (scannt Assembly nach Validators)
+        services.AddValidatorsFromAssembly(assembly);
+
+        return services;
+    }
+}

DocumentOperator.Application/DocumentOperator.Application.csproj

@@ -17,15 +17,12 @@
   </ItemGroup>
 
   <ItemGroup>
-    <Folder Include="Common\Behaviors\" />
-    <Folder Include="Common\DTOs\" />
     <Folder Include="Common\Mappings\" />
     <Folder Include="DependencyInjection\" />
     <Folder Include="Features\Documents\ExtractAttachments\" />
     <Folder Include="Features\Documents\ConcatenatePdfs\" />
     <Folder Include="Features\Documents\ApplyStamp\" />
     <Folder Include="Features\Documents\EmbedCertificate\" />
-    <Folder Include="Features\Documents\ValidatePdf\" />
   </ItemGroup>
 
 </Project>

DocumentOperator.Application/Features/Documents/ValidatePdf/ValidatePdfHandler.cs

@@ -0,0 +1,33 @@
+using DocumentOperator.Application.Common.Interfaces;
+using DocumentOperator.Domain.Models.ValueObjects;
+using MediatR;
+
+namespace DocumentOperator.Application.Features.Documents.ValidatePdf;
+
+/// <summary>
+/// Handler for ValidatePdfQuery
+/// Orchestrates PDF validation using IPdfProcessor
+/// </summary>
+public class ValidatePdfHandler : IRequestHandler<ValidatePdfQuery, PdfMetadata>
+{
+    private readonly IPdfProcessor _pdfProcessor;
+
+    public ValidatePdfHandler(IPdfProcessor pdfProcessor)
+    {
+        _pdfProcessor = pdfProcessor;
+    }
+
+    /// <summary>
+    /// Validates PDF and returns metadata
+    /// </summary>
+    public async Task<PdfMetadata> Handle(ValidatePdfQuery request, CancellationToken cancellationToken)
+    {
+        // Value Object ? Byte Array
+        byte[] pdfBytes = request.PdfContent.ToByteArray();
+
+        // DevExpress Service aufrufen (kann PdfProcessingException werfen)
+        var metadata = await _pdfProcessor.ValidateAsync(pdfBytes);
+
+        return metadata;
+    }
+}

DocumentOperator.Application/Features/Documents/ValidatePdf/ValidatePdfQuery.cs

@@ -0,0 +1,10 @@
+using DocumentOperator.Domain.Models.ValueObjects;
+using MediatR;
+
+namespace DocumentOperator.Application.Features.Documents.ValidatePdf;
+
+/// <summary>
+/// Query to validate a PDF document and return metadata
+/// </summary>
+/// <param name="PdfContent">PDF content as Base64 string (validated by Value Object)</param>
+public record ValidatePdfQuery(Base64String PdfContent) : IRequest<PdfMetadata>;

DocumentOperator.Application/Features/Documents/ValidatePdf/ValidatePdfValidator.cs

@@ -0,0 +1,17 @@
+using FluentValidation;
+
+namespace DocumentOperator.Application.Features.Documents.ValidatePdf;
+
+/// <summary>
+/// Validator for ValidatePdfQuery
+/// Validates that PdfContent is not null (Base64String already validates format in its constructor)
+/// </summary>
+public class ValidatePdfValidator : AbstractValidator<ValidatePdfQuery>
+{
+    public ValidatePdfValidator()
+    {
+        RuleFor(x => x.PdfContent)
+            .NotNull()
+            .WithMessage("PDF content is required");
+    }
+}