Add domain exceptions and update project structure

Implemented a structured exception-handling mechanism in the
domain layer with the addition of `DomainException`,
`DomainValidationException`, `NotFoundException`, and
`PdfProcessingException` classes. These exceptions provide
specific error handling for domain logic and integrate with
centralized middleware.

Updated `ROADMAP.md` to mark Step 2.1 (Domain Exceptions) as
completed and Step 2.2 (Value Objects) as the next task.
Added timeline entries to reflect progress.

Cleaned up `DocumentOperator.Domain.csproj` by removing
unused folder inclusions, indicating a project structure
reorganization.

DocumentOperator.Domain/Common/Exceptions/DomainException.cs

@@ -0,0 +1,25 @@
+namespace DocumentOperator.Domain.Common.Exceptions;
+
+/// <summary>
+/// Base exception for all domain-related exceptions.
+/// Caught by the Exception Handling Middleware in the API layer.
+/// </summary>
+public abstract class DomainException : Exception
+{
+    /// <summary>
+    /// Error code for categorization and logging.
+    /// </summary>
+    public string ErrorCode { get; }
+
+    protected DomainException(string message, string errorCode) 
+        : base(message)
+    {
+        ErrorCode = errorCode;
+    }
+
+    protected DomainException(string message, string errorCode, Exception innerException) 
+        : base(message, innerException)
+    {
+        ErrorCode = errorCode;
+    }
+}

DocumentOperator.Domain/Common/Exceptions/DomainValidationException.cs

@@ -0,0 +1,28 @@
+namespace DocumentOperator.Domain.Common.Exceptions;
+
+/// <summary>
+/// Exception thrown when domain validation fails (e.g., invalid Value Objects).
+/// Maps to HTTP 400 Bad Request in the API layer.
+/// </summary>
+public class DomainValidationException : DomainException
+{
+    public string PropertyName { get; }
+
+    public DomainValidationException(string message)
+        : base(message, "DOMAIN_VALIDATION_ERROR")
+    {
+        PropertyName = string.Empty;
+    }
+
+    public DomainValidationException(string propertyName, string message)
+        : base(message, "DOMAIN_VALIDATION_ERROR")
+    {
+        PropertyName = propertyName;
+    }
+
+    public DomainValidationException(string message, Exception innerException)
+        : base(message, "DOMAIN_VALIDATION_ERROR", innerException)
+    {
+        PropertyName = string.Empty;
+    }
+}

DocumentOperator.Domain/Common/Exceptions/NotFoundException.cs

@@ -0,0 +1,25 @@
+namespace DocumentOperator.Domain.Common.Exceptions;
+
+/// <summary>
+/// Exception thrown when a requested resource is not found.
+/// Maps to HTTP 404 Not Found in the API layer.
+/// </summary>
+public class NotFoundException : DomainException
+{
+    public string ResourceType { get; }
+    public object ResourceId { get; }
+
+    public NotFoundException(string resourceType, object resourceId)
+        : base($"{resourceType} with ID '{resourceId}' was not found.", "RESOURCE_NOT_FOUND")
+    {
+        ResourceType = resourceType;
+        ResourceId = resourceId;
+    }
+
+    public NotFoundException(string resourceType, object resourceId, string customMessage)
+        : base(customMessage, "RESOURCE_NOT_FOUND")
+    {
+        ResourceType = resourceType;
+        ResourceId = resourceId;
+    }
+}

DocumentOperator.Domain/Common/Exceptions/PdfProcessingException.cs

@@ -0,0 +1,34 @@
+namespace DocumentOperator.Domain.Common.Exceptions;
+
+/// <summary>
+/// Exception thrown when PDF processing operations fail.
+/// Maps to HTTP 500 Internal Server Error or 422 Unprocessable Entity in the API layer.
+/// </summary>
+public class PdfProcessingException : DomainException
+{
+    public string Operation { get; }
+
+    public PdfProcessingException(string operation, string message)
+        : base($"PDF processing failed during '{operation}': {message}", "PDF_PROCESSING_ERROR")
+    {
+        Operation = operation;
+    }
+
+    public PdfProcessingException(string operation, string message, Exception innerException)
+        : base($"PDF processing failed during '{operation}': {message}", "PDF_PROCESSING_ERROR", innerException)
+    {
+        Operation = operation;
+    }
+
+    public PdfProcessingException(string message)
+        : base(message, "PDF_PROCESSING_ERROR")
+    {
+        Operation = "Unknown";
+    }
+
+    public PdfProcessingException(string message, Exception innerException)
+        : base(message, "PDF_PROCESSING_ERROR", innerException)
+    {
+        Operation = "Unknown";
+    }
+}

DocumentOperator.Domain/DocumentOperator.Domain.csproj

@@ -7,7 +7,6 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <Folder Include="Common\Exceptions\" />
     <Folder Include="Common\Results\" />
     <Folder Include="Constants\" />
     <Folder Include="Models\Enums\" />

ROADMAP.md

@@ -722,15 +722,15 @@ DocumentOperator.Domain/
 
 ---
 
-#### 🔄 Step 2.1: Domain Exceptions erstellen - **NEXT**
+#### ✅ Step 2.1: Domain Exceptions erstellen - **COMPLETED**
 
 **Aufgabe:** Custom Exception-Klassen für fachliche Fehler
 
-**Zu erstellen:**
-1. [ ] `DomainException.cs` (Basis-Exception)
-2. [ ] `DomainValidationException.cs` (Value Object Validierung)
-3. [ ] `NotFoundException.cs` (Resource nicht gefunden)
-4. [ ] `PdfProcessingException.cs` (PDF-spezifische Fehler)
+**Erstellt:**
+1. [x] `DomainException.cs` (Basis-Exception)
+2. [x] `DomainValidationException.cs` (Value Object Validierung)
+3. [x] `NotFoundException.cs` (Resource nicht gefunden)
+4. [x] `PdfProcessingException.cs` (PDF-spezifische Fehler)
 
 **Wo:** `Domain/Common/Exceptions/`
 
@@ -755,7 +755,7 @@ if (notFound)
 
 ---
 
-#### ⏳ Step 2.2: Value Objects erstellen
+#### 🔄 Step 2.2: Value Objects erstellen - **NEXT**
 
 **Aufgabe:** Typsichere, selbst-validierende Wert-Objekte
 
@@ -1566,7 +1566,8 @@ Request mit X-API-Key → Middleware
 
 ### 🔄 In Progress
 - **Phase 2:** Domain Layer
-  - **NEXT:** Step 2.1 - Domain Exceptions erstellen
+  - ✅ Step 2.1 - Domain Exceptions
+  - **NEXT:** Step 2.2 - Value Objects
 
 ### ⏳ Pending
 - Phase 3-9
@@ -1629,7 +1630,8 @@ Request mit X-API-Key → Middleware
 | 2024-XX-XX | Phase 1 | Configuration, Serilog, Options Pattern |
 | 2024-XX-XX | Phase 1 | **Decision:** Exception-based statt Ardalis.Result |
 | 2024-XX-XX | Phase 1 | ✅ Phase 1 completed |
-| 2024-XX-XX | Phase 2 | 🔄 Starting Domain Layer - Exceptions |
+| 2024-XX-XX | Phase 2 | ✅ Step 2.1 completed - Domain Exceptions created |
+| 2024-XX-XX | Phase 2 | 🔄 Starting Step 2.2 - Value Objects |
 
 ---