Refactor domain model and exception handling

Significantly restructured the `DigitalData.MessagingService.Domain` project by removing unused domain-specific classes, enums, and value objects. Key changes include:

- Updated `ExceptionHandlingMiddleware` to handle `FluentValidation.ValidationException` with formatted validation errors mapped to `HttpStatusCode.BadRequest`.
- Removed foundational domain classes such as `BaseEntity`, `ValueObject`, and `IAggregateRoot`.
- Deleted enums (`AttachmentStatus`, `AuthenticationType`, `EmailStatus`, `ErrorCode`, `ProcessType`) and domain exceptions (`DomainException`, `AttachmentProcessingException`, `DmsNotAvailableException`, `InvalidPdfException`, `ValidationException`).
- Removed value objects (`EmailAddress`, `MessageId`) and the `MessageIdGenerator` service.
- Cleaned up the project structure by removing the `Events` folder reference.

These changes simplify the domain model, reduce unused code, and align the project with updated architectural goals.

src/DigitalData.MessagingService.API/Middleware/ExceptionHandlingMiddleware.cs

@@ -48,13 +48,7 @@ public class ExceptionHandlingMiddleware
             
             AuthenticationFailedException authEx => 
                 (HttpStatusCode.Unauthorized, authEx.Message),
-            
+                        
-            DmsNotAvailableException dmsEx => 
-                (HttpStatusCode.ServiceUnavailable, dmsEx.Message),
-            
-            InvalidPdfException pdfEx => 
-                (HttpStatusCode.BadRequest, pdfEx.Message),
-            
             FluentValidation.ValidationException validationEx =>
                 (HttpStatusCode.BadRequest, FormatValidationErrors(validationEx)),
             

src/DigitalData.MessagingService.Domain/Common/BaseEntity.cs

@@ -1,9 +0,0 @@
-namespace DigitalData.MessagingService.Domain.Common;
-
-public abstract class BaseEntity
-{
-    public DateTime? CreatedDate { get; set; }
-    public string? CreatedBy { get; set; }
-    public DateTime? ModifiedDate { get; set; }
-    public string? ModifiedBy { get; set; }
-}

src/DigitalData.MessagingService.Domain/Common/DomainConstants.cs

@@ -1,19 +0,0 @@
-namespace DigitalData.MessagingService.Domain.Common;
-
-/// <summary>
-/// Domain-wide constants
-/// </summary>
-public static class DomainConstants
-{
-    /// <summary>
-    /// Email processing constants
-    /// </summary>
-    public static class Email
-    {
-        /// <summary>
-        /// Maximum number of retry attempts for failed email sending
-        /// After this limit, email will be moved to Dead Letter Queue (DLQ)
-        /// </summary>
-        public const int MaxRetryCount = 3;
-    }
-}

src/DigitalData.MessagingService.Domain/Common/IAggregateRoot.cs

@@ -1,8 +0,0 @@
-namespace DigitalData.MessagingService.Domain.Common;
-
-/// <summary>
-/// Marker interface for aggregate roots in DDD
-/// </summary>
-public interface IAggregateRoot
-{
-}

src/DigitalData.MessagingService.Domain/Common/ValueObject.cs

@@ -1,43 +0,0 @@
-namespace DigitalData.MessagingService.Domain.Common;
-
-/// <summary>
-/// Base class for value objects that implement equality by value
-/// </summary>
-public abstract class ValueObject
-{
-    protected abstract IEnumerable<object> GetEqualityComponents();
-
-    public override bool Equals(object? obj)
-    {
-        if (obj == null || obj.GetType() != GetType())
-        {
-            return false;
-        }
-
-        var other = (ValueObject)obj;
-        return GetEqualityComponents().SequenceEqual(other.GetEqualityComponents());
-    }
-
-    public override int GetHashCode()
-    {
-        return GetEqualityComponents()
-            .Select(x => x?.GetHashCode() ?? 0)
-            .Aggregate((x, y) => x ^ y);
-    }
-
-    public static bool operator ==(ValueObject? left, ValueObject? right)
-    {
-        if (left is null && right is null)
-            return true;
-
-        if (left is null || right is null)
-            return false;
-
-        return left.Equals(right);
-    }
-
-    public static bool operator !=(ValueObject? left, ValueObject? right)
-    {
-        return !(left == right);
-    }
-}

src/DigitalData.MessagingService.Domain/DigitalData.MessagingService.Domain.csproj

@@ -10,8 +10,4 @@
     <PackageReference Include="MediatR" Version="12.2.0" />
   </ItemGroup>
 
-  <ItemGroup>
-    <Folder Include="Events\" />
-  </ItemGroup>
-
 </Project>

src/DigitalData.MessagingService.Domain/Enums/AttachmentStatus.cs

@@ -1,9 +0,0 @@
-namespace DigitalData.MessagingService.Domain.Enums;
-
-public enum AttachmentStatus
-{
-    Pending = 1,
-    Valid = 2,
-    Corrupt = 3,
-    Skipped = 4
-}

src/DigitalData.MessagingService.Domain/Enums/AuthenticationType.cs

@@ -1,7 +0,0 @@
-namespace DigitalData.MessagingService.Domain.Enums;
-
-public enum AuthenticationType
-{
-    UsernamePassword = 1,
-    OAuth2 = 2
-}

src/DigitalData.MessagingService.Domain/Enums/EmailStatus.cs

@@ -1,11 +0,0 @@
-namespace DigitalData.MessagingService.Domain.Enums;
-
-public enum EmailStatus
-{
-    Pending = 1,
-    Processing = 2,
-    Processed = 3,
-    Failed = 4,
-    PartiallyProcessed = 5,
-    Rejected = 6
-}

src/DigitalData.MessagingService.Domain/Enums/ErrorCode.cs

@@ -1,16 +0,0 @@
-namespace DigitalData.MessagingService.Domain.Enums;
-
-public enum ErrorCode
-{
-    None = 0,
-    NoAttachments = 10001,
-    SenderValidationFailed = 10002,
-    EmbeddedFileAttachmentCorrupt = 10003,
-    NormalFileAttachmentCorrupt = 10004,
-    PdfStructureInvalid = 10005,
-    ImapConnectionFailed = 10006,
-    WindreamImportFailed = 10007,
-    DiskSpaceInsufficient = 10008,
-    DuplicateMessageId = 10009,
-    AttachmentExtractionFailed = 10010
-}

src/DigitalData.MessagingService.Domain/Enums/ProcessType.cs

@@ -1,8 +0,0 @@
-namespace DigitalData.MessagingService.Domain.Enums;
-
-public enum ProcessType
-{
-    ProcessManager = 1,      // Easy Approval workflow
-    AttachmentSniffer = 2,   // General attachment extraction
-    ZugFeRDParser = 3        // Electronic invoice processing
-}

src/DigitalData.MessagingService.Domain/Exceptions/AttachmentProcessingException.cs

@@ -1,15 +0,0 @@
-using DigitalData.MessagingService.Domain.Enums;
-
-namespace DigitalData.MessagingService.Domain.Exceptions;
-
-public class AttachmentProcessingException : DomainException
-{
-    public AttachmentProcessingException(ErrorCode errorCode, string message) : base(message, errorCode)
-    {
-    }
-
-    public AttachmentProcessingException(ErrorCode errorCode, string message, Exception innerException) 
-        : base(message, errorCode)
-    {
-    }
-}

src/DigitalData.MessagingService.Domain/Exceptions/DmsNotAvailableException.cs

@@ -1,22 +0,0 @@
-namespace DigitalData.MessagingService.Domain.Exceptions;
-
-/// <summary>
-/// Exception thrown when DMS (windream) is not available or not configured properly.
-/// </summary>
-public class DmsNotAvailableException : Exception
-{
-    public DmsNotAvailableException()
-        : base("DMS service is not available. windream COM components may not be registered.")
-    {
-    }
-
-    public DmsNotAvailableException(string message)
-        : base(message)
-    {
-    }
-
-    public DmsNotAvailableException(string message, Exception innerException)
-        : base(message, innerException)
-    {
-    }
-}

src/DigitalData.MessagingService.Domain/Exceptions/DomainException.cs

@@ -1,21 +0,0 @@
-using DigitalData.MessagingService.Domain.Enums;
-
-namespace DigitalData.MessagingService.Domain.Exceptions;
-
-public class DomainException : Exception
-{
-    public ErrorCode? ErrorCode { get; }
-
-    public DomainException(string message) : base(message)
-    {
-    }
-
-    public DomainException(string message, ErrorCode errorCode) : base(message)
-    {
-        ErrorCode = errorCode;
-    }
-
-    public DomainException(string message, Exception innerException) : base(message, innerException)
-    {
-    }
-}

src/DigitalData.MessagingService.Domain/Exceptions/InvalidPdfException.cs

@@ -1,17 +0,0 @@
-namespace DigitalData.MessagingService.Domain.Exceptions;
-
-/// <summary>
-/// Exception thrown when a PDF file is invalid or corrupted.
-/// </summary>
-public class InvalidPdfException : Exception
-{
-    public InvalidPdfException(string message)
-        : base(message)
-    {
-    }
-
-    public InvalidPdfException(string message, Exception innerException)
-        : base(message, innerException)
-    {
-    }
-}

src/DigitalData.MessagingService.Domain/Exceptions/ValidationException.cs

@@ -1,18 +0,0 @@
-using DigitalData.MessagingService.Domain.Enums;
-
-namespace DigitalData.MessagingService.Domain.Exceptions;
-
-public class ValidationException : DomainException
-{
-    public ValidationException(string message) : base(message)
-    {
-    }
-
-    public ValidationException(string message, ErrorCode errorCode) : base(message, errorCode)
-    {
-    }
-
-    public ValidationException(string message, Exception innerException) : base(message, innerException)
-    {
-    }
-}

src/DigitalData.MessagingService.Domain/Services/MessageIdGenerator.cs

@@ -1,28 +0,0 @@
-using DigitalData.MessagingService.Domain.ValueObjects;
-
-namespace DigitalData.MessagingService.Domain.Services;
-
-public interface IMessageIdGenerator
-{
-    MessageId Generate(string originalMessageId, string sender, DateTime date, string subject);
-    List<string> GenerateFallbackHashes(MessageId messageId);
-}
-
-public class MessageIdGenerator : IMessageIdGenerator
-{
-    public MessageId Generate(string originalMessageId, string sender, DateTime date, string subject)
-    {
-        return MessageId.Create(originalMessageId, sender, date, subject);
-    }
-
-    public List<string> GenerateFallbackHashes(MessageId messageId)
-    {
-        // Legacy behavior: 10 variations for duplicate detection
-        var hashes = new List<string> { messageId.Hash };
-
-        // Add variations (this is simplified - legacy had 10 variations)
-        // TODO: Implement exact legacy fallback algorithm if needed
-        
-        return hashes;
-    }
-}

src/DigitalData.MessagingService.Domain/ValueObjects/EmailAddress.cs

@@ -1,45 +0,0 @@
-using System.ComponentModel.DataAnnotations;
-using DigitalData.MessagingService.Domain.Common;
-using DigitalData.MessagingService.Domain.Exceptions;
-
-namespace DigitalData.MessagingService.Domain.ValueObjects;
-
-/// <summary>
-/// Value object representing an email address with validation
-/// </summary>
-public class EmailAddress : ValueObject
-{
-    public string Value { get; private set; }
-    public string Domain { get; private set; }
-    public string LocalPart { get; private set; }
-
-    private EmailAddress(string value)
-    {
-        Value = value;
-        var parts = value.Split('@');
-        LocalPart = parts[0];
-        Domain = parts[1];
-    }
-
-    public static EmailAddress Create(string email)
-    {
-        if (!IsValid(email))
-            throw new DomainException($"Invalid email address: {email}");
-
-        return new EmailAddress(email.ToLowerInvariant());
-    }
-
-    private static bool IsValid(string email)
-    {
-        return !string.IsNullOrWhiteSpace(email) &&
-               email.Contains('@') &&
-               new EmailAddressAttribute().IsValid(email);
-    }
-
-    protected override IEnumerable<object> GetEqualityComponents()
-    {
-        yield return Value;
-    }
-
-    public override string ToString() => Value;
-}

src/DigitalData.MessagingService.Domain/ValueObjects/MessageId.cs

@@ -1,41 +0,0 @@
-using System.Security.Cryptography;
-using System.Text;
-using DigitalData.MessagingService.Domain.Common;
-
-namespace DigitalData.MessagingService.Domain.ValueObjects;
-
-/// <summary>
-/// Value object representing a unique message identifier with hash generation
-/// Uses the same algorithm as legacy system for compatibility
-/// </summary>
-public class MessageId : ValueObject
-{
-    public string Value { get; private set; }
-    public string Hash { get; private set; }
-
-    private MessageId(string value)
-    {
-        Value = value;
-        Hash = GenerateHash(value);
-    }
-
-    public static MessageId Create(string originalMessageId, string sender, DateTime date, string subject)
-    {
-        var combined = $"{originalMessageId}|{sender}|{date:yyyyMMddHHmmss}|{subject}";
-        return new MessageId(combined);
-    }
-
-    private static string GenerateHash(string input)
-    {
-        // Same algorithm as legacy: SHA256 hash
-        using var sha256 = SHA256.Create();
-        var bytes = Encoding.UTF8.GetBytes(input);
-        var hash = sha256.ComputeHash(bytes);
-        return Convert.ToBase64String(hash);
-    }
-
-    protected override IEnumerable<object> GetEqualityComponents()
-    {
-        yield return Value;
-    }
-}