Attachment Add and Delete commands implemented

ModernKeePass.Application/Entry/Commands/DeleteAttachment/DeleteAttachmentCommand.cs

@@ -0,0 +1,33 @@
+using System.Collections.Generic;
+using MediatR;
+using ModernKeePass.Application.Common.Interfaces;
+using ModernKeePass.Application.Entry.Models;
+using ModernKeePass.Domain.Exceptions;
+
+namespace ModernKeePass.Application.Entry.Commands.DeleteAttachment
+{
+    public class DeleteAttachmentCommand : IRequest
+    {
+        public EntryVm Entry { get; set; }
+        public string AttachmentName { get; set; }
+
+        public class DeleteAttachmentCommandHandler : IRequestHandler<DeleteAttachmentCommand>
+        {
+            private readonly IDatabaseProxy _database;
+
+            public DeleteAttachmentCommandHandler(IDatabaseProxy database)
+            {
+                _database = database;
+            }
+
+            public void Handle(DeleteAttachmentCommand message)
+            {
+                if (!_database.IsOpen) throw new DatabaseClosedException();
+
+                if (!message.Entry.Attachments.ContainsKey(message.AttachmentName)) throw new KeyNotFoundException("AttachmentDoesntExist");
+                _database.DeleteAttachment(message.Entry.Id, message.AttachmentName);
+                message.Entry.Attachments.Remove(message.AttachmentName);
+            }
+        }
+    }
+}