Attachment Add and Delete commands implemented

ModernKeePass.Application/Entry/Commands/AddAttachment/AddAttachmentCommand.cs

@@ -0,0 +1,34 @@
+using System;
+using MediatR;
+using ModernKeePass.Application.Common.Interfaces;
+using ModernKeePass.Application.Entry.Models;
+using ModernKeePass.Domain.Exceptions;
+
+namespace ModernKeePass.Application.Entry.Commands.AddAttachment
+{
+    public class AddAttachmentCommand : IRequest
+    {
+        public EntryVm Entry { get; set; }
+        public string AttachmentName { get; set; }
+        public byte[] AttachmentContent { get; set; }
+
+        public class AddAttachmentCommandHandler : IRequestHandler<AddAttachmentCommand>
+        {
+            private readonly IDatabaseProxy _database;
+
+            public AddAttachmentCommandHandler(IDatabaseProxy database)
+            {
+                _database = database;
+            }
+
+            public void Handle(AddAttachmentCommand message)
+            {
+                if (!_database.IsOpen) throw new DatabaseClosedException();
+
+                if (message.Entry.Attachments.ContainsKey(message.AttachmentName)) throw new ArgumentException("AttachmentAlreadyExists", nameof(message.AttachmentName));
+                _database.AddAttachment(message.Entry.Id, message.AttachmentName, message.AttachmentContent);
+                message.Entry.Attachments.Add(message.AttachmentName, message.AttachmentContent);
+            }
+        }
+    }
+}