Create Attachments from Sitecore MediaItems and attach to emails

RetrieveAttachments.cs

private List<Attachment> RetrieveAttachments(ID formId, IEnumerable<AdaptedControlResult> fields)
{
    var attachments = new List<Attachment>();
 
    Item item = Sitecore.Context.Database.Items[formId];
    if (item != null)
    {
        var mediaItemIds = new List<string>();
 
        var formItem = new FormItem(item);
 
        foreach (AdaptedControlResult field in fields)
        {
            GetMediaIds(formItem, field, mediaItemIds);
        }
 
        GetAttachmentsFromMediaItems(mediaItemIds, attachments);
    }
 
    return attachments;
}
 
private static void GetMediaIds(FormItem formItem, AdaptedControlResult field, List<string> mediaItemIds)
{
    if (formItem.Fields.Any(f => f.ID.ToString() == field.FieldID))
    {
        FieldItem fieldItem = formItem.Fields.First(f => f.ID.ToString() == field.FieldID);
        if (fieldItem.Type.ID == Enumerators.SitecoreConfig.Guids.Templates.HiddenEmailAttachmentId)
        {
            var value = HttpUtility.HtmlDecode(field.Value);
 
            var regex = new Regex(@"<item>(.*?)</item>");
            var matches = regex.Matches(value);
 
            foreach (Match match in matches)
            {
                if (!string.IsNullOrEmpty(match.Groups[1].Value))
                {
                    mediaItemIds.Add(match.Groups[1].Value);
                }
            }
        }
    }
}