prs/prs.shared/EmailUtils.cs


using System.Diagnostics;
using System.IO;
using System.Net.Mail;
using System.Reflection;
using System.Text;
using InABox.Clients;
using InABox.Core;

namespace PRS.Shared
{
    public class EmailUtils
    {
        /// <summary>
        /// Creates and opens an email with the default email app - selected by the user.
        /// This method is for emails with a PDF attachment. Provide the file name and data.
        /// Optionally provide from, subject and body.
        /// If from is not provided, an attempt will be made to find the User's email address - if empty it will throw an error (cannot be empty)
        /// </summary>
        /// <param name="attachmentname"></param>
        /// <param name="attachmentdata"></param>
        /// <param name="from"></param>
        /// <param name="subject"></param>
        /// <param name="body"></param>
        public static void CreateEMLFile(string attachmentname, byte[] attachmentdata, string from = "", string subject = "", string body = "")
        {
            var message = CreateMessage(from, subject, body);

            message = AddAttachment(message, attachmentname, attachmentdata);

            OpenEmail(message, attachmentname);
        }

        /// <summary>
        /// Creates and opens an email with the default email app - selected by the user.
        /// This method is for emails with no attachments.
        /// Optionally provide from, subject and body.
        /// If from is not provided, an attempt will be made to find the User's email address - if empty it will throw an error (cannot be empty)
        /// </summary>
        /// <param name="from"></param>
        /// <param name="subject"></param>
        /// <param name="body"></param>
        public static void CreateEMLFile(string from = "", string subject = "", string body = "")
        {
            var message = CreateMessage(from, subject, body);

            OpenEmail(message, "Message from " + from);
        }

        private static void OpenEmail(MailMessage message, string name)
        {
            var filename = Path.Combine(Path.GetTempPath(), Path.ChangeExtension(name, ".eml"));

            using (var filestream = File.Open(filename, FileMode.Create))
            {
                var binaryWriter = new BinaryWriter(filestream);
                //Write the Unsent header to the file so the mail client knows this mail must be presented in "New message" mode
                binaryWriter.Write(Encoding.UTF8.GetBytes("X-Unsent: 1" + Environment.NewLine));

                var assembly = typeof(SmtpClient).Assembly;
                var mailWriterType = assembly.GetType("System.Net.Mail.MailWriter")!;

                // Get reflection info for MailWriter contructor
                var mailWriterConstructor =
                    mailWriterType.GetConstructor(BindingFlags.Instance | BindingFlags.NonPublic, null, new Type[] { typeof(Stream), typeof(bool) }, null)!;

                // Construct MailWriter object with our FileStream
                var mailWriter = mailWriterConstructor.Invoke(new object[] { filestream, true });

                // Get reflection info for Send() method on MailMessage
                var sendMethod = typeof(MailMessage).GetMethod("Send", BindingFlags.Instance | BindingFlags.NonPublic)!;

                sendMethod.Invoke(message, BindingFlags.Instance | BindingFlags.NonPublic, null, new[] { mailWriter, true, true }, null);

                // Finally get reflection info for Close() method on our MailWriter
                var closeMethod = mailWriter.GetType().GetMethod("Close", BindingFlags.Instance | BindingFlags.NonPublic)!;

                // Call close method
                closeMethod.Invoke(mailWriter, BindingFlags.Instance | BindingFlags.NonPublic, null, new object[] { }, null);
            }

            // Open the file with the default associated application registered on the local machine
            Process.Start(new ProcessStartInfo(filename) { UseShellExecute = true });
        }

        private static MailMessage CreateMessage(string from, string subject, string body)
        {
            var message = new MailMessage();
            if (string.IsNullOrWhiteSpace(from))
                from = GetAddressFromUser();
            message.From = new MailAddress(from);
            message.Subject = subject;
            message.IsBodyHtml = true;
            message.Body = body;
            return message;
        }

        private static string GetAddressFromUser()
        {
            CoreTable table = new Client<User>().Query(new Filter<User>(x => x.ID).IsEqualTo(ClientFactory.UserGuid)
                , new Columns<User>(x => x.EmailAddress));
            User user = table.Rows.FirstOrDefault().ToObject<User>();

            if (!string.IsNullOrWhiteSpace(user.EmailAddress))
                return user.EmailAddress;
            else
                MessageBox.Show("Unable to send email. Current User Email Address is blank - please fill in", "Error");

            return "";

        }

        private static MailMessage AddAttachment(MailMessage message, string attachmentname, byte[] attachmentdata)
        {
            var attachment = Path.Combine(Path.GetTempPath(), Path.ChangeExtension(attachmentname, ".pdf"));
            File.WriteAllBytes(attachment, attachmentdata);

            message.Attachments.Add(new Attachment(attachment));

            return message;
        }
    }
}