DD.WellWorkover.Cloud/AsbCloudInfrastructure/Services/EmailService.cs

using AsbCloudApp.Exceptions;
using AsbCloudApp.Services;
using Microsoft.Extensions.Configuration;
using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Net.Mail;
using System.Text.RegularExpressions;
using System.Threading;
using System.Threading.Tasks;

namespace AsbCloudInfrastructure.Services
{
    public class EmailService : IEmailService
    {
        private readonly IBackgroundWorkerService backgroundWorker;
        private readonly bool IsConfigured;
        private readonly string sender;
        private readonly string smtpServer;
        private readonly string smtpPassword;

        public EmailService(IBackgroundWorkerService backgroundWorker, IConfiguration configuration)
        {
            sender = configuration.GetValue<string>("email:sender", null);
            smtpPassword = configuration.GetValue<string>("email:password", null);
            smtpServer = configuration.GetValue<string>("email:smtpServer", null);

            var configError = (string.IsNullOrEmpty(sender) ||
                string.IsNullOrEmpty(smtpPassword) ||
                string.IsNullOrEmpty(smtpServer));

            IsConfigured = !configError;

            this.backgroundWorker = backgroundWorker;
        }

        public void EnqueueSend(IEnumerable<string> addresses, string subject, string htmlBody)
        {
            if(!IsConfigured)
            {
                Trace.TraceWarning("smtp is not configured");
                return;
            }
            var jobId = CalcJobId(addresses, subject, htmlBody);
            if (!backgroundWorker.Contains(jobId))
            {
                var action = MakeEmailSendJobAsync(addresses, subject, htmlBody);
                backgroundWorker.Enqueue(jobId, action);
            }            
        }

        private Func<string, CancellationToken, Task> MakeEmailSendJobAsync(IEnumerable<string> addresses, string subject, string htmlBody)
        {
            var mailAddresses = new List<MailAddress>();
            foreach (var address in addresses)
            {
                if (MailAddress.TryCreate(address, out MailAddress mailAddress))
                    mailAddresses.Add(mailAddress);
                else
                    Trace.TraceWarning($"Mail {address} is not correct.");
            }

            if (!mailAddresses.Any())
                throw new ArgumentException($"No valid email found. List:[{string.Join(',', addresses)}]", nameof(addresses));

            if (string.IsNullOrEmpty(subject))
                throw new ArgumentInvalidException($"{nameof(subject)} should be set", nameof(subject));
            
            var func = async (string id, CancellationToken token) =>
            {
                var from = new MailAddress(sender);

                var message = new MailMessage();
                message.From = from;

                foreach (var mailAddress in mailAddresses)
                    message.To.Add(mailAddress);
                
                message.Subject = subject;
                message.Body = htmlBody;
                message.IsBodyHtml = true;

                var client = new SmtpClient(smtpServer);
                client.EnableSsl = true;
                client.UseDefaultCredentials = false;
                client.Credentials = new System.Net.NetworkCredential(sender, smtpPassword);
                
                // TODO: uncomment next when tested
                //await client.SendMailAsync(message, token);
                await Task.Delay(0);
                Trace.TraceInformation($"Send email to {string.Join(',', addresses)} subj:{subject}");
            };
            return func;
        }        

        private string CalcJobId(IEnumerable<string> addresses, string subject, string content)
        {
            var hash = GetHashCode(addresses);
            hash ^= subject.GetHashCode();
            hash ^= content.GetHashCode();
            return hash.ToString("x");
        }

        private static int GetHashCode(IEnumerable<string> strings)
        {
            int hash = -1397075115;
            var enumerator = strings.GetEnumerator();

            while(enumerator.MoveNext())
                hash ^= enumerator.Current.GetHashCode();
            return hash;
        }
    }
}