DigitalData.MessagingService/src/infrastructure/DigitalData.MessagingService.Infrastructure/Services/LimilabsEmailService.cs

using System.Text;
using DigitalData.MessagingService.Application.Common.Interfaces;
using DigitalData.MessagingService.Domain.Exceptions;
using Limilabs.Client.SMTP;
using Limilabs.Mail;
using Limilabs.Mail.Headers;
using DigitalData.MessagingService.Infrastructure.Services.Extensions;
using DigitalData.MessagingService.Abstraction;

namespace DigitalData.MessagingService.Infrastructure.Services;

/// <summary>
/// Email service using Limilabs Mail.dll for SMTP operations (send-only).
/// Commercial-grade library with superior Exchange support.
/// SMTP configuration is injected via IOptions&lt;EmailAccountsOptions&gt; from appsettings.json.
/// Uses the first account in the list whose <see cref="EmailAccountDto.Name"/> equals <c>"default"</c>,
/// or falls back to the first account if none is named "default".
/// </summary>
public class LimilabsEmailService(
    IEncryptionService encryptionService) : IEmailService
{
    // Register encoding provider for Limilabs (requires windows-1252 and other code pages)
    static LimilabsEmailService()
    {
        Encoding.RegisterProvider(CodePagesEncodingProvider.Instance);
    }

    public async Task SendEmailAsync(EmailAccountDto from, IEnumerable<string> recipients, string subject, string body, bool isHtml = true, CancellationToken cancellationToken = default)
    {
        using var smtp = new Smtp();

        try
        {
            await ConnectAndAuthenticateSmtpAsync(smtp, from);

            var builder = new MailBuilder();
            builder.From.Add(new MailBox(from.Username));

            foreach (var recipient in recipients)
                builder.To.Add(new MailBox(recipient));

            builder.Subject = subject;

            if (isHtml)
            {
                builder.Html = body;
            }
            else
            {
                builder.Text = body;
            }

            var mail = builder.Create();

            var result = await smtp.SendMessageAsync(mail, cancellationToken);

            if (result.Status != SendMessageStatus.Success)
            {
                throw new InvalidOperationException($"Failed to send email. Status: {result.Status}");
            }

            await smtp.CloseAsync(cancellationToken);
            await Task.CompletedTask; // For async consistency
        }
        catch (Limilabs.Client.ServerException ex)
        {
            await smtp.CloseSafelyAsync();
            throw new AuthenticationFailedException("SMTP authentication failed. Check credentials or OAuth2 configuration.", ex);
        }
        catch (Exception ex)
        {
            await smtp.CloseSafelyAsync();
            throw new InvalidOperationException("Failed to send email via SMTP server.", ex);
        }
    }

    private async Task ConnectAndAuthenticateSmtpAsync(Smtp smtp, EmailAccountDto smtpAccount)
    {
        if (smtpAccount.SmtpUseSsl)
        {
            await smtp.ConnectSSLAsync(smtpAccount.SmtpServer, smtpAccount.SmtpPort);
        }
        else
        {
            await smtp.ConnectAsync(smtpAccount.SmtpServer, smtpAccount.SmtpPort);
        }

        if (smtpAccount.UseOAuth2)
        {
            throw new NotSupportedException("OAuth2 is not configured for this SMTP account. UseOAuth2 must be false.");
        }
        else
        {
            var password = smtpAccount.PasswordEncrypted ? encryptionService.Decrypt(smtpAccount.Password) : smtpAccount.Password;

            await smtp.LoginAsync(smtpAccount.Username, password);
        }
    }
}