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

using System.Text;
using DigitalData.EmailProfiler.Application.Common.Dtos;
using DigitalData.EmailProfiler.Application.Common.Interfaces;
using DigitalData.EmailProfiler.Domain.Exceptions;
using Limilabs.Client.SMTP;
using Limilabs.Mail;
using Limilabs.Mail.Headers;
using Microsoft.Extensions.Options;

namespace DigitalData.EmailProfiler.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;EmailAccountDto&gt; from appsettings.json.
/// </summary>
public class LimilabsEmailService(
    IEncryptionService encryptionService,
    IOptions<EmailAccountDto> smtpConfig) : IEmailService
{
    private readonly EmailAccountDto _smtpAccount = smtpConfig.Value;

    // Register encoding provider for Limilabs (requires windows-1252 and other code pages)
    static LimilabsEmailService()
    {
        Encoding.RegisterProvider(CodePagesEncodingProvider.Instance);
    }

    public async Task SendEmailAsync(string to, string subject, string body, bool isHtml = true, CancellationToken cancellationToken = default)
    {
        using var smtp = new Smtp();

        try
        {
            await ConnectAndAuthenticateSmtpAsync(smtp);

            var builder = new MailBuilder();
            builder.From.Add(new MailBox(_smtpAccount.Username));
            builder.To.Add(new MailBox(to));
            builder.Subject = subject;

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

            var mail = builder.Create();

            var result = smtp.SendMessage(mail);

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

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

    // --- Private Helper Methods ---

    private async Task ConnectAndAuthenticateSmtpAsync(Smtp smtp)
    {
        if (_smtpAccount.SmtpUseSsl)
        {
            smtp.ConnectSSL(_smtpAccount.SmtpServer, _smtpAccount.SmtpPort);
        }
        else
        {
            smtp.Connect(_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;

            smtp.Login(_smtpAccount.Username, password);
        }

        await Task.CompletedTask; // For async consistency
    }

    private static void DisconnectSafely(Smtp smtp)
    {
        try
        {
            if (smtp.Connected)
                smtp.Close();
        }
        catch { /* Ignore disconnect errors */ }
    }
}