Mjml Email Templates

public interface IMjmlTemplateRenderer{    Task<string> RenderTemplateAsync(        string templateName,        IReadOnlyDictionary<string, string> variables,        CancellationToken ct = default);}
public sealed partial class MjmlTemplateRenderer : IMjmlTemplateRenderer{    private readonly MjmlRenderer _mjmlRenderer = new();    private readonly Assembly _assembly;    private readonly string _siteUrl;
    public MjmlTemplateRenderer(IConfiguration config)    {        _assembly = typeof(MjmlTemplateRenderer).Assembly;        _siteUrl = config["SiteUrl"] ?? "https://myapp.com";    }
    public async Task<string> RenderTemplateAsync(        string templateName,        IReadOnlyDictionary<string, string> variables,        CancellationToken ct = default)    {        // Load content template        var contentMjml = await LoadTemplateAsync(templateName, ct);
        // Load layout and inject content        var layoutMjml = await LoadTemplateAsync("_Layout", ct);        var combinedMjml = layoutMjml.Replace("{{Content}}", contentMjml);
        // Merge variables (layout + template-specific)        var allVariables = new Dictionary<string, string>        {            { "SiteUrl", _siteUrl }        };        foreach (var kvp in variables)            allVariables[kvp.Key] = kvp.Value;
        // Substitute variables        var processedMjml = SubstituteVariables(combinedMjml, allVariables);
        // Compile to HTML        var result = await _mjmlRenderer.RenderAsync(processedMjml, null, ct);
        if (result.Errors.Any())            throw new InvalidOperationException(                $"MJML compilation failed: {string.Join(", ", result.Errors.Select(e => e.Error))}");
        return result.Html;    }
    private async Task<string> LoadTemplateAsync(string templateName, CancellationToken ct)    {        var resourceName = $"MyApp.Infrastructure.Mailing.Templates.{templateName.Replace('/', '.')}.mjml";
        await using var stream = _assembly.GetManifestResourceStream(resourceName)            ?? throw new FileNotFoundException($"Template '{templateName}' not found");
        using var reader = new StreamReader(stream);        return await reader.ReadToEndAsync(ct);    }
    private static string SubstituteVariables(string mjml, IReadOnlyDictionary<string, string> variables)    {        return VariableRegex().Replace(mjml, match =>        {            var name = match.Groups[1].Value;            return variables.TryGetValue(name, out var value) ? value : match.Value;        });    }
    [GeneratedRegex(@"\{\{([^}]+)\}\}", RegexOptions.Compiled)]    private static partial Regex VariableRegex();}

public interface IUserEmailComposer{    Task<EmailMessage> ComposeSignupInvitationAsync(        EmailAddress recipientEmail,        PersonName recipientName,        PersonName inviterName,        OrganizationName organizationName,        AbsoluteUri invitationUrl,        DateTimeOffset expiresAt,        CancellationToken ct = default);}
public sealed class UserEmailComposer : IUserEmailComposer{    private readonly IMjmlTemplateRenderer _renderer;
    public UserEmailComposer(IMjmlTemplateRenderer renderer)    {        _renderer = renderer;    }
    public async Task<EmailMessage> ComposeSignupInvitationAsync(        EmailAddress recipientEmail,        PersonName recipientName,        PersonName inviterName,        OrganizationName organizationName,        AbsoluteUri invitationUrl,        DateTimeOffset expiresAt,        CancellationToken ct = default)    {        var variables = new Dictionary<string, string>        {            { "PreviewText", $"You've been invited to join {organizationName.Value}" },            { "InviteeName", recipientName.Value },            { "InviterName", inviterName.Value },            { "OrganizationName", organizationName.Value },            { "InvitationLink", invitationUrl.ToString() },            { "ExpirationDate", expiresAt.ToString("MMMM d, yyyy") }        };
        var html = await _renderer.RenderTemplateAsync(            "UserInvitations/UserSignupInvitation",            variables,            ct);
        return new EmailMessage(            To: recipientEmail,            Subject: $"You've been invited to join {organizationName.Value}",            HtmlBody: html);    }}

app.MapGet("/admin/emails/preview/{template}", async (    string template,    IMjmlTemplateRenderer renderer) =>{    var sampleVariables = GetSampleVariables(template);    var html = await renderer.RenderTemplateAsync(template, sampleVariables);
    return Results.Content(html, "text/html");}).RequireAuthorization("AdminOnly");

// DO: Use strongly-typed value objectsTask<EmailMessage> ComposeAsync(    EmailAddress to,    PersonName name,    AbsoluteUri actionUrl);
// DON'T: Use raw stringsTask<EmailMessage> ComposeAsync(    string email,    string name,    string url);