using System;

using System.Threading.Tasks;

using System.Reflection;

using System.IO;

using System.Linq;

​

public class MailWrapper {

    public async Task Send(string recipientEmailAddress, string recipientDisplayName, string subject, string htmlBody) {}

}

​

public class Message

{

    public string To { get; set; }

    public string ToName { get; set; }

}

​

public abstract class MessageController<TMessage> where TMessage : Message

{

    private readonly MailWrapper _mailWrapper;

​

    protected abstract string TemplatePath { get; }

    protected abstract string Subject { get; }

​

    protected MessageController(MailWrapper mailWrapper)

    {

        _mailWrapper = mailWrapper;

    }

​

    public async Task Send(TMessage message) =>

        await _mailWrapper.Send(message.To, message.ToName, RenderSubject(message), await RenderEmail(message));

​

    private string RenderSubject(Message message) =>

        message.GetType().GetProperties().Aggregate(Subject, (current, property) =>

            current.Replace("{{" + property.Name + "}}", property.GetValue(message)?.ToString(),

                StringComparison.InvariantCultureIgnoreCase));

​

​

    public virtual async Task<string> RenderEmail(Message message) =>

        message.GetType().GetProperties().Aggregate(

            await new StreamReader(Assembly.GetExecutingAssembly().GetManifestResourceStream(TemplatePath)!)

                .ReadToEndAsync(),

            (current, property) =>

                current.Replace("{{" + property.Name + "}}", property.GetValue(message)?.ToString(),

                    StringComparison.InvariantCultureIgnoreCase));

}

​

public class ClaimMessage : Message

{

    public int ClaimId { get; set; }

}

​

public abstract class ClaimMessageController<TMessage> : MessageController<ClaimMessage>

{

    private readonly MailWrapper _mailWrapper;

​

​

    protected ClaimMessageController(MailWrapper mailWrapper) : base(mailWrapper)

    {

        _mailWrapper = mailWrapper;

    }

​

    public override Task<string> RenderEmail(TMessage message)

    {

        return base.RenderEmail(message);

    }

​

    public override async Task<string> RenderEmail(TMessage message) => (await base.RenderEmail((ClaimMessage)message)).Replace(

        "{{ClaimUrl}}", $"https://foo/claim/{((ClaimMessage)message).ClaimId}",

        StringComparison.InvariantCultureIgnoreCase);

}

​