// https://medium.com/@kevinrodrguez/enabling-email-verification-in-asp-net-core-identity-ui-2-1-b87f028a97e0

// To fix this, we will create a new Services folder in our project and inside of it, our EmailSender.cs service:
using Microsoft.AspNetCore.Identity.UI.Services;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;

namespace MailSenderApp.Services {
    public class EmailSender : IEmailSender {
        public Task SendEmailAsync(string email, string subject, string htmlMessage) {
            throw new NotImplementedException();
        }
    }
}

// ... Usings
using Microsoft.AspNetCore.Identity.UI.Services;
using MailSenderApp.Services;

namespace MailSenderApp {
    public class Startup {
        
        // ... Startup initializer and other methods
        
        public void ConfigureServices(IServiceCollection services)
        {
            // ... Other services
            services.AddDefaultIdentity<IdentityUser>().AddEntityFrameworkStores<ApplicationDbContext>();

            services.AddTransient<IEmailSender, EmailSender>();

            services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_1);
        }
    }
}


// Then, we are going to register our new service into the Dependency Injection bag by adding the following line of code to the 
// Startup.cs class of our project:
// services.AddTransient<IEmailSender, EmailSender>()

using Microsoft.AspNetCore.Identity.UI.Services;
using System;
using System.Collections.Generic;
using System.Net;
using System.Net.Mail;
using System.Text;
using System.Threading.Tasks;

namespace MailSenderApp.Services {
    public class EmailSender : IEmailSender {

        // Our private configuration variables
        private string host;
        private int port;
        private bool enableSSL;
        private string userName;
        private string password;
        
        // Get our parameterized configuration
        public EmailSender(string host, int port, bool enableSSL, string userName, string password) {
            this.host = host;
            this.port = port;
            this.enableSSL = enableSSL;
            this.userName = userName;
            this.password = password;
        }
        
        // Use our configuration to send the email by using SmtpClient
        public Task SendEmailAsync(string email, string subject, string htmlMessage) {
            var client = new SmtpClient(host, port) {
                Credentials = new NetworkCredential(userName, password),
                EnableSsl = enableSSL
            };
            return client.SendMailAsync(
                new MailMessage(userName, email, subject, htmlMessage) { IsBodyHtml = true }
            );
        }
    }
}


// appsettings.json
{
  "ConnectionStrings": {
    "DefaultConnection": "Server=myHost\\SQLINSTANCE;Database=myDataBase;Trusted_Connection=True;MultipleActiveResultSets=true"
  },
  "EmailSender": {
    "Host": "smtp.yourprovider.com",
    "Port": 587,
    "EnableSSL": true,
    "UserName": "your@username.com",
    "Password":  "Y0urP4ssw0rd!!!"
  },
  "Logging": {
    "LogLevel": {
      "Default": "Warning"
    }
  },
  "AllowedHosts": "*"
}

// And finally, we need to modify our Startup.cs to use our configuration from the appsettings.json file and passing it as parameters 
// to our EmailSender service:

using Microsoft.AspNetCore.Identity.UI.Services;
using MailSenderApp.Services;

namespace MailSenderApp {
    public class Startup {
        
        // ... Startup initializer and other methods
        
        public void ConfigureServices(IServiceCollection services)
        {
            // ... Other services
            services.AddDefaultIdentity<IdentityUser>().AddEntityFrameworkStores<ApplicationDbContext>();

            services.AddTransient<IEmailSender, EmailSender>(i => 
                new EmailSender(
                    Configuration["EmailSender:Host"],
                    Configuration.GetValue<int>("EmailSender:Port"),
                    Configuration.GetValue<bool>("EmailSender:EnableSSL"),
                    Configuration["EmailSender:UserName"],
                    Configuration["EmailSender:Password"]
                )
            );

            services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_1);
        }
    }
}