WebAPISignalRChat/Backend/Diligent.WebAPI.Host/Mediator/Notifications/Handlers/AddNotificationHandler.cs

using Diligent.WebAPI.Business.Interfaces;
using Diligent.WebAPI.Data.Entities;
using Diligent.WebAPI.Host.Exceptions;
using Diligent.WebAPI.Host.Mediator.Notifications.Commands;
using MediatR;

namespace Diligent.WebAPI.Host.Mediator.Notifications.Handlers
{
    public class AddNotificationHandler : IRequestHandler<AddNotificationCommand, Unit>
    {
        private readonly ICustomerService _customerService;

        public AddNotificationHandler(ICustomerService customerService)
        {
            _customerService = customerService;
        }

        public async Task<Unit> Handle(AddNotificationCommand request, CancellationToken cancellationToken)
        {
            var receiver = await _customerService.GetCustomerById(request.Notification.ReceiverId);

            if (receiver == null)
            {
                throw new NotFoundException();
            }

            var notificationExists = receiver.Notifications.Where(x => x.RoomId == request.Notification.RoomId).FirstOrDefault();
            
            if (notificationExists == null)
            {
                var notification = new Notification
                {
                    Count = 1,
                    RoomId = request.Notification.RoomId
                };

                receiver.Notifications.Add(notification);
            }
            else
            {
                notificationExists.Count++;
            }

            await _customerService.AddNotification(receiver);

            return new Unit();
        }
    }
}