ChatHub.cs

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Threading.Tasks;
using ChatApp.API.Data;
using ChatApp.API.Models;
using Microsoft.AspNetCore.SignalR;

namespace ChatApp.API
{
    public class ChatHub : Hub
    {
        private readonly IChatRepository _repo;
        public ChatHub(IChatRepository repo)
        {
            _repo = repo;
        }

        public override async Task OnConnectedAsync()
        {
            // add user to users online on connect
            var httpContext = Context.GetHttpContext();
            var username = httpContext.Request.Query["name"];
            var connectionId = Context.ConnectionId;
            var userToAdd = new User
            {
                ConnectionId = connectionId,
                Username = username
            };

            var onlineUsers = await _repo.AddOnlineUser(userToAdd);
            await Clients.All.SendAsync("GetOnlineUsers", onlineUsers);

            var messages = await _repo.GetChatHistory();
            await Clients.Caller.SendAsync("ChatHistory", messages);
            await base.OnConnectedAsync();

        }

        public override async Task OnDisconnectedAsync(Exception exception)
        {
            // remove user from users online on disconnect
            var onlineUsers = await _repo.RemoveOnlineUser(Context.ConnectionId);            
            await Clients.All.SendAsync("GetOnlineUsers", onlineUsers);

            await base.OnDisconnectedAsync(exception);
        }

        public async Task SendMessage(string user, string message)
        {
            try
            {
                var msgToSave = new ChatMessage
                {
                    User = user,
                    Message = message,
                    Sent = DateTime.UtcNow
                };
                _repo.Add(msgToSave);
                await _repo.SaveAllAsync();

                await Clients.All.SendAsync("ReceiveMessage", msgToSave);
            }
            catch { }
        }

        public async Task GetHistory()
        {
            var messages = await _repo.GetChatHistory();
            await Clients.Caller.SendAsync("ChatHistory", messages);
        }
    }
}