Notes/NoteHub.cs

using BinaryDad.Notes.Services;
using Microsoft.AspNetCore.Authorization;
using Microsoft.AspNetCore.SignalR;

namespace BinaryDad.Notes
{
    [Authorize]
    public class NoteHub : Hub
    {
        private readonly INoteService noteService;
        private readonly ILogger<NoteHub> logger;

        public NoteHub(INoteService noteService, ILogger<NoteHub> logger)
        {
            this.noteService = noteService;
            this.logger = logger;
        }

        public override Task OnConnectedAsync()
        {
            var noteName = Context.GetHttpContext().Request.Query["noteName"];

            NoteContext.ClientNotes[Context.ConnectionId] = noteName;

            return base.OnConnectedAsync();
        }

        public async Task SaveNote(string content, string noteName)
        {
            try
            {
                noteService.SaveNote(content, noteName);

                // find all other connections except for the current one
                var clientConnections = NoteContext.ClientNotes
                    .Where(c => c.Value == noteName && c.Key != Context.ConnectionId)
                    .Select(c => c.Key)
                    .ToList();

                // update note for all other clients
                await Clients
                    .Clients(clientConnections)
                    .SendAsync("updateNote", content);

                logger.LogInformation($"Note \"{noteName}\" saved! Updated {clientConnections.Count} other client(s).");
            }
            catch (Exception ex)
            {
                logger.LogError($"Unable to save note \"{noteName}\" => {ex}");
            }
        }
    }
}