Nexus.Reader/src/NexusReader.Infrastructure/Handlers/UpdateReadingProgressCommandHandler.cs

using FluentResults;
using MediatR;
using Microsoft.AspNetCore.SignalR;
using Microsoft.EntityFrameworkCore;
using NexusReader.Application.Commands.Sync;
using NexusReader.Domain.Entities;
using NexusReader.Data.Persistence;
using NexusReader.Infrastructure.RealTime;

namespace NexusReader.Infrastructure.Handlers;

public class UpdateReadingProgressCommandHandler : IRequestHandler<UpdateReadingProgressCommand, Result>
{
    private readonly IDbContextFactory<AppDbContext> _dbContextFactory;
    private readonly IHubContext<SyncHub> _hubContext;

    public UpdateReadingProgressCommandHandler(
        IDbContextFactory<AppDbContext> dbContextFactory, 
        IHubContext<SyncHub> hubContext)
    {
        _dbContextFactory = dbContextFactory;
        _hubContext = hubContext;
    }

    public async Task<Result> Handle(UpdateReadingProgressCommand request, CancellationToken cancellationToken)
    {
        using var context = await _dbContextFactory.CreateDbContextAsync(cancellationToken);
        var user = await context.Users.FirstOrDefaultAsync(u => u.Id == request.UserId, cancellationToken);
        if (user == null)
        {
            return Result.Fail("User not found.");
        }

        var now = DateTime.UtcNow;
        user.LastReadPageId = request.PageId;
        user.LastReadAt = now;

        await context.SaveChangesAsync(cancellationToken);

        // Broadcast to other devices
        var group = _hubContext.Clients.Group($"User_{request.UserId}");
        
        if (!string.IsNullOrEmpty(request.ExcludedConnectionId))
        {
            await _hubContext.Clients
                .GroupExcept($"User_{request.UserId}", request.ExcludedConnectionId)
                .SendAsync("ProgressUpdated", request.PageId, now, cancellationToken);
        }
        else
        {
            await group.SendAsync("ProgressUpdated", request.PageId, now, cancellationToken);
        }

        return Result.Ok();
    }
}