RpgRoller/RpgRoller/Api/StateEventEndpoints.cs

using RpgRoller.Contracts;
using RpgRoller.Services;

namespace RpgRoller.Api;

internal static class StateEventEndpoints
{
    public static RouteGroupBuilder MapStateEventEndpoints(this RouteGroupBuilder group)
    {
        group.MapGet("/events/state", async Task<IResult> (Guid campaignId, HttpContext context, IGameService game) =>
        {
            var sessionToken = context.GetRequiredSessionToken();
            var versionResult = game.GetCampaignVersion(sessionToken, campaignId);
            if (!versionResult.Succeeded)
            {
                return versionResult.Error!.Code == "unauthorized" ? TypedResults.Unauthorized() : TypedResults.BadRequest(new ApiError(versionResult.Error.Message));
            }

            context.Response.Headers.CacheControl = "no-cache";
            context.Response.Headers.Connection = "keep-alive";
            context.Response.ContentType = "text/event-stream";

            var lastVersion = versionResult.Value;
            await context.Response.WriteAsync($"event: state\ndata: {{\"campaignId\":\"{campaignId}\",\"version\":{lastVersion}}}\n\n");
            await context.Response.Body.FlushAsync();

            try
            {
                while (!context.RequestAborted.IsCancellationRequested)
                {
                    await Task.Delay(TimeSpan.FromSeconds(1), context.RequestAborted);

                    var currentVersionResult = game.GetCampaignVersion(sessionToken, campaignId);
                    if (!currentVersionResult.Succeeded)
                        break;

                    if (currentVersionResult.Value != lastVersion)
                    {
                        lastVersion = currentVersionResult.Value;
                        await context.Response.WriteAsync($"event: state\ndata: {{\"campaignId\":\"{campaignId}\",\"version\":{lastVersion}}}\n\n");
                    }
                    else
                        await context.Response.WriteAsync(": heartbeat\n\n");

                    await context.Response.Body.FlushAsync();
                }
            }
            catch (OperationCanceledException)
            {
            }

            return TypedResults.Empty;
        });

        return group;
    }
}