using System.Threading.Channels;
public sealed record WorkRequest(int Value);
public sealed record WorkReceipt(int Value,int ScopeId);
public sealed record WorkMessage(int Value,CancellationToken Token) { public TaskCompletionSource<WorkReceipt> Completion { get; }=new(TaskCreationOptions.RunContinuationsAsynchronously); }
public sealed class WorkQueue {
    public Channel<WorkMessage> Items { get; }=Channel.CreateBounded<WorkMessage>(4);
}
public sealed class ScopeEvidence {
    private int created,disposed,live;
    public int Created=>Volatile.Read(ref created); public int Disposed=>Volatile.Read(ref disposed); public int Live=>Volatile.Read(ref live);
    public int Start() { Interlocked.Increment(ref live); return Interlocked.Increment(ref created); }
    public void End() { Interlocked.Decrement(ref live); Interlocked.Increment(ref disposed); }
}
public sealed class ScopedOperation : IAsyncDisposable {
    private readonly ScopeEvidence evidence; private int disposed; public int Id { get; }
    public ScopedOperation(ScopeEvidence evidence) { this.evidence=evidence; Id=evidence.Start(); }
    public async Task<WorkReceipt> ProcessAsync(int value,CancellationToken token) { await Task.Delay(2,token); return new(value*2,Id); }
    public ValueTask DisposeAsync() { if(Interlocked.Exchange(ref disposed,1)==0)evidence.End(); return ValueTask.CompletedTask; }
}
public sealed class ScopedWorker(WorkQueue queue,IServiceScopeFactory scopes) : BackgroundService {
    protected override async Task ExecuteAsync(CancellationToken stoppingToken) {
        await foreach(var item in queue.Items.Reader.ReadAllAsync(stoppingToken)) {
            using var owner=CancellationTokenSource.CreateLinkedTokenSource(stoppingToken,item.Token);
            try {
                WorkReceipt result;
                await using(var scope=scopes.CreateAsyncScope()) result=await scope.ServiceProvider.GetRequiredService<ScopedOperation>().ProcessAsync(item.Value,owner.Token);
                item.Completion.TrySetResult(result);
            } catch(OperationCanceledException) { item.Completion.TrySetCanceled(owner.Token); }
        }
    }
    public override async Task StopAsync(CancellationToken token) {
        queue.Items.Writer.TryComplete();
        try { if(ExecuteTask is not null) await ExecuteTask.WaitAsync(token); }
        finally { await base.StopAsync(token); }
    }
}
public static class WorkerLabs {
    public static void Map(WebApplication app) {
        app.MapPost("/worker",async(WorkRequest input,WorkQueue queue,CancellationToken token)=> {
            if(input.Value is <1 or >10)return Results.BadRequest(); var item=new WorkMessage(input.Value,token);
            if(!queue.Items.Writer.TryWrite(item))return Results.StatusCode(429);
            return Results.Ok(await item.Completion.Task.WaitAsync(token));
        });
        app.MapGet("/worker/evidence",(ScopeEvidence evidence)=>new { evidence.Created,evidence.Disposed,evidence.Live });
    }
}