// .NET 8+. Paired scaffold; no networking or fabricated SDK.
// beginVerified owns an atomic transaction including verification, authority,
// state, challenge consumption and signed receipt. Dispose rolls back otherwise.
using System;
namespace BringPass.Draft;
public enum Op { REGISTER, USE, REVOKE, RETRACT }
public sealed record Envelope(string[] Fields, string Signature);
public sealed record Result(Envelope Receipt, bool Fresh);
public interface ITransaction : IDisposable {
  Op Operation { get; }
  Envelope? Cached();
  void RegisterNewKey(); void RequireCurrentEntitlement();
  void RevokeTarget(); void RetractRelationship();
  Envelope SignResult(); void CommitOnce(Envelope result);
}
public interface IPorts {
  Envelope Challenge(Op op, string rid, string target, string trustedContext);
  void VerifyProviderAndApprove(Envelope challenge);
  Envelope SignProof(Envelope challenge);
  void VerifyResultAndApply(Envelope result);
  ITransaction BeginVerified(Envelope proof, string trustedContext);
  Envelope RecoverRevoke(string rid, string target, string trustedContext);
}
public sealed class TokenSide(IPorts ports) {
  public Envelope Respond(Envelope challenge) {
    ports.VerifyProviderAndApprove(challenge); return ports.SignProof(challenge);
  }
  public void Accept(Envelope result) => ports.VerifyResultAndApply(result);
}
public sealed class ProviderSide(IPorts ports) {
  public Envelope Start(Op op, string rid, string target, string context) =>
    ports.Challenge(op, rid, target, context);
  public Result Finish(Envelope proof, string trustedContext) {
    using var tx = ports.BeginVerified(proof, trustedContext);
    var cached = tx.Cached();
    if (cached is not null) return new(cached, false);
    switch (tx.Operation) {
      case Op.REGISTER: tx.RegisterNewKey(); break;
      case Op.USE: tx.RequireCurrentEntitlement(); break;
      case Op.REVOKE: tx.RevokeTarget(); break;
      case Op.RETRACT: tx.RetractRelationship(); break;
      default: throw new InvalidOperationException("Unsupported operation");
    }
    var result = tx.SignResult(); tx.CommitOnce(result); return new(result, true);
  }
  public Envelope Lost(string rid, string target, string context) =>
    ports.RecoverRevoke(rid, target, context);
}
public static class Legacy {
  public static string Present(string value, bool approved, bool selected) {
    if (!approved || !selected || String.IsNullOrEmpty(value))
      throw new InvalidOperationException("Local approval/selection required");
    return value; // Only input to the approved renderer or existing NFC driver.
  }
}