// Swift 5.9+. BOTH peers, no transport or presumed smartcard capabilities.
// Ports implement the verified-transaction contract in examples/README.md.
// close() rolls back unless committed; cached retries must not repeat an actuation.
import Foundation

enum Op { case register, use, revoke, retract }
struct Envelope { let fields: [String]; let signature: String }
struct Outcome { let receipt: Envelope; let fresh: Bool }
enum DraftError: Error { case localApprovalRequired }
protocol Transaction {
  var operation: Op { get }
  func cached() -> Envelope?
  func registerNewKey() throws
  func requireCurrentEntitlement() throws
  func revokeTarget() throws
  func retractRelationship() throws
  func signResult() throws -> Envelope
  func commitOnce(_ result: Envelope) throws
  func close()
}
protocol Ports {
  func challenge(_ op: Op, _ rid: String, _ target: String, _ context: String) throws -> Envelope
  func verifyProviderAndApprove(_ challenge: Envelope) throws
  func signProof(_ challenge: Envelope) throws -> Envelope
  func verifyResultAndApply(_ result: Envelope) throws
  func beginVerified(_ proof: Envelope, _ context: String) throws -> any Transaction
  func recoverRevoke(_ rid: String, _ target: String, _ context: String) throws -> Envelope
}
struct TokenSide {
  let ports: any Ports
  func respond(_ q: Envelope) throws -> Envelope {
    try ports.verifyProviderAndApprove(q); return try ports.signProof(q)
  }
  func accept(_ result: Envelope) throws { try ports.verifyResultAndApply(result) }
}
struct ProviderSide {
  let ports: any Ports
  func start(_ op: Op, _ rid: String, _ target: String, _ context: String) throws -> Envelope {
    try ports.challenge(op,rid,target,context)
  }
  func finish(_ proof: Envelope, _ context: String) throws -> Outcome {
    let tx = try ports.beginVerified(proof,context); defer { tx.close() }
    if let old = tx.cached() { return Outcome(receipt: old,fresh: false) }
    switch tx.operation {
      case .register: try tx.registerNewKey()
      case .use: try tx.requireCurrentEntitlement()
      case .revoke: try tx.revokeTarget()
      case .retract: try tx.retractRelationship()
    }
    let result = try tx.signResult(); try tx.commitOnce(result)
    return Outcome(receipt: result,fresh: true)
  }
  func lost(_ rid: String, _ target: String, _ context: String) throws -> Envelope {
    try ports.recoverRevoke(rid,target,context)
  }
}
func legacyValue(_ value: String, approved: Bool, selected: Bool) throws -> String {
  guard approved && selected && !value.isEmpty else { throw DraftError.localApprovalRequired }
  return value // Renderer/standard driver input only.
}