위치도 없이 "응"이라고 한 날

import Foundation

// "Am I on the right road?" answered only from evidence fresh enough to count.
// The report is the shape Pathfinder sends beside each fix, cut to three fields.

enum NavState: String { case idle, guiding, offRoute = "off_route", rerouting, arrived }

struct NavReport {
  var state: NavState
  var offRouteMetres: Double?
  var updatedAt: Date
}

enum Answer: CustomStringConvertible {
  case onRoute(age: Int)
  case offRoute(metres: Int?, age: Int)
  case arrived
  case cannotKnow(String)

  var description: String {
    switch self {
    case .onRoute(let age): "Yes. The route matches you (report \(age) s old)."
    case .offRoute(let metres, let age):
      "No. You left the planned route\(metres.map { " by about \($0) m" } ?? "") (report \(age) s old)."
    case .arrived: "You're there."
    case .cannotKnow(let why): "I can't tell: \(why). Where are you?"
    }
  }
}

let maxAge: TimeInterval = 120  // older than this, a report is history

func rightRoad(_ report: NavReport?, now: Date) -> Answer {
  guard let report else { return .cannotKnow("no navigation report reached me") }
  let age = now.timeIntervalSince(report.updatedAt)
  guard abs(age) <= maxAge else { return .cannotKnow("the last report is \(Int(age)) s old") }
  switch report.state {
  case .guiding: return .onRoute(age: Int(age))
  case .offRoute, .rerouting: return .offRoute(metres: report.offRouteMetres.map { Int($0) }, age: Int(age))
  case .arrived: return .arrived
  case .idle: return .cannotKnow("nothing is being guided")
  }
}

let now = Date()
let cases: [(String, NavReport?)] = [
  ("no report", nil),
  ("stale", NavReport(state: .guiding, updatedAt: now.addingTimeInterval(-600))),
  ("guiding", NavReport(state: .guiding, updatedAt: now.addingTimeInterval(-12))),
  ("off route", NavReport(state: .offRoute, offRouteMetres: 84, updatedAt: now.addingTimeInterval(-5))),
]
for (name, report) in cases {
  print("\(name.padding(toLength: 10, withPad: " ", startingAt: 0)) -> \(rightRoad(report, now: now))")
}

// Output:
// no report  -> I can't tell: no navigation report reached me. Where are you?
// stale      -> I can't tell: the last report is 600 s old. Where are you?
// guiding    -> Yes. The route matches you (report 12 s old).
// off route  -> No. You left the planned route by about 84 m (report 5 s old).

def active_navigation(
    now: datetime | None = None, max_age: float = NAV_MAX_AGE_S,
) -> tuple[str, dict[str, Any]] | None:
    """The freshest report of a drive in progress (not idle, not older than
    ``max_age``), as (reporter, report)."""
    now = now or datetime.now(timezone.utc)
    best_row: tuple[str, dict[str, Any]] | None = None
    best_at: datetime | None = None
    for key, nav in navigation_reports().items():
        if nav.get("state") == "idle":
            continue
        updated = parse_stamp(nav.get("updated_at"))
        if updated is None or abs((now - updated).total_seconds()) > max_age:
            continue
        if best_at is None or updated > best_at:
            best_row, best_at = (key, nav), updated
    return best_row