찍힌 그대로의 사실

/// Where a moment happened: one foreground sample, taken only while a
/// capture surface is open, and the place's name resolved on the device.
/// Never blocks a capture: no fix in a few seconds means no place.
@MainActor
final class PlaceSampler: NSObject, CLLocationManagerDelegate {
    private let manager = CLLocationManager()
    private var waiting: [CheckedContinuation<CLLocation?, Never>] = []

    override init() {
        super.init()
        manager.delegate = self
        manager.desiredAccuracy = kCLLocationAccuracyHundredMeters
    }

    /// Ask once, when the capture surface opens.
    func prepare() {
        if manager.authorizationStatus == .notDetermined { manager.requestWhenInUseAuthorization() }
    }

    func sample(timeout: Duration = .seconds(4)) async -> PlaceSample? {
        let status = manager.authorizationStatus
        guard status == .authorizedWhenInUse || status == .authorizedAlways else { return nil }
        let location: CLLocation? = await withCheckedContinuation { continuation in
            waiting.append(continuation)
            manager.requestLocation()
            Task { @MainActor in
                try? await Task.sleep(for: timeout)
                self.finish(nil)
            }
        }
        guard let location else { return nil }
        let name = await Self.placeName(location)
        return PlaceSample(lat: location.coordinate.latitude, lon: location.coordinate.longitude,
                           accuracyM: location.horizontalAccuracy >= 0 ? location.horizontalAccuracy : nil,
                           name: name, sampledAt: CaptureTruth.isoWithOffset(location.timestamp, zone: .current))
    }

    /// Capture truth from a photo's own clock when it has one, else now.
    static func truth(takenAt: String?, otherwise: CaptureTruth? = nil) -> CaptureTruth {
        guard let takenAt, CaptureTruth.instant(from: takenAt) != nil else { return otherwise ?? CaptureTruth.now() }
        return CaptureTruth(capturedAt: takenAt,
                            capturedLocalDate: String(takenAt.prefix(10)),
                            timezone: TimeZone.current.identifier)
    }

export interface CaptureTruth {
  captured_at: string;
  timezone: string;
  local_date: string;
}

function pad(value: number): string {
  return String(value).padStart(2, "0");
}

/** ISO 8601 with the device's own offset, plus its zone and local date. */
export function captureTruth(now: Date = new Date(), timezone?: string): CaptureTruth {
  const offsetMinutes = -now.getTimezoneOffset();
  const sign = offsetMinutes >= 0 ? "+" : "-";
  const abs = Math.abs(offsetMinutes);
  const local =
    `${now.getFullYear()}-${pad(now.getMonth() + 1)}-${pad(now.getDate())}` +
    `T${pad(now.getHours())}:${pad(now.getMinutes())}:${pad(now.getSeconds())}`;
  return {
    captured_at: `${local}${sign}${pad(Math.floor(abs / 60))}:${pad(abs % 60)}`,
    timezone: timezone ?? Intl.DateTimeFormat().resolvedOptions().timeZone ?? "UTC",
    local_date: local.slice(0, 10),
  };
}