TimeWatcher.swift

/// Watcher for time measure.
///
/// ! Non thread safe
public class TimeWatcher {
  
  // MARK: - Static
  
  public enum Interval: UInt64 {
    case nanos = 1
    case mills = 1_000_000
    case seconds = 1_000_000_000
  }
  
  // MARK: - Private
  
  private static var currentMills: DispatchTime {
    return DispatchTime.now()
  }
  
  // MARK: - Instance variables

  var startTime: DispatchTime = TimeWatcher.currentMills
  
  // MARK: - Public

  public init() {
    self.startTime = TimeWatcher.currentMills
  }
  
  /// Resets initial time 
  public func start() {
    self.startTime = TimeWatcher.currentMills
  }
  
  /// Returns diff between initial time and now
  public func measure(_ interval: Interval = .mills) -> UInt64 {
    let diff = TimeWatcher.currentMills.rawValue - startTime.rawValue
    return UInt64(diff / interval.rawValue)
  }
}