RelativeDate.swift

extension Date {

  var secondPassedFromNow: TimeInterval {
    return -timeIntervalSince(Date())
  }

  var relativeDate: String {
    // if second is negative, means its in future
    let seconds = secondPassedFromNow.rounded(.down)
    guard seconds >= 0 else { return "\(seconds)" }

    switch seconds {
    case 0..<60:
      return "\(Int(seconds))秒前"
    case 60..<3600:
      return "\(Int(seconds/60))分鐘前"
    case 3600..<86400:
      return "\(Int(seconds/3600))小時前"
    case 86400..<604800:
      return "\(Int(seconds/86400))天前"
    default:
      let formatter = DateFormatter()
      formatter.dateFormat = "MMM d yyyy"
      return formatter.string(from: self)
    }
  }

}


Date(timeInterval: -53.23, since: Date()).relativeDate // "53秒前"
Date(timeInterval: -2123.213213, since: Date()).relativeDate // "35分鐘前"
Date(timeInterval: -7300.2, since: Date()).relativeDate // "2小時前"
Date(timeInterval: -186400, since: Date()).relativeDate // "2天前"
Date(timeInterval: -2222253.23, since: Date()).relativeDate // "Jun 22 2018"