投稿日時を「X年前,X時間前」とか分かりやすい文字列に変換する

func timeAgoString(postTimeInterval:TimeInterval)->String{
  guard timeInterval > 0 else{return ""}

  let now = Date()
  let postTime = Date(timeIntervalSince1970: postTimeInterval)

  let c = Calendar.current.dateComponents([.year, .month, .day, .hour, .minute, .second], from: postTime, to: now)

  if let year = c.year, year > 0 { return "\(year)年前" }
  else if let month = c.month, month > 0{ return "\(month)月前" }
  else if let day = c.day, Int(day/7) > 0{ return "\(Int(day/7))週前" }
  else if let day = c.day, day > 0{ return "\(day)日前" }
  else if let hour = c.hour, hour > 0{ return "\(hour)時間前" }
  else if let minute = c.minute, minute > 0{ return "\(minute)分前" }
  else if let second = c.second, second > 0{ return "\(second)秒前" }
  return "今"
}