DateIntervalで遊んだ（友達待ってる間の暇つぶし） #CodePiece

CodePiece.swift

import Foundation

extension Date {
    var elasticDateFormat: String {
        let calendar = Calendar.current
        let date = Date()
        let dateInterval = calendar.dateInterval(of: .month, for: self)

        if calendar.dateInterval(of: .day, for: self)!.contains(date) {
            return "HH:mm"
        } else if calendar.dateInterval(of: .month, for: self)!.contains(date) {
            return "M/d"
        } else {
            return "yyyy/MM/dd"
        }
    }

    func toString(format: String) -> String {
        let dateFormatter = DateFormatter()
        dateFormatter.dateFormat = format
        return dateFormatter.string(from: self)
    }
}

let date = Date().addingTimeInterval(-86401)
let format = date.elasticDateFormat
let string = date.toString(format: format)
print(string) // 1/3