print gregorian calendar year with japanease calendar year

jyear.swift

import Foundation
//
// print gregorian calendar year with japanease calendar year
// siwftc -o jyear jyear.swift
// ./jyear startYearInGregorianCalendar // (-length 10)
// ./jyear startYearInGregorianCalendar -length years
// ./jyear startYearInGregorianCalendar stopYearInGregorianCalendar
//
let japanease = Calendar(identifier: .japanese)
let gregorian = Calendar(identifier: .gregorian)

let locale = Locale(identifier: "ja")
let format = DateFormatter()
format.calendar = japanease
format.dateFormat = "Gy年"
format.locale = locale

func print(year:Int) {
    let comp = DateComponents(calendar: gregorian, era: 1, year: year, month: 1, day: 1)
    guard let date = comp.date else {
        return
    }

    let string = format.string(from: date)
    let gYear = gregorian.component(.year, from: date)
    print("\(gYear)年\t"+string)
}

func printYears(startYear:Int, stopYear:Int) {

    for year in startYear...stopYear {
	print(year:year)
    }

}

    var startYear = 2001
    var length = 10
    
    let argv = ProcessInfo.processInfo.arguments

//    print("count = \(argv.count)")

    if argv.count > 1 {
        let value = Int(argv[1])!
        if value < 2100 && value > 645 {
            startYear = value
        }
    }

    if argv.count > 2 {
        if argv[2] == "-length" {
            if argv.count > 3 {
                if let value = Int(argv[3]) {
                    if value > 0 {
                        length = value
                    }
                }
            }
        } else {
	        let value = Int(argv[2])!
		if value < 2100 && value > 645 {
	            let stopYear = value
	            if stopYear > startYear {
	                length = stopYear - startYear
		    }
		}
        }
    }

    printYears(startYear: startYear, stopYear: startYear+length)