Kotlin - verify whether the time format is yyyy MM DD hh:mm:ss

Regular matching

fun valiDateTimeWithLongFormat(timeStr: String): Boolean {
        val format = "((19|20)[0-9]{2})-(0?[1-9]|1[012])-(0?[1-9]|[12][0-9]|3[01]) " + "([01]?[0-9]|2[0-3]):[0-5][0-9]:[0-5][0-9]"
        var pattern = Pattern.compile(format)
        var matcher = pattern.matcher(timeStr)
        if (matcher.matches()) {
            pattern = Pattern.compile("(\\d{4})-(\\d+)-(\\d+).*")
            matcher = pattern.matcher(timeStr)
            if (matcher.matches()) {
                val y = Integer.valueOf(matcher.group(1))
                val m = Integer.valueOf(matcher.group(2))
                val d = Integer.valueOf(matcher.group(3))
                if (d > 28) {
                    val c = Calendar.getInstance()
                    c.set(y, m - 1, 1)
                    val lastDay = c.getActualMaximum(Calendar.DAY_OF_MONTH)
                    return lastDay >= d
                }
            }
            return true
        }
        return false
    }