Technical test for Igloohome

CaesarCipher.kt

fun CaesarCipher(str: String, num: Int): String {
    val result = StringBuilder()
    for(i in str.indices) {
        if(str[i].toLowerCase() in 'a'..'z') {
            val a = 'a'.toLong()
            val A = 'A'.toLong()
            val shift = (str[i] + num).toLong()
            val letterLower = shift - a
            val letterUpper = shift - A
            val lower = ('z' + 1).toLong() - a
            val upper = ('Z' + 1).toLong() - A
            when {
                str[i].isLowerCase() && shift < a -> {
                    val position = (letterLower % lower)
                    result.append((if(position < 0) lower + position + a else position + a).toChar())
                }
                str[i].isUpperCase() && shift < a -> {
                    val position = (letterUpper % upper)
                    result.append((if(position < 0) upper + position + A else position + A).toChar())
                }
                str[i].isLowerCase() -> result.append(((letterLower % lower) + a).toChar())
                str[i].isUpperCase() -> result.append(((letterUpper % upper) + A).toChar())
                else -> result.append(str[i])
            }
        }
        else result.append(str[i])
    }

    return result.toString()
}