Caeser Cipher

CaeserCipher.kt

class CaeserCipherTests {
    @Test
    fun `should decipher the caeser cipher`() {
        val alphabet = arrayOf("a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k", "l", "m", "n", "o", "p", "q", "r", "s", "t", "u", "v", "w", "x", "y", "z")
        assertThat(alphabet).hasSize(26)

        val cipher = "GBKXGMK UXOKTZ TKYZ XKYARZ"

        val possiblePlaintexts = mutableListOf<String>()
        val buffer = StringBuilder()
        for (shift in 1 .. alphabet.size) {
            for (char in cipher) {
                val substitute = if (char != ' ') {
                    var letterIndex = (alphabet.indexOf(char.toString().lowercase(Locale.getDefault())) - shift) % alphabet.size
                    if (letterIndex < 0) {
                        letterIndex += alphabet.size
                    }
                    alphabet[letterIndex]
                } else {
                    ' '
                }
                buffer.append(substitute)
            }
            possiblePlaintexts.add(buffer.toString())
            buffer.clear()
        }

        assertThat(possiblePlaintexts).containsAnyOf("average orient nest result")
    }
}