import java.math.BigInteger
import java.nio.charset.StandardCharsets
/**
* Encodes a text string into its arbitrary-precision Base-36 string equivalent.
* * Algorithm:
* 1. Convert the input string into a raw byte array (base-256).
* 2. Parse the bytes as a positive BigInteger using signum = 1 (to avoid negative interpretation).
* 3. Convert the BigInteger directly to a Base-36 string representation via standard radix translation.
*/
fun encodeToBase36(text: String): String {
if (text.isEmpty()) return ""
// Convert string to bytes safely using UTF-8
val bytes = text.toByteArray(StandardCharsets.UTF_8)
// Construct a positive BigInteger out of the byte array magnitude
val bigInt = BigInteger(1, bytes)
// BigInteger natively handles radix conversion up to base 36
return bigInt.toString(36).uppercase()
}
/**
* Decodes a Base-36 encoded string back into its original text representation.
* * Algorithm:
* 1. Parse the Base-36 string into a BigInteger specifying radix 36.
* 2. Extract the underlying raw big-endian byte array.
* 3. Safely strip off any leading padding byte (0x00) which BigInteger sometimes appends to keep the sign bit positive.
*/
fun decodeFromBase36(encoded: String): String {
if (encoded.isEmpty()) return ""
// Parse the alphanumeric base-36 string back into a BigInteger
val bigInt = BigInteger(encoded, 36)
// toByteArray() returns a signed big-endian two's-complement byte array
val rawBytes = bigInt.toByteArray()
// If the leading byte is zero and it's not a standalone zero byte,
// it's an artificial sign-padding byte introduced by BigInteger. We slice it off.
val cleanBytes = if (rawBytes.isNotEmpty() && rawBytes[0] == 0.toByte() && rawBytes.size > 1) {
rawBytes.copyOfRange(1, rawBytes.size)
} else {
rawBytes
}
return String(cleanBytes, StandardCharsets.UTF_8)
}
fun main() {
val text = "Hello Universe!"
val encoded = encodeToBase36(text)
val decoded = decodeFromBase36(encoded)
println("Original: $text")
println("Base-36 encoded: $encoded")
println("Decoded: $decoded")
}
/*
run:
Original: Hello Universe!
Base-36 encoded: LP4N024HJ1YVBVD84Y8TYQP
Decoded: Hello Universe!
*/
