XYOracleNetwork/sdk-ble-flutter

@file:JvmName("Base58")

package network.xyo.ble.xyo_ble

/**
 * Base58 is a way to encode addresses (or arbitrary data) as alphanumeric strings.
 * Compared to base64, this encoding eliminates ambiguities created by O0Il and potential splits from punctuation
 *
 * The basic idea of the encoding is to treat the data bytes as a large number represented using
 * base-256 digits, convert the number to be represented using base-58 digits, preserve the exact
 * number of leading zeros (which are otherwise lost during the mathematical operations on the
 * numbers), and finally represent the resulting base-58 digits as alphanumeric ASCII characters.
 *
 * This is the Kotlin implementation of base58 - it is based implementation of base58 in java
 * in bitcoinj (https://bitcoinj.github.io) - thanks to  Google Inc. and Andreas Schildbach
 *
 */

import java.util.*

private const val ENCODED_ZERO = '1'
private const val CHECKSUM_SIZE = 4

private const val alphabet = "123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz"
private val alphabetIndices by lazy {
    IntArray(128) { alphabet.indexOf(it.toChar()) }
}

/**
 * Encodes the bytes as a base58 string (no checksum is appended).
 *
 * @return the base58-encoded string
 */
@kotlin.ExperimentalUnsignedTypes
fun ByteArray.toBase58String(): String {

    val input = copyOf(size) // since we modify it in-place
    if (input.isEmpty()) {
        return ""
    }
    // Count leading zeros.
    var zeros = 0
    while (zeros < input.size && input[zeros].toInt() == 0) {
        ++zeros
    }
    // Convert base-256 digits to base-58 digits (plus conversion to ASCII characters)
    val encoded = CharArray(input.size * 2) // upper bound
    var outputStart = encoded.size
    var inputStart = zeros
    while (inputStart < input.size) {
        encoded[--outputStart] = alphabet[divmod(input, inputStart.toUInt(), 256.toUInt(), 58.toUInt()).toInt()]
        if (input[inputStart].toInt() == 0) {
            ++inputStart // optimization - skip leading zeros
        }
    }
    // Preserve exactly as many leading encoded zeros in output as there were leading zeros in data.
    while (outputStart < encoded.size && encoded[outputStart] == ENCODED_ZERO) {
        ++outputStart
    }
    while (--zeros >= 0) {
        encoded[--outputStart] = ENCODED_ZERO
    }
    // Return encoded string (including encoded leading zeros).
    return String(encoded, outputStart, encoded.size - outputStart)
}

/**
 * Decodes the base58 string into a [ByteArray]
 *
 * @return the decoded data bytes
 * @throws NumberFormatException if the string is not a valid base58 string
 */
@kotlin.ExperimentalUnsignedTypes
@Throws(NumberFormatException::class)
fun String.fromBase58(): ByteArray {
    if (isEmpty()) {
        return ByteArray(0)
    }
    // Convert the base58-encoded ASCII chars to a base58 byte sequence (base58 digits).
    val input58 = ByteArray(length)
    for (i in 0 until length) {
        val c = this[i]
        val digit = if (c.toInt() < 128) alphabetIndices[c.toInt()] else -1
        if (digit < 0) {
            throw NumberFormatException("Illegal character $c at position $i")
        }
        input58[i] = digit.toByte()
    }
    // Count leading zeros.
    var zeros = 0
    while (zeros < input58.size && input58[zeros].toInt() == 0) {
        ++zeros
    }
    // Convert base-58 digits to base-256 digits.
    val decoded = ByteArray(length)
    var outputStart = decoded.size
    var inputStart = zeros
    while (inputStart < input58.size) {
        decoded[--outputStart] = divmod(input58, inputStart.toUInt(), 58.toUInt(), 256.toUInt()).toByte()
        if (input58[inputStart].toInt() == 0) {
            ++inputStart // optimization - skip leading zeros
        }
    }
    // Ignore extra leading zeroes that were added during the calculation.
    while (outputStart < decoded.size && decoded[outputStart].toInt() == 0) {
        ++outputStart
    }
    // Return decoded data (including original number of leading zeros).
    return Arrays.copyOfRange(decoded, outputStart - zeros, decoded.size)
}

/**
 * Divides a number, represented as an array of bytes each containing a single digit
 * in the specified base, by the given divisor. The given number is modified in-place
 * to contain the quotient, and the return value is the remainder.
 *
 * @param number     the number to divide
 * @param firstDigit the index within the array of the first non-zero digit
 * (this is used for optimization by skipping the leading zeros)
 * @param base       the base in which the number's digits are represented (up to 256)
 * @param divisor    the number to divide by (up to 256)
 * @return the remainder of the division operation
 */
@kotlin.ExperimentalUnsignedTypes
private fun divmod(number: ByteArray, firstDigit: UInt, base: UInt, divisor: UInt): UInt {
    // this is just long division which accounts for the base of the input digits
    var remainder = 0.toUInt()
    for (i in firstDigit until number.size.toUInt()) {
        val digit = number[i.toInt()].toUByte()
        val temp = remainder * base + digit
        number[i.toInt()] = (temp / divisor).toByte()
        remainder = temp % divisor
    }
    return remainder
}