kotlin implementation to read Hearthstone Deck Strings

DeckStringDecoder.kt

typealias Cards = Map<Int, Int>

data class Deck(val version: Int, val format: Int, val cards: Cards, val heros: List<Int>)

fun ByteArrayInputStream.readVarInt() = getVarInt(this)

fun decodeDeckString(deckString: String): Deck {
    val bytes = Base64.decodeBase64(deckString)
    val byteStream = ByteArrayInputStream(bytes)

    //Zero byte
    byteStream.read()

    //Version - currently unused, always 1
    val version = byteStream.readVarInt()

    //Format - determined dynamically
    val format = byteStream.readVarInt()

    //Num Heroes - always 1
    val numHeros = byteStream.readVarInt()
    val heros = IntRange(0, numHeros - 1).map { byteStream.readVarInt() }

    val cards = HashMap<Int, Int>()

    // Read Single Cards
    val singleCardCount = byteStream.readVarInt()
    repeat(singleCardCount) {
        val id = byteStream.readVarInt()

        // add card with quantity of 1
        cards.put(id, 1)
    }

    // Read Double Cards
    val doubleCardCount = byteStream.readVarInt()

    repeat(doubleCardCount) {
        val id = byteStream.readVarInt()

        // add card with quantity of 2
        cards.put(id, 2)
    }

    // Read Multi Cards
    val multiCardCount = byteStream.readVarInt()
    repeat(multiCardCount) {
        val id = byteStream.readVarInt()
        val count = byteStream.readVarInt()

        // add card with quantity of count
        cards.put(id, count)
    }

    return Deck(version, format, cards, heros)
}

@Throws(IOException::class)
private fun getVarInt(inputStream: InputStream): Int {
    var result = 0
    var shift = 0
    var b: Int
    do {
        if (shift >= 32) {
            // Out of range
            throw IndexOutOfBoundsException("varint too long")
        }
        // Get 7 bits from next byte
        b = inputStream.read()
        result = result or (b and 0x7F shl shift)
        shift += 7
    } while (b and 0x80 != 0)
    return result
}