package com.infendro.encoding

import com.infendro.encoding.exception.IllegalByteException
import com.infendro.encoding.util.BigInt
import com.infendro.encoding.util.log2
import kotlin.math.ceil

class NumericEncoding internal constructor(
    override val alphabet: ByteArray,
) : Encoding {
    override fun encode(bytes: ByteArray): ByteArray {
        if (bytes.isEmpty()) return byteArrayOf()

        val size = ceil(bytes.size * 8 / log2(base)).toInt()
        val result = ByteArray(size)

        var i = result.size
        var x = BigInt.from(bytes)
        while (!x.isZero()) {
            val (quotient, remainder) = x.divRem(base)
            x = quotient
            result[--i] = alphabet[remainder]
        }

        return result.copyOfRange(i, result.size)
    }

    override fun decode(bytes: ByteArray): ByteArray {
        if (bytes.isEmpty()) return byteArrayOf()

        var value = BigInt.zero
        for (i in 0..<bytes.size) {
            val byte = bytes[i]

            val index = alphabet.indexOf(byte)
            if (index == -1) throw IllegalByteException(byte)

            value = value.timesAdd(base, index)
        }

        return value.toByteArray()
    }
}