package com.infendro.kdf

import com.infendro.bytes.bytearray.xorInto
import com.infendro.bytes.int.copyInto
import com.infendro.hash.HashFunction
import com.infendro.kdf.util.ceilDiv
import com.infendro.mac.HMAC

class PBKDF2(
    override val bytes: Int,
    private val iterations: Int,
    function: HashFunction,
) : KDF {
    init {
        require(bytes > 0)
        require(iterations > 0)
    }

    private val hmac = HMAC(function)

    override fun hashInto(value: ByteArray, salt: ByteArray, destination: ByteArray, destinationOffset: Int) {
        for (iteration in 1..bytes.ceilDiv(hmac.bytes)) {
            val offset = (iteration - 1) * hmac.bytes
            val block = minOf(bytes - offset, hmac.bytes)

            val s = ByteArray(salt.size + 4)
            salt.copyInto(s)
            iteration.copyInto(s, salt.size)

            val buffer = hmac.hash(value, s)
            buffer.copyInto(destination, destinationOffset + offset, endIndex = block)
            repeat(iterations - 1) {
                hmac.hashInto(value, buffer, buffer)
                buffer.xorInto(destination, destinationOffset + offset, endIndex = block)
            }
        }
    }
}