package com.infendro.hash.keccak

import com.infendro.bytes.ByteOrder.LITTLE_ENDIAN
import com.infendro.bytes.bytearray.copyInto
import com.infendro.bytes.long.copyInto
import com.infendro.hash.HashFunction

open class Keccak(
    bytes: Int,
    private val rate: Int,
    private val domain: Byte,
) : HashFunction(bytes, rate) {
    init {
        require(bytes > 0)
        require(rate in 8..192 step 8)
    }

    private var state = LongArray(25)

    private val w = LongArray(block / 8)
    private val b = LongArray(25)
    private val c = LongArray(5)
    private val d = LongArray(5)

    override fun reset() {
        super.reset()
        state.fill(0L)
    }

    override fun process() {
        absorb(buffer.value)
        permute()
    }

    private fun finalize() {
        buffer.append(domain)
        if (buffer.free < 1) {
            process()
            buffer.reset()
        }
        buffer.jumpTo(block - 1)
        buffer.append(0x80.toByte())

        process()
    }

    override fun digestInto(destination: ByteArray, destinationOffset: Int) {
        finalize()
        squeeze(destination, destinationOffset)
        reset()
    }

    private fun absorb(block: ByteArray) {
        block.copyInto(w, order = LITTLE_ENDIAN)
        for (i in w.indices) {
            state[i] = state[i] xor w[i]
        }
    }

    private fun squeeze(destination: ByteArray, destinationOffset: Int) {
        val buffer = ByteArray(8)
        val threshold = rate / 8

        var consumed = 0
        var i = 0
        while (consumed < bytes) {
            if (i == threshold) {
                permute()
                i = 0
            }

            val length = minOf(bytes - consumed, 8)
            state[i].copyInto(buffer, order = LITTLE_ENDIAN)
            buffer.copyInto(destination, destinationOffset + consumed, endIndex = length)

            consumed += length
            i++
        }
    }

    private fun permute() = repeat(24) { round ->
        val a = state

        // θ
        for (x in 0..4) {
            c[x] = a[x] xor a[x + 5] xor a[x + 10] xor a[x + 15] xor a[x + 20]
        }
        for (x in 0..4) {
            d[x] = c[(x + 4) % 5] xor c[(x + 1) % 5].rotateLeft(1)
        }
        for (x in 0..4) for (y in 0..4) {
            a[x + 5 * y] = a[x + 5 * y] xor d[x]
        }

        // ρ and π
        for (x in 0..4) for (y in 0..4) {
            b[y + 5 * ((2 * x + 3 * y) % 5)] = a[x + 5 * y].rotateLeft(rotation[x][y])
        }

        // χ
        for (x in 0..4) for (y in 0..4) {
            a[x + 5 * y] = b[x + 5 * y] xor ((b[((x + 1) % 5) + 5 * y].inv()) and b[((x + 2) % 5) + 5 * y])
        }

        // ι
        a[0] = a[0] xor rc[round]
    }

    companion object {
        private val rc = longArrayOf(
            +0x0000000000000001, +0x0000000000008082, -0x7fffffffffff7f76, -0x7fffffff7fff8000,
            +0x000000000000808b, +0x0000000080000001, -0x7fffffff7fff7f7f, -0x7fffffffffff7ff7,
            +0x000000000000008a, +0x0000000000000088, +0x0000000080008009, +0x000000008000000a,
            +0x000000008000808b, -0x7fffffffffffff75, -0x7fffffffffff7f77, -0x7fffffffffff7ffd,
            -0x7fffffffffff7ffe, -0x7fffffffffffff80, +0x000000000000800a, -0x7fffffff7ffffff6,
            -0x7fffffff7fff7f7f, -0x7fffffffffff7f80, +0x0000000080000001, -0x7fffffff7fff7ff8,
        )

        private val rotation = arrayOf(
            intArrayOf(0, 36, 3, 41, 18),
            intArrayOf(1, 44, 10, 45, 2),
            intArrayOf(62, 6, 43, 15, 61),
            intArrayOf(28, 55, 25, 21, 56),
            intArrayOf(27, 20, 39, 8, 14),
        )
    }
}