package com.infendro.hash.blake2

import com.infendro.bytes.ByteOrder.LITTLE_ENDIAN
import com.infendro.bytes.bytearray.toIntArray
import com.infendro.bytes.intarray.toByteArray
import com.infendro.hash.HashFunction
import com.infendro.hash.util.align

class Blake2s(
    override val bytes: Int,
) : HashFunction {
    init {
        require(bytes in 1..32)
    }

    override val block: Int
        get() = 64

    private val initial = intArrayOf(
        +0x6a09e667, -0x4498517b,
        +0x3c6ef372, -0x5ab00ac6,
        +0x510e527f, -0x64fa9774,
        +0x1f83d9ab, +0x5be0cd19,
    )

    private val sigma = arrayOf(
        intArrayOf(0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15),
        intArrayOf(14, 10, 4, 8, 9, 15, 13, 6, 1, 12, 0, 2, 11, 7, 5, 3),
        intArrayOf(11, 8, 12, 0, 5, 2, 15, 13, 10, 14, 3, 6, 7, 1, 9, 4),
        intArrayOf(7, 9, 3, 1, 13, 12, 11, 14, 2, 6, 5, 10, 4, 0, 15, 8),
        intArrayOf(9, 0, 5, 7, 2, 4, 10, 15, 14, 1, 11, 12, 6, 8, 3, 13),
        intArrayOf(2, 12, 6, 10, 0, 11, 8, 3, 4, 13, 7, 5, 15, 14, 1, 9),
        intArrayOf(12, 5, 1, 15, 14, 13, 4, 10, 0, 7, 6, 3, 9, 2, 8, 11),
        intArrayOf(13, 11, 7, 14, 12, 1, 3, 9, 5, 0, 15, 4, 8, 6, 2, 10),
        intArrayOf(6, 15, 14, 9, 11, 3, 0, 8, 12, 2, 13, 7, 1, 4, 10, 5),
        intArrayOf(10, 2, 8, 4, 7, 6, 1, 5, 15, 11, 9, 14, 3, 12, 13, 0),
    )

    override fun hashInto(value: ByteArray, destination: ByteArray, destinationOffset: Int) {
        val length = value.size.toULong()
        val input = pad(value)
        val h = initial.copyOf()
        h[0] = h[0] xor (0x01010000 or bytes)
        var t = 0U

        for (i in input.indices step block) {
            t += minOf(length - t, 64UL).toUInt()
            val block = input.sliceArray(i..<(i + block))
            compress(h, block, t, t < 1024UL)
        }
        h.toByteArray(LITTLE_ENDIAN).copyInto(destination, destinationOffset, endIndex = bytes)
    }

    private fun pad(value: ByteArray): ByteArray {
        val size = maxOf(value.size.align(block), block)
        return ByteArray(size).also {
            value.copyInto(it)
        }
    }

    private fun compress(h: IntArray, block: ByteArray, t: UInt, last: Boolean) {
        val m = block.toIntArray()
        val v = IntArray(16)
        for (i in 0..<8) v[i] = h[i]
        for (i in 0..<8) v[i + 8] = initial[i]
        v[12] = v[12] xor t.toInt()
        if (last) v[14] = v[14].inv()

        repeat(10) { r ->
            val s = sigma[r]

            mix(v, 0, 4, 8, 12, m[s[0]], m[s[1]])
            mix(v, 1, 5, 9, 13, m[s[2]], m[s[3]])
            mix(v, 2, 6, 10, 14, m[s[4]], m[s[5]])
            mix(v, 3, 7, 11, 15, m[s[6]], m[s[7]])

            mix(v, 0, 5, 10, 15, m[s[8]], m[s[9]])
            mix(v, 1, 6, 11, 12, m[s[10]], m[s[11]])
            mix(v, 2, 7, 8, 13, m[s[12]], m[s[13]])
            mix(v, 3, 4, 9, 14, m[s[14]], m[s[15]])
        }

        for (i in 0..<8) {
            h[i] = h[i] xor v[i] xor v[i + 8]
        }
    }

    private fun mix(v: IntArray, a: Int, b: Int, c: Int, d: Int, x: Int, y: Int) {
        v[a] += v[b] + x
        v[d] = (v[d] xor v[a]).rotateRight(16)
        v[c] += v[d]
        v[b] = (v[b] xor v[c]).rotateRight(12)
        v[a] += v[b] + y
        v[d] = (v[d] xor v[a]).rotateRight(8)
        v[c] += v[d]
        v[b] = (v[b] xor v[c]).rotateRight(7)
    }
}