package com.infendro.hash.sha2

import com.infendro.bytes.bytearray.copyInto
import com.infendro.bytes.intarray.copyInto
import com.infendro.hash.HashFunction

class `SHA-256` : HashFunction(32, 64) {
    private val h = initial.copyOf()

    private val w = IntArray(64)
    private val v = IntArray(8)

    override fun reset() {
        super.reset()
        initial.copyInto(h)
    }

    override fun process() = process(buffer.value)

    private fun finalize() {
        buffer.append(0x80.toByte())
        if (buffer.free < 8) {
            process(buffer.value)
            buffer.reset()
        }
        buffer.jumpTo(56)
        buffer.append(length * 8)

        process(buffer.value)
    }

    override fun digestInto(destination: ByteArray, destinationOffset: Int) {
        finalize()
        h.copyInto(destination, destinationOffset)
        reset()
    }

    private fun process(block: ByteArray) {
        block.copyInto(w)
        for (i in 16..<64) {
            val s0 = w[i - 15].rotateRight(7) xor w[i - 15].rotateRight(18) xor (w[i - 15] ushr 3)
            val s1 = w[i - 2].rotateRight(17) xor w[i - 2].rotateRight(19) xor (w[i - 2] ushr 10)
            w[i] = (w[i - 16] + s0 + w[i - 7] + s1)
        }
        h.copyInto(v)

        repeat(64) { i ->
            val s0 = v[0].rotateRight(2) xor v[0].rotateRight(13) xor v[0].rotateRight(22)
            val s1 = v[4].rotateRight(6) xor v[4].rotateRight(11) xor v[4].rotateRight(25)
            val ch = (v[4] and v[5]) xor (v[4].inv() and v[6])
            val temp1 = v[7] + s1 + ch + c[i] + w[i]
            val maj = (v[0] and v[1]) xor (v[0] and v[2]) xor (v[1] and v[2])
            val temp2 = s0 + maj

            v[7] = v[6]
            v[6] = v[5]
            v[5] = v[4]
            v[4] = v[3] + temp1
            v[3] = v[2]
            v[2] = v[1]
            v[1] = v[0]
            v[0] = temp1 + temp2
        }

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

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

        internal val c = intArrayOf(
            +0x428a2f98, +0x71374491, -0x4a3f0431, -0x164a245b, +0x3956c25b, +0x59f111f1, -0x6dc07d5c, -0x54e3a12b,
            -0x27f85568, +0x12835b01, +0x243185be, +0x550c7dc3, +0x72be5d74, -0x7f214e02, -0x6423f959, -0x3e640e8c,
            -0x1b64963f, -0x1041b87a, +0x0fc19dc6, +0x240ca1cc, +0x2de92c6f, +0x4a7484aa, +0x5cb0a9dc, +0x76f988da,
            -0x67c1aeae, -0x57ce3993, -0x4ffcd838, -0x40a68039, -0x391ff40d, -0x2a586eb9, +0x06ca6351, +0x14292967,
            +0x27b70a85, +0x2e1b2138, +0x4d2c6dfc, +0x53380d13, +0x650a7354, +0x766a0abb, -0x7e3d36d2, -0x6d8dd37b,
            -0x5d40175f, -0x57e599b5, -0x3db47490, -0x3893ae5d, -0x2e6d17e7, -0x2966f9dc, -0x0bf1ca7b, +0x106aa070,
            +0x19a4c116, +0x1e376c08, +0x2748774c, +0x34b0bcb5, +0x391c0cb3, +0x4ed8aa4a, +0x5b9cca4f, +0x682e6ff3,
            +0x748f82ee, +0x78a5636f, -0x7b3787ec, -0x7338fdf8, -0x6f410006, -0x5baf9315, -0x41065c09, -0x398e870e,
        )
    }
}