package com.infendro.hash.sha1

import com.infendro.bytes.bytearray.copyInto
import com.infendro.bytes.intarray.copyInto
import com.infendro.bytes.ulong.copyInto
import com.infendro.hash.HashFunction
import com.infendro.hash.util.ceilPow2

object SHA1 : HashFunction {
    override val bytes: Int
        get() = 20

    override val block: Int
        get() = 64

    private val initial = uintArrayOf(
        0x67452301U, 0xefcdaB89U,
        0x98badcfeU, 0x10325476U,
        0xc3d2e1f0U,
    ).asIntArray()

    private val k = uintArrayOf(
        0x5a827999U, 0x6ed9eba1U,
        0x8f1bbcdcU, 0xca62c1d6U,
    ).asIntArray()

    override fun hashInto(value: ByteArray, destination: ByteArray) {
        val input = pad(value)
        val h = initial.copyOf()
        val w = IntArray(80)
        val v = IntArray(5)

        for (i in input.indices step block) {
            process(h, input, i, w, v)
        }
        h.copyInto(destination)
    }

    private fun pad(value: ByteArray): ByteArray {
        val length = value.size.toULong() * 8UL

        val size = ceilPow2(value.size + 9, block)
        val result = ByteArray(size)
        value.copyInto(result)
        result[value.size] = 0x80U.toByte()
        length.copyInto(result, result.size - 8)
        return result
    }

    private fun process(h: IntArray, value: ByteArray, offset: Int, w: IntArray, v: IntArray) {
        value.copyInto(w, startIndex = offset, endIndex = offset + block)
        for (i in 16..<80) {
            w[i] = (w[i - 3] xor w[i - 8] xor w[i - 14] xor w[i - 16]).rotateLeft(1)
        }
        h.copyInto(v)

        repeat(80) { i ->
            val f = when (i) {
                in 0..<20 -> (v[1] and v[2]) or (v[1].inv() and v[3])
                in 20..<40 -> v[1] xor v[2] xor v[3]
                in 40..<60 -> (v[1] and v[2]) or (v[1] and v[3]) or (v[2] and v[3])
                else -> v[1] xor v[2] xor v[3]
            }
            val temp = v[0].rotateLeft(5) + f + v[4] + k[i / 20] + w[i]
            v[4] = v[3]
            v[3] = v[2]
            v[2] = v[1].rotateLeft(30)
            v[1] = v[0]
            v[0] = temp
        }

        for (i in 0..<5) {
            h[i] += v[i]
        }
    }
}