package com.infendro.hash.sha1

import com.infendro.bytearray.toUByteArray
import com.infendro.bytearray.toUIntArray
import com.infendro.hash.HashFunction

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

    override val block: Int
        get() = 64

    override fun hash(
        value: UByteArray,
    ): UByteArray {
        var h0 = 0x67452301U
        var h1 = 0xefcdaB89U
        var h2 = 0x98badcfeU
        var h3 = 0x10325476U
        var h4 = 0xc3d2e1f0U
        val ml = value.size.toULong() * 8UL

        val paddedValue = buildList {
            addAll(value)
            add(0x80U)
            while (size % 64 != 56) {
                add(0x00U)
            }
            addAll(ml.toUByteArray())
        }

        val chunks = paddedValue
            .chunked(64) { it.toUByteArray() }
        for (chunk in chunks) {
            val w = buildList {
                addAll(chunk.toUIntArray())
                for (i in 16..<80) {
                    val word = (get(i - 3) xor get(i - 8) xor get(i - 14) xor get(i - 16)).rotateLeft(1)
                    add(word)
                }
            }

            var a = h0
            var b = h1
            var c = h2
            var d = h3
            var e = h4

            for (i in 0..<80) {
                val f = when (i) {
                    in 0..<20 -> (b and c) or (b.inv() and d)
                    in 20..<40 -> b xor c xor d
                    in 40..<60 -> (b and c) or (b and d) or (c and d)
                    else -> b xor c xor d
                }
                val k = when (i) {
                    in 0..<20 -> 0x5a827999U
                    in 20..<40 -> 0x6ed9eba1U
                    in 40..<60 -> 0x8f1bbcdcU
                    else -> 0xca62c1d6U
                }
                val temp = a.rotateLeft(5) + f + e + k + w[i]
                e = d
                d = c
                c = b.rotateLeft(30)
                b = a
                a = temp
            }

            h0 += a
            h1 += b
            h2 += c
            h3 += d
            h4 += e
        }

        return ubyteArrayOf(
            *h0.toUByteArray(),
            *h1.toUByteArray(),
            *h2.toUByteArray(),
            *h3.toUByteArray(),
            *h4.toUByteArray(),
        )
    }
}