package com.infendro.hash.md

import com.infendro.bytes.ByteOrder.LITTLE_ENDIAN
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.align

object MD5 : HashFunction {
    override val bytes: Int
        get() = 16

    override val block: Int
        get() = 64

    private val initial = uintArrayOf(
        0x67452301U, 0xefcdab89U,
        0x98badcfeU, 0x10325476U,
    ).asIntArray()

    private val c = uintArrayOf(
        0xd76aa478U, 0xe8c7b756U, 0x242070dbU, 0xc1bdceeeU,
        0xf57c0fafU, 0x4787c62aU, 0xa8304613U, 0xfd469501U,
        0x698098d8U, 0x8b44f7afU, 0xffff5bb1U, 0x895cd7beU,
        0x6b901122U, 0xfd987193U, 0xa679438eU, 0x49b40821U,
        0xf61e2562U, 0xc040b340U, 0x265e5a51U, 0xe9b6c7aaU,
        0xd62f105dU, 0x02441453U, 0xd8a1e681U, 0xe7d3fbc8U,
        0x21e1cde6U, 0xc33707d6U, 0xf4d50d87U, 0x455a14edU,
        0xa9e3e905U, 0xfcefa3f8U, 0x676f02d9U, 0x8d2a4c8aU,
        0xfffa3942U, 0x8771f681U, 0x6d9d6122U, 0xfde5380cU,
        0xa4beea44U, 0x4bdecfa9U, 0xf6bb4b60U, 0xbebfbc70U,
        0x289b7ec6U, 0xeaa127faU, 0xd4ef3085U, 0x04881d05U,
        0xd9d4d039U, 0xe6db99e5U, 0x1fa27cf8U, 0xc4ac5665U,
        0xf4292244U, 0x432aff97U, 0xab9423a7U, 0xfc93a039U,
        0x655b59c3U, 0x8f0ccc92U, 0xffeff47dU, 0x85845dd1U,
        0x6fa87e4fU, 0xfe2ce6e0U, 0xa3014314U, 0x4e0811a1U,
        0xf7537e82U, 0xbd3af235U, 0x2ad7d2bbU, 0xeb86d391U,
    ).asIntArray()

    private val shifts = intArrayOf(
        7, 12, 17, 22, 7, 12, 17, 22,
        7, 12, 17, 22, 7, 12, 17, 22,
        5, 9, 14, 20, 5, 9, 14, 20,
        5, 9, 14, 20, 5, 9, 14, 20,
        4, 11, 16, 23, 4, 11, 16, 23,
        4, 11, 16, 23, 4, 11, 16, 23,
        6, 10, 15, 21, 6, 10, 15, 21,
        6, 10, 15, 21, 6, 10, 15, 21,
    )

    override fun hashInto(value: ByteArray, destination: ByteArray, destinationOffset: Int) {
        val input = pad(value)
        val h = initial.copyOf()
        val w = IntArray(16)
        val v = IntArray(4)

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

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

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

    private fun process(h: IntArray, value: ByteArray, offset: Int, w: IntArray, v: IntArray) {
        value.copyInto(w, startIndex = offset, endIndex = offset + block, order = LITTLE_ENDIAN)
        h.copyInto(v)

        repeat(64) { i ->
            var f = when (i) {
                in 0..<16 -> (v[1] and v[2]) or (v[1].inv() and v[3])
                in 16..<32 -> (v[3] and v[1]) or (v[3].inv() and v[2])
                in 32..<48 -> v[1] xor v[2] xor v[3]
                else -> v[2] xor (v[1] or v[3].inv())
            }
            val g = when (i) {
                in 0..<16 -> i
                in 16..<32 -> (5 * i + 1) % 16
                in 32..<48 -> (3 * i + 5) % 16
                else -> (7 * i) % 16
            }
            f += v[0] + c[i] + w[g]
            v[0] = v[3]
            v[3] = v[2]
            v[2] = v[1]
            v[1] += f.rotateLeft(shifts[i])
        }

        for (i in 0..<4) {
            h[i] += v[i]
        }
    }
}