package com.infendro.hash

import com.infendro.hash.util.ByteOrder.LITTLE_ENDIAN
import com.infendro.hash.util.addAll
import com.infendro.hash.util.toByteArray
import com.infendro.hash.util.toUIntArray

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

    private val s = arrayOf(
        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,
    )

    private val k = arrayOf(
        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,
    )

    override fun hash(
        value: ByteArray,
    ): ByteArray {
        var a0 = 0x67452301U
        var b0 = 0xefcdab89U
        var c0 = 0x98badcfeU
        var d0 = 0x10325476U
        val ml = value.size.toULong() * 8UL

        val paddedValue = buildList {
            addAll(value)
            add(0x80.toByte())
            while (size % 64 != 56) {
                add(0x00.toByte())
            }
            addAll(ml.toByteArray(LITTLE_ENDIAN))
        }

        val chunks = paddedValue
            .chunked(64)
        for (chunk in chunks) {
            val w = buildList {
                addAll(chunk.toUIntArray(LITTLE_ENDIAN))
            }

            var a = a0
            var b = b0
            var c = c0
            var d = d0

            for (i in 0..<64) {
                val f = when (i) {
                    in 0..15 -> (b and c) or (b.inv() and d)
                    in 16..31 -> (d and b) or (d.inv() and c)
                    in 32..47 -> b xor c xor d
                    else -> c xor (b or d.inv())
                }
                val g = when (i) {
                    in 0..15 -> i
                    in 16..31 -> (5 * i + 1) % 16
                    in 32..47 -> (3 * i + 5) % 16
                    else -> (7 * i) % 16
                }
                a = d
                d = c
                c = b
                b += (f + a + k[i] + w[g]).rotateLeft(s[i])
            }

            a0 += a
            b0 += b
            c0 += c
            d0 += d
        }

        return byteArrayOf(
            *a0.toByteArray(LITTLE_ENDIAN),
            *b0.toByteArray(LITTLE_ENDIAN),
            *c0.toByteArray(LITTLE_ENDIAN),
            *d0.toByteArray(LITTLE_ENDIAN),
        )
    }
}