package com.xsn.explorer.gcs

import com.google.common.primitives.Longs
import com.xsn.explorer.models.values.Blockhash

/**
 * Represents a SipHash key using a 128-bit value, compatible with Guava.
 *
 * @param k0 the first half of the key
 * @param k1 the second half of the key
 */
case class SipHashKey(k0: Long, k1: Long) {

  override def toString: String = {
    s"SipHashKey(${java.lang.Long.toUnsignedString(k0)}, ${java.lang.Long.toUnsignedString(k1)})"
  }
}

object SipHashKey {

  /**
   * Parses a SipHash key in the same way that the Btcutil (https://github.com/btcsuite/btcutil)
   * library does, which uses https://github.com/aead/siphash
   *
   * @param key 16 bytes representing the key
   */
  def fromBtcutil(key: List[Byte]): SipHashKey = {
    require(key.size == 16, "Invalid SipHash key, it must have 16 bytes")

    /**
     * the bytes are represented as a 128-bit encoded in little-endian
     * while guava parses the values in big-endian, that's the reason to reverse them.
     */
    val k0 = Longs.fromByteArray(key.take(8).reverse.toArray)
    val k1 = Longs.fromByteArray(key.drop(8).reverse.toArray)
    SipHashKey(k0, k1)
  }

  def fromBtcutil(hash: Blockhash): SipHashKey = {
    val bytes = hash
        .string
        .take(32)
        .grouped(2)
        .map { hex => Integer.parseInt(hex, 16).asInstanceOf[Byte] }
        .toList

    fromBtcutil(bytes)
  }
}