package gs.hex.v0

/** Type Class for decoding hexadecimal strings to some type.
  */
trait HexDecode[A]:
  /** Given some hexadecimal string representing encoded data, parse that string
    * to reconstruct that data.
    *
    * @param data
    *   The encoded hexadecimal string.
    * @return
    *   The decoded data, or nothing if the input is invalid.
    */
  def fromHexString(data: String): Option[A]

  extension (data: String) def fromHex(): Option[A] = fromHexString(data)

object HexDecode:

  /** Retrieve the [[HexDecode]] instance for the given type.
    *
    * @param H
    *   The type.
    * @return
    *   The [[HexDecode]] instance for the given type.
    */
  def apply[A](
    using
    H: HexDecode[A]
  ): HexDecode[A] = H

  given HexDecode[Array[Byte]] = new HexDecode[Array[Byte]] {

    /** @inheritDoc
      */
    def fromHexString(data: String): Option[Array[Byte]] =
      Hex.fromHexString(data)

  }

  given HexDecode[String] = new HexDecode[String] {

    /** @inheritDoc
      */
    def fromHexString(data: String): Option[String] =
      Hex.fromHexString(data).map(bytes => new String(bytes))

  }

  given HexDecode[Boolean] = new HexDecode[Boolean] {

    /** @inheritDoc
      */
    def fromHexString(data: String): Option[Boolean] =
      if data == "1" then Some(true)
      else if data == "0" then Some(false)
      else None

  }

  given HexDecode[Int] = new HexDecode[Int] {

    /** @inheritDoc
      */
    def fromHexString(data: String): Option[Int] =
      Hex.fromHexString(data).flatMap { bytes =>
        if bytes.length != 4 then None
        else Some(java.nio.ByteBuffer.wrap(bytes).getInt())
      }

  }

  given HexDecode[Long] = new HexDecode[Long] {

    /** @inheritDoc
      */
    def fromHexString(data: String): Option[Long] =
      Hex.fromHexString(data).flatMap { bytes =>
        if bytes.length != 8 then None
        else Some(java.nio.ByteBuffer.wrap(bytes).getLong())
      }

  }

end HexDecode