defmodule BitcoinLib.Script.Opcodes.FlowControl.Return do
  @moduledoc """
  Based on https://en.bitcoin.it/wiki/Script

  Word OP_RETURN
  Opcode 106
  Hex 0x6a
  Input Nothing
  Output fail
  Description
    Marks transaction as invalid. Since bitcoin 0.9, a standard way of attaching extra data
    to transactions is to add a zero-value output with a scriptPubKey consisting of OP_RETURN
    followed by data. Such outputs are provably unspendable and specially discarded from
    storage in the UTXO set, reducing their cost to the network. Since 0.12, standard relay
    rules allow a single output with OP_RETURN, that contains any sequence of push statements
    (or OP_RESERVED[1]) after the OP_RETURN provided the total scriptPubKey length is at most
    83 bytes.

  """

  @behaviour BitcoinLib.Script.Opcode

  defstruct []

  alias BitcoinLib.Script.Opcodes.FlowControl.Return

  @value 0x6A

  @doc """
  Returns 0x6A

  ## Examples
      iex> BitcoinLib.Script.Opcodes.FlowControl.Return.v()
      0x6a
  """
  @spec v() :: 0x6A
  def v do
    @value
  end

  @doc """
  Returns <<0x6a>>

  ## Examples
      iex> BitcoinLib.Script.Opcodes.FlowControl.Return.encode()
      <<0x6a>>
  """
  @spec encode() :: <<_::8>>
  def encode() do
    <<@value::8>>
  end

  @doc """
  Marks transaction as invalid. Since bitcoin 0.9, a standard way of attaching extra data
  to transactions is to add a zero-value output with a scriptPubKey consisting of OP_RETURN
  followed by data. Such outputs are provably unspendable and specially discarded from
  storage in the UTXO set, reducing their cost to the network. Since 0.12, standard relay
  rules allow a single output with OP_RETURN, that contains any sequence of push statements
  (or OP_RESERVED[1]) after the OP_RETURN provided the total scriptPubKey length is at most
  83 bytes.

  ## Examples
      iex> stack = [3]
      ...> %BitcoinLib.Script.Opcodes.FlowControl.Return{}
      ...> |> BitcoinLib.Script.Opcodes.FlowControl.Return.execute(stack)
      {:error, "OP_RETURN has been hit"}
  """
  @spec execute(%Return{}, list()) :: {:error, binary()}
  def execute(%Return{}, _stack) do
    {:error, "OP_RETURN has been hit"}
  end
end