defmodule BitcoinLib.Block do
  @moduledoc """
  Represents a Bitcoin Block

  Based on https://learnmeabitcoin.com/technical/block-header
  """
  defstruct [:header, transactions: []]

  alias BitcoinLib.Block
  alias BitcoinLib.Block.{Header, Transactions}

  @doc """
  Converts a hex binary into a %Block{}

  ## Examples
      Decode the genesis block

      iex> "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"
      ...> |> Binary.from_hex()
      ...> |> BitcoinLib.Block.decode()
      {
        :ok,
        %BitcoinLib.Block{
          header: %BitcoinLib.Block.Header{
            version: 1,
            previous_block_hash: <<0::256>>,
            merkle_root_hash: <<0x4a5e1e4baab89f3a32518a88c31bc87f618f76673e2cc77ab2127b7afdeda33b::256>>,
            time: ~U[2009-01-03 18:15:05Z],
            bits: 486604799,
            nonce: 2083236893
          },
          transactions: [
            %BitcoinLib.Transaction{
              version: 1,
              id: "4a5e1e4baab89f3a32518a88c31bc87f618f76673e2cc77ab2127b7afdeda33b",
              inputs: [
                %BitcoinLib.Transaction.Input{
                  txid: "0000000000000000000000000000000000000000000000000000000000000000",
                  vout: 0xffffffff,
                  script_sig: <<0x04ffff001d0104455468652054696d65732030332f4a616e2f32303039204368616e63656c6c6f72206f6e206272696e6b206f66207365636f6e64206261696c6f757420666f722062616e6b73::616>>,
                  sequence: 0xffffffff
                }
              ],
              outputs: [
                %BitcoinLib.Transaction.Output{
                  value: 5000000000,
                  script_pub_key: [
                    %BitcoinLib.Script.Opcodes.Data{value: <<0x04678afdb0fe5548271967f1a67130b7105cd6a828e03909a67962e0ea1f61deb649f6bc3f4cef38c4f35504e51ec112de5c384df7ba0b8d578a4c702b6bf11d5f::520>>},
                    %BitcoinLib.Script.Opcodes.Crypto.CheckSig{script: <<0x4104678afdb0fe5548271967f1a67130b7105cd6a828e03909a67962e0ea1f61deb649f6bc3f4cef38c4f35504e51ec112de5c384df7ba0b8d578a4c702b6bf11d5fac::536>>}
                  ]
                }
              ],
              locktime: 0,
              segwit?: false,
              coinbase?: true,
              witness: []
            }
          ]
        }
      }
  """
  @spec decode(binary()) :: {:ok, %Block{}} | {:error, binary()}
  def decode(<<header_data::bitstring-640, transactions_data::bitstring>>) do
    with {:ok, header} <- Header.decode(header_data),
         {:ok, transactions} <- Transactions.decode(transactions_data) do
      {:ok, %Block{header: header, transactions: transactions}}
    else
      {:error, message} -> {:error, message}
    end
  end
end