.map(|txin| {
                  self.transactions[&txin.previous_output.txid].output
                    [txin.previous_output.vout as usize]
                    .value
                })
                .sum::<u64>()
                - tx.output.iter().map(|txout| txout.value).sum::<u64>();
              self.transactions.insert(tx.txid(), tx.clone());

              fee
            })
            .sum::<u64>(),
        script_pubkey: ScriptBuf::new(),
      }],
    };

    self.transactions.insert(coinbase.txid(), coinbase.clone());

    let block = Block {
      header: Header {
        version: Version::ONE,
        prev_blockhash: *self.hashes.last().unwrap(),
        merkle_root: TxMerkleNode::all_zeros(),
        time: self.blocks.len().try_into().unwrap(),
        bits: CompactTarget::from_consensus(0),
        nonce: self.nonce,
      },
      txdata: std::iter::once(coinbase)
        .chain(self.mempool.drain(0..))
        .collect(),
    };

    for tx in block.txdata.iter() {
      for input in tx.input.iter() {