You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: main.rs
    path of file: ./repos/darkfi/script/research/gg/src
    
    the code of the file until where you have to start completion: /* This file is part of DarkFi (https://dark.fi)
 *
 * Copyright (C) 2020-2024 Dyne.org foundation
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License as
 * published by the Free Software Foundation, either version 3 of the
 * License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Affero General Public License for more details.
 *
 * You should have received a copy of the GNU Affero General Public License
 * along with this program.  If not, see <https://www.gnu.org/licenses/>.
 */

use std::{
    fs::{read_dir, read_to_string},
    io::{stdin, Read},
};

use anyhow::Result;
use clap::{Parser, Subcommand};
use darkfi::{
    blockchain::{BlockInfo, Blockchain, BlockchainOverlay},
    cli_desc,
    tx::Transaction,
    util::{encoding::base64, path::expand_path, time::Timestamp},
    validator::verification::verify_genesis_block,
};
use darkfi_contract_test_harness::vks;
use darkfi_serial::{deserialize, serialize};

#[derive(Parser)]
#[command(about = cli_desc!())]
struct Args {
    #[command(subcommand)]
    command: Subcmd,
}

#[derive(Subcommand)]
enum Subcmd {
    /// Read a Darkfi genesis block from stdin and display it
    Display,

    /// Generate a Darkfi genesis block and write it to stdin
    Generate {
        #[arg(short, long, default_value = "genesis_txs")]
        /// Path to folder containing the genesis transactions
        txs_folder: String,

        #[arg(short, long)]
        /// Genesis timestamp to use, instead of current one
        genesis_timestamp: Option<u64>,
    },

    /// Read a Darkfi genesis block from stdin and verify it
    Verify,
}

/// Auxiliary function to read a bs58 genesis block from stdin
fn read_block() -> Result<BlockInfo> {
    eprintln!("Reading genesis block from stdin...");
    let mut buf = String::new();
    stdin().read_to_string(&mut buf)?;
    let bytes = base64::decode(buf.trim()).unwrap();
    let block = deserialize(&bytes)?;
    Ok(block)
}

#[async_std::mai
    
async fn main() -> Result<()> {
    // Parse arguments
    let args = Args::parse();

    // Execute a subcommand
    match args.command {
        Subcmd::Display => {
            let genesis_block = read_block()?;
            println!("{genesis_block:#?}");
            Ok(())
        }

        Subcmd::Generate { txs_folder, genesis_timestamp } => {
            // Grab genesis transactions from folder
            let txs_folder = expand_path(&txs_folder).unwrap();
            let mut genesis_txs: Vec<Transaction> = vec![];
            for file in read_dir(txs_folder)? {
                let bytes = base64::decode(read_to_string(file?.path())?.trim()).unwrap();
                let tx = deserialize(&bytes)?;
                genesis_txs.push(tx);
            }

            // Generate the genesis block
            let mut genesis_block = BlockInfo::default();

            // Update timestamp if one was provided
            if let Some(timestamp) = genesis_timestamp {
                genesis_block.header.timestamp = Timestamp(timestamp);
            }

            // Retrieve genesis producer transaction
            let producer_tx = genesis_block.txs.pop().unwrap();

            // Append genesis transactions
            if !genesis_txs.is_empty() {
                genesis_block.append_txs(genesis_txs)?;
            }
            genesis_block.append_txs(vec![producer_tx])?;

            // Write generated genesis block to stdin
            let encoded = base64::encode(&serialize(&genesis_block));
            println!("{encoded}");

            Ok(())
        }

        Subcmd::Verify => {
            let genesis_block = read_block()?;
            let hash = genesis_block.hash()?;

            println!("Verifying genesis block: {hash}");

            // Initialize a temporary sled database
            let sled_db = sled::Config::new().temporary(true).open()?;
            let (_, vks) = vks::get_cached_pks_and_vks()?;
            vks::inject(&sled_db, &vks)?;

            // Create an overlay over whole blockchain
            let blockchain = Blockchain::new(&sled_db)?;
            let overlay = BlockchainOverlay::new(&blockchain)?;

            verify_genesis_block(&overlay, &genesis_block).await?;

            println!("Genesis block {hash} verified successfully!");

            Ok(())
        }
    }
}