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/bin/vanityaddr/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::{
    process::{exit, ExitCode},
    sync::{mpsc::channel, Arc},
    thread::available_parallelism,
};

use arg::Args;
use darkfi::{util::cli::ProgressInc, ANSI_LOGO};
use darkfi_money_contract::model::TokenId;
use darkfi_sdk::crypto::{ContractId, PublicKey, SecretKey};
use rand::rngs::OsRng;
use rayon::iter::ParallelIterator;

const ABOUT: &str =
    concat!("vanityaddr ", env!("CARGO_PKG_VERSION"), '\n', env!("CARGO_PKG_DESCRIPTION"));

const USAGE: &str = r#"
Usage: vanityaddr [OPTIONS] <PREFIX> <PREFIX> ...

Arguments:
  <PREFIX>    Prefixes to search

Options:
  -c    Make the search case-sensitive
  -t    Number of threa
    
fn main() -> ExitCode {
    let argv;
    let mut hflag = false;
    let mut cflag = false;
    let mut addrflag = false;
    let mut toknflag = false;
    let mut ctrcflag = false;

    let mut n_threads = available_parallelism().unwrap().get();

    {
        let mut args = Args::new().with_cb(|args, flag| match flag {
            'c' => cflag = true,
            'A' => addrflag = true,
            'T' => toknflag = true,
            'C' => ctrcflag = true,
            't' => n_threads = args.eargf().parse::<usize>().unwrap(),
            _ => hflag = true,
        });

        argv = args.parse();
    }

    if hflag || argv.is_empty() {
        usage();
        return ExitCode::FAILURE
    }

    if (addrflag as u8 + toknflag as u8 + ctrcflag as u8) != 1 {
        eprintln!("The search flags are mutually exclusive. Use only one of -A/-C/-T.");
        return ExitCode::FAILURE
    }

    // Validate search prefixes
    for (idx, prefix) in argv.iter().enumerate() {
        match bs58::decode(prefix).into_vec() {
            Ok(_) => {}
            Err(e) => {
                eprintln!("Error: Invalid base58 for prefix #{}: {}", idx, e);
                return ExitCode::FAILURE
            }
        }
    }

    // Handle SIGINT
    let (tx, rx) = channel();
    ctrlc::set_handler(move || tx.send(()).expect("Could not send signal on channel"))
        .expect("Error setting SIGINT handler");

    // Something fancy
    let progress = Arc::new(ProgressInc::new());

    // Threadpool
    let progress_ = progress.clone();
    let rayon_pool = rayon::ThreadPoolBuilder::new().num_threads(n_threads).build().unwrap();
    rayon_pool.spawn(move || {
        if addrflag {
            let addr = rayon::iter::repeat(DrkAddr::new)
                .inspect(|_| progress_.inc(1))
                .map(|create| create())
                .find_any(|address| address.starts_with_any(&argv, cflag))
                .expect("Failed to find an address match");

            // The above will keep running until it finds a match or until
            // the program terminates. Only if a match is found shall the
            // following code be executed and the program exit successfully:
            let attempts = progress_.position();
            progress_.finish_and_clear();

            println!(
                "{{\"address\":\"{}\",\"attempts\":{},\"secret\":\"{}\"}}",
                addr.public, attempts, addr.secret,
            );
        }

        if toknflag {
            let tid = rayon::iter::repeat(DrkToken::new)
                .inspect(|_| progress_.inc(1))
                .map(|create| create())
                .find_any(|token_id| token_id.starts_with_any(&argv, cflag))
                .expect("Failed to find a token ID match");

            let attempts = progress_.position();
            progress_.finish_and_clear();

            println!(
                "{{\"token_id\":\"{}\",\"attempts\":{},\"secret\":\"{}\"}}",
                tid.token_id, attempts, tid.secret,
            );
        }

        if ctrcflag {
            let cid = rayon::iter::repeat(DrkContract::new)
                .inspect(|_| progress_.inc(1))
                .map(|create| create())
                .find_any(|contract_id| contract_id.starts_with_any(&argv, cflag))
                .expect("Failed to find a contract ID match");

            let attempts = progress_.position();
            progress_.finish_and_clear();

            println!(
                "{{\"contract_id\":\"{}\",\"attempts\":{},\"secret\":\"{}\"}}",
                cid.contract_id, attempts, cid.secret,
            );
        }

        exit(0);
    });

    // This now blocks and lets our threadpool execute in the background.
    rx.recv().expect("Could not receive from channel");
    progress.finish_and_clear();
    eprintln!("\r\x1b[2KCaught SIGINT, exiting...");
    ExitCode::FAILURE
}