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// Copyright 2015-2020 Parity Technologies (UK) Ltd.
// This file is part of OpenEthereum.

// OpenEthereum is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.

// OpenEthereum 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 General Public License for more details.

// You should have received a copy of the GNU General Public License
// along with OpenEthereum.  If not, see <http://www.gnu.org/licenses/>.

use parity_crypto::publickey::{Error, Generator, KeyPair, Random};

/// Tries to find keypair with address starting with given prefix.
pub struct Prefix {
    prefix: Vec<u8>,
    iterations: usize,
}

impl Prefix {
    pub fn new(prefix: Vec<u8>, iterations: usize) -> Self {
        Prefix { prefix, iterations }
    }

    pub fn generate(&mut self) -> Result<KeyPair, Error> {
        for _ in 0..self.iterations {
            let keypair = Random.generate();
            if keypair.address().as_ref().starts_with(&self.prefix) {
                return Ok(keypair);
            }
        }

        Err(Error::Custom("Could not find keypair".into()))
    }
}

#[cfg(test)]
mod tests {
    use Prefix;

    #[test]
    fn prefix_generator() {
        let prefix = vec![0xffu8];
        let keypair = Prefix::new(prefix.clone(), usize::max_value())
            .generate()
            .unwrap();
        assert!(keypair.address().as_bytes().starts_with(&prefix));
    }
}