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use secp256k1::RecoveryId;
use tiny_keccak::{Hasher, Keccak};

const PREFIX: &str = "\x19Ethereum Signed Message:\n";

/// Hash a message according to EIP-191.
///
/// The data is a UTF-8 encoded string and will enveloped as follows:
/// `"\x19Ethereum Signed Message:\n" + message.length + message` and hashed
/// using keccak256.
pub fn hash_message<S>(message: S) -> [u8; 32]
where
    S: AsRef<[u8]>,
{
    let message = message.as_ref();

    let mut eth_message = format!("{}{}", PREFIX, message.len()).into_bytes();
    eth_message.extend_from_slice(message);

    keccak256(&eth_message)
}

/// Compute the Keccak-256 hash of input bytes.
pub fn keccak256(bytes: &[u8]) -> [u8; 32] {
    let mut output = [0u8; 32];
    let mut hasher = Keccak::v256();
    hasher.update(bytes);
    hasher.finalize(&mut output);
    output
}

/// Applies [EIP155](https://github.com/ethereum/EIPs/blob/master/EIPS/eip-155.md)
pub fn to_eip155_v(recovery_id: RecoveryId, chain_id: Option<u8>) -> u8 {
    let standard_v = recovery_id.serialize() as u8;
    if let Some(chain_id) = chain_id {
        // When signing with a chain ID, add chain replay protection.
        standard_v + 35 + chain_id * 2
    } else {
        // Otherwise, convert to 'Electrum' notation.
        standard_v + 27
    }
}