use bip39::Mnemonic;

use crate::errors::ProtocolError;

/// Encode 32 bytes as a BIP39 mnemonic (24 words).
pub fn seed_to_mnemonic(seed: &[u8; 32]) -> String {
    // BIP39 with 256 bits of entropy = 24 words
    let mnemonic = Mnemonic::from_entropy(seed).expect("32 bytes is valid BIP39 entropy");
    mnemonic.to_string()
}

/// Decode a BIP39 mnemonic back to 32 bytes.
pub fn mnemonic_to_seed(words: &str) -> Result<[u8; 32], ProtocolError> {
    let mnemonic: Mnemonic = words.parse().map_err(|_| ProtocolError::InvalidMnemonic)?;
    let entropy = mnemonic.to_entropy();
    if entropy.len() != 32 {
        return Err(ProtocolError::InvalidSeedLength);
    }
    let mut seed = [0u8; 32];
    seed.copy_from_slice(&entropy);
    Ok(seed)
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn roundtrip() {
        let seed = [0xab; 32];
        let words = seed_to_mnemonic(&seed);
        let word_count = words.split_whitespace().count();
        assert_eq!(word_count, 24);
        let recovered = mnemonic_to_seed(&words).unwrap();
        assert_eq!(seed, recovered);
    }
}