use crate::constants::COMMITMENT_BYTES;
use crate::util::*;
use bls12_381_plus::Scalar;
use serde::{Deserialize, Serialize};
use subtle::CtOption;

/// A challenge generated by fiat-shamir heuristic
#[derive(Debug, Copy, Clone, Eq, PartialEq, Deserialize, Serialize)]
pub struct Challenge(pub Scalar);

impl Default for Challenge {
    fn default() -> Self {
        Challenge(Scalar::zero())
    }
}

impl Challenge {
    /// The number of bytes in a challenge
    pub const BYTES: usize = 32;

    /// Hash arbitrary data to a challenge
    pub fn hash<B: AsRef<[u8]>>(data: B) -> Self {
        Self(hash_to_scalar(data))
    }

    /// Get the byte sequence that represents this challenge
    pub fn to_bytes(&self) -> [u8; Self::BYTES] {
        scalar_to_bytes(self.0)
    }

    /// Convert a big-endian representation of the challenge
    pub fn from_bytes(bytes: &[u8; Self::BYTES]) -> CtOption<Self> {
        scalar_from_bytes(bytes).map(|s| Self(s))
    }

    /// Convert a 48 byte digest into a challenge
    pub fn from_okm(bytes: &[u8; COMMITMENT_BYTES]) -> Self {
        Self(Scalar::from_okm(bytes))
    }
}
