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//! This module includes some field helpers that are useful for Cairo

use ark_ff::Field;
use o1_utils::FieldHelpers;

//(TODO move to utils inside FieldHelpers)

/// Field element helpers for Cairo
pub trait CairoFieldHelpers<F> {
    /// Return field element as byte, if it fits. Otherwise returns least significant byte
    fn lsb(&self) -> u8;

    /// Return `pos`-th 16-bit chunk as another field element
    fn u16_chunk(&self, pos: usize) -> F;

    /// Return first 64 bits of the field element
    fn to_u64(&self) -> u64;

    /// Return a field element in hexadecimal in big endian
    fn to_hex_be(&self) -> String;
}

impl<F: Field> CairoFieldHelpers<F> for F {
    fn lsb(&self) -> u8 {
        self.to_bytes()[0]
    }

    fn u16_chunk(&self, pos: usize) -> F {
        let bytes = self.to_bytes();
        let chunk = u16::from(bytes[2 * pos]) + u16::from(bytes[2 * pos + 1]) * 2u16.pow(8);
        F::from(chunk)
    }

    fn to_u64(&self) -> u64 {
        let bytes = self.to_bytes();
        let mut acc: u64 = 0;
        for i in 0..8 {
            acc += 2u64.pow(i * 8) * (bytes[i as usize] as u64);
        }
        acc
    }

    fn to_hex_be(&self) -> String {
        let mut bytes = self.to_bytes();
        bytes.reverse();
        hex::encode(bytes)
    }
}