//! Conversion from [`U512`] into a `[u8; 64]` big-endian byte array.
use super::U512;

/// Converts a [`U512`] into a 64-byte array in big-endian order where
/// byte `[0]` is the most significant and byte `[63]` is the least
/// significant.
///
/// This is the inverse of [`U512::from_be_bytes`]. Each of the eight
/// `u64` limbs is serialized via `u64::to_be_bytes` into the
/// corresponding 8-byte slice.
///
/// # Examples
///
/// ```
/// use cnfy_uint::u512::U512;
///
/// let v = U512::from_be_limbs([0, 0, 0, 0, 0, 0, 0, 1]);
/// let bytes: [u8; 64] = v.into();
/// assert_eq!(bytes[63], 1);
/// assert_eq!(bytes[0], 0);
/// ```
impl From<U512> for [u8; 64] {
    #[inline]
    fn from(value: U512) -> Self {
        let w0 = value.0[7].to_be_bytes();
        let w1 = value.0[6].to_be_bytes();
        let w2 = value.0[5].to_be_bytes();
        let w3 = value.0[4].to_be_bytes();
        let w4 = value.0[3].to_be_bytes();
        let w5 = value.0[2].to_be_bytes();
        let w6 = value.0[1].to_be_bytes();
        let w7 = value.0[0].to_be_bytes();
        [
            w0[0], w0[1], w0[2], w0[3], w0[4], w0[5], w0[6], w0[7],
            w1[0], w1[1], w1[2], w1[3], w1[4], w1[5], w1[6], w1[7],
            w2[0], w2[1], w2[2], w2[3], w2[4], w2[5], w2[6], w2[7],
            w3[0], w3[1], w3[2], w3[3], w3[4], w3[5], w3[6], w3[7],
            w4[0], w4[1], w4[2], w4[3], w4[4], w4[5], w4[6], w4[7],
            w5[0], w5[1], w5[2], w5[3], w5[4], w5[5], w5[6], w5[7],
            w6[0], w6[1], w6[2], w6[3], w6[4], w6[5], w6[6], w6[7],
            w7[0], w7[1], w7[2], w7[3], w7[4], w7[5], w7[6], w7[7],
        ]
    }
}

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

    /// Round-trip: from_be_bytes then into bytes returns the original.
    #[test]
    fn round_trip() {
        let mut bytes = [0u8; 64];
        bytes[0] = 0xAB;
        bytes[31] = 0xCD;
        bytes[63] = 0xEF;
        let v = U512::from_be_bytes(bytes);
        let back: [u8; 64] = v.into();
        assert_eq!(back, bytes);
    }

    /// Zero produces all-zero bytes.
    #[test]
    fn zero() {
        let bytes: [u8; 64] = U512::ZERO.into();
        assert_eq!(bytes, [0u8; 64]);
    }

    /// MAX produces all-0xFF bytes.
    #[test]
    fn max() {
        let bytes: [u8; 64] = U512::MAX.into();
        assert_eq!(bytes, [0xFF; 64]);
    }

    /// Byte 63 holds the LSB of the lowest limb.
    #[test]
    fn lsb_position() {
        let v = U512::from_be_limbs([0, 0, 0, 0, 0, 0, 0, 0x42]);
        let bytes: [u8; 64] = v.into();
        assert_eq!(bytes[63], 0x42);
        assert_eq!(bytes[62], 0);
    }
}
