use super::*;

#[cfg(test)]
pub fn encode(n: u128) -> Vec<u8> {
  let mut v = Vec::new();
  encode_to_vec(n, &mut v);
  v
}

pub fn encode_to_vec(mut n: u128, v: &mut Vec<u8>) {
  let mut out = [0; 19];
  let mut i = 18;

  out[i] = n.to_le_bytes()[0] & 0b0111_1111;

  while n > 0b0111_1111 {
    n = n / 128 - 1;
    i -= 1;
    out[i] = n.to_le_bytes()[0] | 0b1000_0000;
  }

  v.extend_from_slice(&out[i..]);
}

pub fn decode(buffer: &[u8]) -> Result<(u128, usize)> {
  let mut n = 0;
  let mut i = 0;

  loop {
    let b = u128::from(buffer.get(i).cloned().ok_or(Error::Varint)?);

    if b < 128 {
      return Ok((n + b, i + 1));
    }

    n += b - 127;

    n = n.checked_mul(128).ok_or(Error::Varint)?;

    i += 1;
  }
}

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

  #[test]
  fn u128_max_round_trips_successfully() {
    let n = u128::max_value();
    let encoded = encode(n);
    let (decoded, length) = decode(&encoded).unwrap();
    assert_eq!(decoded, n);
    assert_eq!(length, encoded.len());
  }

  #[test]