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pub trait Padding {
    fn encode(&self, input_vec: Vec<u8>) -> Vec<u8>;
    fn decode(&self, source: Vec<u8>) -> Result<Vec<u8>, &'static str>;
}

#[derive(Debug)]
pub struct ZeroPadding(pub usize);

impl Padding for ZeroPadding {
    #[inline(always)]
    fn encode(&self, mut input_vec: Vec<u8>) -> Vec<u8> {
        let pad_size = self.0 - ((input_vec.len() + self.0 - 1) % self.0 + 1);
        input_vec.append(&mut vec![0u8; pad_size]);
        input_vec
    }

    #[inline(always)]
    fn decode(&self, source: Vec<u8>) -> Result<Vec<u8>, &'static str> {
        if (source.len() % self.0) != 0 {
            return Err("Invalid size");
        };
        let mut offset = source.len();
        if offset == 0 {
            return Ok(vec![]);
        }
        let end = (offset - self.0) + 1;
        while offset > end {
            offset -= 1;
            if source.get(offset).is_some() {
                return Ok(source[..(offset + 1)].into());
            }
        }
        Ok(source[..end].into())
    }
}