#[derive(Clone, Copy)]

    fn deref(&self) -> &[u8] {

        &self.bytes[..usize::from(self.length)]

    }

    fn cmp(&self, other: &Self) -> Ordering {

        (**self).cmp(&**other)

    }

    fn partial_cmp(&self, other: &Self) -> Option<std::cmp::Ordering> {

        Some(self.cmp(other))

    }

    fn eq(&self, other: &Self) -> bool {

        **self == **other

    }

        f.write_str("DocumentId(")?;

        arc_bytes::print_bytes(self, f)?;

        f.write_char(')')

    }

        if let Ok(string) = std::str::from_utf8(self.as_ref()) {

            if string.bytes().all(|b| (32..=127).contains(&b)) {

                return f.write_str(string);

            }

        }

        if let Some((first_nonzero_byte, _)) = self

            .as_ref()

            .iter()

            .copied()

            .enumerate()

            .find(|(_index, b)| *b != 0)

            if first_nonzero_byte > 0 {

                write!(f, "{:x}$", first_nonzero_byte)?;

                f.write_char('$')?;

            for (index, byte) in self[first_nonzero_byte..].iter().enumerate() {

                if index > 0 {

                    write!(f, "{:02x}", byte)?;

                    write!(f, "{:x}", byte)?;

            Ok(())

            write!(f, "{:x}$", self.len())

    }

    fn hash<H: std::hash::Hasher>(&self, state: &mut H) {

        (**self).hash(state);

    }

    fn from(id: DocumentId) -> Self {

        Identifier::from(id.to_vec())

    }

    fn from(id: &'a DocumentId) -> Self {

        Identifier::from(&**id)

    }

#[test]

fn document_id_identifier_tests() {

    assert_eq!(

        Identifier::from(DocumentId::new(String::from("hello")).unwrap()),

        Identifier::from("hello")

    );

    assert_eq!(

        Identifier::from(DocumentId::from_u64(1)),

        Identifier::from(1)

    );

}

const fn decode_hex_nibble(byte: u8) -> Result<u8, InvalidHexadecimal> {

    match byte {

        b'0'..=b'9' => Ok(byte - b'0'),

        b'A'..=b'F' => Ok(byte - b'A' + 10),

        b'a'..=b'f' => Ok(byte - b'a' + 10),

}

    fn from_str(s: &str) -> Result<Self, Self::Err> {

        if s.is_empty() {

        }

        let mut id = Self::default();

        let bytes = s.as_bytes();

        if let Some((pound_offset, _)) = s.bytes().enumerate().find(|(_index, b)| *b == b'$') {

            if pound_offset > 2 {

            }

            let preceding_zeroes = if pound_offset > 0 {

                let mut length = [0_u8];

                decode_big_endian_hex(&bytes[0..pound_offset], &mut length)?;

                usize::from(length[0])

                0

            let decoded_length = decode_big_endian_hex(&bytes[pound_offset + 1..], &mut id.bytes)?;

            if preceding_zeroes > 0 {

                let total_length = preceding_zeroes + usize::from(decoded_length);

                if total_length > Self::MAX_LENGTH {

                }

                // The full length indicated a longer ID, so we need to prefix some null bytes.

                id.bytes

                    .copy_within(0..usize::from(decoded_length), preceding_zeroes);

                id.bytes[0..preceding_zeroes].fill(0);

                id.length = u8::try_from(total_length).unwrap();

            } else {

                id.length = decoded_length;

            }

        } else if bytes.len() > Self::MAX_LENGTH {

        } else {

            // UTF-8 representable

            id.length = u8::try_from(bytes.len()).unwrap();

            id.bytes[0..bytes.len()].copy_from_slice(bytes);

        }

        Ok(id)

    }

fn decode_big_endian_hex(bytes: &[u8], output: &mut [u8]) -> Result<u8, crate::Error> {

    let mut length = 0;

    let mut chunks = if bytes.len() & 1 == 0 {

        bytes.chunks_exact(2)

        output[0] = decode_hex_nibble(bytes[0])?;

        length = 1;

        bytes[1..].chunks_exact(2)

    for chunk in &mut chunks {

        let write_at = length;

        length += 1;

        if length > output.len() {

        }

        let upper = decode_hex_nibble(chunk[0])?;

        let lower = decode_hex_nibble(chunk[1])?;

        output[write_at] = upper << 4 | lower;

    if !chunks.remainder().is_empty() {

    }

    Ok(u8::try_from(length).unwrap())

}

#[test]

fn document_id_parsing() {

    fn test_id(bytes: &[u8], display: &str) {

        let id = DocumentId::try_from(bytes).unwrap();

        let as_string = id.to_string();

        assert_eq!(as_string, display);

        let parsed = DocumentId::from_str(&as_string).unwrap();

        assert_eq!(&*parsed, bytes);

    }

    test_id(b"hello", "hello");

    test_id(b"\x00\x0a\xaf\xfa", "1$aaffa");

    test_id(&1_u128.to_be_bytes(), "f$1");

    test_id(&17_u8.to_be_bytes(), "$11");

    test_id(&[0_u8; 63], "3f$");

    // The above test is the same as this one, at the time of writing, but in

    // case we update MAX_LENGTH in the future, this extra test will ensure the

    // max-length formatting is always tested.

    test_id(

        &[0_u8; DocumentId::MAX_LENGTH],

        &format!("{:x}$", DocumentId::MAX_LENGTH),

    );

}

    fn default() -> Self {

        Self {

            length: 0,

            bytes: [0; Self::MAX_LENGTH],

        }

    }

    fn try_from(bytes: &'a [u8]) -> Result<Self, Self::Error> {

        if bytes.len() <= Self::MAX_LENGTH {

            let mut new_id = Self {

                length: u8::try_from(bytes.len()).unwrap(),

                ..Self::default()

            };

            new_id.bytes[..bytes.len()].copy_from_slice(bytes);

            Ok(new_id)

    }

    pub fn new<PrimaryKey: for<'k> Key<'k>, PrimaryKeyRef: for<'k> KeyEncoding<'k, PrimaryKey>>(

        value: PrimaryKeyRef,

    ) -> Result<Self, crate::Error> {

        let bytes = value

            .as_ord_bytes()

            .map_err(|err| crate::Error::Serialization(err.to_string()))?;

        Self::try_from(&bytes[..])

    }

    pub fn from_u64(id: u64) -> Self {

        Self::try_from(&id.to_be_bytes()[..]).unwrap()

    }

    pub fn deserialize<'a, PrimaryKey: Key<'a>>(&'a self) -> Result<PrimaryKey, crate::Error> {

        PrimaryKey::from_ord_bytes(self.as_ref())

            .map_err(|err| crate::Error::Serialization(err.to_string()))

    }

    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>

    where

        S: serde::Serializer,

    {

        serializer.serialize_bytes(self.as_ref())

    }

    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>

    where

        D: serde::Deserializer<'de>,

    {

        deserializer.deserialize_byte_buf(DocumentIdVisitor)

    }

    fn visit_bytes<E>(self, v: &[u8]) -> Result<Self::Value, E>

    where

        E: serde::de::Error,

    {

        if v.len() <= DocumentId::MAX_LENGTH {

            let mut document_id = DocumentId {

                length: u8::try_from(v.len()).unwrap(),

                ..DocumentId::default()

            };

            document_id.bytes[..v.len()].copy_from_slice(v);

            Ok(document_id)

    }

    fn as_ord_bytes(&'k self) -> Result<Cow<'k, [u8]>, Self::Error> {

        Ok(Cow::Borrowed(self))

    }