use std::{borrow::Borrow, fmt, io, ops::Deref}; use crate::{borrowed::oid, SIZE_OF_SHA1_DIGEST}; /// An owned hash identifying objects, most commonly Sha1#[derive(PartialEq, Eq, Hash, Ord, PartialOrd, Clone, Copy)]#[cfg_attr(feature = "serde1", derive(serde::Serialize, serde::Deserialize))]pub enum ObjectId {    Sha1([u8; SIZE_OF_SHA1_DIGEST]),} impl std::fmt::Debug for ObjectId {    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {        match self {            ObjectId::Sha1(_hash) => f.write_str("Sha1(")?,        }        for b in self.as_bytes() {            write!(f, "{:02x}", b)?;        }        f.write_str(")")    }} /// Access and conversionimpl ObjectId {    /// Returns the kind of hash used in this `Id`    pub fn kind(&self) -> crate::Kind {        crate::Kind::Sha1    }    /// Return the raw byte slice representing this hash    pub fn as_slice(&self) -> &[u8] {        match self {            Self::Sha1(b) => b.as_ref(),        }    }    /// Return the raw mutable byte slice representing this hash    pub fn as_mut_slice(&mut self) -> &mut [u8] {        match self {            Self::Sha1(b) => b.as_mut(),        }    }     /// Write ourselves to `out` in hexadecimal notation    pub fn write_hex_to(&self, mut out: impl io::Write) -> io::Result<()> {        out.write_all(&self.to_sha1_hex())    }     pub const fn empty_tree() -> ObjectId {        ObjectId::Sha1(*b"\x4b\x82\x5d\xc6\x42\xcb\x6e\xb9\xa0\x60\xe5\x4b\xf8\xd6\x92\x88\xfb\xee\x49\x04")    }     /// Returns true if this hash consists of all null bytes    pub fn is_null(&self) -> bool {        match self {            ObjectId::Sha1(digest) => &digest[..] == Self::null_sha1().as_bytes(),        }    }     /// Returns an Digest representing a hash with whose memory is zeroed.    pub const fn null_sha(kind: crate::Kind) -> ObjectId {        match kind {            crate::Kind::Sha1 => Self::null_sha1(),        }    }} /// Sha1 hash specific methodsimpl ObjectId {    /// Returns ourselves as slice of 20 bytes.    ///    /// Panics if this instance is not a sha1 hash.    pub fn sha1(&self) -> &[u8; SIZE_OF_SHA1_DIGEST] {        match self {            Self::Sha1(b) => b,        }    }     /// Return ourselves as array of 40 hexadecimal bytes.    ///    /// Panics if this instance is not a sha1 hash.    pub fn to_sha1_hex(self) -> [u8; SIZE_OF_SHA1_DIGEST * 2] {        match self {            Self::Sha1(b) => {                let mut hex_buf = [0u8; 40];                hex::encode_to_slice(b, &mut hex_buf).expect("we can count");                hex_buf            }        }    }     /// Return ourselves as hexadecimal string with a length of 40 bytes.    ///    /// Panics if this instance is not a sha1 hash.    pub fn to_sha1_hex_string(self) -> String {        let buf = self.to_sha1_hex();        std::str::from_utf8(&buf).expect("hex is valid UTF-8").to_string()    }     /// Instantiate an Digest from 20 bytes of a Sha1 digest.    pub fn new_sha1(id: [u8; SIZE_OF_SHA1_DIGEST]) -> Self {        ObjectId::Sha1(id)    }     /// Instantiate an Digest from a slice 20 borrowed bytes of a Sha1 digest.    ///    /// Panics of the slice doesn't have a length of 20.    pub fn from_20_bytes(b: &[u8]) -> ObjectId {        let mut id = [0; SIZE_OF_SHA1_DIGEST];        id.copy_from_slice(b);        ObjectId::Sha1(id)    }     /// Instantiate an Digest from a borrowed array of 20 bytes of a Sha1 digest.    pub fn from_borrowed_sha1(b: &[u8; SIZE_OF_SHA1_DIGEST]) -> ObjectId {        let mut id = [0; SIZE_OF_SHA1_DIGEST];        id.copy_from_slice(&b[..]);        ObjectId::Sha1(id)    }     /// Returns an Digest representing a Sha1 with whose memory is zeroed.    /// TODO: remove this method replace its usage with `null_sha(kind)` to probably become hash independent.    pub const fn null_sha1() -> ObjectId {        ObjectId::Sha1([0u8; 20])    }} impl From<[u8; SIZE_OF_SHA1_DIGEST]> for ObjectId {    fn from(v: [u8; 20]) -> Self {        Self::new_sha1(v)    }} impl From<&crate::oid> for ObjectId {    fn from(v: &oid) -> Self {        match v.kind() {            crate::Kind::Sha1 => ObjectId::from_20_bytes(v.as_bytes()),        }    }} impl Deref for ObjectId {    type Target = oid;     fn deref(&self) -> &Self::Target {        self.as_ref()    }} impl AsRef<crate::oid> for ObjectId {    fn as_ref(&self) -> &oid {        oid::try_from(self.as_slice()).expect("sibling type always implements all hashes we support")    }} impl Borrow<crate::oid> for ObjectId {    fn borrow(&self) -> &oid {        self.as_ref()    }} impl fmt::Display for ObjectId {    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {        for b in self.as_bytes() {            write!(f, "{:02x}", b)?;        }        Ok(())    }} impl PartialEq<&crate::oid> for ObjectId {    fn eq(&self, other: &&oid) -> bool {        self.as_ref() == *other    }}