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use git_hash::SIZE_OF_SHA1_DIGEST as SHA1_SIZE;
use std::io;

const _TYPE_EXT1: u8 = 0;
const COMMIT: u8 = 1;
const TREE: u8 = 2;
const BLOB: u8 = 3;
const TAG: u8 = 4;
const _TYPE_EXT2: u8 = 5;
const OFS_DELTA: u8 = 6;
const REF_DELTA: u8 = 7;

/// An representing an full- or delta-object within a pack
#[derive(PartialEq, Eq, Debug, Hash, Ord, PartialOrd, Clone)]
#[cfg_attr(feature = "serde1", derive(serde::Serialize, serde::Deserialize))]
pub struct Entry {
    /// The entry's header
    pub header: Header,
    /// The decompressed size of the object in bytes
    pub decompressed_size: u64,
    /// absolute offset to compressed object data in the pack, just behind the entry's header
    pub data_offset: u64,
}

/// Access
impl Entry {
    /// Compute the pack offset to the base entry of the object represented by this entry.
    pub fn base_pack_offset(&self, distance: u64) -> u64 {
        let pack_offset = self.data_offset - self.header_size() as u64;
        pack_offset.checked_sub(distance).expect("in-bound distance of deltas")
    }
    /// The pack offset at which this entry starts
    pub fn pack_offset(&self) -> u64 {
        self.data_offset - self.header_size() as u64
    }
    /// The amount of bytes used to describe this entry in the pack. The header starts at [`Self::pack_offset()`]
    pub fn header_size(&self) -> usize {
        self.header
            .to_write(self.decompressed_size, io::sink())
            .expect("io::sink() to never fail")
    }
}

mod decode;

mod header;
pub use header::Header;