//! Operations on a single commit-graph file.

mod access;

pub mod commit;
pub use commit::Commit;

mod init;
pub mod verify;

pub use init::Error;

use filebuffer::FileBuffer;
use git_hash::SIZE_OF_SHA1_DIGEST as SHA1_SIZE;
use std::{
    fmt::{Display, Formatter},
    ops::Range,
    path::PathBuf,
};

const COMMIT_DATA_ENTRY_SIZE: usize = SHA1_SIZE + 16;
const FAN_LEN: usize = 256;
const SIGNATURE: &[u8] = b"CGPH";

/// A single commit-graph file.
///
/// All operations on a `File` are local to that graph file. Since a commit graph can span multiple
/// files, all interesting graph operations belong on [`Graph`][crate::Graph].
pub struct File {
    base_graph_count: u8,
    base_graphs_list_offset: Option<usize>,
    commit_data_offset: usize,
    data: FileBuffer,
    extra_edges_list_range: Option<Range<usize>>,
    fan: [u32; FAN_LEN],
    oid_lookup_offset: usize,
    path: PathBuf,
}

/// The position of a given commit within a graph file, starting at 0.
///
/// Commits within a graph file are sorted in lexicographical order by OID; a commit's lexigraphical position
/// is its position in this ordering. If a commit graph spans multiple files, each file's commits
/// start at lexigraphical position 0, so it is unique across a single file but is not unique across
/// the whole commit graph. Each commit also has a graph position ([`graph::Position`][crate::graph::Position]),
/// which is unique /// across the whole commit graph. In order to avoid accidentally mixing lexigraphical positions with graph
/// positions, distinct types are used for each.
#[derive(Clone, Copy, Debug, Eq, Hash, Ord, PartialEq, PartialOrd)]
pub struct Position(pub u32);

impl Display for Position {
    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
        self.0.fmt(f)
    }
}