// Copyright 2018-2020 Georges Racinet <georges.racinet@octobus.net>

//           and Mercurial contributors

//

// This software may be used and distributed according to the terms of the

// GNU General Public License version 2 or any later version.

//! Mercurial concepts for handling revision history

/// Mercurial revision numbers

///

/// As noted in revlog.c, revision numbers are actually encoded in

/// 4 bytes, and are liberally converted to ints, whence the i32

pub type Revision = i32;

/// Marker expressing the absence of a parent

///

/// Independently of the actual representation, `NULL_REVISION` is guaranteed

/// to be smaller than all existing revisions.

pub const NULL_REVISION: Revision = -1;

/// Same as `mercurial.node.wdirrev`

///

/// This is also equal to `i32::max_value()`, but it's better to spell

/// it out explicitely, same as in `mercurial.node`

pub const WORKING_DIRECTORY_REVISION: Revision = 0x7fffffff;

/// The simplest expression of what we need of Mercurial DAGs.

pub trait Graph {

    /// Return the two parents of the given `Revision`.

    ///

    /// Each of the parents can be independently `NULL_REVISION`

    fn parents(&self, rev: Revision) -> Result<[Revision; 2], GraphError>;

}

#[derive(Clone, Debug, PartialEq)]

pub enum GraphError {

    ParentOutOfRange(Revision),

    WorkingDirectoryUnsupported,

}