// dagops.rs

//

// Copyright 2019 Georges Racinet <georges.racinet@octobus.net>

//

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

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

//! Bindings for the `hg::dagops` module provided by the

//! `hg-core` package.

//!

//! From Python, this will be seen as `mercurial.rustext.dagop`

use crate::PyRevision;

use crate::{conversion::rev_pyiter_collect, exceptions::GraphError};

use cpython::{PyDict, PyModule, PyObject, PyResult, Python};

use hg::dagops;

use hg::Revision;

use std::collections::HashSet;

use vcsgraph::graph::Rank;

use crate::revlog::py_rust_index_to_graph;

/// Using the the `index`, return heads out of any Python iterable of Revisions

///

/// This is the Rust counterpart for `mercurial.dagop.headrevs`

pub fn headrevs(

    py: Python,

    index: PyObject,

    revs: PyObject,

) -> PyResult<HashSet<PyRevision>> {

    let py_leaked = py_rust_index_to_graph(py, index)?;

    // Safety: we don't leak the "faked" reference out of `UnsafePyLeaked`

    let index = &*unsafe { py_leaked.try_borrow(py)? };

    let mut as_set: HashSet<Revision> = rev_pyiter_collect(py, &revs, index)?;

    dagops::retain_heads(index, &mut as_set)

        .map_err(|e| GraphError::pynew(py, e))?;

    Ok(as_set.into_iter().map(Into::into).collect())

}

/// Computes the rank, i.e. the number of ancestors including itself,

/// of a node represented by its parents.

///

/// Currently, the pure Rust index supports only the REVLOGV1 format, hence

/// the only possible return value is that the rank is unknown.

///

/// References:

/// - C implementation, function `index_fast_rank()`.

/// - `impl vcsgraph::graph::RankedGraph for Index` in `crate::cindex`.

pub fn rank(

    py: Python,

    _index: PyObject,

    _p1r: PyRevision,

    _p2r: PyRevision,

) -> PyResult<Rank> {

    Err(GraphError::pynew_from_vcsgraph(

        py,

        vcsgraph::graph::GraphReadError::InconsistentGraphData,

    ))

}

/// Create the module, with `__package__` given from parent

pub fn init_module(py: Python, package: &str) -> PyResult<PyModule> {

    let dotted_name = &format!("{}.dagop", package);

    let m = PyModule::new(py, dotted_name)?;

    m.add(py, "__package__", package)?;

    m.add(py, "__doc__", "DAG operations - Rust implementation")?;

    m.add(

        py,

        "headrevs",

        py_fn!(py, headrevs(index: PyObject, revs: PyObject)),

    )?;

    m.add(

        py,

        "rank",

        py_fn!(py, rank(index: PyObject, p1r: PyRevision, p2r: PyRevision)),

    )?;

    let sys = PyModule::import(py, "sys")?;

    let sys_modules: PyDict = sys.get(py, "modules")?.extract(py)?;

    sys_modules.set_item(py, dotted_name, &m)?;

    // Example C code (see pyexpat.c and import.c) will "give away the

    // reference", but we won't because it will be consumed once the

    // Rust PyObject is dropped.

    Ok(m)

}