// cindex.rs

//

// Copyright 2018 Georges Racinet <gracinet@anybox.fr>

//

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

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

//! Bindings to use the Index defined by the parsers C extension

//!

//! Ideally, we should use an Index entirely implemented in Rust,

//! but this will take some time to get there.

use cpython::{

    exc::ImportError, exc::TypeError, ObjectProtocol, PyClone, PyErr,

    PyObject, PyResult, PyTuple, Python, PythonObject,

};

use hg::revlog::{Node, RevlogIndex};

use hg::{Graph, GraphError, Revision, WORKING_DIRECTORY_REVISION};

use libc::{c_int, ssize_t};

const REVLOG_CABI_VERSION: c_int = 2;

#[repr(C)]

pub struct Revlog_CAPI {

    abi_version: c_int,

    index_length:

        unsafe extern "C" fn(index: *mut revlog_capi::RawPyObject) -> ssize_t,

    index_node: unsafe extern "C" fn(

        index: *mut revlog_capi::RawPyObject,

        rev: ssize_t,

    ) -> *const Node,

    index_parents: unsafe extern "C" fn(

        index: *mut revlog_capi::RawPyObject,

        rev: c_int,

        ps: *mut [c_int; 2],

    ) -> c_int,

}

py_capsule!(

    from mercurial.cext.parsers import revlog_CAPI

        as revlog_capi for Revlog_CAPI);

/// A `Graph` backed up by objects and functions from revlog.c

///

/// This implementation of the `Graph` trait, relies on (pointers to)

/// - the C index object (`index` member)

/// - the `index_get_parents()` function (`parents` member)

///

/// # Safety

///

/// The C index itself is mutable, and this Rust exposition is **not

/// protected by the GIL**, meaning that this construct isn't safe with respect

/// to Python threads.

///

/// All callers of this `Index` must acquire the GIL and must not release it

/// while working.

///

/// # TODO find a solution to make it GIL safe again.

///

/// This is non trivial, and can wait until we have a clearer picture with

/// more Rust Mercurial constructs.

///

/// One possibility would be to a `GILProtectedIndex` wrapper enclosing

/// a `Python<'p>` marker and have it be the one implementing the

/// `Graph` trait, but this would mean the `Graph` implementor would become

/// likely to change between subsequent method invocations of the `hg-core`

/// objects (a serious change of the `hg-core` API):

/// either exposing ways to mutate the `Graph`, or making it a non persistent

/// parameter in the relevant methods that need one.

///

/// Another possibility would be to introduce an abstract lock handle into

/// the core API, that would be tied to `GILGuard` / `Python<'p>`

/// in the case of the `cpython` crate bindings yet could leave room for other

/// mechanisms in other contexts.

pub struct Index {

    index: PyObject,

    capi: &'static Revlog_CAPI,

}

impl Index {

    pub fn new(py: Python, index: PyObject) -> PyResult<Self> {

        let capi = unsafe { revlog_capi::retrieve(py)? };

        if capi.abi_version != REVLOG_CABI_VERSION {

            return Err(PyErr::new::<ImportError, _>(

                py,

                format!(

                    "ABI version mismatch: the C ABI revlog version {} \

                     does not match the {} expected by Rust hg-cpython",

                    capi.abi_version, REVLOG_CABI_VERSION

                ),

            ));

        }

        let compat: u64 = index.getattr(py, "rust_ext_compat")?.extract(py)?;

        if compat == 0 {

            return Err(PyErr::new::<TypeError, _>(

                py,

                "index object not compatible with Rust",

            ));

        }

        Ok(Index { index, capi })

    }

    /// return a reference to the CPython Index object in this Struct

    pub fn inner(&self) -> &PyObject {

        &self.index

    }

    pub fn append(&mut self, py: Python, tup: PyTuple) -> PyResult<PyObject> {

        self.index.call_method(

            py,

            "append",

            PyTuple::new(py, &[tup.into_object()]),

            None,

        )

    }

}

impl Clone for Index {

    fn clone(&self) -> Self {

        let guard = Python::acquire_gil();

        Index {

            index: self.index.clone_ref(guard.python()),

            capi: self.capi,

        }

    }

}

impl PyClone for Index {

    fn clone_ref(&self, py: Python) -> Self {

        Index {

            index: self.index.clone_ref(py),

            capi: self.capi,

        }

    }

}

impl Graph for Index {

    /// wrap a call to the C extern parents function

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

        if rev == WORKING_DIRECTORY_REVISION {

            return Err(GraphError::WorkingDirectoryUnsupported);

        }

        let mut res: [c_int; 2] = [0; 2];

        let code = unsafe {

            (self.capi.index_parents)(

                self.index.as_ptr(),

                rev as c_int,

                &mut res as *mut [c_int; 2],

            )

        };

        match code {

            0 => Ok(res),

            _ => Err(GraphError::ParentOutOfRange(rev)),

        }

    }

}

impl RevlogIndex for Index {

    /// Note C return type is Py_ssize_t (hence signed), but we shall

    /// force it to unsigned, because it's a length

    fn len(&self) -> usize {

        unsafe { (self.capi.index_length)(self.index.as_ptr()) as usize }

    }

    fn node(&self, rev: Revision) -> Option<&Node> {

        let raw = unsafe {

            (self.capi.index_node)(self.index.as_ptr(), rev as ssize_t)

        };

        if raw.is_null() {

            None

        } else {

            // TODO it would be much better for the C layer to give us

            // a length, since the hash length will change in the near

            // future, but that's probably out of scope for the nodemap

            // patch series.

            //

            // The root of that unsafety relies in the signature of

            // `capi.index_node()` itself: returning a `Node` pointer

            // whereas it's a `char *` in the C counterpart.

            Some(unsafe { &*raw })

        }

    }

}